JP4409779B2 - Method for forming reflective liquid crystal display device - Google Patents

Description

【０１１０】
となる。単位面積ｄｓは，図２０に示される通り，
【０１１１】
【数２】

【０１１２】
であるので，（１）式に（２）式を代入して，光強度ｄＬを入射角θiを０〜π／２，方位角φiを０〜２πに渡って積分すれば，表示パネルの入射光強度Ｌは，次のように表される。
【０１１３】
【数３】

【０１１４】
従って，極角θ_i方向から入射する光強度f(θ_i)は（３）式の積分内の関数で表され，それは次のようになる。
【０１１５】
【数４】

【０１１６】
この（４）式のsinθiは，単位入射角θi毎の積分球の拡散光源の面積に起因するものであり，表示パネルの真上（入射角θi＝０）からの入射光の光源面積は狭く（sinθi＝０），表示パネルの横方向（入射角θi＝π／２）からの入射光の光源面積が広い（sinθi＝１）ことを意味する。また，（４）式のcosθiは，入射角による減衰成分であり，表示パネルの真上（入射角θi＝０）からの入射光の減衰度は殆どなく（cosθi＝１），表示パネルの横方向（入射角θi＝π／２）からの入射光の減衰度が大きい（cosθi＝０）ことを意味する。
【０１１７】
図２１は，反射型表示装置に光が入射して反射する場合を示す図である。図２で示した反射型液晶表示装置では，表示側ガラス基板および液晶層の屈折率ｎはほぼ1.5程度の値を有しているので，図２１に示される通り，の反射電極を有する基板からなる反射板６０を，その上に形成される液晶層や表示側基板からなる屈折率ｎの媒体６１が覆う構造と仮定することができる。すると，空気層から入射角θiで入射された入射光は，媒体６１内で入射角θ_i'となり，反射板６０で反射角θ_o'で反射し，空気層内で反射角θoで出ていくことになる。
【０１１８】
空気層から媒体６１に入る時，その一部が反射光Ｒとなって媒体内に入射されないので，それを考慮すると，反射板６１に入射角θ_i'で入射する光の強度f(θ_i')は，次のように表すことができる。
【０１１９】
【数５】

【０１２０】
ただし，R(θ_i)は上記の空気層と屈折率nの媒体６１の界面で反射する光の反射率である。そして，空気層での入射角θ_iと媒体６１内での入射角θ_i'との間には次のような関係が成り立つ。
【０１２１】
【数６】

【０１２２】
ここで，空気層の屈折率を1，ガラスおよび液晶の屈折率をnとした。θ_iは空気層での入射角，θ_i'は液晶層内での入射角である。
【０１２３】
図２２は，反射板６１に入射する光の強度f(θ_i')と入射角θ_i'との関係を示す図であり，上記式（５）に式（６）を代入して計算した。ただし，光強度はI(θ_i, φ_i)=1として計算した。図２２より理解されるとおり，積分球からの均一な拡散光を仮定した場合，反射板６０に対しては，入射角θ_i'＝０から入射角が増大するに従い入射光強度が増大し，ある入射角θ_i'の範囲で入射光強度が最大となり，入射角４５°付近で入射光強度が大きく減衰する。つまり，入射光強度が最大となる入射角θ_i'が存在し，媒体の屈折率ｎによってその入射角が異なることがわかる。
【０１２４】
図２３は，図２２の入射光強度が最大となる入射角θ_i'と媒体の屈折率nとの関係を示す図である。図２３より，液晶の屈折率nが大きいほど入射光強度が最大となる入射角θ_i'が小さくなることがわかる。そして，典型的な液晶の屈折率は1.4〜1.8程度であることから，入射光強度が最大となる入射角θ_i'は約３０〜３８°となる。
【０１２５】
次に，図２２のような入射光強度分布を有する入射光が，反射板６１の凹凸の傾斜面で反射することを検討する。図２４は，反射凹凸の傾斜面に対する入射角，反射角，傾斜角との関係を示す図である。入射光と反射光は，傾斜面に垂直な線に左右対称であり，ミクロな鏡面における局所的な入射角αは局所的な反射角βと等しいので，傾斜角ξ，入射角θ_i'，反射角θ_o'は次のような関係になる。
【０１２６】
【数７】

【０１２７】
そして，一般には表示パネルに垂直方向から表示を観察することが多い。そこで，凹凸を有する反射板に入射角_iθ'で入射する光を0°方向に反射させることを考えると，上記（７）式は，ξ＝θ_i'／２となる。つまり，傾斜角ξを入射角θ_i'の１／２にすれば表示パネルに垂直な方向に反射させることができるのである。
【０１２８】
図２２に示した通り，積分球の拡散光に対して反射板の凹凸面に入射する入射光の分布は，入射角０〜４５°の領域であるピークを有する。従って，反射板の凹凸面の傾斜面分布も図２２の光強度分布に対応した分布にすることが望ましい。つまり，光強度が高い入射角に対応する傾斜角の存在確率を高くし，光強度が低い入射角に対応する傾斜角の存在確率を低くして，全体で反射光強度を高くすることが望ましい。
【０１２９】
図２５は，図２２の入射光強度分布に対応した傾斜角の存在確率の分布を示す図である。図２５の例は，図２２の屈折率ｎ＝1.5の場合を示し，確率の総和が１になるように規格化した。横軸が反射凹凸面の傾斜角ξを，縦軸が存在確率（％）を示す。そこで，図２５に示したような傾斜角の存在確率分布を有するサンプルにおいて，存在確率が最大となる傾斜角を変化させた場合の，反射率を求める。図２６は，かかる反射特性のシミュレーション結果を示す図である。具体的には，図２５に示した分布の幅ｗを変化させて存在確率が最大となる傾斜角を変化させ，そのときの反射率Ｙを演算した。
【０１３０】
図２６から明らかな通り，存在確率が最大になる傾斜角ξ（＝θ_i'／２）の範囲が，ξ＝約１５〜１９°（θ_i'＝約３０〜３８°）の領域で反射率が最も高くなることが理解される。つまり，図２２に示した入射光強度がピーク値を持つ入射角θ_i'＝３０〜３８°の入射光を，表示パネルに垂直な方向に反射できる傾斜角ξ＝１５〜１９°の存在確率を最も高くすることが，全体の反射率を高めるために望ましいのである。
【０１３１】
以上のとおり，積分球の均一な拡散光下において有効に光を反射させるためには，反射用凹凸による傾斜角は約15〜19°の領域でその存在確率が最大になる必要があることが理論的に明らかになった。
【０１３２】
図２７は，実際に試作したサンプルを使って，積分球の均一な拡散光に対する反射率を測定した結果を示す図である。試作した反射板において，存在確率が最大の傾斜角ξpと，測定された反射率との関係が示される。
【０１３３】
図２８は，その試作した反射板の形成方法を示す断面図である。まず，図２８(a)に示したように，ガラス基板６２上にレジスト（シプレイ社製LC-200）６３を1000〜2000rpmで20秒間スピンコートする。そして，90℃で30分間プリベークした後，図２８(b)に示すように，マスク６４を用いて紫外線露光を行う。次に，現像液（シプレイ社製MF319）を用いて現像を行い，図２８(c)のようにガラス基板上に凸部を形成する。次に，図２８(d)に示すように120〜200℃で60分間のポストベークを行い，凸部に丸みを持たせた。その後，図２８(e)に示すようにアルミニウム層６５を200nm蒸着して，反射板を作製した。
【０１３４】
上記のように形成した反射板とガラス基板との間に液晶層を形成し，図２８（ｆ）に示されるような反射型液晶表示装置を作製した。ここで，液晶層は，メルク社製液晶材料MJ961213を使用し，その厚みを3.5μm径のスペーサで制御した。このように試作した反射型液晶表示装置に，積分球を使用して，拡散光を入射させた場合の反射率を測定した。更に，その試作品の反射板の凹凸の傾斜角分布を測定し，存在確率が最大となる傾斜角ξ_pも求めた。その結果が，前述の図２７に示される。
【０１３５】
この実験結果から，存在確率が最大になる傾斜角ξ_pを16〜19°付近にすることで，最大の反射率が得られていることがわかる。この実験結果は，図２６に示したシミュレーション結果を概ね裏付けている。従来，最適値といわれてきた傾斜角が10°の場合と比較しても，存在確率が最大になる傾斜角ξ_pを16〜19°付近にしたサンプルがより高い反射率を有することがわかる。
【０１３６】
図２９は，反射板の凹凸を形成するための，マスク６４のパターン例を示す図である。図２９（ａ）はサイズが異なる大小の円のパターンを混在させた例であり，図２９（ｂ）は三角形，四角形，六角形，八角形などの多角形を混在させた例である。但し，本発明はこれらのパターンに限定されるわけではない。
【０１３７】
反射用凹凸の別の形成例として，図３〜６で示したＵＶ照射して熱変形特性の分布を形成しその後最終ベークしてマイクログルーブを形成するプロセスを採用することができる。マイクログルーブの凹凸形状は，前述したプロセス条件でコントロールすることができるので，存在確率が最大になる傾斜角ξ_pが15〜19°付近になるようにその凹凸形状が制御される。
【０１３８】
以上，本実施の形態例では，反射板の凹凸による傾斜角は，少なくとも０°〜２５°の範囲に分布し，15〜19°付近でその存在確率が最大になるように分布することで，種々の環境化において，より高い反射率を有する反射型液晶表示装置を提供することができる。
【０１３９】
［反射板の傾斜角分布の制御（その２）］
図３０は，上記した積分球の拡散光に対して高い反射率が得られる反射板の凹凸の傾斜角分布を示す図である。横軸が傾斜角ξを，縦軸はその存在確率を示す。即ち，すでに説明した通り，傾斜角の存在確率は，反射板への入射強度が高い入射角の入射光をより多く表示パネルに垂直な方向に反射させるような分布にすることが望ましい。図３０には，＋15〜19°付近の傾斜角と−15〜19°付近の傾斜角の存在確率が最大になるような分布を示す。＋側と−側が存在するのは，表示パネルの一定方向に沿って傾斜角を見た場合，一方向からの入射光に対応した傾斜角を＋側，反対方向からの入射光に対応した傾斜角を−側に示した。従って，図３０の分布図を傾斜角０°を中心に折り曲げると，図２５に示したような傾斜角分布になる。
【０１４０】
ところで，液晶表示装置は，ノート型パーソナルコンピュータの表示パネルとして使用される場合が多い。図３１は，反射型液晶表示装置がノート型パーソナルコンピュータのモニターとして搭載された状態を示す図である。図示されるとおり，反射型液晶表示装置７０が，水平方向に対してを角度αだけ傾けた状態で使用されることが多い。その場合，図３１に示される通り，表示装置７０は紙面に垂直な面である。そして，図示されるとおりＸ−Ｙ−Ｚ軸の方向を定義する。
【０１４１】
表示装置７０への入射光を検討すると，座標のＸＹ面に沿った入射角θ_i分布は，何も入射光を遮るものがないので，θ_i ＝-90〜90°となる。一方，座標のＸＺ面に沿った入射角分布は，キーボード部分により入射光が遮られるので，必ずしもθ_i ＝-90〜90°とはならない。つまり，表示装置７０の最も高い位置７０Ａと最も低い位置７０Ｂとで，入射角範囲が異なる。最も高い位置７０Ａが，最も広い入射角範囲でθ_i ＝-90〜α+β°となり，最も低い位置７０Ｂが，最も狭い入射角範囲でθ_i ＝-90〜α°になる。
【０１４２】
従って，表示パネルの垂直方向に沿うＸＺ面方向の入射光は，入射角度α〜90°（またはα+β°〜90°）の角度から入射する光がほとんど存在しない。従って，表示パネルのＸＺ面方向に配列したミクロの鏡面の傾斜角には，この角度範囲から入射する光を表示パネルの法線（0°）方向に反射させる傾斜角は必要ないことになる。
【０１４３】
例えば，表示パネルの傾きα=30°および液晶層とガラス基板の屈折率n_LC=1.5であれば，30〜90°に入射される光を0°方向に反射させる傾斜角は，前述の（６）式および（７）式より10〜21°となる。つまり，表示パネルの垂直方向（ＸＺ面方向）を向いた凹凸の傾斜分布には，10〜21°の傾斜角は必要ない。
【０１４４】
従って，ＸＹ面方向およびＸＺ面方向の傾斜角の分布は，図３２に示されるとおりにすることが望ましい。即ち，ＸＹ面方向の傾斜角分布は，図３０に示したのと同じ分布であり，ＸＺ面方向の傾斜角分布は，マイナス側は図３０と同じであり，プラス側は10〜21°の範囲に存在しない分布となる。図３２の分布を，傾斜角０°を中心に折り返すと，図３３のようになる。
【０１４５】
図３３は，反射板の凹凸により形成される傾斜角分布について，ＸＹ面方向の傾斜面の分布とＸＺ面方向の傾斜面の分布とが示される。この図から明らかな通り，ノート型パーソナルコンピュータなど傾けて使用される場合は，表示パネルにおける水平方向の傾斜面の分布は，傾斜角15〜19°の範囲で存在確率が最大になるようにし，表示パネルの垂直方向の傾斜面の分布は，傾斜角8〜10°の範囲と傾斜角15〜19°の範囲で存在確率がピークを持つようにすることが望ましい。このように，表示パネルの方向に応じて，反射用凹凸による傾斜面の角度分布を，一つの方向は１つの存在確率のピークを有し，別の方向は２つの存在確率のピークを有することで，入射光方向に異方性がある環境下で使用されても，最大の反射率を実現することができる。
【０１４６】
本発明者らは，上記の傾斜面分布の反射板を試作して，その反射率を確認した。図３４は，サンプルの反射板の形成方法を示す断面図である。まず，図３４(a)に示したように，ガラス基板６２上にレジスト（例えばシプレイ社製のLC-200）６３を1000rpmで20秒間スピンコートして形成する。そして90℃で20分間プリベークした後，図３４(b)に示すようにマスク６４を用いて紫外線露光を行う。次に現像液（例えばシプレイ社製MF319）を用いて現像を行い，図３４(c)のようにガラス基板上にレジストによる凸部を形成する。図３４(a)〜(c)の工程を，図３５に示したマスクパターン(a)〜(d)を順次使用して４回繰り返し，図３４(d)のような傾斜角が異なる凸部を形成する。次に，図３４(e)のように，200℃で80分間のポストベークを行い，凸部に丸みを持たせた。その後，図３４(f)のようにアルミニウム６６を200nm蒸着して，反射板を作製した。
【０１４７】
図３６は，上記のように形成された反射板の凸部の平面形状及び断面形状を示す図である。凸部６７の平面形状は，基板６２の垂直方向Ｖについては，異なる傾斜面を有し，基板６２の水平方向Ｈについては同じ傾斜面を有する。図３６に示された平面図には，凸部６７に等高線を示し，その傾斜面形状が示される。ポストベークにより凸部は丸みを持たせているので，その傾斜角分布は，およそ０〜２０°の範囲に分布する。そして，基板の垂直方向Ｖにおいては，傾斜面（ξ1＞ξ2）が異なるので，図３３に示した通り，存在確率がピークになる領域が２つあり，基板の水平方向Ｈにおいては，傾斜面（ξ1）が左右対称であるので，図３３に示した通り，存在確率がピークになる領域が１つ存在することになる。
【０１４８】
以上の様に，反射用凹凸の形状を水平方向と垂直方向とで異ならせることで，水平方向の傾斜角の分布と，垂直方向の傾斜角の分布とを異ならせることができる。また，図３６に示される通り，半円形と半楕円形とを組み合わせた形状にすることで，水平方向の傾斜角と垂直方向の傾斜角の分布をそれぞれ異ならせることができる。
【０１４９】
本発明者らは，菱光社製の非接触3次元形状測定装置nh-3を用いて形状を測定し，試作した反射板の傾斜分布を求めた。図３７は，その試作した反射板の傾斜角分布の測定結果を示す。図に示される通り，試作した反射板は，絶対値で8°と18°に存在確率の極大が存在していた。また，比較のために，図３７には存在確率の極大が0°および10°にある反射板，それぞれ従来例1および従来例2，の傾斜角分布も示されている。
【０１５０】
図３８は，上記反射板を用いて作成した反射型液晶表示装置の概略断面図である。液晶層（例えばメルク社製液晶材料MJ961213）を，3.5μm径のスペーサで厚みを制御して，反射板とガラス基板の間に注入した。そして，その反射型液晶表示装置を鉛直方向から30°傾けた状態で固定し，積分球の均一拡散光を照射して，輝度計（例えばトプコン社製のBM-5）を用いて反射率を測定した。図３９は，その反射率の測定結果を示す図である。この図表より明らかな通り，本発明の反射板を用いると反射率が６１％となり，従来例１，２の３１％，５３％に比較して10〜25%の反射率向上が実現されていることが確認された。
【０１５１】
図３３には理想的な傾斜角分布を示したが，その前提として，液晶層やガラス基板の屈折率ｎを1.5とし，反射型液晶表示装置の水平線に対する角度（図３１に示した傾きα）をα＝３０°とした。そこで，液晶層の屈折率n_LCと反射型液晶表示装置の傾き角度αを変化させた場合に，理想的な反射用凹凸において存在確率が極大になる傾斜角範囲をそれぞれ調べた。
【０１５２】
図４０は，反射型液晶表示装置の傾き角度と，液晶層の屈折率に対する，存在確率が極大になる傾斜角範囲を示す図である。典型的な液晶材料の屈折率n_LCが1.4〜1.8程度であるので，屈折率n_LCを1.4〜1.8で変化させた。一般的な使用状態では，反射型液晶表示装置のサイズが小さいほど傾きαが大きくなる傾向
にあり，表示パネルの傾きαを0〜45°の範囲で変化させることにした。
【０１５３】
まず，表示パネルの傾斜角αが３０°の場合は，図３２，３３で示した通り，一方で15〜19°の範囲で凹凸の傾斜角の存在確率が極大になり，他方では8〜10°の範囲と15〜19°の範囲との２つの範囲で凹凸の傾斜角の存在確率が極大になるのが望ましい。また，表示パネルの傾斜角αが０°の場合は，表示パネルが垂直に置かれた場合であり，表示パネルの垂直方向の傾斜角ξは，主に上方からの入射光を垂直方向に反射するために15〜19°の範囲で凹凸の傾斜角の存在確率が極大になり，下方からの入射光はあまりないので下方側を向いた傾斜面は必要ない。そして，表示パネルの傾斜角αが９０°の場合は，表示パネルが水平に置かれた場合であり，図４０に示されないが，15〜19°の範囲で凹凸の傾斜角の存在確率が極大になることが望ましい。表示パネルが水平の場合は，図３０に示した分布例と同じである。
【０１５４】
図４０に示される通り，表示パネルの傾斜角αが０°〜４５°の範囲であれば，反射用凹凸における存在確率が極大となる一方の傾斜角は0〜16°，他方の傾斜角は14〜19°の範囲内に存在すれば，反射率を最大にすることができることが判明した。屈折率n_LCが小さいほどそれぞれ極大になる傾斜角は大きくなる傾向にある。
【０１５５】
ノート型パーソナルコンピュータは，オペレータの好みによって，その表示パネルの傾きが異なる。そこで，複数の傾きにおいて最大の反射率が実現できるように，画素領域内に，反射用凹凸の傾斜角の存在確率が極大になる領域が異なる複数の領域を形成することが望ましい。例えば，図４０に示される通り，表示装置の傾斜角αが３０°と４０°に対応して求められた，存在確率が極大になる傾斜角領域が，8〜10°と15〜19°の第１の組合せと，10〜12°と15〜19°の第２の組合せとを，同じ画素領域内に併存させる。或いは，表示装置の傾斜角αが３０°，３５°，４０°に対応して求められた，３つの組合せの領域を併存させる。或いは，３種類の凸パターンを併存させる。それにより，表示パネルの傾きがある程度異なっても，比較的大きな反射率を実現することができる。
【０１５６】
以上説明した反射用凹凸の傾斜角分布を有する反射電極を画素電極に利用して，図２に示した構造の反射型液晶表示装置を形成し，液晶層３４に画素電極と表示側の透明電極とから所定の電界をかけることで，当該液晶層３４に複屈折作用を持たせて，所望の表示を行うことができる。即ち，液晶層３４が電界効果複屈折モードで駆動される。また，液晶層３４に色素を含ませて，ゲストホスト型の液晶表示装置にすることもできる。
【０１５７】
［異なる指向性が混在する反射用凹凸の例］
特開平11-295750号公報には，画素電極を反射電極として利用する反射型液晶表示装置が記載されている。この公報には，画素電極内を２つの領域に分割して，一方の領域に指向性の強い反射特性を有する凹凸形状を形成し，他方の領域に拡散性の強い反射特性を有する凹凸形状を形成する。
【０１５８】
しかし，より高精細な液晶表示装置の場合は，画素領域がより狭くなり，上記従来例のように画素領域を２つの領域に分けて異なる凹凸形状をそれぞれに形成することはより困難になることが予想される。
【０１５９】
そこで，本実施の形態例では，画素領域内に指向性の強い反射特性を有する凹凸形状と拡散性の強い反射特性を有する凹凸形状とを混在させるようにする。図４１は，かかる画素領域内に混在する２つの反射凹凸形状を示す断面図である。凹凸Ａは，膜厚が薄くなだらかな傾斜面を有し上面が比較的平らになっているので，反射光の方向は垂直方向に指向性を有する。一方，凹凸Ｂは，膜厚が厚く急な傾斜面を有し上面が突起状になっているので，反射光は広く拡散する。
【０１６０】
図４２は，本実施の形態例における画素領域ＰＸの平面図である。図示される通り，画素領域ＰＸ内に，図４１に示した凹凸Ａと凹凸Ｂとが混在して設けられる。
【０１６１】
図４３は，図４２の反射用凹凸を形成する製造プロセスを示す断面図である。まず，図４２(a)に示すように，ガラス基板６２上に感光性樹脂であるレジスト（例えばシプレイ社製のLC-200）を2000rpmで20秒間スピンコートする。そして，90℃で20分間プリベークした後，図４２(b)に示すようにマスク６４Ａを用いて紫外線露光を行う。次に，現像液（例えばシプレイ社製MF319）を用いて現像を行い，図４２(c)のようにガラス基板６２上に凹凸Ａに対応する凸部を形成する。その後，図４２(d)のように200°で80分間のポストベークを行い，凸部に丸みを持たせて凹凸Ａを形成する。
【０１６２】
次に，図４２(e)に示すように，前記レジストを1000rpmで20秒間スピンコートする。これにより，前述のレジストよりもより厚いレジスト層を形成することができる。そして，90℃で20分間プリベークした後，図４２(f)に示すように，マスク６４Ｂを用いて紫外線露光を行う。次に前記の現像液を用いて現像を行い，図４２(g)のようにガラス基板に凹凸Ｂに対応する凸部を形成する。そして，図４２(h)のように120℃で80分間のポストベークを行い，凸部に丸みを持たせて，凹凸Ｂを形成する。このポストベークは，凹凸Ａを形成するよりも低い温度であるので，厚いレジスト膜の加熱によるダレの程度が少なく，より拡散性の強い凹凸Ｂが形成される。
【０１６３】
その後，図４２(i)のように，アルミニウム６４を200nm蒸着して反射板（画素電極）を作製した。上記のように，凹凸Ａと凹凸Ｂとでレジストの膜厚およびポストベークの温度を変えることで，凹凸の丸みを変えることができ，散乱の際の指向性が異なる凹凸が混在する反射面を構成することができた。
【０１６４】
前述の通り，反射型液晶表示装置の反射板は，あらゆる方向からの入射光を表示面に垂直な方向に反射することが望ましい。そのため，レジスト層をパターニングしてベーキングにより丸みを付けて傾斜面を形成する場合，傾斜面が３６０°の方向に向いているのが好ましい。そこで，従来，レジスト膜のパターンとして，円形のパターンが提案されている。例えば，特開平11-337935号公報，特開平11-337964号公報，特開平5-281533号公報などである。これらの公報には，円形のパターンをランダムに形成して反射光の干渉によるモアレ模様が形成されることを防止したり，半径が大きいドーナツ型パターンと半径が小さい円形パターンとをランダムに形成して反射特性を改善することなどが提案されている。
【０１６５】
特開平5-281533号は，大きい円形パターンと小さい円形パターンとをランダムに混在させることが示されている。例えば，図４４に示される通りである。しかし，半径が大きい円形パターンをランダムに配置すると，近接するレジストパターンが，露光・現像後のポストベーキング工程の時に加熱による断面形状のダレによって，合体する現象が生じる。図４４の斜線で示した円形パターンは，近接しすぎてベーキング時に合体してしまった状態を示す。
【０１６６】
そこで，本実施の形態例では，図４５に示される通り，レジストのパターンを，半径が大きい円形パターンと半径が小さい円形パターンとを混在させたものにし，且つ，大きい円形パターンと小さい円形パターンとの距離が，大きい円形パターン同士の距離よりも常に小さくなるように配置する。つまり，大きい円形パターンに対して，別の大きい円形パターンを近接させることを禁止するようにする。できれば，大きい円形パターンの周囲には小さい円形パターンを配置し，大きい円形パターン同士が近接することがないようにする。それにより，傾斜面の密度を高くすると共に，ベーキング時にパターン同士が合体する領域を少なくすることができる。
【０１６７】
図４６は，本実施の形態例におけるレジストのパターンを説明する図である。
【０１６８】
図４６（Ａ）は，比較的大きい円形パターンを配置した例である。画素領域ＰＸ内に大きい円形パターンＰ１が４個配置される。レジストパターンは，ある程度の大きさを有することが必要である。パターンが小さすぎると，ポストベーク時の断面形状のダレで傾斜角度が十分な大きさにならないからである。但し，図４６（Ａ）のパターンでは，形成される傾斜面の密度が薄く，反射率を高めることができない。
【０１６９】
そこで，図４６（Ｂ）に示される通り，大きい円形パターンＰ１の密度を高くすることが考えられる。しかし，大きな円形パターンＰ１が近接しあうと，ポストベーク時の熱によるダレで，斜線で示される通り，円形パターンの周縁部が合体することがある。かかる合体は，設計通りの傾斜面の面積を減らしてしまい，好ましくない。
【０１７０】
そこで，本実施の形態例では，図４５で説明した通り，図４６（Ｃ）に示されるように，比較的大きな円形パターンＰ１の密度は図４６（Ａ）のように疎な状態にして，パターンＰ１間の距離Ｌ１を比較的大きいままに保ち，その大きな円形パターンＰ１の隙間に比較的小さい円形パターンＰ２を配置し，傾斜面密度を高くするようにする。これにより，比較的大きな円形パターン同士の合体は少なくなり，合体が生じても大きな円形パターンＰ１と小さい円形パターンＰ２との間（図４６（Ｃ）中の斜線）だけに限定されるようにする。このような合体の領域は，大きい円形パターンＰ１同士の合体領域に比較して狭くなり，傾斜面領域の減少を最小限に抑えることができる。
【０１７１】
図４６（Ｃ）に示される通り，大きな円形パターンＰ１間の距離Ｌ１は，合体が生じない程度に長くし，それら円形パターンＰ１の間の領域に，小さな円形パターンＰ２を配置する。その結果，大きい円形パターンＰ１とそれに最も近接する小さい円形パターンＰ２との間の距離Ｌ２は，その大きい円形パターンＰ１とそれに最も近接する大きい円形パターンＰ１との間の距離Ｌ１より常に短くなる。
【０１７２】
図４７は，別のレジストパターンを示す図である。上記の例は，反射用凹凸の傾斜面が３６０°の方向に向くように円形パターンを利用したが，円形でなくても，各辺の方向が複数，好ましくは３つ以上存在する多角形であっても，同様の高い反射率を実現することができる。
【０１７３】
図４７は，画素領域ＰＸ内に，多数の六角形を，互いに隣接する辺が平行になるように近接させたレジストのパターン例である。画素領域ＰＸの周縁には，六角形全体が収納できずに，台形や５角形になっているが，基本的には，六角形がタイルのように敷き詰められたレジストパターンである。各辺が平行になるようにすることで，各六角形パターンをできるだけ近接させても，ポストベーク時の合体を防止することができる。
【０１７４】
このようなマスクパターンを利用してレジスト層を露光現像して，ポストベークを行うことにより，断面形状が熱によりダレて，少なくとも３つの方向を向いた傾斜面を有する反射用凹凸を形成することができる。
【０１７５】
図４８は，他のレジストパターンを示す図である。図４８の例は，画素領域内に六角形ではなく，複数の正三角形を，各辺が平行に近接するように配置している。この場合も，レジスト層を露光・現像して，ポストベークを行うことにより，断面形状が熱によりダレて，傾斜面が少なくとも３つの方向を向いた反射用凹凸を形成することができる。本実施の形態例は，他の多角形形状であっても，同様に高密度の傾斜面を有する反射用凹凸を形成することができる。
【０１７６】
図４５，４７，４８のパターンを利用した場合の反射用凹凸の形成プロセスは，図２８に示したプロセスと同じである。レジスト層の露光工程のマスク６４に，図４５，４７，４８のパターンが利用される。それにより，ポストベーク工程で，パターン同士が合体することなく，高密度の傾斜面分布を形成することができ，反射板の反射率を高くすることができる。
【０１７７】
［フロントライト構造］
反射型液晶表示装置は，バックライトを設けずに外光を反射して表示面を明るくする。従って，消費電力が少なく，携帯用の情報端末，携帯電話などの表示パネルとして有用である。しかしながら，外光を利用するので，明るい場所での使用に限定される問題がある。そこで，暗いところで使用する時のみ点灯させるフロントライト付きの液晶表示装置が提案されている。
【０１７８】
図４９は，従来提案されているフロントライト付き反射型液晶表示パネルの構成図である。図示される通り，反射型液晶表示パネル７３の表示側にフロントライト７０が設けられる。反射型液晶表示パネル７３は，反射板構造を有する背面側基板７３Ｂと表示側基板７３Ａとの間に，図示しない液晶層が挿入されている。そして，表示側基板７３Ａの上には，フロントライト７０が設けられ，フロントライト７０は，光源７１と，その光源からの光を表示面全面に導き，表面に形成した散乱層またはプリズム層により表示パネル７３側に散乱する透明基板７２とを有する。透明基板７２の表面に形成された散乱層またはプリズム層と空気層との間の屈折率の違いにより，光源７１の光が散乱し，その一部が表示パネル７３側に散乱する。
【０１７９】
しかし，図４９のように構成された反射型液晶表示装置は，透明基板７２の表面に散乱層またはプリズム層が形成されており，観察者は，この散乱層やプリズム層を介して表示パネル７３の文字や画像を見ることになる。そのため，散乱層やプリズム層により文字や画像が歪んだりぼやけたりすることになり，画質の低下を招いている。
【０１８０】
そこで，本実施の形態例では，フロントライト構造を光源が点灯した時のみ光を導く透明基板に散乱性を持たせ，光源が点灯しない時は透明基板の散乱性がなくなるようにする。かかる構成にすることで，外光を利用する通常の使用時には，フロントライト構造が，散乱機能を有しないので，観察される表示パネルの文字や画像の歪み，ぼけはなくなる。一方，暗い場所で使用する時などの限定された場合には，フロントライト構造が光源からの光を与えるので，多少文字や画像に歪み，ぼけが生じても，表示パネルを明るくして表示パネルとしての最低限の機能を確保することができる。
【０１８１】
図５０は，フロントライトの第１の例を示す図である。図５０に示されるフロントライト７０は，例えばアクリル製の透明基板の表面をサンドブラスト加工して表面に散乱層７５を設けた透明基板７４と，アクリル製透明基板７６と，それら基板の間に充填されるシリコーン・オイルなどの流動体７７と，流動体ポンプ７８と，流動体タンク７９とを有する。フロントライト７０は，更に，冷陰極蛍光管による線状光源７１を有する。基板７４，７６との間には，流動体タンク７９に収納されている流動体が流動体ポンプ７８により充填されたり，抜き取られたりする。そして，この流動体７７の屈折率は透明基板７４，７６と概ね同じｎ＝1.5である。
【０１８２】
図５０（ａ）に示される通り，明るい場所で反射型液晶表示パネルを使用する場合は，光源７１がオフ状態にあり，両透明基板７４，７６の間隙に流動体７７が充填される。これにより，散乱層７５は流動体７７と屈折率に差がないため，観視者側からは見えない。従って，明るい場所で使用される時は，表示パネル７３の文字や画像がぼけたり，歪んだりすることがない。
【０１８３】
一方，図５０（ｂ）に示される通り，暗い場所で反射型表示パネルを使用する場合は，光源がオン状態になり，流動体７７は両透明基板７４，７６の間隙から，流動体ポンプ７８により抜き取られ，基板の間隙には空気層が充填されている。このため，散乱層７５では透明基板材料のアクリル（屈折率約1.5）と空気（屈折率1.0）との間に屈折率差が生じ，本来の散乱層としての機能を有する。従って，透明基板７４，７６の端にある光源７１から内部反射を繰り返して導光してきた光は，この散乱層７５で散乱され，反射型液晶表示パネル７３を照明する。従って，暗い場所であっても，明るい表示パネルが実現できる。
【０１８４】
但し，観視者側からこのフロントライト７０を眺めると，透明基板７４の散乱層７５が見え，反射型液晶表示パネル７３の表示は歪む。しかし，かかる歪みは，従来のフロントライト付反射型液晶表示パネルと同等である。
【０１８５】
以上のとおり，明るい場所で使用される時は，フロントライトがない反射型表示パネルと同じ表示が得られ，また，暗い場所で使用される時は，点灯した光源からの光を有効に反射型液晶表示パネルの照明に使うことができ，明るい表示が実現できる。
【０１８６】
図５１は，本実施の形態例におけるフロントライト付き反射型液晶表示パネルの第２の例を示す図である。この例では，ガラスなどの２枚の透明基板７４，７６の表面に酸化インジウムを主成分とする透明電極（ITO)８１を形成し，その間隙に電界により状態が変化する液晶層８０を挟み込んでいる。そして，スイッチSWにより透明電極８１間に電圧Ｖ１が印加されたりされなかったりする。通常，このような液晶層８０は，透明電極間に電圧Ｖ１を印加した場合に透明状態になり，透明電極間の電圧を０にした場合に散乱状態になる。従って，明るい場所では，スイッチSWをオンにして，液晶層８０を透明にし，暗い場所では，スイッチSWをオフにして，液晶層８０を散乱状態にする。
【０１８７】
散乱状態と透過状態とが切り替え可能な液晶材料としては，（１）動的散乱効果を利用した液晶，（２）コレステリック相とネマティック相との間の相転移効果を利用した液晶，（３）ポリマー分散型液晶があり，いずれかの液晶が利用可能である。
【０１８８】
図５１の例は，図５０の例に比較して，散乱層を付けた透明基板，ポンプ，タンクなどが不要であり，また，流動体を充填したり引き抜いたりする時間が不要である。更に，ポリマー分散型液晶の場合は，ポリマー内の球形液晶体の屈折率異方性の程度を，印加電圧で調整することができる。従って，印加電圧を調整することで，液晶層８０の散乱度を調整することができ，光源７１の光に対する散乱度を上げて明るくするか，散乱度を下げて表示画面の歪みを抑えるかを，観察者の好みで調整させることができる。
【０１８９】
図５１の例でも，光源７１がオンして液晶層８０が散乱性を有している時は，反射型液晶表示パネルの表示が曇りガラスを通したように見えるが，それは，従来のフロントライト付反射型液晶表示パネルと同等である。そして，光源７１がオフの明るい状態では，液晶層８０が透明になり，表示がぼけたり歪んだりすることはない。すなわち，この例は，フロントライト付反射型液晶表示パネルであるが，フロントライト未点灯時はフロントライトなし反射型液晶表示パネルと同等の表示品質を可能とし，フロントライト点灯時は通常のフロントライト付反射型液晶表示パネルと同等の表示品質を有する。
【０１９０】
図５２は，フロントライト付き反射型液晶表示パネルの第３の例を示す図である。この例では，ガラスなどの透明基板７４，７６の内面に透明電極８１を形成し，更に，透明基板７４の内側に，プリズム状の細かい凹凸を有するプリズム層８２を形成する。そして，透明基板７４，７６との間に，屈折率異方性を持つ液晶層８０を封入する。屈折率異方性を有する液晶分子は，電界によって分子の配向方向が変わり，屈折率異方性の方向が変わる。そこで，屈折率異方性を持つ液晶層８０の一方の屈折率にプリズム層８２の屈折率を一致させる。
【０１９１】
図５２（ａ）に示されるとおり，明るい場所での使用では，液晶層８０に電圧を印加し，あるいは電圧無印加にし，表示側から反射型表示パネル７３に向かう方向において，プリズム層８２の屈折率と液晶層８０の屈折率とを一致させる。この状態では，表示側から反射型表示パネル７３に向かう方向において，プリズム層８２と液晶層８０との間で屈折率が一致し，プリズム層８２による散乱状態がなくなり，フロントライト構造は透明になる。その結果，フロントライトが設けられいない反射型液晶表示パネルと同じ状態になり，表示画面がぼけたり歪んだりすることがなくなる。
【０１９２】
一方，図５２（ｂ）に示されるとおり，暗い場所での使用では，液晶層８０には電圧無印加状態，あるいは印加状態にし，表示側から反射型表示パネル７３に向かう方向において，プリズム層８２の屈折率と液晶層８０の屈折率とを異ならせる。これにより，プリズム層８２と液晶層８０との界面で両者に屈折率差が生じ，光源７１からの光が屈折する。この屈折光が，反射型液晶表示パネル７３の照明光となり，明るい表示が実現できる。
【０１９３】
この例では，透明基板７４の表面にプリズム形状を形成しているが，サンドブラスト工程により透明基板７４の表面に散乱層を形成しても同様の効果が期待できる。
【０１９４】
本構造を適用することにより，上記例２と同様の効果があり，更に，液晶層８０の性質上，透過状態と散乱状態との切り替えスピードをより一層改善することができる。また，上記例２のポリマー分散型液晶に比較すると，液晶層８０への印加電圧は液晶層８０に直接電圧を印加できるので，ポリマー分散型液晶を利用するより，印加電圧をより低く抑えられる。そして，液晶層８０への電圧を印加しない状態で，液晶層の屈折率をプリズム層８２の屈折率と一致させることにより，明るい場所での使用時には，光源７１と透明電極８１への電圧印加が不要になり，より一層の低電力化を図ることができる。
【０１９５】
図５３は，フロントライト付き反射型液晶表示パネルの第４の例を示す図である。この例では，フロントライト７０の導光板である透明基板７４に形成した透明電極81Aを短冊状に分割し，それぞれに対して電圧印加81A-1，電圧無印加81A-2を選択できる構造となっている。そして，透明基板７４，７６の間に，電圧の印加により状態が変化する液晶層が充填される。図５３（ａ）は，断面構造を示し，図５３（ｂ）は分割された透明電極８１Ａの平面構造を示す。
【０１９６】
この構造にすることにより，電圧を印加する透明電極８１Ａの本数を変えることで，散乱状態になる液晶層の面積を適宜変更することが可能となり，照明光量をある程度調整することができる。従って，本構成では，散乱度の調整のできない散乱型液晶，動的散乱効果を利用した液晶，コレステリック相とネマティック相との間の相転移効果を利用した液晶などを液晶層８０に利用しても，電圧を印加する透明電極を選択することで，その散乱度を調整することができる。
【０１９７】
フロントライト付きの反射型液晶表示パネルは，フロントライトの液晶層による散乱度が大きいと，光源７１からの光をよく散乱し，反射型液晶表示パネル７３をよく照明できるため，反射型液晶表示パネルを高輝度化できる。しかし，観察者と反射型液晶表示パネルとの間に散乱層が入るため，表示画像が曇り，解像度が低下して見える。したがって，散乱度の調整が可能であれば，これを観察者が調整して，観察者にとって最適な表示品質にすることができる。
【０１９８】
図５４は，フロントライト付き反射型液晶表示パネルの第５の例を示す図である。この例では，フロントライト７０が，図５２で示した第２の例と同様に，２つの透明基板７４，７６の内側に透明電極８１が形成され，それらの間に液晶層８０が充填されている。そして，この液晶層８０は，ポリマー分散型液晶であって，ポリマーに屈折率異方性樹脂が用いられ，液晶粒９０の常光屈折率と異常光屈折率が，透明電極間に電圧が印加されない状態でポリマーの二方向の屈折率と一致するように構成されている。
【０１９９】
ポリマー分散型液晶の詳細が，図５４の右側に示される。ポリマー分散型液晶Ａは，屈折率異方性のないポリマー内に屈折率異方性を有する液晶粒９０が分散されているのに対して，ポリマー分散型液晶Ｂは，屈折率異方性があるポリマー内に屈折率異方性を有する液晶粒９０が分散されている。
【０２００】
結晶粒９０が，透明電極間に電圧を印加しない状態で，フロントライト７０の厚み方向に分子が配列して，フロントライトの厚み方向の屈折率がポリマー９２や透明基板７４，７６と一致し，透明電極間に電圧を印加した状態で，同屈折率が不一致になると仮定する。
【０２０１】
その場合，ポリマー分散型液晶Ａは，図示されるとおり，液晶粒９０の上下方向の屈折率がポリマー９２と透明基板７４，７６に一致し，上下方向の光線には屈折率差がないため，屈折，散乱が起こらない。しかし，ポリマー９２と液晶粒９０との間には水平方向の屈折率に差があるため，水平の光だけではなく，斜めからの光でも若干の，すなわち，光線の水平方向ベクトル成分に対し，屈折が生じる。このため，斜めからこの反射型液晶表示パネル７３を見た場合，この屈折によりフロントパネル７０が曇ってみえる。
【０２０２】
それに対して，ポリマー分散型液晶Ｂを透明基板７４，７６間に充填すると，透明電極間に電圧を印加しない状態で，フロントライトの厚み方向に液晶分子が配列して，液晶粒９０の屈折率異方性の方向とポリマー９２の屈折率異方性の方向とが一致する。従って，この状態では，液晶粒９０とポリマー９２との屈折率差がどの方向からも全くなくなり，フロントライトはどの方向からも透明になる。そのため，ポリマー分散型液晶Ａを利用する場合に比較して，明るいところでの使用時において斜めからの画像の歪み，曇りを防止することが可能となる。
【０２０３】
一方，暗い場所で使用する場合に，透明電極間に電圧を印加すると，図中に示されるとおり，液晶粒９０の屈折率異方性の方向が，ポリマー９２の屈折率異方性の方向と不一致状態になる。ポリマー９２の異方性の方向は，電界により変化しないからである。そのため，フロントライト７０は散乱状態になり，光源７１からの光が反射型液晶表示パネル７３側に散乱し，液晶表示面を明るくする。但し，液晶層８０がクリーム色になり，表示画面にボケや歪みが生じる。
【０２０４】
その場合，透明電極間に印加する電圧を調整することにより，液晶粒９０の屈折率異方性の方向を調整することができる。つまり，印加電圧を上げると，液晶層での散乱度が大きくなり，反射型液晶表示パネル７３への入射光が多くなり画面が明るくなるが，画面が白くなりすぎて見えにくくなる。一方，印加電圧を下げると，液晶層での散乱度が小さくなり，画面が暗くなるが，画面の透明度が増すことになる。そこで，この印加電圧を調整することにより，画面の輝度の程度と，コントラストの程度を観察者の好みに応じて設定することができる。
【０２０５】
図５５は，フロントライト付き反射型液晶表示パネルの第６の例を示す図である。図５０〜５４の従前の例では，光源７１のからの光を２枚の透明基板内を導光させている。それに対して，図５５の例では，２枚の透明基板の内，表示面側の基板７４の側面に光源７１を配置し，その表示面側基板７４内を主に光を導光させる。そして，この基板７４の反射型液晶表示パネル７３側面に配置したプリズム状凹凸８２により光を散乱させ，反射型液晶表示パネル７３を照明する。透明基板７４，７６には，図示しない透明電極が形成され，その間に液晶層８０が充填されている。
【０２０６】
図５０〜５４のように，上下２枚の透明基板７４，７６に光を導光させた場合，プリズム状凹凸８２へは上下の透明基板から導光する光が当たる。その場合，上方の透明基板７４からの光は屈折散乱を起こして下方側に透過し，下方の透明基板７６からの光は反射散乱を起こしてやはり下方側に反射することが望まれる。しかし，実際には，光は屈折散乱して透過するほうが，反射散乱して下方側に向かうよりも多く，下方側の基板からの光を効率的に反射散乱させることは困難である。
【０２０７】
それに対して，図５５の構成の場合は，プリズム層８２が，光源からの光を伝わる透明基板７４の表示パネル７３側に設けられている。従って，プリズム層８２に照射される光は，上方の透明基板７４を伝わってきた光であり，プリズム層８２を屈折散乱してより多くの光が反射型液晶表示パネル７３側に入射する。従って，プリズム状凹凸８２を，屈折散乱形状とすればよく，形状の簡単化，照明効率の向上を図ることができる。
【０２０８】
同様に，散乱性を発現する液晶層８０を封入した場合も，その液晶層８０に対して，上方から光のより多くが散乱して下方側に通過し，反射散乱する光の量は少ない。従って，上記の構造のほうが，照明効率を高くすることができる。また，光源７１からの光は，１枚の透明基板７４しか導光せず光源からの入射量が減るが，透明基板７４の厚みを厚くすることにより，光源７１からの光の入射量を改善することができる。
【０２０９】
図５６は，フロントライト付き反射型液晶表示パネルの第７の例を示す図である。図５６の構成は，図５５の構成を改良したものである。即ち，図５６は，側面に光源７１を配置した透明導光板９４と，２枚の透明基板７４，７６に散乱性を発現する要素を封入した基板を貼り合せた構造である。具体的には，ガラスなどからなる透明基板７４，７６の間に，プリズム層８２を形成し，電界により屈折率状態が変化する液晶層８０を充填した散乱用基板が，透明の導光板９４に光学接着９６により張り合わされる。この構造の場合は，散乱性を発現する要素を封入した２枚の透明基板７４，７６の製造と，光源付導光板９４の製造を分離することができ，製造工程の分離，歩留まりの向上が可能となる。また，液晶層８０を挟むガラス基板７４，７６は，例えば０．５〜０．７mmと薄型しており，その分前記光源７１を配置した透明導光板９４の板厚を厚くして，光源からの光の入射効率を改善することも容易になる。
【０２１０】
以上，本実施の形態例におけるフロントライト構造は，暗い場所で光源を点灯したて使用するときのみ，光源からの照射光を散乱させて反射型液晶表示パネル側に入射させ，光源を点灯しない通常使用時は，散乱性がなくなる。従って，通常使用時の，表示画面の文字や画像のボケや歪みをなくすことができ，コントラストを向上させることができる。しかも，暗い場所でも明るい表示画面を実現することができる。
以上の実施の形態をまとめると以下の付記の通りになる。
（付記１）反射型液晶表示装置の製造方法において，
（ａ）所定の膜厚を有する感光性樹脂層の表面に露光エネルギーを有する光を照射して，感光性樹脂層の厚さ方向または平面方向に熱的変形特性の分布を形成する工程と，
（ｂ）その後熱処理を行って感光性樹脂層の表面にランダムな凹凸を形成する工程とを有することを特徴とする反射型液晶表示装置の形成方法。
（付記２）反射型液晶表示装置の製造方法において，
（ａ）所定の膜厚を有する感光性樹脂層を，酸，アルカリ溶液，４級アンモニウム塩溶液，HMDSのいずれかを有する薬液に浸して，感光性樹脂層の厚さ方向または平面方向に熱的変形特性の分布を形成する工程と，
（ｂ）その後熱処理を行って感光性樹脂層の表面にランダムな凹凸を形成する工程とを有することを特徴とする反射型液晶表示装置の形成方法。
（付記３）付記１において，
前記工程（ａ）において，前記露光エネルギーを有する光は，遠紫外線であることを特徴とする反射型液晶表示装置の形成方法。
（付記４）付記１において，
前記工程（ａ）において，前記露光エネルギーを有する光を，感光性樹脂層の表面全面に照射して変質させ，感光性樹脂層の厚さ方向に熱的変形特性の分布を形成することを特徴とする反射型液晶表示装置の形成方法。
（付記５）付記１において，
前記工程（ａ）において，前記露光エネルギーを有する光を，感光性樹脂層の表面の一部の領域に照射して変質させ，感光性樹脂層の平面方向に熱的変形特性の分布を形成することを特徴とする反射型液晶表示装置の形成方法。
（付記６）付記１または２において，
前記工程（ａ）の前に，前記感光性樹脂層にその膜厚が少なくなる分離ラインを形成する工程を更に有することを特徴とする反射型液晶表示装置の形成方法。
（付記７）反射型液晶表示装置の製造方法において，
（ａ）表面にトランジスタが形成された基板上に，所定の膜厚を有する感光性樹脂層を形成する工程と，
（ｂ）前記感光性樹脂層を一部露光，現像するフォトリソグラフィ工程により前記トランジスタの電極へのコンタクトホールを形成する工程と，
（ｃ）前記感光性樹脂層を第１の温度に加熱するポストベーク工程と，
（ｄ）前記感光性樹脂層の表面に露光エネルギーを有する光を照射して，感光性樹脂層の厚さ方向または平面方向に熱的変形特性の分布を形成する工程と，
（ｅ）その後前記第１の温度以上の高い第２の温度で熱処理を行って前記感光性樹脂層の表面にランダムな凹凸を形成する最終ベーク工程とを有することを特徴とする反射型液晶表示装置の形成方法。
（付記８）付記７において，
前記工程（ｅ）の後に，前記トランジスタの電極に前記スルーホールを介して接続される画素電極を前記感光性樹脂層の上に形成する工程を更に有することを特徴とする反射型液晶表示装置の形成方法。
（付記９）付記７において，
前記工程（ｃ）の前に，前記感光性樹脂層を所定のパターンで露光またはハーフ露光し，現像して，該感光性樹脂層を分離する分離ラインを形成する工程を更に有することを特徴とする反射型液晶表示装置の形成方法。
（付記１０）付記７において，
前記工程（ａ）における感光性樹脂層の膜厚，前記工程（ｃ）におけるポストベーク温度及び時間，前記工程（ｄ）における照射エネルギー量を制御して，前記凹凸の平均傾斜角が０〜１５°になるようにすることを特徴とする反射型液晶表示装置の形成方法。
（付記１１）付記１０において，
前記画素電極を形成する工程の後に，配向膜を形成し，表示側基板の配向膜との間に液晶層を形成する工程とを有することを特徴とする反射型液晶表示装置の形成方法。
（付記１２）反射型液晶表示装置において，
液晶層が形成された基板を有し，前記基板の液晶層側に形成される反射用凹凸の傾斜角が少なくとも０°〜２０°の範囲に分布し，前記傾斜角の存在確率が１５°〜１９°の範囲でピークになることを特徴とする反射型液晶表示装置。
（付記１３）付記１２において，
前記反射用凹凸の平面パターンが，円形，多角形，ストライプ形状またはこれらの組み合わせを有することを特徴とする反射型液晶表示装置。
（付記１４）反射型液晶表示装置において，
液晶層が形成された基板を有し，前記基板の液晶層側に形成される反射用凹凸の傾斜角が，第１の方向に沿ってその存在確率が１つのピークを有し，前記第１の方向と異なる第２の方向に沿ってその存在確率が２つのピークを有するように分布することを特徴とする反射型液晶表示装置。
（付記１５）付記１４において，
前記反射型液晶表示装置の表示面が傾けて配置され，
前記第１の方向が水平方向であり，前記第２の方向が垂直方向であることを特徴とする反射型液晶表示装置。
（付記１６）付記１４または１５において，
前記第１の方向に沿った存在確率が，１５°〜１９°の範囲で１回ピークになり，前記第２の方向に沿った存在確率が，１５°〜１９°の範囲と０°〜１４°の範囲それぞれでピークになることを特徴とする反射型液晶表示装置。
（付記１７）付記１４または１５において，
表示面内の画素領域それぞれにおいて，第１の領域では前記第２の方向に沿った存在確率が第１の角度範囲と第２の角度範囲でピークを有し，第２の領域では前記第２の方向に沿った存在確率が該第１の角度範囲と第３の角度範囲でピークを有することを特徴とする反射型液晶表示装置。
（付記１８）付記１２乃至１５のいずれかにおいて，
更に，前記基板と共に前記液晶層を挟む表示側基板と，当該表示側基板の表示側に形成された偏光板を有し，前記液晶層が電界効果複屈折モードで駆動されることを特徴とする反射型液晶表示装置。
（付記１９）反射型液晶表示装置において，
基板上に反射用凹凸を有し，単一の画素領域内に，反射光について第１の指向性と第１の散乱性を有する第１の凸部と，前記反射光について前記第１の指向性より弱い第２の指向性と前記第１の散乱性より強い第２の散乱性を有する第２の凸部とがランダムに混在することを特徴とする反射型液晶表示装置。
（付記２０）反射型液晶表示装置において，
基板上に反射用凹凸を有し，前記凹凸は，感光性樹脂膜により形成され，第１の円形パターン同士が第１の距離以上離間して配置され，前記第１の円形パターンより小さい第２の円形パターンが前記第１の円形パターンと前記第１の距離未満離間して配置されていることを特徴とする反射型液晶表示装置。
（付記２１）反射型液晶表示装置において，
基板上に反射用凹凸を有し，前記凹凸は，感光性樹脂膜により形成され，複数の多角形パターンが隣接する多角形の辺どうしが平行になるように配置されていることを特徴とする反射型液晶表示装置。
（付記２２）反射型液晶表示装置において，
反射型液晶表示パネルと，
前記反射型液晶表示パネル上に設けられ，導光板と，該導光板の端部に配置した光源と，前記光源が点灯した時に該導光板を伝わる光に対して光散乱性を発現し，前記光源が非点灯時に前記光散乱性が減少する光散乱手段とを有するフロントライトとを有することを特徴とする反射型液晶表示装置。
（付記２３）付記２２において，
前記導光板及び光散乱手段は，１対の透明基板と，その対向面に形成された透明電極と，前記透明基板対間に形成された液晶層とを有する液晶パネルを有し，前記液晶層は，前記透明電極間に印加される電界に応じて光散乱性を発現することを特徴とする反射型液晶表示装置。
（付記２４）付記２３において，
前記光源が，前記１対の透明基板のうち表示側の透明基板の側面に配置され，前記液晶層が，当該表示側の透明基板と前記反射型液晶表示パネル側の透明基板との間に設けられていることを特徴とする反射型液晶表示装置。
（付記２５）付記２２において，
前記光散乱手段は，１対の透明基板と，その対向面に形成された透明電極と，前記透明基板対間に形成された液晶層とを有する液晶パネルを有し，前記液晶層は，前記透明電極間に印加される電界に応じて光散乱性を発現し，前記１対の透明基板が前記導光板に張り合わされていることを特徴とする反射型液晶表示装置。
（付記２６）付記２３乃至２５のいずれかにおいて，
前記液晶層は，印加される電界に応じて屈折率異方性の方向が変化し，
前記透明基板のいずれか一方と前記液晶層との間に，透明なプリズム状の凹凸層が設けられ，前記凹凸層の屈折率が，液晶層の一方の屈折率と整合することを特徴とする反射型液晶表示装置。
（付記２７）付記２３乃至２５のいずれかにおいて，
前記透明電極が複数に分離され，当該分離された透明電極に選択的に電圧を印加して，前記液晶層の光散乱の程度が調整されることを特徴とする反射型液晶表示装置。
（付記２８）付記２３乃至２５のいずれかにおいて，
前記液晶層は，動的散乱効果を利用した液晶材料，コレステリック相とネマティック相との間の相転換効果を利用した液晶材料，ポリマー内に屈折率異方性を有する液晶粒を有する第１のポリマー分散型液晶材料，屈折率異方性を有するポリマー内に屈折率異方性を有する液晶粒を有する第２のポリマー分散型液晶材料のうち，いずれかであることを特徴とする反射型液晶表示装置。
【０２１１】
【発明の効果】
以上，本発明によれば，反射型液晶表示装置の反射用凹凸を，簡単なプロセスで形成することができ，しかも，所望の凹凸による傾斜面分布を制御性良く形成することができる。更に，本発明によれば，最適な反射用凹凸による傾斜面分布を得ることができ，反射率を向上させることができる。
【図面の簡単な説明】
【図１】本実施の形態例が適用される液晶表示装置の回路図の例である。
【図２】本実施の形態例が適用される反射型液晶表示装置の断面図の例を示す図である。
【図３】本実施の形態例における反射型液晶表示装置の製造プロセスの一部を示す断面図である。
【図４】感光性樹脂層２０の膜厚とＵＶ照射エネルギーを変化させて形成された反射パネルのマイクログルーブの表面形状の顕微鏡写真を示す図である。
【図５】感光性樹脂層２０の膜厚とＵＶ照射エネルギーを変化させて形成された反射パネルのマイクログルーブの表面形状の顕微鏡写真を示す図である。
【図６】感光性樹脂層２０の膜厚とＵＶ照射エネルギーを変化させて形成された反射パネルのマイクログルーブの表面形状の顕微鏡写真を示す図である。
【図７】感光性樹脂層２０の膜厚とＵＶ照射エネルギーを変化させて形成された反射パネルのマイクログルーブの表面形状の顕微鏡写真を示す図である。
【図８】３つの反射パネルのサンプルのAFM像を示す図である。
【図９】拡散光源に対する反射膜の平均傾斜角と反射率との関係を示すグラフ図である。
【図１０】図８の３つのサンプルに対するレジスト膜厚と反射率との関係を示すグラフ図である。
【図１１】本実施の形態例により形成される樹脂層のマイクログルーブの凹凸形状を模式的に示す図である。
【図１２】本実施の形態例により形成されるマイクログルーブの平面パターン例を示す図である。
【図１３】マイクログルーブを形成するために必要なＵＶ照射例を示す図である。
【図１４】第１のサンプルの製造プロセスを示す断面図である。
【図１５】第１，第２，第３のサンプルに積分球の拡散光源を照射した時の反射率を比較したグラフ図である。
【図１６】感光性樹脂層の分離を説明する図である。
【図１７】感光性樹脂層の分離ラインを形成するプロセスを示す断面図である。
【図１８】分離ラインを形成した場合と形成しない場合のマイクログルーブの顕微鏡写真を示す図である。
【図１９】本実施の形態例が想定する反射型液晶表示装置が使用される実環境を示す図である。
【図２０】入射光の入射角θiと方位角φiを示す図である。
【図２１】反射型表示装置に光が入射して反射する場合を示す図である。
【図２２】反射板に入射する光の強度f(θ_i')と入射角θ_i'との関係を示す図である。
【図２３】図２３の入射光強度が最大となる入射角θ_i'と媒体の屈折率nとの関係を示す図である。
【図２４】反射凹凸の傾斜面に対する入射角，反射角，傾斜角との関係を示す図である。
【図２５】図２２の入射光強度分布に対応した傾斜角の存在確率の分布を示す図である。
【図２６】反射特性のシミュレーション結果を示す図である。
【図２７】実際に試作したサンプルを使って，積分球の均一な拡散光に対する反射率を測定した結果を示す図である。
【図２８】試作した反射板の形成方法を示す断面図である。
【図２９】反射板の凹凸を形成するための，マスク６４のパターン例を示す図である。
【図３０】積分球の拡散光に対して高い反射率が得られる反射板の凹凸の傾斜角分布を示す図である。
【図３１】反射型液晶表示装置がノート型パーソナルコンピュータのモニターとして搭載された状態を示す図である。
【図３２】ノート型パーソナルコンピュータの表示装置として利用される場合の，高い反射率を有するＸＹ面方向およびＸＺ面方向の傾斜角の分布を示す図である。
【図３３】図３２の傾斜角分布を，傾斜角０°を中心に折り返した分布を示す図である。
【図３４】サンプルの反射板の形成方法を示す断面図である。
【図３５】図３４のマスクパターンの例を示す図である。
【図３６】図３４の凸部の平面，断面形状の例を示す図である。
【図３７】試作した反射板の傾斜角分布の測定結果を示す。
【図３８】試作した反射板を用いて作成した反射型液晶表示装置の概略断面図である。
【図３９】図３８の反射型液晶表示装置の反射率の測定結果を示す図である。
【図４０】反射型液晶表示装置の傾き角度と，液晶層の屈折率に対する，存在確率が極大になる傾斜角範囲を示す図である。
【図４１】画素領域内に混在する２つの反射凹凸形状を示す断面図である。
【図４２】本実施の形態例における画素領域ＰＫの平面図である。
【図４３】図４２の反射用凹凸を形成する製造プロセスを示す断面図である。
【図４４】従来のレジストの円形パターン例を示す図である。
【図４５】本実施の形態例におけるレジストの円形パターン例を示す図である。
【図４６】図４５の円形パターンを説明するための図である。
【図４７】本実施の形態例におけるレジストの多角形パターン例を示す図である。
【図４８】本実施の形態例におけるレジストの多角形パターン例を示す図である。
【図４９】従来提案されているフロントライト付き反射型液晶表示パネルの構成図である。
【図５０】フロントライト付き反射型液晶表示パネルの第１の例を示す図である。
【図５１】フロントライト付き反射型液晶表示パネルの第２の例を示す図である。
【図５２】フロントライト付き反射型液晶表示パネルの第３の例を示す図である。
【図５３】フロントライト付き反射型液晶表示パネルの第４の例を示す図である。
【図５４】フロントライト付き反射型液晶表示パネルの第５の例を示す図である。
【図５５】フロントライト付き反射型液晶表示パネルの第６の例を示す図である。
【図５６】フロントライト付き反射型液晶表示パネルの第７の例を示す図である。
【符号の説明】
１０ 絶縁基板
２０ 感光性樹脂層（レジスト層）
２２ 反射電極
３４ 液晶層
６０ 反射板
ＣＨ コンタクトホール
ＭＧ マイクログルーブ，反射用凹凸[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reflective liquid crystal display device and a manufacturing method thereof, and more particularly to a reflective liquid crystal display device having a scattering reflector structure having a high reflectance by a simple process and a manufacturing method thereof.
[0002]
[Prior art]
In recent years, a reflection type liquid crystal display device which can realize a light weight, a thin shape, and low power consumption in a liquid crystal panel using an active matrix has been attracting attention. The reflection type liquid crystal display device takes in light from the outside into the display panel and reflects it with a reflector provided on the back side, thereby eliminating the need for a backlight and reducing power consumption. Therefore, it is useful as a display device for a portable information terminal or a cellular phone.
[0003]
External light depends on the environment in which the display device is used. Therefore, it is desirable that the reflection plate provided in the display panel has a light scattering reflection structure that reflects light entering from a random direction in a random direction.
[0004]
As such a reflective liquid crystal display device, a structure is proposed in which pixel electrodes are formed in a film shape having irregularities, and external light is irregularly reflected by the pixel electrodes having irregularities. For example, JP-A-5-232465 and JP-A-8-338993. The reflection type liquid crystal display devices described in these publications use a photolithographic process using a mask pattern or a combination of a polishing process and an etching process to form irregularities on the pixel electrode. Yes.
[0005]
In these conventional examples, a high reflectance can be obtained by forming an arbitrary uneven pattern on the reflective electrode. However, controlling the shape of the reflective electrode using photolithography is a complicated process. Furthermore, there is a problem that the margin of the manufacturing process is narrow because the reflection characteristics greatly change when the shape changes depending on the exposure conditions.
[0006]
As a method for improving this, Japanese Patent Laid-Open No. 5-80327 discloses a method of simplifying the process by using a thin film resin layer having a different thermal expansion coefficient from that of the reflective electrode. However, in this method, after forming the organic film, a metal film is formed by a heat sputtering method to form irregularities on the surface of the pixel electrode. However, this method may cause degassing from the organic film during the heating process in vacuum, resulting in a change in the film quality of the reflective film, or formation of minute irregularities on the reflective film that degrade the reflective properties. , Not a practical process.
[0007]
Japanese Patent Application Laid-Open No. 2000-193807 discloses a technique for forming a fine concavo-convex shape in an organic film using a fluororesin having a fluoroaliphatic ring structure in the main chain. However, this method requires a baking process at a high temperature of 350 ° C in addition to using a special resin. Further, as shown in this publicly known example, since the resin itself is not photosensitive, when forming irregularities on the pixel electrode connected to the thin film transistor, a resist is separately coated and contacted by a photolithography process. Holes need to be formed, complicating the process.
[0008]
Furthermore, Japanese Patent Application No. 10-253977 has a random uneven distribution by forming unevenness having a variation distribution in the depth direction by using the intensity distribution of speckles generated when irradiated with coherent light. The formation of a reflector is described. However, this method requires a special exposure apparatus, and the exposure apparatus itself is large and expensive, which is not practical.
[0009]
[Problems to be solved by the invention]
As described above, various reflection type liquid crystal display devices using the scattering reflection electrode as the pixel electrode have been proposed. In any case, it is possible to form the scattering reflection electrode having sufficient reflectance by a simple manufacturing process. Can not. Furthermore, in order to form an optimal reflective electrode structure, for example, it is necessary to control the average inclination angle of unevenness and the inclination angle distribution within an optimal range. No manufacturing process has been proposed that can be well controlled.
[0010]
Further, the inclination angle of the unevenness of the reflector in the conventional reflection type liquid crystal display device is selected so as to obtain the maximum reflectance with respect to the incident light from a specific direction. In the conventionally proposed reflector, the inclination angle of the unevenness is set to, for example, 10 ° to 20 ° (Japanese Patent Laid-Open No. 11-259018), and the inclination angle of the unevenness of the reflection plate is 5 ° to 25 °. A uniform angle (Japanese Patent Laid-Open No. 08-227071), the average inclination angle of the unevenness of the reflector is 30 ° or less (Japanese Patent Laid-Open No. 56-156865), and the height of the unevenness is a Gaussian distribution. Yes, the average inclination angle of the irregularities is 10 ° (Tohru Koizumi and Tatsuo Uchida, Proceedings of the SID, vol.29, p.157, 1988), and the reflector surface is a smooth irregular surface and The uneven average inclination angle is selected to be 4 to 15 ° (Japanese Patent Laid-Open No. 6-175126).
[0011]
However, in these conventional examples, no examination is made as to whether the reflectance is highest when external light is incident on the display panel from all directions. Therefore, no reflection type liquid crystal display device is proposed in the prior art, which is brightened by reflection of external light with high reflectivity even in various environments.
[0012]
Furthermore, in the conventional example, it is assumed that the external light incident on the display panel of a notebook computer or the like is omnidirectional in a certain direction and has a specific direction in a different direction. No shape has been proposed.
[0013]
Further, a reflecting plate structure has been conventionally proposed in which a resist film is formed, exposed and developed with a predetermined mask pattern, and then baked to smooth the cross-sectional structure of the resist film to form a desired inclined surface. However, no optimum pattern shape has been proposed in such a manufacturing process. In addition, a method for forming a reflective concavo-convex shape having both directivity and scattering within the same pixel region has not been proposed.
[0014]
Furthermore, since the reflective liquid crystal display device uses external light, it is necessary to provide a light source in order to use it in a dark place. However, when a structure in which light from the light source is scattered and incident on the display panel side is employed, there is a problem that the display image is blurred by the scattering structure and the contrast is deteriorated.
[0015]
Accordingly, an object of the present invention is to manufacture a liquid crystal display device that can realize a simplified reflector, a yield improvement, a reduction in manufacturing cost, and a reflector that can stably realize high reflection characteristics. It is to provide a method.
[0016]
Furthermore, another object of the present invention is to provide a reflection type liquid crystal display device having a reflector having a high reflectance even when external light is incident from various directions.
[0017]
Furthermore, another object of the present invention is to provide a reflection type liquid crystal display device having a reflection plate having a high reflectance on a display screen of a notebook personal computer or the like.
[0018]
Furthermore, another object of the present invention is to provide a reflective liquid crystal display device having an optimum resist film pattern shape for forming reflective irregularities.
[0019]
Furthermore, another object of the present invention is to provide a reflective liquid crystal display device with a front light which can be used in a dark place and has improved contrast by eliminating blurring of the display screen during normal use. is there.
[0020]
[Means for Solving the Problems]
In order to achieve the above object, according to a first aspect of the present invention, in a method for manufacturing a liquid crystal display device, light having exposure energy is irradiated on the surface of a photosensitive resin layer having a predetermined film thickness, thereby After forming the distribution of thermal deformation characteristics in the thickness direction (or plane direction) of the photosensitive resin layer, heat treatment is performed to cause random irregularities (micro grooves, fine grooves, or fine wrinkles on the surface of the photosensitive resin layer. ).
[0021]
The photosensitive resin layer is irradiated with light having exposure energy such as deep ultra violet (DUV), for example, and is partially exposed to partially change the photosensitive resin layer. Thereby, a distribution of thermal deformation characteristics can be formed in the thickness direction (or plane direction) of the photosensitive resin layer. Thereafter, by performing a heat treatment at a glass transition temperature or higher, random irregularities can be formed on the surface of the photosensitive resin layer.
[0022]
It is preferable that the DUV irradiation is controlled to energy irradiation that only a part of the surface side in the depth direction of the photosensitive resin layer is exposed. As a result, up to a certain depth on the surface side of the photosensitive resin layer is altered by the crosslinking / decomposition reaction, and the surface side region and the back side region have different thermal deformation characteristics. Therefore, during the subsequent heat treatment, random irregularities are formed on the surface due to the difference in thermal deformation characteristics between the front side and the back side of the photosensitive resin layer.
[0023]
Or you may perform energy irradiation of the grade which exposes DUV irradiation only to the one part area | region of the surface of the photosensitive resin layer. In that case, an exposure process using a mask film is required. Even if the distribution of thermal deformation characteristics is formed in the plane direction, different thermal deformation occurs in the plane direction in the subsequent heat treatment process, and random irregularities are formed on the surface.
[0024]
The pitch and height difference (roughness and fineness of the unevenness) of the above-mentioned random unevenness-shaped grooves and ridges can be controlled with good reproducibility by the film thickness of the photosensitive resin layer, irradiation energy, and the like. Furthermore, the uneven shape can also be controlled by the heat treatment temperature and time for the photosensitive resin layer before irradiation with energy light.
[0025]
For example, when the thickness of the photosensitive resin layer is small, the height difference of the unevenness is small and the pitch is small, and when the thickness of the photosensitive resin layer is large, the height difference of the unevenness is large and the pitch is large. In addition, when the irradiation energy is small, the uneven height difference is small and the pitch is small, and when the irradiation energy is large, the uneven height difference is large and the pitch is large. Furthermore, when the heat treatment temperature before irradiation with energy light is low and the time is short, the uneven height difference is large and the pitch is large, and when the heat treatment temperature is high and the time is long, the uneven height difference is small and the pitch is small.
[0026]
Therefore, a random uneven shape can be processed into a desired shape by appropriately selecting the above conditions. Moreover, the process is an extremely simple process of irradiating energy light and then performing heat treatment, and is very practical.
[0027]
The photosensitive resin layer of the present invention is preferably used for an insulating film between a source electrode and a pixel electrode of a thin film transistor for driving the pixel electrode. In that case, it is necessary to form a contact hole for connecting the pixel electrode and the source electrode. However, a contact hole is formed by subjecting the photosensitive resin layer to a photolithography process, and partially exposing and developing. can do. And the desired random uneven | corrugated shape can be formed in the surface by performing irradiation of said energy light and subsequent heat processing to the photosensitive resin layer. By forming a pixel electrode on such a photosensitive resin layer, a reflective pixel electrode having desired random irregularities can be formed.
[0028]
Instead of irradiation with light having the above-described photosensitive energy, wet treatment with any one of an acid, an alkali solution, a quaternary ammonium salt solution, and HMDS (Hexa-methyl-di-silazane) can be used. By immersing the photosensitive resin layer in such a chemical solution, it is possible to cause a chemical reaction on the surface of the photosensitive resin layer and to change the material into materials having different thermal deformation characteristics.
[0029]
In order to achieve the above object, a second aspect of the present invention provides a reflective liquid crystal display device having a substrate on which a liquid crystal layer is formed, and having reflective irregularities formed on the liquid crystal layer side of the substrate. The inclination angle is distributed in a range of at least 0 ° to 20 °, and the existence probability of the inclination angle peaks in a range of 15 ° to 19 °.
[0030]
In the case of having the distribution of the inclination angles of the reflection unevenness, the highest reflectance can be obtained in an environment where external light is incident on the display surface from all directions. That is, when considering diffused light from an integrating sphere in which external light is incident on the display surface from all directions, the incident light intensity into the liquid crystal layer is within the range of 30 ° to 38 ° in the liquid crystal layer. The intensity is strongest at other angles, and the incident intensity decreases at other incident angles. Therefore, in order to reflect the incident light in the range of the incident angle of 30 ° to 38 ° where the incident light intensity becomes the highest in the normal direction of the display surface, the existence probability of the inclination angle of the reflection unevenness is 15 °. It is necessary to have a peak in the range of ˜19 °.
[0031]
However, since there is an incident angle in a range other than the incident angle of 30 ° to 38 °, it is preferable that the inclination angle of the reflection unevenness is distributed in the range of at least 0 ° to 20 ° accordingly.
[0032]
In this case, the inclination angle distribution is more preferably a distribution corresponding to the incident intensity of the incident light in the liquid crystal layer. For example, by setting the distribution of the inclination angle of the reflection unevenness corresponding to the incident intensity distribution of the incident light in the liquid crystal layer specified by the incident state of the external light in the environment where the display panel is used, A high amount of reflected light can be obtained.
[0033]
In order to achieve the above object, a third aspect of the present invention provides a reflective liquid crystal display device having a substrate on which a liquid crystal layer is formed, and reflecting irregularities formed on the liquid crystal layer side of the substrate. The inclination angle is distributed so that the existence probability has one peak along the first direction and the existence probability has two peaks along a second direction different from the first direction. It is characterized by.
[0034]
According to the above invention, for example, when the display panel of a notebook computer is tilted in a certain direction, external light is incident at a relatively wide range of incident angles in the horizontal direction of the display panel. In the vertical direction of the panel, external light is incident at a relatively narrow incident angle because it is blocked by the keyboard. Under such an environment, along the horizontal direction of the display panel, the inclination angle distribution of the reflection unevenness has a peak in the range where the existence probability is, for example, 15 ° to 19 °, and is along the vertical direction of the display panel. Therefore, it is preferable that the inclination angle distribution of the unevenness for reflection has a peak in two ranges of existence probabilities. In this way, the highest reflected light amount can be realized by changing the inclination angle distribution of the reflection unevenness according to the direction of the incident angle.
[0035]
In order to achieve the above object, according to a fourth aspect of the present invention, there is provided a reflective liquid crystal display device having reflective irregularities on a substrate, and a first directivity for reflected light within a single pixel region. And a first convex part having a first scattering property, a second directivity weaker than the first directivity for the reflected light, and a second scattering property stronger than the first scattering property. The two convex portions are mixed randomly.
[0036]
According to the above-described invention, it is possible to efficiently reflect the reflected light with respect to the incident light by mixing the convex portion having strong directivity and the convex portion having strong scattering property in a single pixel region.
[0037]
In order to achieve the above object, according to a fifth aspect of the present invention, there is provided a reflective liquid crystal display device having a reflective unevenness on a substrate, the unevenness being formed by a photosensitive resin film, The circular patterns are arranged apart from each other by a first distance or more, and a second circular pattern smaller than the first circular pattern is arranged apart from the first circular pattern by less than the first distance. It is characterized by.
[0038]
According to the above invention, the relatively large circular pattern is arranged so as not to be merged at the time of post-baking after exposure / development of the photosensitive resin film. it can. In addition, since the relatively small circular pattern is arranged in the vicinity of the large circular pattern, the density of the inclined surface can be increased. Even if a small circular pattern and a large circular pattern are merged during post-baking, the merged area is narrow, so the adverse effects caused by this are limited.
[0039]
In order to achieve the above object, according to a sixth aspect of the present invention, there is provided a reflective liquid crystal display device having reflective irregularities on a substrate, wherein the irregularities are formed of a photosensitive resin film, The square pattern is arranged so that sides of adjacent polygons are parallel to each other.
[0040]
According to the above invention, the opposing sides are arranged in parallel so that adjacent patterns do not merge at the time of post-baking after exposure / development of the photosensitive resin film. And since the polygonal pattern in which the inclined surface faces in a plurality of directions is arranged with high density, the randomness in the direction of the inclined surface can be made equal to the circular pattern.
[0041]
In order to achieve the above object, according to a seventh aspect of the present invention, in a reflective liquid crystal display device, a reflective liquid crystal display panel, a light guide plate provided on the reflective liquid crystal display panel, and the light guide plate A light source arranged at the end of the light source, and a light scattering means that expresses light scattering for light transmitted through the light guide plate when the light source is turned on and reduces the light scattering when the light source is not turned on And a front light.
[0042]
According to the above invention, when used in a dark state, the light source is turned on and the display screen is brightened by the incidence of scattered light, and when used in a bright state, the light source is turned off and displayed by outside light. The screen is brightened and the light scattering property of scattering the light from the light source is reduced, thereby preventing the display image from being blurred or distorted.
[0043]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. However, this embodiment does not limit the technical scope of the present invention.
[0044]
FIG. 1 is an example of a circuit diagram of a liquid crystal display device to which this embodiment is applied. Pixels are formed in a matrix in the display area 11 of the insulating substrate 10 on the back side. The pixel has drive transistors T00 to Tmn and pixel electrodes P00 to Pmn, and the drive transistors T00 to Tmn include scanning lines S0 to Sm arranged in the row direction and data lines D0 to Dn arranged in the column direction. And connected respectively. Outside the display area 11, a scanning line driving circuit 12 for driving scanning lines and a data line driving circuit 13 for driving data lines are provided.
[0045]
FIG. 2 is a diagram showing an example of a cross-sectional view of a reflective liquid crystal display device to which the present embodiment is applied. In the reflective liquid crystal display device, a liquid crystal layer 34 is provided between the insulating substrate 10 on the back side and the transparent substrate 30 on the display side, and the reflective electrode 22 is formed on the insulating substrate 10 on the back side. The incident external light is reflected on the surface of the reflective electrode 22, passes through the liquid crystal layer 34, and is emitted to the display side again.
[0046]
On the insulating substrate 10, a gate electrode 15 connected to a scanning line (not shown), an insulating layer 16, a drain electrode 17 connected to the semiconductor layer 19 and the data line, and a source electrode 18 are formed. Further, a reflective electrode 22 as a pixel electrode is formed on the resin layer 20 of the interlayer insulating film, and the reflective electrode 22 is connected to the source electrode 18 through the contact hole CH. An alignment film 23 made of polyimide or the like is formed on the resin layer 20 and the reflective electrode 22. Random irregularities for irregularly reflecting incident light are formed on the surface of the resin layer 22, and accordingly, random irregularities are also formed on the surface of the pixel electrode (reflecting electrode) 22 deposited thereon.
[0047]
The transparent substrate 30 on the display side is formed with a transparent electrode 31 such as ITO (a material containing indium oxide as a main component) and an alignment film 32 on one side and a polarizing plate 33 on the other side. A liquid crystal layer 34 is inserted between the alignment film 32 on the display side and the alignment film 23 on the back side. The alignment direction of the liquid crystal molecules in the liquid crystal layer 34 is a direction corresponding to the surface shape of the alignment films 32 and 23 and the characteristics thereof.
[0048]
[Method of forming microgrooves]
FIG. 3 is a cross-sectional view showing a part of the manufacturing process of the reflective liquid crystal display device according to the present embodiment. FIG. 3 shows a part of the source electrode 18 of the thin film transistor shown in FIG. As shown in FIG. 3A, after forming the insulating layer 16, each electrode of the thin film transistor, and the semiconductor layer on the insulating substrate 10, the photosensitive resin 20, for example, LC200 (novolak resin), which is a general-purpose resist manufactured by Shipley, is used. , Is applied. The resin layer 20 is spin-coated by a spinner with a film thickness of about 0.5 to 2.0 μm. In this case, for example, the first resist layer is formed by spin coating for 3 seconds at a rotation speed of about 350 rpm, and further the resist layer is formed by spin coating for 20 seconds at a number of lines of about 800 rpm.
[0049]
Since the film thickness of the resin layer 20 affects the roughness (level difference, pitch length) of the unevenness of the microgrooves formed on the surface, an appropriate film thickness is selected. As will be described later, when the thickness of the photosensitive resin layer 20 is large, the unevenness becomes rougher (large difference in elevation and pitch length), and when the film thickness is small, the unevenness becomes finer (small difference in elevation and pitch length). .
[0050]
Thereafter, a pre-bake treatment is performed at a temperature of about 90 ° C. for 30 minutes. In this pre-baking process, the temperature is not so high that the resist reacts, and the solvent is slightly blown away. This prevents the resist layer from dripping due to heat during post-bake described later.
[0051]
As shown in FIG. 3B, known stepper exposure processing and development processing using a mask substrate 40 are performed to form contact holes for the display electrodes. As a result, a contact hole CH is formed on the source electrode 18 of the resin layer 20.
[0052]
After the contact hole CH is formed, the photosensitive resin layer 20 is subjected to a post-bake treatment. The post-bake treatment is, for example, a heat treatment at 120 ° C. for 40 minutes, and the purpose is to sufficiently remove the solvent of the photosensitive resin. The temperature of the post-baking process is lower than the temperature (for example, about 200 ° C.) at which the photosensitive resin photosensitive agent reacts, and it is necessary to prevent the photosensitive agent from reacting in the post-baking process. Further, the post-baking temperature is lower than the glass transition temperature of the resin (for example, about 200 ° C.), and it is necessary to prevent the resin from curing.
[0053]
If the post-baking temperature is high and the time is long, the amount of residual solvent decreases, and the microgroove irregularities become fine. Conversely, if the temperature is low and the time is long, the microgroove irregularities become rough. Accordingly, the conditions for the post-baking process are appropriately selected so that an optimal microgroove shape can be formed.
[0054]
Next, as shown in FIG. 3C, light having a sufficiently high energy for photosensitivity, for example, far ultraviolet rays (DUV) having a wavelength of λ = 360 nm or less, is applied to the entire surface of the photosensitive resin layer 20. 2600mj / cm²Irradiate with. By this DUV irradiation, the photosensitive agent undergoes a photosensitive reaction and the novolac resin undergoes a cross-linking reaction from the surface portion (surface side in the film thickness direction) of the photosensitive resin layer 20, and the upper layer portion of the resin layer is denatured. As a result, the resin layer 20 has different thermal deformation characteristics between the front side and the back side. This DUV irradiation was performed using, for example, an ORC UV irradiation apparatus.
[0055]
The energy of UV irradiation also affects the shape of the microgroove. If the energy is too low, the microgroove itself is not formed, but if the energy exceeding a certain threshold is irradiated, the microgroove is formed. In this case, the microgroove is fine when the irradiation energy (energy per unit time × irradiation time) is low, and rough when it is high. Therefore, the irradiation energy amount is also selected according to the optimal microgroove shape.
[0056]
Next, as shown in FIG. 3D, the resist 20 is finally baked. This heat treatment is performed, for example, at a temperature of 200 ° C. for about 40 minutes. The temperature of the heat treatment in the final bake needs to be higher than the temperature of the heat treatment (post bake) before UV irradiation. Then, by performing the heat treatment in the final baking, random microgrooves MG are formed on the surface of the resin layer 20 as illustrated.
[0057]
The heat treatment temperature of the final baking needs to be a temperature higher than that of the post baking, and is preferably sufficiently higher than the baking temperature of the alignment film, which is a subsequent heat treatment step, so that the resin layer 20 is sufficiently cured.
[0058]
Thereafter, as shown in FIG. 2, about 2000 mm of aluminum is grown by sputtering or heat evaporation, and patterned by a known photolithography method to form the pixel electrode 22. As a result, random irregularities are formed on the surface of the pixel electrode 22 and function as a reflective electrode that scatters and reflects light. Further, an alignment film 23 made of, for example, about 5000 mm of polyimide is formed on the entire surface by spin coating and baking (about 120 ° C.). Concavities and convexities are also formed on the surface of the alignment film 23, and the alignment direction of the liquid crystal molecules of the liquid crystal layer 34 inserted thereon is aligned according to the groove direction of the concavities and convexities.
[0059]
The reason why the microgroove is formed is not yet certain, but according to the knowledge of the inventors, the surface layer portion of the resin layer 20 is altered by the DUV irradiation, and the surface side and the back surface of the resin layer 20 are subjected to the final baking heat treatment. It seems that micro-grooves (micro grooves) or micro-links (micro ridges) are formed on the surface due to different thermal deformations on the sides due to stress between the upper and lower layers. For example, it is considered that microgrooves are formed on the surface side by shrinking the back side of the resin layer 20 by heat treatment. This is considered to be due to the fact that the level of cross-linking reaction of the resin in the thickness direction on the resin layer differs due to UV irradiation.
[0060]
According to experiments by the inventors, the microgrooves formed in this manner have been confirmed to have random irregularities necessary for irregularly reflecting incident external light as described later.
[0061]
The UV irradiation in the above process may be performed only on a partial region in the plane direction using a predetermined mask pattern instead of being performed on the entire surface of the resin layer 20. As a result, the resin layer 20 is partially altered in the planar direction, and a distribution of thermal deformation characteristics is formed in the planar direction. Due to the distribution of the thermal deformation characteristics in the horizontal direction, the same microgroove is formed in the subsequent heat treatment in the final baking.
[0062]
Furthermore, in place of the UV irradiation in the above process, a wet treatment with any one of an acid, an alkali solution, a quaternary ammonium salt solution, and HMDS can be used. By immersing the photosensitive resin layer in such a chemical solution, it is possible to cause a chemical reaction on the surface of the photosensitive resin layer and to change the material into materials having different thermal deformation characteristics.
[0063]
In this embodiment, the roughness of the microgroove is controlled by the film thickness of the resin layer 20 and the UV irradiation energy. 4 to 7 are micrographs (about 20 times) of the surface shape of the microgroove formed by changing the film thickness of the photosensitive resin layer 20 and the UV irradiation energy. The sample of the micrograph's reflection panel was made by the following process.
[0064]
A resist (for example, general-purpose resist LC200 manufactured by Shipley Co., Ltd.) is formed on the panel by spin coating (350 rpm for 3 seconds and 800 rpm for 20 seconds twice), and after pre-baking at 90 ° C. for 30 minutes, the panel is fully exposed. , Develop to the desired film thickness (2.0 μm, 1.7 μm, 1.4 μm, 1.0 μm). Then, after post-baking at 120 ° C for 40 minutes, the desired energy (5200mj / cm², 3900 mj / cm², 2600 mj / cm², 1300 mj / cm², 0 mj / cm²) DUV irradiation was performed, and a final baking was performed at 200 ° C. for 40 minutes. Finally, aluminum was formed as a reflective film on the resist film by an evaporation method of about 2000 mm.
[0065]
FIG. 4 shows that the film thickness of the photosensitive resin layer 20 is 2.0 μm and the UV irradiation energy is 5200 mj / cm.², 3900 mj / cm², 2600 mj / cm², 1300 mj / cm², Micrographs of five samples made zero. When UV irradiation is not performed, irradiation energy is 1300 mj / cm²If it is small, microgrooves are not formed on the surface of the resin layer. However, the irradiation energy is 1300 mj / cm²If it is larger, it is confirmed that microgrooves are formed on the surface of the resin layer. In that case, the height difference and pitch length (roughness) of the microgroove is rougher when the UV irradiation energy is higher (large difference in height and pitch length) and finer when the irradiation energy is low (small difference in height and pitch length). That is confirmed.
[0066]
The shape of the microgroove formed on the surface of the resin layer 20 is random. As shown in the photograph, at least two or more of the curved shape, the curved shape of the sharp curve, the bent shape of the sharp angle, the closed loop shape, the Y-shaped branch shape and the like are mixed. The microgroove according to the present embodiment has a shape that cannot be obtained by unevenness by a lithography process using a conventional artificially created constant mask pattern.
[0067]
Then, by controlling the roughness of the microgroove, it is possible to appropriately control the average inclination angle and inclination angle distribution of the unevenness.
[0068]
FIG. 5 shows that the thickness of the photosensitive resin layer 20 is 1.7 μm and the UV irradiation energy is 5200 mj / cm.², 3900 mj / cm², 2600 mj / cm², 1300 mj / cm², Micrographs of five samples made zero. Since the thickness of the resist layer is made smaller than that of the sample of FIG. 4, it is confirmed that the formed microgroove is finer. The microgrooves are not formed when the UV irradiation energy is too low, as in the sample of FIG.
[0069]
FIG. 6 shows that the film thickness of the photosensitive resin layer 20 is 1.4 μm, and the UV irradiation energy is 5200 mj / cm.², 3900 mj / cm², 2600 mj / cm², 1300 mj / cm², Micrographs of five samples made zero. In this case, the microgroove is even finer.
[0070]
FIG. 7 shows that the film thickness of the photosensitive resin layer 20 is 1.0 μm and the UV irradiation energy is 5200 mj / cm.², 3900 mj / cm², 2600 mj / cm², 1300 mj / cm², Micrographs of five samples made zero. In this case, the microgroove becomes finer and the UV irradiation energy is 2600 mj / cm.²However, it is confirmed that the formation of microgrooves is not sufficient.
[0071]
As described above, as is clear from the surface photographs of the 20 samples, the concave and convex shape of the microgroove becomes smaller as the UV irradiation energy becomes lower. Furthermore, the microgroove itself is not formed unless irradiation energy exceeding a certain reference value is given. In addition, there is a film thickness dependency of the resist after the final baking, and the uneven shape of the microgroove becomes smaller as the film thickness is thinner.
[0072]
FIG. 8 is a diagram showing AFM images of three more reflective panel samples. This sample is the same reflective panel sample as above, and the UV irradiation energy is 5200mj / cm.²The resist film thickness is 1.7 μm, 1.4 μm, and 1.0 μm, and a 2000 mm aluminum reflective film is formed on the resist layer.
[0073]
As shown in FIG. 8A, in the sample in which the resist film thickness, which is the photosensitive resin layer, is 1.7 μm, the shape of the microgroove on the surface is large, the height difference of the unevenness is 1.3 μm, and the average inclination The angle was measured to be 13 °.
[0074]
As shown in FIG. 8B, in the sample in which the film thickness of the resist film as the photosensitive resin layer is 1.4 μm, the shape of the microgroove on the surface is slightly small, the unevenness of the unevenness is 1.1 μm, the average The tilt angle was measured to be 11 °.
[0075]
Further, as shown in FIG. 8C, in the sample in which the resist film thickness as the photosensitive resin layer is 1.0 μm, the shape of the microgroove on the surface is further smaller, and the height difference of the unevenness is 0.5 μm. The average tilt angle was measured to be 8 °.
[0076]
As is apparent from the observation results in FIG. 8, it is understood that the average inclination angle due to the unevenness also changes depending on the shape of the microgroove. That is, as the resist film becomes thinner, the height difference of the unevenness and the average inclination angle become smaller. Therefore, according to the manufacturing process of the present embodiment, the average tilt angle can be controlled. The average inclination angle is an important factor for increasing the reflectance of the reflective panel. Therefore, the fact that the average inclination angle can be controlled by the manufacturing process of the present embodiment has an important practical significance.
[0077]
FIG. 9 is a graph showing the relationship between the average inclination angle of the reflective film and the reflectance with respect to the diffused light source. FIG. 9 shows five integrating spheres having a distribution of incident angles in the range of 0 °, 15 °, 30 °, 45 ° and 0 ° to ± 90 ° as incident light to the reflective panel as diffuse light sources incident on the reflective panel. It is shown that the reflectance Y depends on the average inclination angle k of the unevenness of the reflective film with respect to the type. This dependency can be obtained from the theoretical formula described later. The inclination angle distribution due to the unevenness is a normal distribution, and the average inclination angle of the normal distribution is theoretically set.
[0078]
As can be understood from the theoretical values in FIG. 9, when the average inclination angle increases as it exceeds 15 °, the reflected light reflected by the reflective film has an angle at the boundary between the liquid crystal on the surface side of the reflective panel and the glass substrate. In many cases, the critical angle is exceeded, and the reflectivity decreases. On the other hand, when the incident angle is 0 ° or 15 °, the reflectance is higher when the average inclination angle is smaller than 5 °, but the display panel is used in an environment where the incident angle is 0 ° or 15 °. Is not so many. Therefore, it is understood from the theoretical values in FIG. 9 that the reflective film having an average inclination angle of 15 ° or less, preferably 8 ° to 13 °, has a relatively high reflectance for any incident light. The
[0079]
Therefore, all the three samples shown in FIG. 8 have an average inclination angle in the range of 8 ° to 13 °. Therefore, it can be understood that the average inclination angle can be controlled within a range in which the reflectance is high by using the manufacturing process of the present embodiment.
[0080]
FIG. 10 is a graph showing the relationship between the resist film thickness and the reflectance when the post-baking is performed (black circle) and when it is not performed (white circle) for the three samples in FIG. In this case, an integrating sphere is used as the diffused light. First, as described with reference to the three samples in FIG. 8, when the post-baking is performed, the resist film thickness is 1 as compared with the top data of the reflectance when the unevenness is formed by the conventional process. It has been proved that the samples according to this embodiment of 7 μm, 1.4 μm, and 1.0 μm all have high reflectance. That is, as shown in the theoretical value of FIG. 9, the sample formed so that the average inclination angle falls within the range of 8 ° to 15 ° has a higher reflectance than the top data of the conventional example.
[0081]
Next, looking at the sample that has not been post-baked as indicated by the white circles in FIG. 10, in the region where the resist film is thick, the reflectance is lower than the conventional top data, but in the region where the resist film is thin. It is high. From this experimental result, it is understood that the post-baking process is important for increasing the reflectance. The reason is probably that when post-baking is not performed, a lot of solvent remains in the resist film after exposure and development, and the residual solvent is generated as degassing in the final baking process after UV irradiation, resulting in defects on the uneven surface. It is estimated that this occurred.
[0082]
Further, it is presumed that the final baking temperature needs to be set higher than the baking temperature for the subsequent alignment film formation. That is, it is estimated from the sample result without post-baking in FIG. 10 that it is necessary to completely remove the solvent in the resist layer in the final baking process so that the degassing phenomenon does not occur in the subsequent heat treatment. Because it is done.
[0083]
FIG. 11 is a diagram schematically showing the concave-convex shape of the microgroove of the resin layer formed according to the present embodiment. When the unevenness of FIG. 11A is rough, the undulation of the surface of the resin layer 20 is large, the pitch length L is long, and the height difference H of the unevenness is also large. As a result, the inclination angle k tends to increase. On the other hand, when the unevenness of FIG. 11B is fine, the surface waviness of the resin layer 20 is small, the pitch length L is short, and the unevenness height difference H is also small. As a result, the inclination angle k tends to decrease.
[0084]
FIG. 12 is a diagram showing an example of a planar pattern of microgrooves formed according to the present embodiment. As described above, according to the present embodiment, the bending pattern of FIG. 12A, the bending pattern of FIG. 12B, the loop pattern of FIG. 12C, the branching pattern of FIG. Mixed microgrooves are formed on the surface of the resin film.
[0085]
FIG. 13 is a diagram showing an example of UV irradiation necessary to form a microgroove. The example of FIG. 13A is a case where the entire surface of the resin layer 20 is irradiated with UV. In this case, a region having a certain depth in the depth direction from the surface indicated by the oblique lines is caused by UV irradiation. Altered by photoreaction. Therefore, it is considered that microgrooves are formed on the surface due to the difference in thermal deformation characteristics between the altered layer and the non-altered layer due to the subsequent heat treatment by the final baking.
[0086]
On the other hand, in the example of FIG. 13B, the shaded area is altered by UV irradiation using a mask on the resin layer 20. As a result, a distribution of an altered layer and an unaltered layer is formed in the lateral direction. Therefore, it is considered that microgrooves are formed on the surface due to the difference in thermal deformation characteristics between the altered layer and the non-altered layer due to the subsequent heat treatment by the final baking. In any method, microgrooves are formed on the surface of the resin layer, but the process of FIG. 13A is more advantageous because a mask is not required in the UV irradiation step.
[0087]
The present inventors conducted a comparative study on the case where the process of final baking by UV irradiation according to the present embodiment is applied to the concavo-convex formation process by half exposure using a conventional mask. That is, (1) a first sample in which irregularities by half exposure are formed on the surface and then UV-irradiated and finally baked; (2) a second sample that is UV-irradiated and finally baked without half-exposure; (3) A third sample was formed as a concavo-convex portion by conventional half exposure and UV irradiation was not performed, and the respective reflectances were compared.
[0088]
The manufacturing process of the second sample has been described with reference to FIG. Therefore, the manufacturing process of the first sample and the second sample will be described. FIG. 14 is a cross-sectional view showing the manufacturing process of the first sample. The first sample is pre-baked by applying the resist film 20 on the substrate 10 by spin coating. Then, as shown in FIG. 14A, the resist film 20 is half-exposed using a mask 42 having a predetermined pattern. Half exposure is exposure with weak energy that does not expose the entire thickness direction of the resist film 20. Thereafter, when developed, as shown in FIG. 14B, a concave portion having a pattern shape of the mask 42 is formed on the surface of the resist film.
[0089]
Therefore, the first sample is subjected to UV irradiation (for example, 5200 mj / cm 2) after the post-baking in the present embodiment.²) Is performed on the entire surface, and the surface is altered. Then, when the above-described final baking is performed, as shown in FIG. 14C, the surface of the resist film 20 is micro-grooved by UV irradiation and post-baking in addition to the undulations corresponding to the pattern by half exposure. Is formed.
[0090]
In the third sample, UV irradiation (for example, 1300 mj / cm 2) with such a low energy that micro-grooves are not formed after the development process of FIG.²) Is performed on the entire surface. After that, when the final baking is performed, irregularities where microgrooves are not formed are formed on the surface of FIG. Since only the very surface of the resist film 20 is deteriorated by the UV irradiation with the low energy, the resist film is prevented from being uneven and flattened in the final baking heating step. However, since the UV irradiation energy is small, microgrooves are not formed.
[0091]
FIG. 15 is a graph comparing the reflectance when the first, second, and third samples formed by the above process are irradiated with an integrating sphere diffuse light source. In the figure, the first sample SM1 includes samples that have been half-exposed with a plurality of types of pattern shapes (octagon, quadrangle, cross, pentagon, donut, triangle, ellipse, fan, octagon). The second sample SM2 uses an area that has not been exposed by half exposure. Similarly to the first sample, the third sample SM3 includes a sample that is half-exposed with a plurality of types of pattern shapes.
[0092]
As understood from the comparative example of FIG. 15, even when the half exposure process is added and this embodiment is applied, there is a case where a reflectance higher than the top data of the conventional process may be obtained. However, the reflectance is highest when the present embodiment is applied without performing half exposure as in the second sample SM2. The third sample SM3 in which unevenness is formed only by the half exposure process has a low reflectance in any pattern. As described above, the process of final baking by UV irradiation according to the present embodiment can achieve a high reflectance even if a half exposure process and a development process using a predetermined pattern are added.
[0093]
It is preferable that the microgroove according to the present embodiment is formed with random irregularities as much as possible. According to the experiments by the present inventors, it was observed that when the surface of the photosensitive resin layer was irradiated with UV and finally baked, thick grooves or ridges were formed to extend long in some places. Such irregularities may be undesirable for the diffuse reflection function of the reflective electrode, for example, the reflection direction is concentrated in a certain direction. Therefore, a method capable of controlling the direction and length of the microgroove to some extent is desired.
[0094]
On the other hand, a pixel electrode is used as the reflective electrode in this embodiment. The pixel electrode is formed separately for each pixel, and a voltage is applied independently. Therefore, the present inventors have separated the photosensitive resin layer in pixel units or line units to prevent the above-described thick grooves or ridges from being formed to extend for a long time, and more uniform in the pixel electrode. We found that it was possible to form microgrooves. The photosensitive resin layer may be completely separated, or may be separated by forming a groove with a certain depth on the surface, and further, the film may be formed so that the film thickness is partially reduced. May be. However, since the pixel electrode is designed so that the capacitance between the data line, the scanning line, and the gate electrode falls within a predetermined range, it is necessary to separate the photosensitive resin layer within a range satisfying such conditions.
[0095]
FIG. 16 is a diagram for explaining separation of the photosensitive resin layer. 16A and 16B are plan views of the back substrate. As shown in FIG. 16A, data lines D and scanning lines S are formed on the surface of the back substrate, and semiconductor layers 19 and source / drain electrodes 17 and 18 are formed at the intersections. A region partitioned by the data line D and the scanning line S becomes a pixel region PX. Accordingly, as shown in FIG. 16B, a contact hole CH for connecting the source electrode 18 and the pixel electrode 22 is formed, and the pixel electrode 22 is provided separately for each pixel region.
[0096]
FIGS. 16C to 16F show examples of separation lines for separating the photosensitive resin layer. (C) is an example in which a separation line 50 is formed along the scanning line S and the data line D, and the photosensitive resin layer is separated into pixel units (pixel electrode region units). (D) is an example in which the separation line 50 is formed along the data line D, and the photosensitive resin layer is separated in data line units. In (E), the separation line 50 is formed along the data line D, and the separation line 50 is also formed in a direction orthogonal thereto. In this case, the separation unit of the photosensitive resin layer is irrelevant to the pixel electrode. (F) is an example in which the separation line 50 is formed along the scanning line S.
[0097]
FIG. 17 is a cross-sectional view showing a process for forming a photosensitive resin layer separation line. In FIG. 17A, a gate electrode 15, an insulating film 16, a semiconductor layer 19, and drain / source electrodes 17 and 18 are formed on an insulating substrate 10, and a photosensitive resin layer 20 made of resist is spin-coated. Shows the pre-baked state. In this state, an exposure process for forming a contact hole in the photosensitive resin layer 20 is performed. In the exposure mask 51 at that time, the region 53 corresponding to the contact hole completely transmits light, the region 55 corresponding to the separation line partially transmits light, and the other region 54 completely blocks light. A mask pattern is formed on the transparent substrate 52. For example, the region 54 can be formed of a light shielding film made of chromium, and the region 55 can be made of a half exposure film made of molybdenum silicide. When exposed using such an exposure mask, the position of the contact hole of the photosensitive resin layer 20 is completely exposed, and the region corresponding to the separation line is half-exposed.
[0098]
Thereafter, when development is performed, as shown in FIG. 17B, a contact hole CH penetrating the resin layer is formed in the photosensitive resin layer 20 at a position corresponding to the source electrode 18, and is constant on the surface of the resin layer. Are formed as the separation line 50. The contact hole CH is formed only in a narrow region and has little function of separating the resin layer 20. However, since the separation line 50 separates at least the surface of the resin layer 20, it prevents a long groove or wrinkle from occurring in the microgroove formed by the subsequent UV irradiation and the final baking process. be able to.
[0099]
In FIG. 17A, a special exposure mask 51 is used. However, patterning of the resin layer shown in FIG. 17B can also be performed by performing normal exposure with the contact hole forming mask and half exposure with the separation line forming mask. Further, the resin layer 20 may be completely separated by the separation line 50 by performing normal exposure with a separation line forming mask.
[0100]
Further, the separation line 50 is not necessarily formed on the surface side of the resin layer 20. For example, it can be formed on the back side. In that case, the presence of the data line D formed on the insulating layer 16 itself may have the function of the separation line 50. This is because the thickness of the resin layer 20 is partially reduced at the portion where the data line D exists. As a result, the formation of microgrooves is divided, and the formation of long extending grooves and ridges is prevented.
[0101]
As shown in FIG. 17B, the separation line 50 is preferably formed in the separation region of the pixel electrode 22 (shown by a broken line in the drawing) formed on the resin layer 20. This is because the influence on the parasitic capacitance between the pixel electrode 22 and the gate electrode 15 and other electrodes can be minimized.
[0102]
FIG. 18 is a diagram showing micrographs of microgrooves with and without a separation line. In this sample, the same reflector as in the samples of FIGS. 6 to 9 described above is formed with and without a separation line. FIG. 18A shows an example of a microgroove when a separation line is formed, and FIG. 18B shows an example of a microgroove when a separation line is not formed.
[0103]
As can be seen from this photograph, the example (B) in which the separation line is not formed has a groove or ridge that extends long in part, whereas the example (A) in which the separation line is formed extends. There are no grooves or wrinkles and the shape is more uniform.
[0104]
In the sample of the above embodiment, a general-purpose resist LP200 manufactured by Shipley Co. was used as the photosensitive resin layer. It was confirmed that microgrooves were formed in the same manner even when resist AFP750 made by Clariant Japan was used as another photosensitive resin.
[0105]
As described above, in this embodiment, a micro-groove having random unevenness is formed on the surface by a simple process of forming a partially altered region in the photosensitive resin layer by UV irradiation or the like and then performing a heat treatment. can do. In addition, the shape and direction of the microgroove can be controlled relatively easily according to various process conditions. Therefore, by forming a reflective layer on the resin layer having such microgrooves, it is possible to realize a reflective function effective for the reflective liquid crystal display device. By using a pixel electrode for the reflective layer, a simpler reflective liquid crystal display device can be realized.
[0106]
[Control of tilt angle distribution of reflector]
FIG. 19 is a diagram showing an actual environment in which the reflective liquid crystal display device assumed in the present embodiment is used. In an environment where a reflective liquid crystal display device is used, light sources exist in various places. Therefore, considering all usage environments, as shown in FIG. 19, it is necessary to assume a case where the reflective liquid crystal display device is placed under a uniform diffused light source disposed on the inner surface of the hemisphere. Under such a use environment, the display panel is irradiated with all incident light existing within the solid angle of the hemisphere.
[0107]
Therefore, in order to obtain the light intensity L incident on the reflective liquid crystal display device, the XYZ axis, the incident angle θi, and the azimuth angle φi are defined as shown in FIG. The incident angle θi is an angle between the Z axis and the incident light, and the azimuth angle is an angle between the incident light and the X axis. Now, suppose that the light intensity per unit area of the hemisphere (hereinafter, integrating sphere) shown in FIG._i, φ_i), The light intensity dL is
dL = I (θ_i, φ_i) ・ Dω
= I (θ_i, φ_iDs / r²
It becomes. Where ω is a solid angle, ds is the unit area of the spherical surface of the integrating sphere, r is the radius of the integrating sphere, and if the integrating sphere is uniform diffused light, the light intensity I is a constant.
[0108]
Furthermore, since the incident light is applied to the display panel from an oblique direction by the incident angle θi, the display panel has a light intensity attenuated by sinθi,
[0109]
[Expression 1]

[0110]
It becomes. The unit area ds is as shown in FIG.
[0111]
[Expression 2]

[0112]
Therefore, if the formula (2) is substituted into the formula (1) and the light intensity dL is integrated over the incident angle θi of 0 to π / 2 and the azimuth angle φi of 0 to 2π, the incident light on the display panel is obtained. The light intensity L is expressed as follows.
[0113]
[Equation 3]

[0114]
Therefore, polar angle θ_iLight intensity incident from the direction f (θ_i) Is expressed as a function in the integral of equation (3), which is as follows.
[0115]
[Expression 4]

[0116]
The sin θi in the equation (4) is caused by the area of the diffusion light source of the integrating sphere for each unit incident angle θi, and the light source area of incident light from directly above the display panel (incident angle θi = 0) is narrow. (Sin θi = 0), which means that the light source area of incident light from the horizontal direction of the display panel (incident angle θi = π / 2) is large (sin θi = 1). In addition, cos θi in the equation (4) is an attenuation component due to the incident angle, and there is almost no attenuation of incident light from directly above the display panel (incident angle θi = 0) (cos θi = 1). This means that the attenuation of incident light from the direction (incident angle θi = π / 2) is large (cos θi = 0).
[0117]
FIG. 21 is a diagram illustrating a case where light is incident on the reflective display device and reflected. In the reflection type liquid crystal display device shown in FIG. 2, the refractive index n of the display side glass substrate and the liquid crystal layer has a value of about 1.5. Therefore, from the substrate having the reflection electrode as shown in FIG. It can be assumed that the reflection plate 60 is covered with a medium 61 having a refractive index n formed of a liquid crystal layer or a display-side substrate formed thereon. Then, the incident light incident from the air layer at the incident angle θi is incident on the medium 61 at the incident angle θ._i', And reflection angle θ_oIt will be reflected by 'and will come out at the reflection angle θo in the air layer.
[0118]
When entering the medium 61 from the air layer, a part thereof is reflected light R and is not incident on the medium._i'Intensity of incident light at f (θ_i') Can be expressed as:
[0119]
[Equation 5]

[0120]
However, R (θ_i) Is the reflectance of light reflected at the interface between the air layer and the medium 61 having a refractive index n. And the incident angle θ in the air layer_iAnd the incident angle θ in the medium 61_iThe following relationship holds with '.
[0121]
[Formula 6]

[0122]
Here, the refractive index of the air layer is 1, and the refractive indexes of glass and liquid crystal are n. θ_iIs the angle of incidence at the air layer, θ_i'Is the incident angle in the liquid crystal layer.
[0123]
FIG. 22 shows the intensity f (θ of light incident on the reflector 61._i') And incident angle θ_iIt is a figure which shows a relationship with ', It computed by substituting Formula (6) to said Formula (5). However, the light intensity is I (θ_i, φ_i) = 1. As is understood from FIG. 22, when uniform diffused light from the integrating sphere is assumed, the incident angle θ with respect to the reflector 60 is assumed._iAs the incident angle increases from '= 0, the incident light intensity increases and a certain incident angle θ_iIn the range of ', the incident light intensity becomes maximum, and the incident light intensity is greatly attenuated in the vicinity of an incident angle of 45 °. That is, the incident angle θ at which the incident light intensity is maximum._iIt can be seen that the angle of incidence differs depending on the refractive index n of the medium.
[0124]
FIG. 23 shows an incident angle θ at which the incident light intensity in FIG._iIt is a figure which shows the relationship between 'and the refractive index n of a medium. From FIG. 23, the incident angle θ at which the incident light intensity becomes maximum as the refractive index n of the liquid crystal increases._iYou can see that 'is smaller. Since the refractive index of a typical liquid crystal is about 1.4 to 1.8, the incident angle θ at which the incident light intensity is maximized._i'Is about 30-38 °.
[0125]
Next, it is considered that the incident light having the incident light intensity distribution as shown in FIG. 22 is reflected by the uneven inclined surface of the reflector 61. FIG. 24 is a diagram illustrating a relationship between an incident angle, a reflection angle, and an inclination angle with respect to the inclined surface of the reflection unevenness. The incident light and the reflected light are symmetrical with respect to a line perpendicular to the inclined surface, and the local incident angle α on the micro mirror surface is equal to the local reflection angle β._i', Reflection angle θ_o'Is the following relationship.
[0126]
[Expression 7]

[0127]
In general, the display is often observed from the vertical direction on the display panel. Therefore, the angle of incidence on the uneven reflector_iConsidering that light incident at θ ′ is reflected in the 0 ° direction, the above equation (7) is expressed as ξ = θ_i'/ 2. In other words, the inclination angle ξ is changed to the incident angle θ._iIf it is 1/2 of ', it can be reflected in a direction perpendicular to the display panel.
[0128]
As shown in FIG. 22, the distribution of incident light that is incident on the uneven surface of the reflecting plate with respect to the diffused light of the integrating sphere has a peak that is a region with an incident angle of 0 to 45 °. Therefore, it is desirable that the distribution of the inclined surface of the uneven surface of the reflector is also a distribution corresponding to the light intensity distribution of FIG. In other words, it is desirable to increase the reflected light intensity as a whole by increasing the existence probability of the inclination angle corresponding to the incident angle where the light intensity is high and decreasing the existence probability of the inclination angle corresponding to the incident angle where the light intensity is low. .
[0129]
FIG. 25 is a diagram showing a distribution of existence probability of inclination angles corresponding to the incident light intensity distribution of FIG. The example of FIG. 25 shows the case where the refractive index n = 1.5 in FIG. 22 and is normalized so that the sum of the probabilities becomes 1. The horizontal axis represents the inclination angle ξ of the reflective uneven surface, and the vertical axis represents the existence probability (%). Therefore, in the sample having the inclination angle existence probability distribution as shown in FIG. 25, the reflectance when the inclination angle that maximizes the existence probability is changed is obtained. FIG. 26 is a diagram showing a simulation result of such reflection characteristics. More specifically, the slope w at which the existence probability is maximized is changed by changing the width w of the distribution shown in FIG. 25, and the reflectance Y at that time is calculated.
[0130]
As is clear from FIG. 26, the inclination angle ξ (= θ at which the existence probability is maximized._i'/ 2) range is ξ = about 15-19 ° (θ_iIt is understood that the reflectance is highest in the region of '= about 30 to 38 °). That is, the incident angle θ at which the incident light intensity shown in FIG._iIt is desirable to increase the existence probability of the inclination angle ξ = 15 to 19 ° at which incident light of '= 30 to 38 ° can be reflected in the direction perpendicular to the display panel in order to increase the overall reflectance.
[0131]
As described above, in order to reflect light effectively under the uniform diffused light of the integrating sphere, it is necessary that the inclination angle due to the unevenness for reflection should be maximized in the region of about 15-19 °. It became clear theoretically.
[0132]
FIG. 27 is a diagram showing a result of measuring the reflectance of the integrating sphere with respect to uniform diffused light using a sample that was actually made as an experiment. In the prototype reflector, the relationship between the tilt angle ξp with the highest existence probability and the measured reflectance is shown.
[0133]
FIG. 28 is a sectional view showing a method for forming the prototyped reflector. First, as shown in FIG. 28A, a resist (LC-200 manufactured by Shipley Co.) 63 is spin-coated on a glass substrate 62 at 1000 to 2000 rpm for 20 seconds. Then, after pre-baking at 90 ° C. for 30 minutes, ultraviolet exposure is performed using a mask 64 as shown in FIG. Next, development is performed using a developer (MF319 manufactured by Shipley Co., Ltd.), and convex portions are formed on the glass substrate as shown in FIG. Next, as shown in FIG. 28 (d), post-baking was performed at 120 to 200 ° C. for 60 minutes to round the convex portions. Thereafter, as shown in FIG. 28 (e), an aluminum layer 65 was deposited by 200 nm to prepare a reflector.
[0134]
A liquid crystal layer was formed between the reflection plate formed as described above and the glass substrate, and a reflection type liquid crystal display device as shown in FIG. Here, the liquid crystal layer was made of Merck's liquid crystal material MJ961213, and its thickness was controlled by a 3.5 μm diameter spacer. Using the integrating sphere, we measured the reflectivity when diffused light was incident on the prototype reflective LCD. Furthermore, the inclination angle distribution of the unevenness of the reflector of the prototype is measured, and the inclination angle ξ that maximizes the existence probability is measured._pAlso asked. The result is shown in FIG.
[0135]
From this experimental result, the inclination angle ξ that maximizes the existence probability_pIt can be seen that the maximum reflectivity is obtained by setting the angle around 16 to 19 °. This experimental result almost supports the simulation result shown in FIG. Inclination angle ξ that maximizes the existence probability compared to the conventional case where the inclination angle is 10 °._pIt can be seen that the sample with the angle around 16-19 ° has a higher reflectance.
[0136]
FIG. 29 is a diagram illustrating a pattern example of the mask 64 for forming the unevenness of the reflecting plate. FIG. 29A is an example in which patterns of large and small circles having different sizes are mixed, and FIG. 29B is an example in which polygons such as triangles, quadrangles, hexagons, and octagons are mixed. However, the present invention is not limited to these patterns.
[0137]
As another example of forming the unevenness for reflection, the process shown in FIGS. 3 to 6 can be adopted in which the distribution of thermal deformation characteristics is formed by UV irradiation and then the final baking is performed to form microgrooves. The concave / convex shape of the microgroove can be controlled by the above-mentioned process conditions, so the inclination angle ξ that maximizes the existence probability_pThe concavo-convex shape is controlled so that is around 15 to 19 °.
[0138]
As described above, in the present embodiment, the inclination angle due to the unevenness of the reflector is distributed in the range of at least 0 ° to 25 °, and the distribution probability is maximized in the vicinity of 15 to 19 °. In various environments, it is possible to provide a reflective liquid crystal display device having a higher reflectance.
[0139]
[Control of tilt angle distribution of reflector (part 2)]
FIG. 30 is a diagram showing the inclination angle distribution of the unevenness of the reflector plate that obtains a high reflectance with respect to the diffused light of the integrating sphere described above. The horizontal axis represents the tilt angle ξ, and the vertical axis represents the existence probability. That is, as already described, it is desirable that the existence probability of the inclination angle be distributed so as to reflect more incident light having an incident angle with a high incident intensity on the reflector in a direction perpendicular to the display panel. FIG. 30 shows a distribution in which the existence probability of an inclination angle near +15 to 19 ° and an inclination angle near −15 to 19 ° is maximized. The positive side and negative side exist when the tilt angle is viewed along a certain direction of the display panel, the tilt angle corresponding to the incident light from one direction is the positive side, and the tilt corresponding to the incident light from the opposite direction. Corners are shown on the-side. Therefore, when the distribution diagram of FIG. 30 is bent around an inclination angle of 0 °, an inclination angle distribution as shown in FIG. 25 is obtained.
[0140]
By the way, the liquid crystal display device is often used as a display panel of a notebook personal computer. FIG. 31 is a diagram illustrating a state in which the reflective liquid crystal display device is mounted as a monitor of a notebook personal computer. As shown in the figure, the reflective liquid crystal display device 70 is often used in a state where it is inclined by an angle α with respect to the horizontal direction. In that case, as shown in FIG. 31, the display device 70 is a surface perpendicular to the paper surface. Then, the directions of the XYZ axes are defined as shown.
[0141]
Considering the incident light on the display device 70, the incident angle θ along the XY plane of the coordinates._iThe distribution has nothing to block the incident light, so θ_i = -90 to 90 °. On the other hand, the incident angle distribution along the XZ plane of coordinates is not necessarily θ because the incident light is blocked by the keyboard portion._i = -90 to 90 °. That is, the incident angle range differs between the highest position 70A and the lowest position 70B of the display device 70. The highest position 70A is θ in the widest incident angle range._i = -90 to α + β °, and the lowest position 70B is θ in the narrowest incident angle range._i = -90 to α °.
[0142]
Therefore, the incident light in the XZ plane direction along the vertical direction of the display panel has almost no light incident from an incident angle α to 90 ° (or α + β ° to 90 °). Accordingly, the inclination angle of the micro mirror surface arranged in the XZ plane direction of the display panel does not need an inclination angle that reflects the light incident from this angle range in the normal (0 °) direction of the display panel.
[0143]
For example, the inclination α of the display panel = 30 ° and the refractive index n of the liquid crystal layer and the glass substrate_LCIf = 1.5, the tilt angle for reflecting the light incident at 30 to 90 ° in the 0 ° direction is 10 to 21 ° from the above-described equations (6) and (7). That is, an inclination angle of 10 to 21 ° is not necessary for the uneven distribution of the unevenness facing the vertical direction (XZ plane direction) of the display panel.
[0144]
Therefore, it is desirable that the distribution of the inclination angles in the XY plane direction and the XZ plane direction is as shown in FIG. That is, the inclination angle distribution in the XY plane direction is the same as that shown in FIG. 30, the inclination angle distribution in the XZ plane direction is the same as that in FIG. 30, and the plus side is 10 to 21 °. The distribution does not exist in the range. When the distribution of FIG. 32 is folded around an inclination angle of 0 °, it is as shown in FIG.
[0145]
FIG. 33 shows a distribution of inclined surfaces in the XY plane direction and a distribution of inclined surfaces in the XZ plane direction with respect to the inclination angle distribution formed by the unevenness of the reflector. As is clear from this figure, when using it with a tilt, such as a notebook personal computer, the distribution of the inclined surface in the horizontal direction on the display panel is such that the existence probability is maximized within the inclination angle range of 15 to 19 °. It is desirable that the distribution of the inclined surface in the vertical direction of the display panel has a peak existence probability in the range of the tilt angle of 8 to 10 ° and the tilt angle of 15 to 19 °. Thus, according to the direction of the display panel, the angle distribution of the inclined surface due to the unevenness for reflection, one direction has one existence probability peak, and the other direction has two existence probability peaks. Thus, even when used in an environment where the incident light direction is anisotropic, the maximum reflectance can be realized.
[0146]
The inventors made a prototype of the reflector having the above-described inclined surface distribution and confirmed the reflectance. FIG. 34 is a cross-sectional view showing a method for forming a sample reflector. First, as shown in FIG. 34A, a resist (for example, LC-200 manufactured by Shipley Co.) 63 is formed on a glass substrate 62 by spin coating at 1000 rpm for 20 seconds. Then, after pre-baking at 90 ° C. for 20 minutes, ultraviolet exposure is performed using a mask 64 as shown in FIG. Next, development is performed using a developer (for example, MF319 manufactured by Shipley Co., Ltd.), and a convex portion made of resist is formed on the glass substrate as shown in FIG. 34 (a) to (c) are repeated four times using the mask patterns (a) to (d) shown in FIG. 35 in order, and the convex portions having different inclination angles as shown in FIG. 34 (d). Form. Next, as shown in FIG. 34 (e), post-baking was performed at 200 ° C. for 80 minutes to round the convex portions. Thereafter, as shown in FIG. 34 (f), aluminum 66 was vapor-deposited to a thickness of 200 nm to produce a reflector.
[0147]
FIG. 36 is a diagram showing a planar shape and a cross-sectional shape of the convex portion of the reflecting plate formed as described above. The planar shape of the projection 67 has different inclined surfaces in the vertical direction V of the substrate 62 and has the same inclined surface in the horizontal direction H of the substrate 62. In the plan view shown in FIG. 36, contour lines are shown on the convex portion 67 and the inclined surface shape is shown. Since the convex portion is rounded by post-baking, the inclination angle distribution is distributed in a range of approximately 0 to 20 °. Since the inclined surface (ξ1> ξ2) is different in the vertical direction V of the substrate, there are two regions where the existence probability peaks as shown in FIG. 33. In the horizontal direction H of the substrate, the inclined surface Since (ξ1) is symmetric, there is one region where the existence probability peaks as shown in FIG.
[0148]
As described above, the distribution of the inclination angle in the horizontal direction and the distribution of the inclination angle in the vertical direction can be made different by changing the shape of the unevenness for reflection in the horizontal direction and the vertical direction. In addition, as shown in FIG. 36, the distribution of the inclination angle in the horizontal direction and the inclination angle in the vertical direction can be made different by combining the semicircular shape and the semielliptical shape.
[0149]
The inventors measured the shape using a non-contact three-dimensional shape measuring device nh-3 manufactured by Ryoko Co., Ltd., and found the inclination distribution of the prototyped reflector. FIG. 37 shows the measurement result of the inclination angle distribution of the prototyped reflector. As shown in the figure, the prototyped reflectors had absolute probabilities at 8 ° and 18 ° in absolute values. For comparison, FIG. 37 also shows the tilt angle distributions of the reflectors having the maximum existence probability at 0 ° and 10 °, and Conventional Example 1 and Conventional Example 2, respectively.
[0150]
FIG. 38 is a schematic cross-sectional view of a reflective liquid crystal display device prepared using the above-described reflector. A liquid crystal layer (for example, a liquid crystal material MJ961213 manufactured by Merck & Co., Inc.) was injected between the reflector and the glass substrate while controlling the thickness with a 3.5 μm diameter spacer. Then, the reflective liquid crystal display device is fixed at an angle of 30 ° from the vertical direction, irradiated with uniform diffused light from an integrating sphere, and the reflectance is measured using a luminance meter (for example, BM-5 manufactured by Topcon). It was measured. FIG. 39 is a diagram showing the measurement results of the reflectance. As is apparent from this chart, when the reflector of the present invention is used, the reflectance is 61%, and the reflectance is improved by 10 to 25% compared to 31% and 53% of the conventional examples 1 and 2. It was confirmed.
[0151]
FIG. 33 shows an ideal tilt angle distribution. As a precondition, the refractive index n of the liquid crystal layer or the glass substrate is 1.5, and the angle with respect to the horizontal line of the reflective liquid crystal display device (the tilt α shown in FIG. 31). Was set to α = 30 °. Therefore, the refractive index n of the liquid crystal layer_LCWhen the tilt angle α of the reflective liquid crystal display device is changed, the tilt angle range where the existence probability is maximized in the ideal reflection unevenness is examined.
[0152]
FIG. 40 is a diagram illustrating a tilt angle range in which the existence probability is maximized with respect to the tilt angle of the reflective liquid crystal display device and the refractive index of the liquid crystal layer. Refractive index n of typical liquid crystal materials_LCIs about 1.4 to 1.8, so the refractive index n_LCWas varied from 1.4 to 1.8. Under general usage conditions, the inclination α tends to increase as the size of the reflective liquid crystal display device decreases.
Therefore, the inclination α of the display panel was changed in the range of 0 to 45 °.
[0153]
First, when the inclination angle α of the display panel is 30 °, as shown in FIGS. 32 and 33, the existence probability of the uneven inclination angle is maximized in the range of 15 to 19 °, and on the other hand, it is 8 to 10 It is desirable that the existence probability of the inclination angle of the unevenness is maximized in two ranges of a range of ° and a range of 15 to 19 °. When the display panel tilt angle α is 0 °, the display panel is placed vertically, and the vertical tilt angle ξ of the display panel mainly reflects incident light from above in the vertical direction. Therefore, the existence probability of the uneven inclination angle becomes maximum in the range of 15 to 19 °, and since there is not much incident light from below, an inclined surface facing downward is not necessary. When the display panel tilt angle α is 90 °, the display panel is placed horizontally and is not shown in FIG. 40, but the existence probability of the uneven tilt angle is maximized in the range of 15 to 19 °. It is desirable to become. When the display panel is horizontal, the distribution example is the same as that shown in FIG.
[0154]
As shown in FIG. 40, when the inclination angle α of the display panel is in the range of 0 ° to 45 °, one inclination angle at which the existence probability in the reflection unevenness is maximized is 0 to 16 °, and the other inclination angle is It was found that the reflectivity can be maximized if it is within the range of 14 to 19 °. Refractive index n_LCThe smaller the is, the larger the inclination angle becomes maximal.
[0155]
A notebook personal computer has a display panel tilted differently depending on the preference of the operator. Therefore, it is desirable to form a plurality of regions in which the existence probability of the inclination angle of the reflection unevenness is maximized in the pixel region so that the maximum reflectance can be realized at a plurality of inclinations. For example, as shown in FIG. 40, the inclination angle region where the inclination probability α of the display device is found corresponding to 30 ° and 40 ° and where the existence probability is maximized is 8 to 10 ° and 15 to 19 °. The first combination and the second combination of 10 to 12 ° and 15 to 19 ° coexist in the same pixel region. Alternatively, the three combinations of regions obtained corresponding to the inclination angle α of the display device corresponding to 30 °, 35 °, and 40 ° coexist. Alternatively, three types of convex patterns are allowed to coexist. Thereby, even if the inclination of the display panel differs to some extent, a relatively large reflectance can be realized.
[0156]
A reflective liquid crystal display device having the structure shown in FIG. 2 is formed by using the reflective electrode having the inclination angle distribution of the reflective irregularities described above as the pixel electrode, and the pixel electrode and the transparent electrode on the display side are formed on the liquid crystal layer 34. By applying a predetermined electric field to the liquid crystal layer 34, the liquid crystal layer 34 can have a birefringence action and desired display can be performed. That is, the liquid crystal layer 34 is driven in the field effect birefringence mode. Further, a pigment can be included in the liquid crystal layer 34 to form a guest-host type liquid crystal display device.
[0157]
[Examples of reflective irregularities with different directivities]
Japanese Patent Application Laid-Open No. 11-295750 describes a reflective liquid crystal display device that uses a pixel electrode as a reflective electrode. In this publication, the pixel electrode is divided into two regions, and an uneven shape having a highly directional reflection characteristic is formed in one region, and an uneven shape having a highly diffusive reflection property is formed in the other region. Form.
[0158]
However, in the case of a higher-definition liquid crystal display device, the pixel area becomes narrower, and it becomes more difficult to divide the pixel area into two areas and form different uneven shapes as in the conventional example. Is expected.
[0159]
Therefore, in the present embodiment, an uneven shape having a highly directional reflection characteristic and an uneven shape having a highly diffusive reflection characteristic are mixed in the pixel region. FIG. 41 is a cross-sectional view showing two reflective uneven shapes mixed in such a pixel region. Since the unevenness A has a gentle inclined surface with a thin film thickness and a relatively flat upper surface, the direction of reflected light has directivity in the vertical direction. On the other hand, the unevenness B is thick and has a steeply inclined surface, and the upper surface has a protruding shape, so that the reflected light diffuses widely.
[0160]
FIG. 42 is a plan view of the pixel region PX in the present embodiment. As shown in the drawing, the unevenness A and the unevenness B shown in FIG. 41 are mixedly provided in the pixel region PX.
[0161]
FIG. 43 is a cross-sectional view showing a manufacturing process for forming the reflective irregularities of FIG. First, as shown in FIG. 42A, a resist (for example, LC-200 manufactured by Shipley Co., Ltd.), which is a photosensitive resin, is spin-coated on a glass substrate 62 at 2000 rpm for 20 seconds. Then, after prebaking at 90 ° C. for 20 minutes, ultraviolet exposure is performed using a mask 64A as shown in FIG. Next, development is performed using a developing solution (for example, MF319 manufactured by Shipley Co., Ltd.), and convex portions corresponding to the concave and convex portions A are formed on the glass substrate 62 as shown in FIG. Thereafter, as shown in FIG. 42 (d), post-baking is performed at 200 ° for 80 minutes, and the projections are rounded to form the projections and depressions A.
[0162]
Next, as shown in FIG. 42E, the resist is spin-coated at 1000 rpm for 20 seconds. Thereby, a thicker resist layer than the above-mentioned resist can be formed. Then, after prebaking at 90 ° C. for 20 minutes, ultraviolet exposure is performed using a mask 64B as shown in FIG. Next, development is performed using the developer described above, and convex portions corresponding to the irregularities B are formed on the glass substrate as shown in FIG. Then, as shown in FIG. 42 (h), post-baking is performed at 120 ° C. for 80 minutes so that the convex portions are rounded to form the concave and convex portions B. Since this post-baking is at a lower temperature than that for forming the unevenness A, the degree of sagging due to the heating of the thick resist film is small, and the unevenness B having a higher diffusibility is formed.
[0163]
Thereafter, as shown in FIG. 42 (i), aluminum 64 was deposited to a thickness of 200 nm to produce a reflector (pixel electrode). As described above, it is possible to change the roundness of the unevenness by changing the resist film thickness and the post-baking temperature between the unevenness A and the unevenness B, and to create a reflective surface in which unevenness having different directivities at the time of scattering is mixed. Could be configured.
[0164]
As described above, it is desirable that the reflection plate of the reflective liquid crystal display device reflects incident light from all directions in a direction perpendicular to the display surface. Therefore, when the resist layer is patterned and rounded by baking to form an inclined surface, the inclined surface is preferably directed in the direction of 360 °. Thus, conventionally, a circular pattern has been proposed as a resist film pattern. For example, JP-A-11-337935, JP-A-11-337964, JP-A-5-215533, and the like. In these publications, a circular pattern is randomly formed to prevent a moire pattern due to interference of reflected light, or a donut pattern having a large radius and a circular pattern having a small radius are formed randomly. It has been proposed to improve the reflection characteristics.
[0165]
Japanese Patent Application Laid-Open No. 5-215533 shows that a large circular pattern and a small circular pattern are randomly mixed. For example, as shown in FIG. However, when circular patterns having a large radius are randomly arranged, the resist patterns that are close to each other are merged due to sagging of the cross-sectional shape due to heating during the post-baking process after exposure and development. The circular pattern shown by diagonal lines in FIG. 44 shows a state in which they are too close together and merged during baking.
[0166]
Therefore, in this embodiment, as shown in FIG. 45, the resist pattern is a mixture of a circular pattern with a large radius and a circular pattern with a small radius, and a large circular pattern and a small circular pattern. The distance is always smaller than the distance between large circular patterns. That is, it is prohibited to bring another large circular pattern close to the large circular pattern. If possible, a small circular pattern is arranged around the large circular pattern so that the large circular patterns do not come close to each other. As a result, the density of the inclined surfaces can be increased, and the area where the patterns are merged during baking can be reduced.
[0167]
FIG. 46 is a diagram for explaining a resist pattern in the present embodiment.
[0168]
FIG. 46A shows an example in which a relatively large circular pattern is arranged. Four large circular patterns P1 are arranged in the pixel region PX. The resist pattern needs to have a certain size. This is because if the pattern is too small, the inclination angle will not be sufficiently large due to the sagging of the cross-sectional shape during post-baking. However, in the pattern of FIG. 46A, the density of the inclined surface formed is thin, and the reflectance cannot be increased.
[0169]
Therefore, as shown in FIG. 46B, it is conceivable to increase the density of the large circular pattern P1. However, when the large circular patterns P1 are close to each other, the peripheral portions of the circular patterns may be merged as shown by the hatched lines due to sagging due to heat during post-baking. Such coalescence is not preferable because it reduces the area of the inclined surface as designed.
[0170]
Therefore, in the present embodiment, as described in FIG. 45, the density of the relatively large circular pattern P1 is sparse as shown in FIG. The distance L1 between the patterns P1 is kept relatively large, and a relatively small circular pattern P2 is arranged in the gap between the large circular patterns P1 so as to increase the inclined surface density. As a result, the coalescence of relatively large circular patterns is reduced, and even if coalescence occurs, it is limited to only between the large circular pattern P1 and the small circular pattern P2 (hatched line in FIG. 46C). . Such a merged region is narrower than the merged region of the large circular patterns P1, and the reduction of the inclined surface region can be minimized.
[0171]
As shown in FIG. 46C, the distance L1 between the large circular patterns P1 is made long to the extent that coalescence does not occur, and the small circular patterns P2 are arranged in the area between the circular patterns P1. As a result, the distance L2 between the large circular pattern P1 and the small circular pattern P2 closest thereto is always shorter than the distance L1 between the large circular pattern P1 and the large circular pattern P1 closest thereto.
[0172]
FIG. 47 is a diagram showing another resist pattern. In the above example, a circular pattern is used so that the inclined surface of the reflecting irregularities faces in the direction of 360 °. However, even if it is not circular, it is a polygon having a plurality of directions, preferably three or more directions on each side. Even if it exists, the same high reflectance can be implement | achieved.
[0173]
FIG. 47 shows an example of a resist pattern in which a large number of hexagons are brought close to each other in the pixel region PX so that adjacent sides are parallel to each other. The entire periphery of the pixel area PX cannot be accommodated in the entire hexagon, but has a trapezoidal shape or a pentagonal shape, but is basically a resist pattern in which the hexagonal shape is spread like a tile. By making each side parallel, even when the hexagonal patterns are as close as possible, coalescence during post-baking can be prevented.
[0174]
By exposing and developing the resist layer using such a mask pattern and performing post-baking, the cross-sectional shape is sagging due to heat, thereby forming reflective irregularities having inclined surfaces facing at least three directions. Can do.
[0175]
FIG. 48 is a diagram showing another resist pattern. In the example of FIG. 48, not a hexagon but a plurality of regular triangles are arranged in the pixel region so that the sides are close to each other in parallel. Also in this case, by exposing and developing the resist layer and performing post-baking, it is possible to form reflection irregularities whose cross-sectional shape is bent by heat and whose inclined surfaces are directed in at least three directions. In the present embodiment, even if it is another polygonal shape, it is possible to form reflective irregularities having a high-density inclined surface.
[0176]
The process of forming the unevenness for reflection when the patterns of FIGS. 45, 47 and 48 are used is the same as the process shown in FIG. 45, 47 and 48 are used for the mask 64 in the resist layer exposure process. Thereby, in a post-bake process, a high-density inclined surface distribution can be formed, without patterns combining, and the reflectance of a reflecting plate can be made high.
[0177]
[Front light structure]
The reflective liquid crystal display device brightens the display surface by reflecting external light without providing a backlight. Therefore, it consumes less power and is useful as a display panel for portable information terminals, mobile phones and the like. However, since external light is used, there is a problem that is limited to use in bright places. Therefore, a liquid crystal display device with a front light that is turned on only when used in a dark place has been proposed.
[0178]
FIG. 49 is a configuration diagram of a reflection type liquid crystal display panel with a front light which has been conventionally proposed. As illustrated, a front light 70 is provided on the display side of the reflective liquid crystal display panel 73. In the reflective liquid crystal display panel 73, a liquid crystal layer (not shown) is inserted between a back substrate 73B having a reflective plate structure and a display substrate 73A. A front light 70 is provided on the display-side substrate 73A. The front light 70 guides light from the light source 71 and the light source to the entire display surface, and displays it by a scattering layer or a prism layer formed on the surface. And a transparent substrate 72 scattered on the panel 73 side. Due to the difference in refractive index between the scattering layer or the prism layer formed on the surface of the transparent substrate 72 and the air layer, the light from the light source 71 is scattered and a part thereof is scattered to the display panel 73 side.
[0179]
However, in the reflection type liquid crystal display device configured as shown in FIG. 49, a scattering layer or a prism layer is formed on the surface of the transparent substrate 72, and an observer can display the display panel 73 via the scattering layer or the prism layer. You will see characters and images. For this reason, characters and images are distorted or blurred by the scattering layer or the prism layer, resulting in a decrease in image quality.
[0180]
Therefore, in this embodiment, the front light structure has a scattering property for the transparent substrate that guides light only when the light source is turned on, and the scattering property of the transparent substrate is lost when the light source is not turned on. With such a configuration, during normal use using external light, the front light structure does not have a scattering function, so that the characters and images on the display panel to be observed and distortion and blur are eliminated. On the other hand, in limited cases such as when used in dark places, the front light structure gives light from the light source. Therefore, even if characters and images are slightly distorted or blurred, the display panel is brightened. As a minimum, it is possible to secure the functions.
[0181]
FIG. 50 is a diagram illustrating a first example of the front light. The front light 70 shown in FIG. 50 is filled with a transparent substrate 74 having a scattering layer 75 on the surface thereof by sandblasting the surface of the transparent substrate made of acrylic, an acrylic transparent substrate 76, and the space between the substrates. A fluid 77 such as silicone oil, a fluid pump 78, and a fluid tank 79. The front light 70 further includes a linear light source 71 using a cold cathode fluorescent tube. The fluid stored in the fluid tank 79 is filled or extracted between the substrates 74 and 76 by the fluid pump 78. The refractive index of the fluid 77 is substantially the same as that of the transparent substrates 74 and 76, n = 1.5.
[0182]
As shown in FIG. 50A, when the reflective liquid crystal display panel is used in a bright place, the light source 71 is in the off state, and the fluid 77 is filled in the gap between the transparent substrates 74 and 76. Thereby, the scattering layer 75 is not visible from the viewer side because there is no difference in refractive index from the fluid 77. Therefore, when used in a bright place, characters and images on the display panel 73 are not blurred or distorted.
[0183]
On the other hand, as shown in FIG. 50B, when the reflective display panel is used in a dark place, the light source is turned on, and the fluid 77 is fluid pump 78 from the gap between the transparent substrates 74 and 76. The gap between the substrates is filled with an air layer. Therefore, in the scattering layer 75, a refractive index difference is generated between acrylic (refractive index: about 1.5) and air (refractive index: 1.0), which are transparent substrate materials, and functions as an original scattering layer. Therefore, the light guided by repeated internal reflection from the light source 71 at the ends of the transparent substrates 74 and 76 is scattered by the scattering layer 75 and illuminates the reflective liquid crystal display panel 73. Therefore, a bright display panel can be realized even in a dark place.
[0184]
However, when the front light 70 is viewed from the viewer side, the scattering layer 75 of the transparent substrate 74 is seen, and the display of the reflective liquid crystal display panel 73 is distorted. However, such distortion is equivalent to that of a conventional reflective liquid crystal display panel with front light.
[0185]
As described above, when used in a bright place, the same display as a reflective display panel without a front light can be obtained, and when used in a dark place, the light from the lit light source is effectively reflected. It can be used to illuminate liquid crystal display panels and can achieve bright display.
[0186]
FIG. 51 is a diagram showing a second example of the reflective liquid crystal display panel with a front light in the present embodiment. In this example, a transparent electrode (ITO) 81 mainly composed of indium oxide is formed on the surface of two transparent substrates 74 and 76 such as glass, and a liquid crystal layer 80 whose state is changed by an electric field is sandwiched between the electrodes. Yes. The voltage V1 may or may not be applied between the transparent electrodes 81 by the switch SW. Normally, such a liquid crystal layer 80 is in a transparent state when a voltage V1 is applied between the transparent electrodes, and is in a scattering state when the voltage between the transparent electrodes is zero. Accordingly, in a bright place, the switch SW is turned on to make the liquid crystal layer 80 transparent, and in a dark place, the switch SW is turned off to bring the liquid crystal layer 80 into a scattering state.
[0187]
Liquid crystal materials that can be switched between a scattering state and a transmission state include (1) liquid crystal using dynamic scattering effect, (2) liquid crystal using phase transition effect between cholesteric phase and nematic phase, (3) There is a polymer-dispersed liquid crystal, and either liquid crystal can be used.
[0188]
Compared with the example of FIG. 50, the example of FIG. 51 does not require a transparent substrate with a scattering layer, a pump, a tank, or the like, and does not require time for filling or withdrawing a fluid. Furthermore, in the case of a polymer dispersion type liquid crystal, the degree of refractive index anisotropy of the spherical liquid crystal in the polymer can be adjusted by an applied voltage. Therefore, by adjusting the applied voltage, the scattering degree of the liquid crystal layer 80 can be adjusted. Whether to increase the scattering degree with respect to the light of the light source 71 to make it brighter or reduce the scattering degree to suppress distortion of the display screen. , Can be adjusted according to the observer's preference.
[0189]
Also in the example of FIG. 51, when the light source 71 is turned on and the liquid crystal layer 80 has a scattering property, the display of the reflective liquid crystal display panel seems to pass through the frosted glass. This is equivalent to a reflective liquid crystal display panel. In a bright state where the light source 71 is off, the liquid crystal layer 80 is transparent, and the display is not blurred or distorted. In other words, this example is a reflective liquid crystal display panel with a front light, but when the front light is not lit, display quality equivalent to that of a reflective liquid crystal display panel without a front light is possible. It has the same display quality as a reflective liquid crystal display panel.
[0190]
FIG. 52 is a diagram showing a third example of the reflective liquid crystal display panel with front light. In this example, a transparent electrode 81 is formed on the inner surface of transparent substrates 74 and 76 such as glass, and a prism layer 82 having prism-shaped fine irregularities is formed inside the transparent substrate 74. A liquid crystal layer 80 having refractive index anisotropy is sealed between the transparent substrates 74 and 76. In liquid crystal molecules having refractive index anisotropy, the orientation direction of the molecules changes depending on the electric field, and the direction of refractive index anisotropy changes. Therefore, the refractive index of the prism layer 82 is matched with one refractive index of the liquid crystal layer 80 having refractive index anisotropy.
[0191]
As shown in FIG. 52 (a), when used in a bright place, a voltage is applied to the liquid crystal layer 80 or no voltage is applied, and the refraction of the prism layer 82 in the direction from the display side toward the reflective display panel 73 is performed. And the refractive index of the liquid crystal layer 80 are matched. In this state, in the direction from the display side toward the reflective display panel 73, the refractive index is the same between the prism layer 82 and the liquid crystal layer 80, the scattering state by the prism layer 82 is eliminated, and the front light structure becomes transparent. . As a result, the reflective liquid crystal display panel without the front light is brought into the same state, and the display screen is not blurred or distorted.
[0192]
On the other hand, as shown in FIG. 52 (b), when used in a dark place, the prism layer 82 is applied to the liquid crystal layer 80 in a state in which no voltage is applied or is applied, and in the direction from the display side toward the reflective display panel 73. And the refractive index of the liquid crystal layer 80 are made different. As a result, a difference in refractive index occurs between the prism layer 82 and the liquid crystal layer 80, and the light from the light source 71 is refracted. This refracted light becomes illumination light for the reflective liquid crystal display panel 73, and a bright display can be realized.
[0193]
In this example, a prism shape is formed on the surface of the transparent substrate 74, but the same effect can be expected even if a scattering layer is formed on the surface of the transparent substrate 74 by a sandblasting process.
[0194]
By applying this structure, the same effects as those of Example 2 can be obtained, and the switching speed between the transmission state and the scattering state can be further improved due to the properties of the liquid crystal layer 80. Compared with the polymer dispersion type liquid crystal of Example 2, the voltage applied to the liquid crystal layer 80 can be directly applied to the liquid crystal layer 80, so that the applied voltage can be kept lower than when the polymer dispersion type liquid crystal is used. Then, by applying the refractive index of the liquid crystal layer to the refractive index of the prism layer 82 in a state where no voltage is applied to the liquid crystal layer 80, voltage application to the light source 71 and the transparent electrode 81 is possible when used in a bright place. It becomes unnecessary and can further reduce power consumption.
[0195]
FIG. 53 is a diagram showing a fourth example of the reflective liquid crystal display panel with front light. In this example, the transparent electrode 81A formed on the transparent substrate 74 which is the light guide plate of the front light 70 is divided into strips, and voltage application 81A-1 and voltage non-application 81A-2 can be selected for each. ing. A liquid crystal layer whose state is changed by application of a voltage is filled between the transparent substrates 74 and 76. 53A shows a cross-sectional structure, and FIG. 53B shows a planar structure of the divided transparent electrode 81A.
[0196]
With this structure, by changing the number of transparent electrodes 81A to which a voltage is applied, the area of the liquid crystal layer that is in a scattering state can be changed as appropriate, and the amount of illumination light can be adjusted to some extent. Therefore, in this configuration, the liquid crystal layer 80 uses a scattering type liquid crystal whose scattering degree cannot be adjusted, a liquid crystal using a dynamic scattering effect, a liquid crystal using a phase transition effect between a cholesteric phase and a nematic phase, and the like. However, the degree of scattering can be adjusted by selecting a transparent electrode to which a voltage is applied.
[0197]
A reflection type liquid crystal display panel with a front light scatters light from the light source 71 well and can illuminate the reflection type liquid crystal display panel 73 well if the degree of scattering by the liquid crystal layer of the front light is large. The brightness can be increased. However, since a scattering layer is inserted between the viewer and the reflective liquid crystal display panel, the displayed image becomes cloudy and the resolution appears to be lowered. Therefore, if the degree of scattering can be adjusted, the observer can adjust it to obtain the optimum display quality for the observer.
[0198]
FIG. 54 is a diagram showing a fifth example of the reflective liquid crystal display panel with front light. In this example, as in the second example shown in FIG. 52, the front light 70 has a transparent electrode 81 formed inside two transparent substrates 74 and 76, and a liquid crystal layer 80 filled between them. Yes. The liquid crystal layer 80 is a polymer-dispersed liquid crystal, and a refractive index anisotropic resin is used for the polymer. The ordinary light refractive index and the extraordinary light refractive index of the liquid crystal grains 90 are not applied with a voltage between the transparent electrodes. It is configured to match the refractive index of the polymer in two directions.
[0199]
Details of the polymer-dispersed liquid crystal are shown on the right side of FIG. In the polymer dispersed liquid crystal A, liquid crystal grains 90 having refractive index anisotropy are dispersed in a polymer having no refractive index anisotropy, whereas in the polymer dispersed liquid crystal B, the refractive index anisotropy is present. Liquid crystal grains 90 having refractive index anisotropy are dispersed in a certain polymer.
[0200]
The crystal grains 90 are aligned in the thickness direction of the front light 70 with no voltage applied between the transparent electrodes, and the refractive index in the thickness direction of the front light matches the polymer 92 and the transparent substrates 74 and 76. Assume that the refractive index is inconsistent when a voltage is applied between the transparent electrodes.
[0201]
In that case, the polymer dispersed liquid crystal A has a refractive index in the vertical direction of the liquid crystal grains 90 matching the polymer 92 and the transparent substrates 74 and 76 as shown in the figure, and there is no refractive index difference between the light beams in the vertical direction. No refraction or scattering occurs. However, since there is a difference in the refractive index in the horizontal direction between the polymer 92 and the liquid crystal grains 90, not only horizontal light but also light from an oblique direction, that is, with respect to the horizontal vector component of the light ray, Refraction occurs. For this reason, when the reflective liquid crystal display panel 73 is viewed obliquely, the front panel 70 appears cloudy due to this refraction.
[0202]
On the other hand, when the polymer dispersed liquid crystal B is filled between the transparent substrates 74 and 76, liquid crystal molecules are aligned in the thickness direction of the front light without applying a voltage between the transparent electrodes, and the refractive index of the liquid crystal grains 90 The direction of anisotropy coincides with the direction of refractive index anisotropy of the polymer 92. Accordingly, in this state, the refractive index difference between the liquid crystal grains 90 and the polymer 92 is completely eliminated from any direction, and the front light becomes transparent from any direction. Therefore, as compared with the case where the polymer dispersion type liquid crystal A is used, it is possible to prevent image distortion and fogging from an oblique direction when used in a bright place.
[0203]
On the other hand, when used in a dark place, when a voltage is applied between the transparent electrodes, the direction of the refractive index anisotropy of the liquid crystal grains 90 is different from the direction of the refractive index anisotropy of the polymer 92 as shown in the figure. It becomes inconsistent state. This is because the anisotropy direction of the polymer 92 is not changed by the electric field. Therefore, the front light 70 is in a scattering state, light from the light source 71 is scattered toward the reflective liquid crystal display panel 73, and the liquid crystal display surface is brightened. However, the liquid crystal layer 80 becomes a cream color, and the display screen is blurred or distorted.
[0204]
In that case, the direction of the refractive index anisotropy of the liquid crystal grains 90 can be adjusted by adjusting the voltage applied between the transparent electrodes. That is, when the applied voltage is increased, the degree of scattering in the liquid crystal layer increases, and the incident light on the reflective liquid crystal display panel 73 increases and the screen becomes brighter, but the screen becomes too white and difficult to see. On the other hand, when the applied voltage is lowered, the degree of scattering in the liquid crystal layer decreases and the screen becomes darker, but the transparency of the screen increases. Therefore, by adjusting this applied voltage, the degree of screen brightness and the degree of contrast can be set according to the preference of the observer.
[0205]
FIG. 55 is a diagram showing a sixth example of the reflective liquid crystal display panel with front light. 50 to 54, the light from the light source 71 is guided through the two transparent substrates. On the other hand, in the example of FIG. 55, the light source 71 is arranged on the side surface of the substrate 74 on the display surface side of the two transparent substrates, and the light is mainly guided through the display surface side substrate 74. Then, light is scattered by the prism-shaped irregularities 82 arranged on the side surface of the reflective liquid crystal display panel 73 of the substrate 74 to illuminate the reflective liquid crystal display panel 73. Transparent electrodes (not shown) are formed on the transparent substrates 74 and 76, and the liquid crystal layer 80 is filled therebetween.
[0206]
As shown in FIGS. 50 to 54, when light is guided to the upper and lower transparent substrates 74 and 76, the light guided from the upper and lower transparent substrates hits the prism-shaped unevenness 82. In that case, it is desirable that the light from the upper transparent substrate 74 is refracted and transmitted downward, and the light from the lower transparent substrate 76 is reflected and scattered and is also reflected downward. In practice, however, light is refracted and transmitted more than light is reflected and scattered and travels downward, making it difficult to efficiently reflect and scatter light from the lower substrate.
[0207]
On the other hand, in the configuration of FIG. 55, the prism layer 82 is provided on the display panel 73 side of the transparent substrate 74 that transmits the light from the light source. Accordingly, the light applied to the prism layer 82 is light transmitted through the upper transparent substrate 74, and more light enters the reflective liquid crystal display panel 73 side by being refracted and scattered by the prism layer 82. Therefore, the prism-shaped irregularities 82 may be formed into a refractive scattering shape, and the shape can be simplified and the illumination efficiency can be improved.
[0208]
Similarly, when the liquid crystal layer 80 exhibiting scattering properties is sealed, more light is scattered from the upper side to the liquid crystal layer 80 and passes downward, and the amount of reflected and scattered light is small. Therefore, the illumination efficiency can be increased with the above structure. Further, the light from the light source 71 guides only one transparent substrate 74 and the amount of incident light from the light source decreases. However, by increasing the thickness of the transparent substrate 74, the amount of incident light from the light source 71 is improved. can do.
[0209]
FIG. 56 is a diagram showing a seventh example of a reflective liquid crystal display panel with a front light. The configuration of FIG. 56 is an improvement of the configuration of FIG. That is, FIG. 56 shows a structure in which a transparent light guide plate 94 having a light source 71 arranged on the side surface and a substrate in which elements exhibiting scattering properties are sealed are bonded to two transparent substrates 74 and 76. Specifically, a scattering substrate in which a prism layer 82 is formed between transparent substrates 74 and 76 made of glass or the like and a liquid crystal layer 80 whose refractive index state is changed by an electric field is filled in a transparent light guide plate 94. Bonded by optical adhesive 96. In the case of this structure, it is possible to separate the production of the two transparent substrates 74 and 76 encapsulating the element that expresses the scattering property and the production of the light guide plate 94 with the light source, so that the production process is separated and the yield is improved. It becomes possible. Further, the glass substrates 74 and 76 sandwiching the liquid crystal layer 80 are as thin as, for example, 0.5 to 0.7 mm, and the thickness of the transparent light guide plate 94 on which the light source 71 is disposed is increased accordingly, so It is also easy to improve the light incidence efficiency.
[0210]
As described above, the front light structure according to the present embodiment normally scatters the light emitted from the light source and makes it incident on the reflective liquid crystal display panel only when the light source is turned on in a dark place and does not turn on the light source. When in use, the scattering is lost. Accordingly, it is possible to eliminate blurring and distortion of characters and images on the display screen during normal use, and to improve contrast. In addition, a bright display screen can be realized even in a dark place.
The above embodiment is summarized as follows.
(Supplementary note 1) In the manufacturing method of the reflective liquid crystal display device,
(A) irradiating the surface of the photosensitive resin layer having a predetermined film thickness with light having exposure energy to form a distribution of thermal deformation characteristics in the thickness direction or planar direction of the photosensitive resin layer;
(B) A method of forming a reflective liquid crystal display device, comprising: performing a heat treatment thereafter to form random irregularities on the surface of the photosensitive resin layer.
(Supplementary Note 2) In the manufacturing method of the reflective liquid crystal display device,
(A) A photosensitive resin layer having a predetermined film thickness is immersed in a chemical solution containing any one of an acid, an alkali solution, a quaternary ammonium salt solution, and HMDS, and heated in the thickness direction or the plane direction of the photosensitive resin layer. Forming a distribution of dynamic deformation characteristics;
(B) A method of forming a reflective liquid crystal display device, comprising: performing a heat treatment thereafter to form random irregularities on the surface of the photosensitive resin layer.
(Appendix 3) In Appendix 1,
In the step (a), the light having the exposure energy is far ultraviolet rays.
(Appendix 4) In Appendix 1,
In the step (a), the entire surface of the photosensitive resin layer is irradiated with light having the exposure energy to change its quality, and a distribution of thermal deformation characteristics is formed in the thickness direction of the photosensitive resin layer. A method for forming a reflective liquid crystal display device.
(Appendix 5) In Appendix 1,
In the step (a), the light having the exposure energy is irradiated to a part of the surface of the photosensitive resin layer to change its quality and form a distribution of thermal deformation characteristics in the plane direction of the photosensitive resin layer. A method for forming a reflective liquid crystal display device.
(Appendix 6) In Appendix 1 or 2,
A method of forming a reflective liquid crystal display device, further comprising the step of forming a separation line with a reduced film thickness in the photosensitive resin layer before the step (a).
(Supplementary note 7) In the manufacturing method of the reflective liquid crystal display device,
(A) forming a photosensitive resin layer having a predetermined film thickness on a substrate having a transistor formed on the surface;
(B) forming a contact hole to the electrode of the transistor by a photolithography process of partially exposing and developing the photosensitive resin layer;
(C) a post-baking step of heating the photosensitive resin layer to a first temperature;
(D) irradiating the surface of the photosensitive resin layer with light having exposure energy to form a distribution of thermal deformation characteristics in the thickness direction or planar direction of the photosensitive resin layer;
(E) a reflective liquid crystal display comprising: a final baking step in which random unevenness is formed on the surface of the photosensitive resin layer by performing heat treatment at a second temperature higher than the first temperature. Device forming method.
(Appendix 8) In Appendix 7,
A reflective liquid crystal display device comprising: a step of forming a pixel electrode connected to the electrode of the transistor through the through hole on the photosensitive resin layer after the step (e); Forming method.
(Appendix 9) In Appendix 7,
Before the step (c), the method further comprises a step of forming a separation line for separating the photosensitive resin layer by exposing or developing the photosensitive resin layer in a predetermined pattern or developing it, and developing the photosensitive resin layer. A reflective liquid crystal display device forming method.
(Appendix 10) In Appendix 7,
By controlling the film thickness of the photosensitive resin layer in the step (a), the post-baking temperature and time in the step (c), and the irradiation energy amount in the step (d), the average inclination angle of the unevenness is 0-15. A method for forming a reflective liquid crystal display device, characterized by:
(Appendix 11) In Appendix 10,
And forming a liquid crystal layer between the alignment film and the alignment film of the display-side substrate after the pixel electrode forming step.
(Supplementary note 12) In a reflective liquid crystal display device,
A substrate on which the liquid crystal layer is formed, the inclination angle of the reflection irregularities formed on the liquid crystal layer side of the substrate is distributed in a range of at least 0 ° to 20 °, and the existence probability of the inclination angle is 15 ° to A reflective liquid crystal display device having a peak in a range of 19 °.
(Appendix 13) In Appendix 12,
A reflective liquid crystal display device, wherein the planar pattern of the concave and convex portions for reflection has a circular shape, a polygonal shape, a stripe shape, or a combination thereof.
(Supplementary note 14) In a reflective liquid crystal display device,
A substrate on which a liquid crystal layer is formed, and the inclination angle of the unevenness for reflection formed on the liquid crystal layer side of the substrate has a peak of existence probability along the first direction; A reflection-type liquid crystal display device, wherein the existence probability is distributed so as to have two peaks along a second direction different from the first direction.
(Appendix 15) In Appendix 14,
The display surface of the reflective liquid crystal display device is disposed at an angle,
The reflective liquid crystal display device, wherein the first direction is a horizontal direction and the second direction is a vertical direction.
(Supplementary Note 16) In Supplementary Note 14 or 15,
The existence probability along the first direction peaks once in the range of 15 ° to 19 °, and the existence probability along the second direction ranges from 15 ° to 19 ° and 0 ° to 14 °. A reflection type liquid crystal display device having a peak in each range of °.
(Supplementary note 17) In Supplementary note 14 or 15,
In each of the pixel regions in the display surface, the existence probability along the second direction in the first region has a peak in the first angle range and the second angle range, and the second region has the second probability in the second region. A reflection-type liquid crystal display device, wherein the existence probability along the direction has a peak in the first angle range and the third angle range.
(Supplementary note 18) In any one of Supplementary notes 12 to 15,
And a display side substrate sandwiching the liquid crystal layer with the substrate, and a polarizing plate formed on the display side of the display side substrate, wherein the liquid crystal layer is driven in a field effect birefringence mode. Reflective liquid crystal display device.
(Supplementary note 19) In a reflective liquid crystal display device,
Reflective irregularities on the substrate, and within a single pixel region, a first convex portion having a first directivity and a first scattering property for reflected light, and the first directivity for the reflected light A reflective liquid crystal display device comprising: a second directivity weaker than the second directivity and a second convex portion having a second scattering property stronger than the first scattering property, which are randomly mixed.
(Supplementary note 20) In a reflective liquid crystal display device,
Reflective irregularities are formed on the substrate, the irregularities are formed of a photosensitive resin film, the first circular patterns are spaced apart from each other by a first distance, and a second smaller than the first circular pattern. The reflective liquid crystal display device is characterized in that the circular pattern is spaced apart from the first circular pattern by less than the first distance.
(Supplementary note 21) In a reflective liquid crystal display device,
The substrate has reflection irregularities, the irregularities are formed of a photosensitive resin film, and a plurality of polygon patterns are arranged so that adjacent polygon sides are parallel to each other. Reflective liquid crystal display device.
(Supplementary Note 22) In a reflective liquid crystal display device,
A reflective liquid crystal display panel;
Provided on the reflective liquid crystal display panel, and a light guide plate, a light source disposed at an end of the light guide plate, and a light scattering property to light transmitted through the light guide plate when the light source is turned on, A reflective liquid crystal display device comprising: a front light having light scattering means for reducing the light scattering property when the light source is not turned on.
(Appendix 23) In Appendix 22,
The light guide plate and the light scattering means have a liquid crystal panel having a pair of transparent substrates, a transparent electrode formed on the opposing surface thereof, and a liquid crystal layer formed between the pair of transparent substrates. Is a reflective liquid crystal display device that exhibits light scattering properties according to an electric field applied between the transparent electrodes.
(Appendix 24) In Appendix 23,
The light source is disposed on a side surface of the transparent substrate on the display side of the pair of transparent substrates, and the liquid crystal layer is provided between the transparent substrate on the display side and the transparent substrate on the reflective liquid crystal display panel side. A reflection-type liquid crystal display device.
(Appendix 25) In Appendix 22,
The light scattering means includes a liquid crystal panel having a pair of transparent substrates, a transparent electrode formed on the opposing surface thereof, and a liquid crystal layer formed between the transparent substrate pairs. A reflection type liquid crystal display device, which exhibits light scattering properties according to an electric field applied between transparent electrodes, and wherein the pair of transparent substrates are bonded to the light guide plate.
(Supplementary note 26) In any one of Supplementary notes 23 to 25,
In the liquid crystal layer, the direction of refractive index anisotropy changes according to the applied electric field,
A transparent prism-like uneven layer is provided between any one of the transparent substrates and the liquid crystal layer, and the refractive index of the uneven layer matches the refractive index of one of the liquid crystal layers. Reflective liquid crystal display device.
(Supplementary note 27) In any one of Supplementary notes 23 to 25,
A reflective liquid crystal display device, wherein the transparent electrode is separated into a plurality of portions, and a voltage is selectively applied to the separated transparent electrodes to adjust the degree of light scattering of the liquid crystal layer.
(Supplementary note 28) In any one of Supplementary notes 23 to 25,
The liquid crystal layer includes a liquid crystal material using a dynamic scattering effect, a liquid crystal material using a phase switching effect between a cholesteric phase and a nematic phase, and a liquid crystal particle having refractive index anisotropy in a polymer. A reflective liquid crystal material which is one of a polymer dispersed liquid crystal material and a second polymer dispersed liquid crystal material having liquid crystal grains having refractive index anisotropy in a polymer having refractive index anisotropy Display device.
[0211]
【The invention's effect】
As described above, according to the present invention, the reflection unevenness of the reflective liquid crystal display device can be formed by a simple process, and the inclined surface distribution due to the desired unevenness can be formed with good controllability. Furthermore, according to the present invention, it is possible to obtain an inclined surface distribution by the optimum reflection unevenness, and improve the reflectance.
[Brief description of the drawings]
FIG. 1 is an example of a circuit diagram of a liquid crystal display device to which this embodiment is applied.
FIG. 2 is a diagram showing an example of a cross-sectional view of a reflective liquid crystal display device to which this embodiment is applied.
FIG. 3 is a cross-sectional view showing a part of the manufacturing process of the reflective liquid crystal display device in the embodiment.
FIG. 4 is a view showing a micrograph of the surface shape of a micro groove of a reflection panel formed by changing the film thickness of a photosensitive resin layer 20 and UV irradiation energy.
FIG. 5 is a view showing a micrograph of the surface shape of a micro groove of a reflection panel formed by changing the film thickness of a photosensitive resin layer 20 and UV irradiation energy.
6 is a view showing a micrograph of the surface shape of a micro groove of a reflection panel formed by changing the film thickness of the photosensitive resin layer 20 and the UV irradiation energy. FIG.
7 is a view showing a micrograph of a surface shape of a micro groove of a reflection panel formed by changing the film thickness of a photosensitive resin layer 20 and UV irradiation energy. FIG.
FIG. 8 is a diagram showing AFM images of samples of three reflective panels.
FIG. 9 is a graph showing the relationship between the average inclination angle of the reflective film and the reflectance with respect to the diffused light source.
10 is a graph showing the relationship between resist film thickness and reflectance for the three samples in FIG. 8. FIG.
FIG. 11 is a diagram schematically showing the concave and convex shape of the microgroove of the resin layer formed according to the present embodiment.
FIG. 12 is a diagram showing an example of a planar pattern of microgrooves formed according to the present embodiment.
FIG. 13 is a diagram showing an example of UV irradiation necessary for forming a microgroove.
FIG. 14 is a cross-sectional view showing the manufacturing process of the first sample.
FIG. 15 is a graph comparing the reflectance when the integrating sphere diffuse light source is irradiated to the first, second and third samples.
FIG. 16 is a diagram illustrating separation of a photosensitive resin layer.
FIG. 17 is a cross-sectional view showing a process for forming a separation line of a photosensitive resin layer.
FIG. 18 is a diagram showing micrographs of microgrooves with and without a separation line.
FIG. 19 is a diagram showing an actual environment in which a reflective liquid crystal display device assumed in the present embodiment is used.
FIG. 20 is a diagram showing an incident angle θi and an azimuth angle φi of incident light.
FIG. 21 is a diagram showing a case where light is incident on and reflected from a reflective display device.
FIG. 22 shows the intensity f (θ of light incident on the reflector plate._i') And incident angle θ_iIt is a figure which shows the relationship with '.
23 is an incident angle θ at which the incident light intensity in FIG. 23 is maximized._iIt is a figure which shows the relationship between 'and the refractive index n of a medium.
FIG. 24 is a diagram showing a relationship between an incident angle, a reflection angle, and an inclination angle with respect to an inclined surface of the reflective unevenness.
25 is a diagram showing a distribution of existence probabilities of inclination angles corresponding to the incident light intensity distribution of FIG.
FIG. 26 is a diagram illustrating simulation results of reflection characteristics.
FIG. 27 is a diagram showing the result of measuring the reflectance of an integrating sphere with respect to uniform diffused light using a sample that was actually prototyped.
FIG. 28 is a cross-sectional view showing a method for forming a prototyped reflector.
FIG. 29 is a diagram showing a pattern example of a mask 64 for forming unevenness of a reflecting plate.
FIG. 30 is a diagram showing the inclination angle distribution of the unevenness of the reflector that provides a high reflectance with respect to the diffused light of the integrating sphere.
FIG. 31 is a diagram showing a state in which a reflective liquid crystal display device is mounted as a monitor of a notebook personal computer.
FIG. 32 is a diagram showing a distribution of inclination angles in the XY plane direction and the XZ plane direction having high reflectivity when used as a display device of a notebook personal computer.
33 is a diagram showing a distribution obtained by folding the inclination angle distribution of FIG. 32 around an inclination angle of 0 °. FIG.
FIG. 34 is a cross-sectional view showing a method for forming a sample reflector.
FIG. 35 is a diagram showing an example of the mask pattern of FIG.
36 is a diagram showing an example of a plane and a cross-sectional shape of the convex portion of FIG. 34. FIG.
FIG. 37 shows the measurement results of the tilt angle distribution of the prototyped reflector.
FIG. 38 is a schematic cross-sectional view of a reflective liquid crystal display device produced using a prototyped reflector.
FIG. 39 is a diagram showing a measurement result of reflectance of the reflective liquid crystal display device of FIG. 38;
FIG. 40 is a diagram illustrating a tilt angle range in which the existence probability is maximized with respect to the tilt angle of the reflective liquid crystal display device and the refractive index of the liquid crystal layer.
FIG. 41 is a cross-sectional view showing two reflective concavo-convex shapes mixed in a pixel region.
FIG. 42 is a plan view of a pixel region PK in the present embodiment example.
43 is a cross-sectional view showing a manufacturing process for forming the reflective irregularities of FIG. 42;
FIG. 44 is a diagram showing an example of a conventional resist circular pattern.
FIG. 45 is a diagram showing an example of a circular pattern of resist in the present embodiment.
46 is a diagram for explaining the circular pattern of FIG. 45. FIG.
47 is a diagram showing an example of a resist polygon pattern in the present embodiment. FIG.
FIG. 48 is a diagram showing an example of a resist polygon pattern in the present embodiment.
FIG. 49 is a configuration diagram of a reflection type liquid crystal display panel with a front light proposed in the past.
FIG. 50 is a diagram showing a first example of a reflective liquid crystal display panel with a front light.
FIG. 51 is a diagram showing a second example of a reflective liquid crystal display panel with a front light.
52 is a diagram showing a third example of the reflective liquid crystal display panel with front light. FIG.
FIG. 53 is a diagram showing a fourth example of a reflective liquid crystal display panel with a front light.
54 is a diagram showing a fifth example of a reflective liquid crystal display panel with a front light. FIG.
FIG. 55 is a diagram showing a sixth example of a reflective liquid crystal display panel with a front light.
FIG. 56 is a diagram showing a seventh example of a reflective liquid crystal display panel with a front light.
[Explanation of symbols]
10 Insulating substrate
20 Photosensitive resin layer (resist layer)
22 Reflective electrode
34 Liquid crystal layer
60 reflector
CH Contact hole
MG micro groove, uneven surface for reflection

Claims (5)

In the manufacturing method of the reflective liquid crystal display device,
(A) a step of irradiating a light having an exposure energy on the surface of the photosensitive resin layer having a predetermined thickness, forming a distribution of thermal deformation properties in the thickness Direction of the sensitive optical resin layer,
(B) that after by heat treating the photosensitive resin layer in which the distribution is formed, the reflection type, characterized by a step of forming a random unevenness on the surface of the sensitive optical resin layer Method for forming a liquid crystal display device. Oite to claim 1,
In the step (a), the light having the exposure energy, the sensation is irradiated on the entire surface of the optical resin layer is deteriorated, the distribution of thermal deformation properties in the thickness direction of the sensitive optical resin layer A method for forming a reflective liquid crystal display device, comprising: forming a reflective liquid crystal display device. Oite to claim 1,
A method of forming a reflective liquid crystal display device, further comprising the step of forming a separation line with a reduced film thickness in the photosensitive resin layer before the step (a). In the manufacturing method of the reflective liquid crystal display device,
(A) forming a photosensitive resin layer having a predetermined film thickness on a substrate having a transistor formed on the surface;
(B) forming a contact hole to the electrode of the transistor by a photolithography process of partially exposing and developing the photosensitive resin layer;
(C) a post-baking step of heating the photosensitive resin layer to a first temperature;
A step of irradiating a light having an exposure energy to the surface of; (d) the photosensitive resin layer to form a distribution of thermal deformation properties in the thickness Direction of the sensitive optical resin layer,
(E) thereafter the first temperature higher than the second temperature, the distribution by heat treating the photosensitive resin layer is formed, before Symbol form a random irregularities on the surface of the photosensitive resin layer And a final baking process. A method for forming a reflective liquid crystal display device. Oite to claim 4,
Before the step (c), the method further comprises a step of forming a separation line for separating the photosensitive resin layer by exposing or developing the photosensitive resin layer in a predetermined pattern or developing it, and developing the photosensitive resin layer. A reflective liquid crystal display device forming method.

Images