JP2002357829A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device wherein alignment defect is reduced by forming a transition nucleus efficiently conducting bend alignment or π-twist alignment form spray alignment with a simple method in an OCB liquid crystal display mode. SOLUTION: In a liquid crystal display panel wherein a liquid crystal is spray-aligned, a projecting part for the transition nucleus is formed by using a conventional color filter material as a nucleus generating means for promoting the transition to the bend alignment or the π-twist alignment from the spray alignment. The cell gap at the part of the transition nucleus is made narrow, or two electrodes having potentials different from each other are provided at the projecting part to reliably conduct the transition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OCB (Optical) using a nematic liquid crystal and having excellent viewing angle characteristics.
ly Compensated Birefringe
(nce) type liquid crystal display device.

[0002]

2. Description of the Related Art A display panel (display element) using a nematic liquid crystal has several modes depending on the orientation of liquid crystal molecules. The most popular is the twisted nematic (T
N) mode, and homeotropic (vertical)
There are birefringence mode and guest-host mode of orientation or homogeneous (horizontal) orientation. Especially in TN mode,
It is the mainstream in an active matrix liquid crystal display panel in which an active element is provided for each pixel electrode on one substrate.

The TN liquid crystal is a state in which a liquid crystal having a positive dielectric anisotropy is sandwiched between substrates with electrodes subjected to horizontal alignment processing and twisted by 90 degrees to make a stable state. Is rotated by 90 degrees, and when the transmission axes of the polarizer and the analyzer arranged with the liquid crystal layer interposed therebetween are orthogonal to each other, white display is performed (normally white mode). When the liquid crystal molecules rise by application of a voltage, the incident polarized light travels through the liquid crystal layer as it is, so that it is absorbed by the analyzer and black display is performed.

[0004] The alignment treatment is usually achieved by rubbing a polyimide, and at this time, a pretilt of the liquid crystal of about several degrees occurs corresponding to the rubbing direction. The twisting direction of the TN liquid crystal is basically determined by the pretilt directions of the upper and lower substrates. That is, the twisting direction is determined by aligning the liquid crystal layer without causing splay distortion. Furthermore, in order to prevent reverse twist orientation and to make the twist direction uniform, the twist direction is determined by adding a small amount of chiral substance (optically active substance) to the liquid crystal, matching the pretilt direction on the upper and lower substrates. I have. The liquid crystal is aligned with a substantially uniform pretilt from near the interface of one substrate to near the interface of the opposite substrate. When a voltage is applied between the upper and lower substrates, first, the liquid crystal molecules at the center of the liquid crystal layer rise in the initially provided pretilt direction, and the entire liquid crystal layer follows the rise.

Therefore, the direction in which the liquid crystal rises is the same in the entire panel, and the manner in which the refractive index of the liquid crystal layer changes according to the direction in which the panel is viewed. Therefore, the light transmittance greatly changes depending on the viewing angle direction. For this reason, a significant reduction in contrast, color change, gradation inversion, and the like occur depending on the viewing angle direction, and there is a serious problem in viewing angle characteristics. In particular, in the normally white mode, the viewing angle characteristics are greatly different between the case of observing from the rising direction of the liquid crystal molecules at the center of the liquid crystal layer (viewing angle direction) and the case of observing from the opposite direction (the opposite viewing angle direction). The gradation inversion phenomenon is severe on the side of the viewing angle from the front, and the contrast is significantly reduced on the side of the opposite viewing angle, and whitening occurs. Normally, the viewing angle direction is set in the vertical direction, so that in the TN mode, the viewing angle characteristics are asymmetric in the vertical direction.

Many methods have been proposed to improve the viewing angle characteristics of the TN mode. For example, "S
As described in “ID 94 DIGEST, 927”, there is an OCB method in which a liquid crystal is bent and a wide viewing angle is obtained by combining the liquid crystal with an optical phase compensation film. The OCB method has a feature that the response speed is much faster than the TN method, and is a very attractive method.

In the OCB method, it is necessary to initially align the liquid crystal in a splay state, and to apply an electric field to the liquid crystal during use to cause an alignment transition to a bend alignment (or π twist alignment). In other words, when the liquid crystal rises by applying a voltage, the distortion of the splay alignment increases,
A transition to a stable bend or π-twist orientation occurs. By observing this state, it can be seen that a nucleus of a desired normal domain having a bend or π twist orientation in the splay orientation is generated and grown.

[0008]

However, according to the experiments of the present inventors, it is not easy to cause a transition from the splay orientation to the bend orientation or the π-twist orientation. (10 V is a voltage applied to the liquid crystal. A liquid crystal display device requires an even higher voltage because the liquid crystal is driven by an alternating current, and a power supply of about 30 V is required). It is generally difficult to apply such a high voltage to the liquid crystal display panel due to restrictions on driving voltage, power consumption, and components (eg, driving LSI).

The nucleation density of a bend-oriented or π-twisted domain generated only by application of an electric field is extremely low, and it takes a considerable time for the domain to spread over the entire region. Further, it is very difficult to cause a transition in all the pixels, and some pixels are left without any transition. If there is a pixel that does not undergo the alignment transition and remains in the splay alignment, the pixel is recognized as a display defect, the display quality as a display is greatly reduced, and the value as a product is lost.

Therefore, in order to realize uniform alignment without alignment defects, a transition nucleus (nucleus generating means) which triggers transition is introduced into the inside of the liquid crystal display device (inside of the liquid crystal panel), and this site is introduced at a low voltage. Japanese Patent Application Laid-Open Nos. Hei 10-20284 and Hei 10-142638 describe inventions by the same applicant to which the inventor of the present application belongs, which have been devised to cause a transition from the above. The points of these inventions are as follows: (1) A conductive convex portion is provided in a pixel electrode portion of a liquid crystal cell to locally strengthen a vertical electric field (an electric field in a direction from a pixel electrode to a counter electrode) (FIG. 4). . (2) A portion having a large pretilt angle or a portion to be vertically aligned is locally introduced into the pixel electrode portion (FIG. 5).

A conventional configuration will be briefly described. FIG. 4 shows an example in which a conductive convex portion is provided in a pixel electrode portion of a liquid crystal cell to locally strengthen a vertical electric field (an electric field in a direction from a pixel electrode to a counter electrode). FIG. 1B is a schematic plan view of a pixel portion of a conventional liquid crystal display device, and FIG. 1A is a schematic cross-sectional view taken along the line AB of the schematic plan view. Is deformed and described from the actual one). In this figure, 16 is a thin film transistor as an active element, 4 is a pixel electrode connected thereto, 2 is a wiring, 3 is an insulating film on the substrate 1, and these form an active matrix substrate substrate (actually, There is a multilayer thin film material necessary for forming the active element of the active matrix substrate, but the details are not shown here because they are not directly related to the present invention). 7 is a substrate, 8 is a black matrix for shielding light, 9a, 9b, 9
c is the color layer of the color filter (usually red-green-blue), 10
Are opposing electrodes, which form an opposing substrate. The liquid crystal 12 is sandwiched between these two substrates via the alignment films 5 and 11 that have been subjected to the alignment process. 13a and 13b are polarizing plates. The liquid crystal display device is completed by attaching peripheral circuit members (not shown) and frames (not shown) to the liquid crystal display device.
In this figure, the gap between the liquid crystal layers is narrowed at the portion 14 where the projection 6 is formed of a conductive member on the pixel electrode 4, so that the electric field intensity is increased and the transition is likely to occur.
In the example shown in FIG. 5, beads 15 for promoting vertical alignment are mixed in the liquid crystal layer to facilitate transition.

However, these conventional structures require a special process (projection formation or partial vertical orientation) and the addition of a material (projection formation material or beads) to form a portion that becomes a transition nucleus. The introduction of nuclear nuclei has led to lower costs due to increased costs and processes. An object of the present invention is to provide a liquid crystal display device that can introduce a transition nucleus without increasing the process load and, in addition, can surely cause a transition. It is another object of the present invention to add a configuration in which metastasis easily occurs.

[0013]

The means of the present invention for solving the above problems will be described below.

The first structure (the first aspect of the present invention) is a liquid crystal display device comprising: an active matrix substrate having pixel electrodes and active elements connected thereto in a matrix; and a counter substrate having a counter electrode;
A liquid crystal that is interposed between the pair of substrates and changes from a splay alignment to a π twist alignment or a bend alignment by applying a voltage between the pixel electrode and the counter electrode; and a π twist alignment or a bend alignment from the splay alignment. A liquid crystal display device comprising: a nucleus generating means for promoting transfer to a liquid crystal display device, wherein a convex portion formed by a color filter coloring layer formed on the active matrix substrate is used as the nucleating means. It is.

The second structure (invention of claim 2) comprises an active matrix substrate having pixel electrodes and active elements connected thereto in a matrix, an opposing substrate having opposing electrodes, and a pair of substrates interposed therebetween. And a liquid crystal that changes from a spray orientation to a π twist orientation or a bend orientation by applying a voltage between the pixel electrode and the counter electrode, and nucleation that promotes a transition from the spray orientation to the π twist or bend orientation. Wherein the first and second liquid crystal display devices have a projection formed by a color filter colored layer formed on the counter substrate as the nucleation means. Preferably, in the liquid crystal display device, the convex portion is formed of a color filter coloring layer of two or more colors. It is when.

Next, a third configuration (invention of claim 4) is:
An active matrix substrate having a pixel electrode and an active element connected thereto in a matrix and an opposing substrate having an opposing electrode, and a voltage interposed between the pair of substrates by applying a voltage between the pixel electrode and the opposing electrode. A liquid crystal display panel comprising: a liquid crystal that transitions from a splay orientation to a π twist orientation or a bend orientation; and a nucleation unit that promotes a transition from the spray orientation to the π twist orientation or a bend orientation. A liquid crystal display device having a convex portion formed thereon and having a portion where two electrodes capable of giving a potential difference on the convex portion are arranged at an interval is a nucleus generating means. . This further ensures that metastasis occurs.

Further, in the third configuration, preferably, the two electrodes are adjacent pixel electrodes, and the liquid crystal display device according to claim 4 is provided.

According to the above-described method, it is possible to surely cause the orientation transition.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1B is a schematic plan view of a pixel portion of the liquid crystal display device of the present invention, and FIG. 1B is a schematic cross-sectional view of a portion corresponding to the line AB.
(A)) (the dimensions and shapes are deformed from actual ones for the sake of explanation). In this embodiment mode, a structure in which a color filter used for a liquid crystal display device is formed on an active matrix substrate (COA: color filter on array) is shown. In this figure, 1 is a glass substrate, 21 is a wiring, 3 is an insulating film (actually, there is a multilayer thin film material necessary for forming an active element of an active matrix substrate, but here it is not directly related to the present invention. 22a, 22b, and 22c are color filter layers. In this case, a photosensitive colored resist is used, and the arrangement is a stripe pattern (((b) in FIG. 1)). In this case, the color filter and the coloring layer are omitted because the drawing becomes complicated.) At this time, a convex portion 22aa was formed by overlapping two colors of the color filter coloring layer in a part of the pixel (the combination of the two colors was combined by the color of each pixel. For example, a green protrusion for red, a red protrusion for blue). Projections). The formation of the projections 22aa was originally patterned at the same time as the processing of the color filter layer, and no additional steps were required to form the projections. The film thickness of the projection is approximately 3 μm. Thereafter, a pixel electrode 23 connected to the active element was formed, and an active matrix substrate was formed. Reference numeral 7 denotes a glass substrate for a counter substrate, and reference numeral 10 denotes a counter electrode (ITO thin film). The liquid crystal 12 is sandwiched between these two substrates via the alignment films 5 and 11. The liquid crystal is a liquid crystal which changes from a splay alignment to a π twist alignment or a bend alignment by applying a voltage between the pixel electrode and the counter electrode. 13a and 1
3b is a polarizing plate. The liquid crystal display device is completed by attaching peripheral circuit members (not shown) and frames (not shown) to the liquid crystal display device. In the present embodiment, the thickness of the liquid crystal layer main body is 5 μm
Therefore, the thickness of the liquid crystal in the convex portion 22aa is approximately 2 μm, and the portion 24 has a structure in which the electric field is concentrated (the electric field is strong) as compared with other portions.

According to the first embodiment, when a voltage is applied between the pixel electrode 23 and the counter electrode 10, the transition to the stable bend alignment or π twist alignment occurs from the projection. The domain spreads over the entire area in a short time.
As described above, the projections 22aa serve as transition nuclei (nucleus generation means), the nucleation density of the alignment domain is increased, the transfer is performed efficiently, and uniform alignment without alignment defects can be achieved as a whole. Therefore, a high-quality OCB type liquid crystal display panel can be obtained without increasing the number of manufacturing steps and members as in the related art.

In this embodiment, each color of red, green and blue is used as the color filter-coloring layer, but it may be black (light shielding layer). In the figure, a small patterned colored layer of another color is superimposed on the colored layer 22b to form a projection 22aa.
Is formed, on the contrary, the colored layer 22b may be overlaid on the colored layer which is patterned in a small size (this configuration is also necessary when actually forming transition nuclei in all pixels). When the transition occurs, the domain spreads sequentially, but it is preferable to provide the transition nucleus in all the pixels.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2B is a schematic plan view of a pixel portion of the liquid crystal display device, and FIG. 2A is a schematic cross-sectional view of a portion corresponding to the line AB (FIG. 2A). Dimensions and shapes are deformed from the actual ones.) This embodiment has almost the same configuration as the first embodiment, and has a COA structure.
The difference is that the projections 33 serving as transition nuclei are formed between adjacent pixel electrodes, and the description of the common parts with the description so far is omitted here. In this figure, reference numeral 31 denotes a wiring (horizontal wiring is shown; in fact, there is a multilayer thin film material necessary for forming an active element of an active matrix substrate, but here, a part which is not directly related to the present invention) 32 is a color filter layer (only one color is shown because the AB line is in the vertical direction in this case), and a photosensitive colored resist is used. A stripe pattern was used. At this time, the convex portion 33 was formed by overlapping two colors of the color filter coloring layer at a portion corresponding to a portion between the adjacent pixel electrodes. The formation of the projections 33 was originally performed at the same time as the patterning of the color filter layer, and no additional steps were required to form the projections. The film thickness of the projection is approximately 3 μm. Thereafter, the pixel electrode 34 connected to the active element is formed, and the liquid crystal is sandwiched between the two substrates via the alignment film as in the first embodiment. The liquid crystal is a liquid crystal which changes from a splay alignment to a π twist alignment or a bend alignment by applying a voltage between the pixel electrode and the counter electrode. The liquid crystal display device is completed by attaching peripheral circuit members (not shown) and frames (not shown) to the liquid crystal display device. In the present embodiment, the thickness of the liquid crystal layer main body is set to 5 μm. Therefore, the thickness of the liquid crystal is approximately 2 μm in the convex portion 33, and the portion 35 has a structure in which the electric field is concentrated (the electric field is strong) as compared with other portions. .

The difference from the first embodiment is that the adjacent pixel electrodes 34 have a narrow interval (4 μm in this case)
m), when a different potential is applied to the pixel electrode, a lateral force is also applied to the liquid crystal, and the liquid crystal molecules move more easily than in the first embodiment, so that the transition is more likely to occur (even during normal display). Since different potentials are applied, it also works to prevent reverse transition (failure to return to the original)),
Thus, stable bend orientation or π
Transition to twisted orientation occurs. The domain spreads over the entire area in a short time. As described above, the projections 33 increase the nucleation density of the alignment domain, efficiently perform transition, and enable uniform alignment without alignment defects as a whole. Therefore, a high-quality OCB type liquid crystal display panel can be obtained without increasing the number of manufacturing steps and members as in the related art.

Next, a liquid crystal display device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view of a portion according to the first embodiment (the figure is deformed from the actual size and shape for the sake of explanation). This embodiment has a structure in which the color layer of the color filter is provided on the counter substrate side. The color filter-colored layers 9a, 9b, and 9c are arranged on the counter substrate side, and the color electrode of two colors is overlapped in a part of the pixel to form a convex portion 9aa. I have. The formation of the projections 9aa was originally performed at the same time as the patterning of the color filter layer, and no additional steps were required to form the projections. As in the first embodiment, the liquid crystal is sandwiched between the two substrates via the alignment film. At this time, the liquid crystal is a liquid crystal that changes from a splay alignment to a π twist alignment or a bend alignment by applying a voltage between the pixel electrode and the counter electrode. The liquid crystal display device is completed by attaching peripheral circuit members (not shown) and frames (not shown) to the liquid crystal display device. In the present embodiment, the thickness of the liquid crystal layer main body is set to 5 μm. Therefore, the thickness of the liquid crystal is approximately 2 μm at the convex portion, and the portion 43 has a structure in which the electric field is concentrated (the electric field is stronger) than other portions.

According to the third embodiment, when a voltage is applied between the pixel electrode and the counter electrode 41, the stable transition to bend alignment or π twist alignment occurs from the projection. The domain spreads over the entire area in a short time. As described above, the projections 9aa increase the nucleation density of the alignment domains, efficiently perform transition, and enable uniform alignment without alignment defects as a whole. Therefore, a high-quality OCB type liquid crystal display panel can be obtained without increasing the number of manufacturing steps and members as in the related art.

The larger the pretilt angle is, the higher the growth rate of the bend orientation or π twist orientation domain is, and the smaller the electric field intensity for maintaining the orientation may be. As a result of the study, it was found that the pretilt angle of the liquid crystal was preferably 3 ° or more. In particular, it is preferable to set 3 ° or more in all the regions. Further, the liquid crystal material used in the present invention is not limited to a fluorine-based material, and any liquid crystal material such as a cyano-based liquid crystal having a positive dielectric anisotropy can be used. However, for an active matrix type liquid crystal display panel, it is necessary to use a liquid crystal composition containing a fluorine-based material having a high voltage holding ratio and excellent reliability as a main component.
Particularly preferred.

[0027]

According to the present invention, it is possible to introduce a nucleus generating means (convex portion) without increasing the number of steps and members in the prior art, and many nuclei of a normal domain having a bend orientation or a π twist orientation are generated. The domain spreads over the entire area in a short time. As described above, the nucleus generating means increases the nucleus generation density of the alignment domain, efficiently performs the transition, and enables uniform alignment without any alignment defects. Therefore, a high-quality OCB liquid crystal display panel can be obtained.

Further, by bringing different electrodes typified by adjacent pixel electrodes close to each other at a narrow interval at the convex portion, the transition can be made more reliable.

[Brief description of the drawings]

1A and 1B show a liquid crystal display device according to a first embodiment of the present invention, wherein FIG. 1A is a schematic cross-sectional view thereof, and FIG.

2A and 2B show a liquid crystal display device according to a second embodiment of the present invention, wherein FIG. 2A is a schematic cross-sectional view and FIG. 2B is a schematic plan view.

FIG. 3 is a schematic cross-sectional view of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a conventional liquid crystal display device having a transition nucleus.

FIG. 5 is a schematic cross-sectional view of another conventional liquid crystal display device having a transition nucleus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2, 21, 31 Wiring 3 Insulating film 4, 23, 34 Pixel electrode 5, 11 Alignment film 6 Convex part by a conductive member 7 Substrate 8 Black matrix 9a, 9b, 9c, 22a, 22b, 22c Color filter coloring layer 10, 41 Counter electrode 12 Liquid crystal 13a, 13b Polarizer 14, 24, 35, 43 Thin portion of liquid crystal layer 15 Bead 16 Thin film transistor 9aa, 22aa, 33 Convex portion 32 Color filter layer

Claims (5)

[Claims] An active matrix substrate having a pixel electrode and an active element connected thereto in a matrix, a counter substrate having a counter electrode, and a voltage between the pixel electrode and the counter electrode interposed between the pair of substrates. The liquid crystal display panel comprising: a liquid crystal that changes from a splay alignment to a π twist alignment or a bend alignment by applying a nucleus; and a nucleation unit that promotes a transition from the spray alignment to the π twist or bend alignment. A liquid crystal display device in which a convex portion formed by a color filter coloring layer formed on a matrix substrate is used as the nucleus generating means. 2. An active matrix substrate having a pixel electrode and an active element connected thereto in a matrix, a counter substrate having a counter electrode, and a voltage interposed between the pair of substrates and a voltage between the pixel electrode and the counter electrode. A liquid crystal transitioning from splay alignment to π twist alignment or bend alignment by applying a liquid crystal display, and nucleation means for promoting the transition from the splay alignment to π twist alignment or bend alignment. A liquid crystal display device in which a projection formed by a color filter coloring layer formed on a substrate is used as the nucleus generation means. 3. The liquid crystal display device according to claim 1, wherein the convex portion is formed of a color filter coloring layer of two or more colors. 4. An active matrix substrate having a pixel electrode and an active element connected thereto in a matrix, a counter substrate having a counter electrode, and a voltage interposed between the pair of substrates and between the pixel electrode and the counter electrode. The liquid crystal display panel comprising: a liquid crystal that changes from a splay alignment to a π twist alignment or a bend alignment by applying a nucleus; and a nucleation unit that promotes a transition from the spray alignment to the π twist or bend alignment. A liquid crystal display device having a convex portion formed on a matrix substrate or a counter substrate, and a portion where two electrodes capable of providing a potential difference on the convex portion are arranged at an interval as nucleus generating means. . 5. The liquid crystal display device according to claim 4, wherein said two electrodes are adjacent pixel electrodes.