JP4092854B2 - LIQUID CRYSTAL DISPLAY ELEMENT AND METHOD FOR DISTRIBUTION OF INTER-PIXEL ORIENTATION OF VERTICALLY ORIENTED LIQUID CRYSTAL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a homeotropic allignment type liquid crystal display element to perform no inter-pixel alignment division but to perform an intra-pixel allignment division. SOLUTION: In the liquid crystal display element, which is composed of at least a pixel electrode substrate 2 pixel electrodes 1 are arranged, a counter substrate 3 arranged oppositely to the substrate 2 and a liquid crystal LC held between them and in which the liquid crystal LC is alligned perpendicularly to the pair of the substrates in the case of applying no electric field, the alignment direction of the liquid crystal is divided into different directions at intervals of one or more pixels in the case of applying electric field.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display element in which liquid crystals are vertically aligned without applying an electric field to a substrate.
[0002]
[Prior art]
As one technique for widening the viewing angle of a liquid crystal display, a technique (vertical alignment technique) for aligning the major axis direction of the liquid crystal perpendicular to the substrate when a non-electric field is applied has been proposed.
[0003]
By the way, in order to obtain a sufficient wide viewing angle characteristic, it is necessary to divide a pixel so as to have a plurality of different orientation directions. As the dividing method, a method of providing a slit portion on an electrode, a method of providing a projection (rib) on the substrate surface, and the like have been proposed (Japanese Patent No. 29473505).
[0004]
Here, when the slit portion is provided in the electrode, as shown in FIG. 8A, the liquid crystal LC in the vicinity of the slit portion S sandwiched between the electrodes E is vertically aligned when off (when no electric field is applied). However, as shown in FIG. 8B, the direction of the electric lines of force EL is directed obliquely when turned on (when an electric field is applied), and the liquid crystal LC is in the direction of the arrow along the electric lines of force (FIG. 8 ( fall to a)). Accordingly, when an electric field is applied, the liquid crystal alignment is divided and a domain is formed in the slit portion S. Furthermore, since the surrounding liquid crystal also falls along the liquid crystal of the slit part S, as a result, when an electric field is applied, a domain is formed by dividing and aligning with the dotted line in FIG. 8B as a boundary. Here, a gap between adjacent pixel electrodes functions as a slit portion. In addition, the dotted line in Fig.8 (a) has shown the direction of the electric force line at the time of applying an electric field.
[0005]
When the protrusion (rib) RIB is provided on the electrode E on the substrate surface, as shown in FIG. 8C, the liquid crystal LC is obliquely aligned along the inclination of the protrusion RIB when turned off. As shown in FIG. 8D, the direction of the electric lines of force EL is directed obliquely when turned on, and the entire liquid crystal LC falls in the direction of the arrow (FIG. 8C) along the electric lines of force EL. In general, since the dielectric constant of the protrusion RIB is lower than the dielectric constant of the liquid crystal LC, the lines of electric force are inclined, and the alignment of the liquid crystal is divided when an electric field is applied by the same effect as the slit. As a result, when the electric field is applied, domains that are divided and oriented with the dotted line in FIG. 8D as a boundary are formed. In addition, the dotted line in FIG.8 (c) has shown the direction of the electric force line at the time of applying an electric field.
[0006]
[Problems to be solved by the invention]
However, in these methods, since one pixel is divided, there is a problem in that the light transmittance is reduced, and the boundary of alignment domains where light is not transmitted is generated in the display region, thereby reducing the effective aperture ratio. For example, since the pixel electrode gap of the pixel electrode substrate functions as the slit portion of the electrode described above, when an electric field is applied, the liquid crystal LC falls down from both ends inward in one pixel as shown in FIG. Domain boundaries occur in the pixels.
[0007]
An object of the present invention is to solve the above-described conventional technique, and it is an object of the present invention to enable vertical alignment liquid crystal display elements to be divided into inter-pixel alignments instead of intra-pixel divisions.
[0008]
[Means for solving the problems]
The inventors divide the orientation of the liquid crystal in different directions every other pixel or every other pixel when an electric field is applied, so that one of the pixel electrode substrate and the counter substrate of the vertical alignment type liquid crystal display element or It has been found that the above-mentioned object can be achieved by providing alignment dividing means for dividing the alignment of liquid crystal in different directions every other pixel or every other pixel when an electric field is applied to both substrates, and the present invention has been completed.
[0009]
That is, the present invention includes at least a pixel electrode substrate provided with a pixel electrode, a counter substrate disposed so as to be opposed to the pixel electrode substrate, and a liquid crystal sandwiched between them. In the liquid crystal display element that is aligned perpendicular to both the substrates, an alignment dividing means for dividing the liquid crystal alignment in different directions is provided for every other pixel or every other pixel when an electric field is applied, and an alignment dividing means for the counter substrate is provided. A liquid crystal display element, characterized in that the width of the pixel electrode gap of the pixel electrode substrate corresponding to the provided position is narrower than the width of the pixel electrode gap corresponding to the position where the alignment dividing means is not provided. To provide .
[0010]
In addition, the present invention includes at least a pixel electrode substrate provided with a pixel electrode, a counter substrate disposed so as to face the pixel electrode substrate, and a liquid crystal sandwiched therebetween, and the pair of liquid crystals is applied when no electric field is applied. With respect to a liquid crystal display element that is aligned perpendicularly to both of the substrates, the liquid crystal alignment is divided into different directions every other pixel or every other pixel when applying an electric field to one or both substrates of the liquid crystal display element. An alignment division unit is provided , and the width of the pixel electrode gap of the pixel electrode substrate corresponding to the position where the alignment division unit of the counter substrate is provided is greater than the width of the pixel electrode gap corresponding to the position where the alignment division unit is not provided. And a method for dividing the alignment between pixels of a vertically aligned liquid crystal, characterized in that it is also narrowed .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described by taking a TFT LCD as an example. However, the present invention is not limited to a TFT LCD but can be applied to a simple matrix drive LCD or the like.
[0012]
In the liquid crystal display element of the present invention, the orientation of the liquid crystal is divided in different directions every other pixel or every plurality of pixels when an electric field is applied. Specifically, alignment dividing means for dividing the alignment of liquid crystal in different directions every other pixel or every plurality of pixels when an electric field is applied is provided on one or both substrates. In this case, it is preferable that the alignment division regulating force of the alignment dividing means is stronger than the alignment division regulating force due to the electric field of the pixel electrode. As a result, when the alignment dividing means is provided every other pixel, the alignment direction is different for each pixel, and the boundary of the alignment domain is located not in the pixel but in the adjacent pixel electrode gap. . The pixel electrode gap is usually an area where data lines, gate lines, and the like are arranged, and is not an opening but an area that does not affect the transmittance. Therefore, it is possible to arrange domain boundaries that lead to a decrease in transmittance (effective aperture ratio) only between pixels.
[0013]
In the present invention, as a preferred example of the alignment dividing means between pixels, as shown in FIG. 1A, a pixel electrode 1 such as ITO is provided for each RGB color, and a glass substrate 2a and a data line 2b are provided. And protrusions RIB provided on every other pixel on the counter substrate 3 facing the pixel electrode substrate 2 made of the planarizing film 2c and the like. In the figure, the alignment of the liquid crystal LC when a non-electric field is applied is as shown in FIG. 1A, but when the electric field is applied, the alignment of the liquid crystal LC is divided for each pixel as shown in FIG. Can do. Here, the dotted line indicates the boundary line of the domain.
[0014]
Here, in order to perform the alignment division more efficiently, it is preferable to make the alignment division regulating force of the projection RIB stronger than the alignment division regulating force of the pixel electrode gap 1S. Specifically, as shown in FIG. 1A, the width d and height h of the protrusion RIB and the width w1 of the pixel electrode gap 1S at the position facing the protrusion RIB are expressed by the following equation.
[Equation 3]
d ≧ w1
h> 0.05 × d
Is preferably satisfied.
[0016]
Further, in order to obtain a strong division restricting force, it is preferable that the protrusion RIB has a cross section close to a triangle. Further, it is preferable that the protrusion RIB has a smaller dielectric constant than the liquid crystal because an inclined electric field can be formed.
[0017]
Further, the electrical characteristics of the protrusion RIB are as follows when the time constant of the liquid crystal material is τ _LC (30 Hz) and the time constant of the protrusion RIB is τ _RIB (30 Hz):
[Expression 4]
0.1 × τ _LC <τ _RIB <10 × τ _LC
Is more preferable. This is because, if the time constants of the liquid crystal material and the protrusion RIB are greatly different from each other, electric charges accumulate on the protrusion RIB, and burn-in and flicker may occur, thereby significantly reducing the display quality.
[0019]
Further, as another aspect of the protrusion RIB as the orientation dividing means, a flat wedge-shaped protrusion RIB may be provided as shown in FIG. 2A, and as shown in FIG. A sawtooth-shaped protrusion RIB may be provided. Further, as shown in FIG. 2 (c), a reverse shape of the protrusion, that is, a wedge-shaped groove Q may be provided. In this case, the counter substrate 3 does not have to be provided with the alignment dividing means.
[0020]
In the present invention, as the orientation dividing means other than the protrusions described above, as shown in FIG. 3, slit portions 3S (counter electrode slits) provided every other pixel on the common electrode (counter electrode) 4 of the counter substrate 3 are listed. It is done. In this case, the alignment division regulating force of the slit portion 3S needs to be stronger than the alignment division regulating force of the pixel electrode gap 1S. Specifically, the width w2 of the slit portion 3S is made larger than the width w1 of the pixel electrode gap 1S.
[0021]
1 to 3, the pixel electrode gap 1S ′ (width w3) that does not correspond to the position of the alignment dividing means (projection RIB) as shown in FIG. 4 is positively made to function as the alignment dividing means. In addition, the pixel electrode gap 1S (width w1) corresponding to the position of the alignment dividing means (projection RIB) is not a restriction force weaker than the alignment division restriction force of the alignment division means (projection RIB). Don't be. Therefore, the width w3 of the pixel electrode gap 1S ′ is made wider than the width w1 of the pixel electrode gap 1S so that the alignment division regulating force of the pixel electrode gap 1S ′ is stronger than the alignment division regulating force of the pixel electrode gap 1S. preferable.
[0022]
As the alignment dividing means other than the protrusions and slits described above, an alignment film formed by a mask rubbing method, a photo-alignment film method, or the like can be cited, particularly when alignment division every two or more pixels is intended. .
[0023]
In addition, when the size of one pixel is too large, when viewing the liquid crystal display element from an oblique direction, the viewing angle characteristic is different at least every other pixel. It is also expected that good alignment control cannot be achieved if the pixel pitch is too long. Therefore, it is preferable that the pixel pitch of at least one side is 60 μm or less (FIG. 5).
[0024]
In the case where each color is formed on a stripe, the form of orientation division may be as shown in FIG. 6 (a) or (b). Here, the arrow indicates the direction in which the liquid crystal falls (alignment direction), and the hatched portion indicates the position of the protrusion.
[0025]
6A and 6B, when the liquid crystal display device is observed obliquely, good display characteristics are obtained because the alignment direction of the liquid crystal of the pixel as shown in FIG. It is the aspect which is arranged in a checkered pattern.
[0026]
By the way, the electric field birefringence mode of the above-described vertical alignment type liquid crystal display element greatly depends on the wavelength of light, and if it is set to be λ / 2 with respect to a certain wavelength, the light of other wavelengths As a result, the transmissivity of the display becomes low and the white display becomes colored. Attempting to compensate for this with a color filter results in a low transmittance.
[0027]
Further, this colored phenomenon is more prominent when viewed obliquely from the front. For example, when the retardation of the liquid crystal at the time of white display is set so that the transmittance considering the visibility is maximized (with a wavelength of 550 nm). When the retardation with respect to light is 275 nm), it looks yellow when observed obliquely, so it is necessary to set a value smaller than the maximum retardation transmittance. This problem can be solved if the cell gap is set to an optimum value for each RGB pixel, that is, the liquid crystal layer retardation is set to approximately λ / 2 of the main transmission wavelength of each color during white display.
[0028]
Specifically, when a color separation filter is formed on at least one substrate, the main wavelength λ of each color and the retardation Δnd of the liquid crystal layer when displaying white are 0.85 × λ / 2 to 1.15 ×. The thickness d of the liquid crystal layer may be different for each color so as to be in the range of λ / 2. Further, the thickness d of the liquid crystal layer of each color may be controlled by changing the thickness of the color separation filter layer between the colors.
[0029]
From another viewpoint, the present invention includes at least a pixel electrode substrate provided with a pixel electrode, a counter substrate disposed so as to oppose the pixel electrode substrate, and a liquid crystal sandwiched between them. Alignment division that divides the orientation of the liquid crystal when an electric field is applied to every other pixel or every other pixel on one or both substrates of the liquid crystal display element that is oriented perpendicular to the pair of both substrates when an electric field is applied It can be regarded as a method for dividing the alignment of the vertically aligned liquid crystal between the pixels, characterized by providing means. Therefore, this inter-pixel alignment division method is also a part of the present invention.
[0030]
【Example】
Example 1
FIG. 7 shows a schematic cross-sectional view of one embodiment of the liquid crystal display element of the present invention. The liquid crystal display element includes a TFT substrate in which a data line 102, a planarizing film 103, a pixel electrode 104, and an alignment film 105 are formed on a glass substrate 101, and an RGB RGB formed on one side of the glass substrate 120 corresponding to the pixels. A vertically aligned liquid crystal layer 130 is sandwiched between a color filter 121 of each color, a common electrode 122, a protrusion RIB provided every other pixel, and a CF substrate formed of an alignment film 123. Polarizing plates 131 and 132 are formed on both surfaces of the liquid crystal display element, respectively, and a retardation plate 133 is formed between the CF substrate and the polarizing plate 131.
[0031]
The liquid crystal display element having this structure was manufactured as described below.
[0032]
That is, a common electrode 122 made of ITO having a thickness of 100 nm is formed on the color filter 121 of the glass substrate 120, and the protrusions RIB are formed in stripes between the pixels as shown in FIG. Arranged. This protrusion RIB was formed by patterning with a photosensitive resin, and was baked at a high temperature of 200 ° C. or higher after baking at 120 to 180 ° C. for 5 minutes in order to obtain a more preferable shape. Its dielectric constant was 3.5, the shape was 10 μm wide and 1.5 μm high in cross section.
[0033]
Next, an alignment film 123 was formed on the surface of the CF substrate on which the protrusions RIB were formed. This alignment film 123 is a printed polyimide vertical alignment film, and was formed by baking at 180 ° C. for 1 hour. The film thickness of the alignment film 123 was 50 to 100 nm. The alignment film was not rubbed.
[0034]
Although not shown in FIG. 7, TFT elements and wirings for active driving are formed on the TFT substrate side. The planarizing film 103 has a thickness of 3 μm and is formed by patterning from a photosensitive resin. The pixel electrode 104 was formed of ITO having a thickness of 100 nm, and the size of each pixel was 40 μm wide and 120 μm long. The width w1 of the pixel electrode gap 1S and the width w3 of the pixel electrode gap 1S ′ are both 7 μm (FIG. 4). An alignment film 105 similar to that on the CF substrate side was formed thereon.
[0035]
An acrylic spacer having a diameter of 3.5 μm was dispersed between these substrates and superimposed, and then liquid crystal was injected between the substrates in a vacuum. The liquid crystal used was a material with Δε = −4 and Δn = 0.1.
[0036]
Polarizing plates 131 (TAC film) and 132 were arranged in the crossed Nicols direction on the obtained liquid crystal display element. In consideration of viewing angle characteristics, a retardation plate 133 ((nx−nz) d = 100 (nx = in-plane direction) having a retardation only in the thickness direction (Z axis) between the polarizing plate 131 and the glass substrate 120. Nz = refractive index in the thickness direction, d = thickness)). Note that the TAC film used as the polarizing plate 131 has a phase difference in the z-axis direction and has the same effect.
[0037]
Further, as Comparative Example 1, a liquid crystal display element in which a protrusion was arranged in the middle of all the pixels so as to divide the orientation in the pixel into two was similarly manufactured.
[0038]
When the obtained liquid crystal display elements of Example 1 and Comparative Example 1 were subjected to IH inversion driving and compared, the liquid crystal display element of Example 1 was more transparent at the time of white display (when 4.5 V was applied to the pixel). Was 15% higher. Also, good viewing angle characteristics without inversion and the like were obtained from all directions.
[0039]
Example 2
Instead of the protrusion of Example 1, a slit portion having a width of 10 μm was formed in the common electrode of the CF substrate. The obtained liquid crystal display element was divided in orientation for each pixel, and good viewing angle characteristics were obtained as in the case of Example 1.
[0040]
Example 3
The width w1 of the pixel electrode gap 1S in Example 1 was 4 μm, and w3 was 10 μm. Display characteristics with less afterimage than Example 1 were obtained.
[0041]
Example 4
The thickness of the color filter layer of Example 1 was R (1.0 μm), G (1.2 μm), and B (1.5 μm), and the dispersed spacer diameter was 4.0 μm. Compared with Example 1, the white display was brighter and the characteristic of less coloring in the viewing angle direction was obtained.
[0042]
Example 5
The arrangement of the protrusions in Example 1 was arranged as shown in FIG. When observed from the viewing angle direction, in Example 1, some uneven stripes were observed in the vertical direction, but in this example, the image quality was uniform in the viewing angle direction.
[0043]
【The invention's effect】
Since the vertically aligned liquid crystal display element of the present invention is not divided into pixels but divided between pixels, it is possible to arrange domain boundaries that lead to a decrease in transmittance (effective aperture ratio) only between pixels. It is.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of alignment dividing means of a liquid crystal display element of the present invention.
FIG. 2 is an explanatory diagram of alignment dividing means of the liquid crystal display element of the present invention.
FIG. 3 is an explanatory diagram of alignment dividing means of the liquid crystal display element of the present invention.
FIG. 4 is an explanatory diagram of alignment dividing means of the liquid crystal display element of the present invention.
FIG. 5 is an explanatory diagram of a form of alignment division and a pixel pitch according to the present invention.
FIG. 6 is an explanatory diagram of a form of orientation division according to the present invention.
FIG. 7 is a schematic cross-sectional view of a liquid crystal display element of the present invention.
FIG. 8 is an explanatory diagram of a conventional alignment division method.
[Explanation of symbols]
1 pixel electrode, 1S, 1S ′ pixel electrode gap, 2 pixel electrode substrate, 3 counter substrate, 4 common electrode, RIB protrusion, 3S slit, LC liquid crystal

Claims (14)

It comprises at least a pixel electrode substrate provided with a pixel electrode, a counter substrate disposed so as to oppose the pixel electrode, and a liquid crystal sandwiched therebetween, and the liquid crystal is applied to the pair of substrates when no electric field is applied. In a vertically aligned liquid crystal display element,
An alignment dividing means for dividing the alignment of the liquid crystal in different directions every other pixel or every other pixel when an electric field is applied is provided,
The width of the pixel electrode gap of the pixel electrode substrate corresponding to the position where the alignment dividing means of the counter substrate is provided is made narrower than the width of the pixel electrode gap corresponding to the position where the alignment dividing means is not provided. A liquid crystal display element characterized by comprising: The Oriented dividing means, every other pixel or every other pixel in the liquid crystal display device according to claim 1 provided on one substrate or both substrates. Oriented alignment division regulating force dividing means, stronger alignment division regulating force by the electric field of the pixel electrode, the liquid crystal display device according to claim 1 or 2, wherein the alignment direction of the liquid crystal is different in every other pixel or every other pixel. The liquid crystal display element according to claim 1, wherein the alignment dividing means is a protrusion formed between pixels of the counter substrate. The width d and height h of the protrusion and the width w1 of the pixel electrode gap at the position facing the protrusion are given by

The liquid crystal display element according to claim 4, wherein   6. The liquid crystal display element according to claim 4, wherein the protrusion has a dielectric constant of 4 or less. When the time constant of the liquid crystal material is τ _LC (30 Hz) and the time constant of the protrusion is τ _RIB (30 Hz),

The liquid crystal display element in any one of Claims 4-6 satisfying these. 3. The liquid crystal display element according to claim 1, wherein the orientation dividing means is a counter electrode slit formed between pixels of the counter substrate. The liquid crystal display device having a width wider claim 1, wherein the pixel electrode gap of the pixel electrode substrate width of the counter electrode slits corresponding to the slit position. The liquid crystal display device according to any one of claims 1-9, at least one side of the pixel pitch is 60μm or less. Arrangement of pixels is a stripe array, and a liquid crystal display device according to any one of claims 1 to 1 0 the direction of the liquid crystal alignment of the pixels are arranged in a checkered pattern.   A color separation filter is formed on at least one substrate, and the main wavelength λ of each color and the retardation Δnd of the liquid crystal layer when displaying white are in the range of 0.85 × λ / 2 to 1.15 × λ / 2. The liquid crystal display element according to claim 1, wherein the thickness d of the liquid crystal layer is different for each color. By varying the thickness of the color separation filter layer for each color, the liquid crystal display device having a thickness of d is different according to claim 1 wherein the liquid crystal layer for each color. It comprises at least a pixel electrode substrate provided with a pixel electrode, a counter substrate disposed so as to oppose the pixel electrode, and a liquid crystal sandwiched therebetween, and the liquid crystal is applied to the pair of substrates when no electric field is applied. to the liquid crystal display element to be oriented vertically,
One or both substrates of the liquid crystal display element are provided with alignment dividing means for dividing the liquid crystal alignment in different directions every other pixel or every plurality of pixels when an electric field is applied,
The width of the pixel electrode gap of the pixel electrode substrate corresponding to the position where the alignment dividing means is provided on the counter substrate is made narrower than the width of the pixel electrode gap corresponding to the position where the alignment dividing means is not provided. An inter-pixel alignment division method for vertically aligned liquid crystals.

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