JP3308100B2 - TFT type liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor type liquid crystal display device having an improved aperture ratio.

[0002]

2. Description of the Related Art Recently, a TFT type liquid crystal display has attracted a great deal of attention because it can be mass-produced using a planar technology widely used for manufacturing semiconductors together with high image quality. This type of TFT type liquid crystal display device generally has a plurality of pixel electrodes provided in a matrix for controlling the arrangement direction of liquid crystal molecules held between glass substrates and selectively controls these pixel electrodes. Thin-film transistor (TF) provided for each pixel electrode
T).

FIG. 5A shows a main part of a conventional TFT type liquid crystal display device. As shown in FIG. 1, the conventional TFT-type liquid crystal display device includes a pixel electrode 8 as a display area and a TFT 10 provided corresponding to the pixel electrode 8. The TFT 10 has a source electrode 16 electrically connected to the source line 3, a drain electrode 17 electrically connected to the pixel electrode 8, and a gate electrode 19 electrically connected to the gate line 2. are doing.

FIG. 5 (b) shows a cross section along line XX in FIG. 5 (a). As shown in the figure, a TFT 10 has an n + region 1 formed on a gate electrode 19 formed on a glass substrate 1 via insulating films 4 and 5 so as to face each other.
4, 15 and amorphous silicon (a-Si)
A source electrode 16 and a drain electrode 17 are formed by depositing a conductive metal such as Al on the n + regions 14 and 15. Here, the drain electrode 17 is electrically connected to the pixel electrode 8 formed on the insulating film 5 and is connected to the source electrode 1.
6 and the gate electrode 19 are the gate wiring 2 and the source wiring 3
Are electrically connected to each other. With such a configuration, each TFT 10 is selectively operated by applying a required voltage signal to the gate wiring 2 and the source wiring 3, and the potential on the pixel electrode 8 connected to the drain electrode 117 of the TFT 10 is reduced. By controlling, the liquid crystal held between the glass substrates is driven.

Here, in the above-mentioned conventional liquid crystal display device,
The area where the pixel electrode 8 is formed is substantially used for the liquid crystal display as a display area. However, the other area, that is, the area where the TFT 10 is formed and the pixel where the gate wiring 2 and the source wiring 3 are formed. The area between the electrodes 8 is a non-display area. The non-display area on the inner surface of the other glass substrate facing the TFT 10 and the pixel electrode 8 is a light-shielding area formed of a light-shielding film made of Cr or the like, although not shown here.

[0006]

As described above, in the conventional TFT type liquid crystal display device, the gate wiring 2 and the source wiring 3 are formed between the pixel electrodes 8 arranged in a matrix, and the TFT 10 is formed. In addition to the non-display area, not only the area between the pixel electrode 8 where the gate wiring 2 and the source wiring 3 are formed is also a non-display area, the ratio of the display area to the entire display screen of the TFT type liquid crystal display device, that is, The aperture ratio can be taken only up to about 40%,
Therefore, it was not possible to obtain a sufficiently bright display on the entire display screen. In particular, in the TFT-type liquid crystal display device, as described above, each TFT 10 is scanned in a line-sequential scanning manner via the gate wiring 2 and the source wiring 3 formed in a lattice between a large number of pixel electrodes 8 arranged in a matrix. Therefore, even if an attempt is made to improve the aperture ratio by reducing the thickness of the gate wiring 2 and / or the source wiring 3, if these wirings are reduced to a certain thickness or more, the gate wiring 2 and / or the source wiring 3 are reduced. An excessive increase in the wiring resistance of the wiring 2 and the source wiring 3 causes a delay in the control signal, thereby deteriorating the performance of screen display.

Further, in the above-described device, when a signal voltage is applied to the gate wiring 2 and the source wiring 3 when driving the liquid crystal, an electric field is generated around these wirings by a current flowing through the gate wiring 2 and the source wiring 3. When this electric field unnecessarily acts on the liquid crystal, there is a problem that the screen display by the liquid crystal flickers. Furthermore, conventional TF
In the T-type liquid crystal display device, since the semiconductor layer 13 of the TFT 10 is provided on the insulating layer 5 in an electrically floating state, when the semiconductor layer 13 is, for example, an n-type conductivity type, the source of the semiconductor layer 13 is When electrons pass through the semiconductor layer 13 from the region 15 toward the drain region 14, the semiconductor layer 1
3 may be gradually positively charged. This is considered to be due to the fact that electrons of Si atoms in the semiconductor layer are repelled by the passing electrons. However, since the accumulated positive charges are not provided with an escape field due to grounding or the like, the semiconductor layer 13 in the vicinity of the drain region is not provided. The positive charges thus accumulated fluctuate the electrical characteristics such as the threshold voltage Vth of the TFT 10 and hinder good display of a screen.

The present invention has been made in view of the above problems, and has as its object to provide a TFT-type liquid crystal display device having an improved aperture ratio and thus improved display brightness.

[0009]

In order to solve the above problems, a TFT type liquid crystal display device of the present invention comprises a glass substrate provided to face each other, a liquid crystal accommodated between the glass substrates, A TFT for driving the liquid crystal,
A plurality of first wirings formed in parallel with a transparent metal on one inner surface of the glass substrate, and a plurality of first wirings formed on the first wirings;
A first insulating film formed on the first insulating film, a plurality of second wires formed on the first wire in parallel with a transparent metal so as to be orthogonal to the first wire, and on the second wire. Formed
A second insulating film, a shield film formed of a transparent metal on the second insulating film and formed to be able to hold a constant potential, a third insulating film formed on the shield film,
A pixel electrode formed of a transparent metal in a region on each of the intersections of the first and second wirings on the third insulating film and on the shield film.

The shield film includes first and second wires and T
An opening is formed to enable each of the FT and the FT to be electrically connected. The transparent metal is made of ITO, and the first to
The three insulating films are formed of at least one of silicon oxide and silicon nitride.

[0011]

A plurality of first wirings formed in parallel with a transparent metal on one inner surface of a glass substrate;
A plurality of second wirings formed in parallel with a transparent metal on the wirings so as to be orthogonal to the wirings; a shield film formed of the transparent metal on the second wirings and formed so as to be held at a constant potential; A pixel electrode formed of a transparent metal in a region on the shield film in each intersection region of the first and second wirings,
, Each intersection area between the first wiring and the second wiring can be used as a display area as it is. Therefore, TF
Except for the region T, it is not necessary to cover the wiring region with the light shielding film as in the conventional case, and only the region between the adjacent wirings needs to be covered with the light shielding film. Can be improved to 80% or more.

Also, since a shield film capable of maintaining a constant potential is provided on substantially the entire surface between the first and second wirings and the liquid crystal, an electric field generated by a current flowing through the first and second wirings. The effect on the liquid crystal can be effectively prevented and T
Even when unnecessary charges are generated in the semiconductor layer of the FT, the generated charges are immediately released via, for example, a ground wiring, so that unnecessary charges are not accumulated in the semiconductor layer.

[0013]

Next, a TFT type liquid crystal display device according to the present invention will be described in detail with reference to FIGS. Although not shown here, the TFT type liquid crystal display device according to the present embodiment is arranged in a matrix on one inner surface of a glass substrate arranged to face each other via the liquid crystal to drive the liquid crystal. It has a plurality of pixel electrodes and a TFT provided for each pixel electrode to control the voltage of these pixel electrodes. On the other glass substrate, a color filter is formed in a region corresponding to a pixel electrode, that is, a display region, and a light-shielding film T made of Cr or the like is formed.
It is formed in a region corresponding to between the FT and the pixel electrode, that is, a light shielding region.

FIG. 1 shows a main part of a TFT type liquid crystal display device of this embodiment. Specifically, a source wiring, a gate wiring, and a source wiring in a unit pixel formed on one glass substrate 1 are shown.
And the positional relationship of the pixel electrodes and the like in plan view. FIG.
Shows a cross section along the line AA in FIG. On one glass substrate 1, as shown best in FIG. 1, one-way ITO (indium tin oxide) as a transparent metal is used.
A plurality of wide band-shaped gate wirings 2 extending substantially over the entire display area of the unit pixel are formed in parallel, and a wide band-shaped source wiring 3 also made of ITO is formed in a direction perpendicular to these gate wirings 2. , A first made of SiO ₂
A plurality of layers are formed in parallel with the insulating film 4 interposed therebetween.

On the source wiring 3, a shield film 6 is formed of Si.
It is also formed of ITO via a second insulating film 5 made of O ₂ . The shield film 6 is formed over substantially the entire surface of the glass substrate 1 except for the source contact opening 11 and the gate contact opening 12, as shown in plan view in FIG. This shield film 6
It is provided so as to be kept at a constant potential such as a ground potential (0 V). For this reason, when a signal current is applied to the gate wiring 2 and / or the source wiring 3, an electric field is generated by the action of these currents.
The shield film 6 maintained at a constant potential is used as the gate wiring 2
In addition, since it is provided between the source wiring 3 and the liquid crystal (not shown), the electric field generated by the current is effectively prevented from being interrupted by the shield film 6 and affecting the liquid crystal.

As best shown in FIG. 1, the gate wiring 2 is wide enough to extend over the entire display area P, for example, a wiring width of about 100 μ and a state of being separated from the adjacent gate wiring by 10 μ, that is, about 110 μ. Are formed in parallel at a wiring pitch of, while the source wiring 3 is also wide, for example, about 3
The wirings are formed in parallel with each other at a wiring width of 20 μ and also at a distance of 10 μ from an adjacent source wiring, that is, at a wiring pitch of about 320 μ. At each edge of each source wiring 3, a concave portion 9 formed in a concave shape in a plan view is formed near a portion intersecting with one edge of the data wiring 2. In these recesses 9, TFTs 10 corresponding to the respective pixel electrodes 8 are formed.

FIG. 4 is an enlarged sectional view showing the TFT 10 shown in FIG. 1 in detail along the line BB.
As best shown in FIG.
Means that amorphous silicon (a-S
i) a semiconductor layer 13 having an n + -type source region 14 and a drain region 15, and a source electrode extending from the source line 3 to the source region 14 of the semiconductor layer 13 via the source contact opening 11 of the shield film 6. 16
A drain electrode 17 for electrically connecting the pixel electrode 8 to the drain region 15 of the semiconductor layer 13; and a SiO 2 on the semiconductor layer 13 through the gate contact opening (see FIG. 3) of the shield film 6 from the gate wiring 2. Fourth insulating film 18 made of
And a gate electrode 18 extended upward.
A light-shielding film made of Cr is formed on the glass substrate 1 below the semiconductor layer 13, that is, on the light-shielding region.

Next, a method of manufacturing the TFT type liquid crystal display device of this embodiment will be described. The upper surface of one of the glass substrates 1 used for the TFT type liquid crystal display device of this embodiment is
A TO film is formed to a thickness of about 3000 angstroms by sputtering and patterned by etching to form a strip-shaped gate wiring 2 having a wiring width of 100 μm by about 10 μm.
It is formed with a wiring interval of μ. In the region where the TFT is to be formed, a light shielding film 19 is formed of Cr by sputtering and etching. Next, Si is formed on the gate wiring 2.
After forming the first insulating film 4 to a thickness of 5000 angstroms at a temperature of 300 ° C. by plasma CVD at a temperature of 300 ° C., the O ₂ is etched into a required pattern, and an ITO film is further formed on the upper surface of the first insulating film 4 by sputtering. A 3,000-Å-thick film is formed, which is patterned by etching to form a strip-shaped source wiring 3 which is perpendicular to the gate wiring 3 and has a wiring width of 320 μm and a wiring interval of about 10 μm. In this case, the recess 9 is formed in the TFT forming region at one edge of the source wiring 3 as described above. After the source wirings 3 are formed, SiO ₂ is again formed on these source wirings 3 by plasma CVD at a temperature of 300 ° C. to a thickness of 5000 Å, and then a second insulating film 5 is formed on the upper surface of the second insulating film 5. Furthermore, about 3000 ITO films are sputtered.
Etching is performed after forming the film to a thickness of Å to form the shield film 6 provided with the source contact opening 11 and the gate contact opening 12. Then
A third insulating film 7 made of SiO _{2 is} formed on the shield film 6 by 50.
After forming the layer to a thickness of 00 Å and etching it to a required pattern, a-Si is formed in the TFT formation region on the shield film 6 at a temperature of 300 ° C. by a plasma CVD method.
Is formed. On the upper surface of the semiconductor layer 13, an n + layer having an n + conductivity type is formed.
By removing the central portion of the + layer by etching, a source region 14 and a drain region 15 made of an n + layer are formed. Next, a pixel electrode 8 is formed by forming an ITO film in a region on the shield film 6 where the gate wiring 2 and the source wiring 3 intersect to have a thickness of about 3000 Å by sputtering and then performing etching. After the formation of the pixel electrode 8, the source electrode 16 made of a conductive metal such as Al is electrically connected between the source region 14 of the semiconductor layer 13 and the source wiring 3 via the source contact opening 11 of the shield film 6. And the drain electrode 17
Is formed so that the drain region 15 of the semiconductor layer 13 and the pixel electrode 8 are electrically connected. Then, the fourth
After the insulating film 18 is formed to a thickness of 5000 angstroms by plasma CVD at a temperature condition of 300 ° C. and the required etching is performed, a gate electrode 19 made of a conductive metal such as Al is removed from the gate wiring 2 to the shield film 6. To extend over the fourth insulating film 18 through the gate contact opening 12 of FIG.

On the other hand, although not shown here, the TFT
The light-shielding region on the glass substrate facing the glass substrate on which the pixel electrodes 10 and the pixel electrodes 8 are formed, that is, the region between the TFT 10 and the adjacent data lines 2 and between the gate lines 3
A film made of is formed by sputtering and then etched to form a light-shielding film of a required pattern, and then a color filter is formed of a required dye in other display regions facing the pixel electrodes.

By using the two glass substrates thus obtained to form a liquid crystal display in the same manner as in the prior art, the TFT liquid crystal display of the present invention can be obtained. In the above embodiment, SiO ₂ by plasma CVD is used for the first to fourth insulating films. However, the present invention is not limited to this, and silicon nitride (SiNx) may be used instead of SiO _2.
May be used. As the conductive metal used for the source electrode and the drain electrode, Al, Ta, Cr, or the like can be used as appropriate.

[Brief description of the drawings]

FIG. 1 is a partially enlarged plan view of an inner side of a glass substrate according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the pixel electrode section taken along line AA of the glass substrate of FIG.

FIG. 3 is a plan view of a shield film of the glass substrate of FIG.

FIG. 4 is a cross-sectional view of the TFT along the line BB of the glass substrate of FIG. 1;

FIG. 5A is a partially enlarged plan view of a conventional TFT-type liquid crystal display device when viewed from the inside of the glass substrate, and FIG. 5B is a cross-sectional view taken along line XX in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Gate wiring 3 Source wiring 6 Shield film 8 Pixel electrode 9 Depression 10 TFT 11 Source contact opening 12 Gate contact opening 13 Semiconductor layer 14 Source region 15 Drain region 16 Source electrode 17 Drain electrode 19 Gate electrode

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-255830 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1368 G09F 9/30 338 H01L 29 / 786

Claims (3)

(57) [Claims] A glass substrate provided to face each other;
A plurality of first liquid crystal substrates, each of which has a liquid crystal housed between the glass substrates and a TFT for driving the liquid crystal, and is formed in parallel with transparent metal on one inner surface of the glass substrate.
A wiring, a first insulating film formed on the first wiring,
A plurality of second wirings formed on the first insulating film in parallel with the first wiring by a transparent metal so as to be orthogonal to the first wiring; a second insulating film formed on the second wiring; The said
2 a shield film which is holdable formed to a constant potential is formed by a transparent metal on the insulating film, forms on the shield film
A third insulating film formed on the third insulating film, and a pixel electrode formed of a transparent metal in a region on each of the intersections of the first and second wirings and on the shield film. A TFT type liquid crystal display device characterized by the above-mentioned. 2. The TFT type liquid crystal display device according to claim 1, wherein an opening is formed in said shield film so that said first and second wirings and said TFT can be electrically connected to each other. Wherein the transparent metal consists ITO, the first
The TFT liquid crystal display device according to claim 1, wherein the third to third insulating films are formed of at least one of silicon oxide and silicon nitride.