JPH11149078A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the degradation in an aperture ratio, simultaneously to lessen the dependence on a visual field angle and to assure good visibility without depending on the visual direction by subjecting respective alignment layers to rubbing treatments in opposite directions at adjacent pixels to prevent the degradation of the aperture ratio and simultaneously to lessen the visual angle dependence ability. SOLUTION: A liquid crystal layer 12 is disposed between a pair of transparent substrates 10, 11 arranged to face each other above and below. Common electrodes 17 and the alignment layer 18 are disposed on the liquid crystal layer 12 side of the upper substrate 11 and pixel electrodes 19 and the alignment layer 20 on the liquid crystal layer 12 side of the lower substrate 10, respectively. The respective alignment layer 18, 20 comprise first perpendicular alignment layers 18a, 20b subjected to the rubbing treatment and second perpendicular alignment layers 18b, 20b not subjected to the rubbing treatment. The region where the second perpendicular alignment layers 18b, 20b are laminated is for one pixel. When a pair of the alignment layers on the upper and lower substrates are viewed, the alignment layers are so arranged that the alignment layer surface laminated with the second perpendicular alignment layers 18b, 20b and not subjected to the rubbing treatment and the alignment layer surface exposed with the first perpendicular alignment layers 18a, 20b and subjected to the rubbing treatment face each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device which has a small viewing angle dependency and has good visibility regardless of a viewing direction.

[0002]

2. Description of the Related Art Generally, in a TN mode liquid crystal display device, the viewing angle dependency is a problem. FIG. 7 shows T
FIG. 7 shows general viewing angle dependence of an N-mode liquid crystal display device, and a portion surrounded by a curve in FIG. 7 indicates a range having a contrast (CR) of 10 or more. As shown in this figure, it is clear that the TN mode liquid crystal display device has good visibility from the left and right directions to some extent, but poor visibility from the upper and lower directions.

[0003] Against this background, various structures have recently been proposed for widening the viewing angle of liquid crystal display devices.
One of them is an orientation division structure for each pixel. The orientation division structure is a structure in which domains (regions) in which liquid crystal molecules rise in different directions when a voltage is applied to each pixel are provided. For example, one pixel is divided into two,
This structure can be realized by performing alignment processing in different directions on the alignment films of the divided pixels. With this alignment division structure, abrupt and asymmetric changes in contrast in the vertical direction, which have been a problem in the TN mode liquid crystal display device, are alleviated and symmetrical, and a region where grayscale inversion in halftone does not occur is enlarged. Therefore, a liquid crystal display device having a wide viewing angle can be realized.

FIG. 6 shows an example of a method of manufacturing a liquid crystal display device having an in-pixel alignment division structure, and particularly shows a procedure of an alignment process. The substrate 1 shown in FIG.
For example, a source wiring (not shown) and a gate wiring (not shown) are arranged in a matrix, and a pixel electrode 2 made of a transparent conductive material such as ITO is provided for each region surrounded by the source wiring and the gate wiring. A thin film transistor (not shown) as a switching element is connected to each pixel electrode 2. The surface of the pixel electrode 2 is covered with an alignment film 3 made of a material such as polyimide. In the drawing, reference numeral 4 denotes a black matrix that covers a non-display area around the pixel electrode, and reference numeral 5 denotes an insulating film.

A rubbing process is performed on the substrate 1 in a direction indicated by an arrow A as shown in FIG. This rubbing treatment can be performed, for example, by rubbing the surface of the alignment film 3 with a roller around which a rubbing cloth is wound.
Next, as shown in FIG. 6B, after forming a photoresist film 6 covering a half area of one pixel, as shown in FIG. 6C, an arrow A shown in FIG. The rubbing process is performed in the direction of arrow B opposite to the above. After that, as shown in FIG. 6D, when the photoresist film 6 is peeled off, the region covered with the photoresist film 6
Since the first rubbing process has not been performed, the rubbing direction is the direction of arrow A.
In the region not covered by the rubbing, the rubbing direction is the direction of arrow B because the second rubbing treatment has been performed on the surface of the alignment film 3. In this manner, two regions having different orientations in one pixel are formed,
As shown in FIG. 6 (e), the substrate 1 thus treated is
7 and the liquid crystal 8 is injected between them to realize an intra-pixel alignment division structure in which the liquid crystal molecules 9 are inclined in the opposite direction in the same pixel.

[0006]

In a liquid crystal display device having an intra-pixel alignment division structure, the alignment of liquid crystal molecules is disturbed (hereinafter, referred to as a disk) near the boundary between two regions in the pixel where the liquid crystal has different alignment directions. This causes light leakage at this portion. Therefore, it is necessary to take measures to make light leakage inconspicuous, for example, by providing a linear black mask on the counter substrate side, but on the other hand, this causes a problem that the aperture ratio is reduced. In particular, it is extremely disadvantageous that this type of black mask must be provided in the center of the pixel. That is, in this method, even if the viewing angle is widened by adopting the in-pixel orientation division structure, the problem that the aperture ratio decreases cannot be avoided.
The present invention has been made in order to solve the above-described problems, and it is an object of the present invention to provide a liquid crystal display device that prevents a decrease in aperture ratio, has little viewing angle dependency, and has good visibility regardless of a viewing direction. The purpose is to provide.

[0007]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a pair of substrates each having an alignment film opposed to each other and a liquid crystal layer provided between these substrates. The rubbing process is performed on each of the alignment films in adjacent pixels in opposite directions.

An example of a method for forming an orientation division structure in such adjacent pixels is as follows. After forming a first vertical alignment film on the entire surface of a substrate, a rubbing process is performed on the alignment film. After every other pixel is covered with an arbitrary mask material or the like, a second vertical alignment film may be formed on pixels not covered with the mask material, and the mask material may be removed. Then, a pair of substrates that have been subjected to such an alignment treatment may be combined and disposed so that the surface of the vertical alignment film that has not been subjected to the rubbing treatment and the surface of the vertical alignment film that has been subjected to the rubbing treatment face each other.

If adjacent pixels are subjected to a rubbing process in the opposite direction to form an orientation-divided structure, the liquid crystal molecules will rise in the opposite direction for each pixel, and will be asymmetric due to the orientation direction of the liquid crystal. The contrast is averaged between two adjacent pixels, and the viewing angle can be broadened as a whole.

Further, in the configuration of the present invention, since the rubbing process in the opposite direction is performed in the adjacent pixels, disclination occurs in the pixels as in a liquid crystal display device having an intra-pixel alignment division structure. Therefore, there is no need to provide a black mask in order to prevent light leakage, so that there is no problem that the aperture ratio is reduced. In the configuration of the present invention, even if disclination occurs, the location is a region between pixels. Since the black mask is originally provided in this region, the disclination does not affect the aperture ratio.

Further, in the liquid crystal display device according to the present invention, the width of each pixel in the lateral direction is 50 μm or less. In a conventional liquid crystal display device, the width of each pixel in the lateral direction is about 100 μm. On the other hand, in the present invention, when two pixels adjacent in the lateral direction are colored by the same color filter and the contrast is averaged, the two pixels are recognized as one dot. By setting the width of the pixel in the lateral direction to 50 μm or less, a liquid crystal display device having a resolution comparable to that of a conventional liquid crystal display device can be obtained.

[0012]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a sectional view showing a schematic configuration of the liquid crystal display device of the present embodiment. As shown in FIG. 1, a liquid crystal layer 12 is disposed between a pair of transparent substrates 10 and 11 which are vertically arranged with a predetermined cell gap therebetween, and a retardation plate 13 and a polarizing plate are provided outside an upper substrate 11. 14
However, a retardation plate 15 and a polarizing plate 16 are provided outside the lower substrate 10. Further, a common electrode 17 and an alignment film 18 are provided on the liquid crystal layer 12 side of the upper substrate 11, and a pixel electrode 19 and an alignment film 20 made of a transparent conductive material such as ITO are provided on the liquid crystal layer 12 side of the lower substrate 10, respectively. ing. Also,
A thin film transistor as a switching element of each pixel is connected to the pixel electrode 19, and a source line and a gate line are connected to each thin film transistor, but these are not shown in FIG. Reference numeral 21 denotes the pixel electrode 19
Is a black matrix for covering a non-display area that does not contribute to the display of liquid crystal around the area, and reference numeral 22 denotes an insulating film.

Each of the alignment films 18 and 20 provided on each of the transparent substrates 10 and 11 includes a rubbed first vertical alignment film 18a, 20a and a first vertical alignment film 1a.
The second vertical alignment films 18b and 20b, which have not been subjected to the rubbing treatment, are stacked on the first vertical alignment films 8a and 20a, and the region where the second vertical alignment films 18b and 20b are stacked is one pixel. Has become. Looking at the pair of alignment films on the upper and lower substrates, the second vertical alignment films 18b and 20b
Are arranged so that the surface of the alignment film that has not been subjected to the rubbing treatment and the surface of the alignment film that has been subjected to the rubbing treatment while exposing the first vertical alignment films 18a and 20a are opposed to each other. Therefore, the liquid crystal molecules 2 between the alignment film 18 and the alignment film 20
5 will be inclined in the opposite direction in the adjacent pixels. A polyimide resin, a polyamide resin, or the like is used as a material of the first and second vertical alignment films.
S-204 (trade name, manufactured by Nippon Synthetic Rubber Co., Ltd.) or the like can be used. As the liquid crystal material, a liquid crystal having a negative dielectric anisotropy, that is, a liquid crystal in which a torque acts so as to be vertically oriented to an electric field is used.
95955 (trade name, manufactured by Merck Japan Ltd.) or the like can be used.

Next, a method of manufacturing the liquid crystal display device having the above configuration, particularly a procedure of an alignment treatment step will be described with reference to FIG. First, as shown in FIG. 3 (a), after applying a first vertical alignment film 20a on the entire surface of the substrate 10, the surface of the alignment film is rubbed in a specific direction with a roller around which a rubbing cloth is wound, and the arrow is drawn. A normal rubbing process in one direction indicated by C is performed. In the case of the vertical alignment film, when no electric field is applied, the liquid crystal molecules rise vertically to the surface of the alignment film. From 3 °
It is in a state inclined to a degree. Next, as shown in FIG. 3B, the photoresist film 23 is applied and patterned to leave the photoresist film 23 at every other adjacent pixel.
Further, as shown in FIG.
The second vertical alignment film 20 is applied to the pixels not covered by the third vertical alignment film 20.
Apply b. The first and second alignment films 20a, 20a
The applied film thickness of b may be about 500 °. Thereafter, as shown in FIG. 3D, the photoresist film 23 is removed. Although FIGS. 3A to 3D show only the lower substrate 10, a series of operations similar to the above are performed on the upper substrate 11.

Then, as shown in FIG. 3 (e), the upper substrate 11 and the lower substrate 10 after the above operation are completed, and the second vertical alignment films 18b and 20b and the first vertical alignment The liquid crystal 12 is disposed between the substrates 10 and 11 so that the films 20a and 18a face each other, that is, the surface of the vertical alignment film that has not been subjected to the rubbing treatment faces the surface of the vertical alignment film that has been subjected to the rubbing treatment. Inject.
Thus, the liquid crystal display device of the present embodiment is created.

In the case of the liquid crystal display of this embodiment, FIG.
As shown in (e), the liquid crystal molecules 25 between the pair of alignment films 18 and 20 rise vertically on the surface side of the second vertical alignment films 18b and 20b (no rubbing treatment), and the first vertical alignment On the surface side of the films 18a, 20a (with rubbing treatment), they are inclined by about 3 ° from the vertical (FIG. 3E).
Is exaggerated). When an electric field is applied from this state, the liquid crystal molecules 25 between the alignment films 18 and 20 are entirely inclined in the rubbing direction.
As shown in FIG. 2A, the liquid crystal molecules rise in the adjacent pixels with a tilt in the opposite direction (the direction of alignment of the liquid crystal in the pixel 27 is indicated by an arrow D in FIG. 2A).
Therefore, according to the structure of the present embodiment, the asymmetric contrast due to the alignment direction of the liquid crystal is averaged between two adjacent pixels, and the viewing angle can be increased as a whole liquid crystal display device.

Further, in the configuration of the present invention, since the rubbing process in the opposite direction is performed in the adjacent pixels, disclination occurs in the pixels as in a liquid crystal display device having an intra-pixel alignment division structure. Therefore, there is no need to provide a black mask in order to prevent light leakage, so that there is no problem that the aperture ratio is reduced. In the configuration of the present invention, even if disclination occurs, the location is a region between pixels. Since the black mask is originally provided in this region, the disclination does not affect the aperture ratio.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, as shown in FIG.
Between two pixels 27, 27 adjacent to each other in the lateral direction of each pixel, an alignment direction parallel to the lateral direction of the pixel and opposite (arrow D)
And an example having an arrow E), the structure shown in FIGS. 3A to 3E is replaced with the structure shown in FIG.
The rubbing direction in (a) is defined as a direction penetrating the paper surface, and as shown in FIG. 2 (b), between two pixels 28, 28 adjacent in the lateral direction of each pixel, parallel to the longitudinal direction of the pixel. A configuration having opposite orientation directions (arrows I and J) may be employed.

Further, as a method of forming the second vertical alignment film every other pixel, in the above-described embodiment, an example in which patterning is performed so as to leave a photoresist film every other pixel has been described. Various methods can be used, such as applying the second vertical alignment film in a state where the mask material covering the region for each pixel is in contact with the substrate. Further, various materials can be used for the material constituting the transparent substrate, the alignment film, the liquid crystal layer and the like, and the specific method of the rubbing treatment and the like.

In the present invention, rubbing may be performed twice on one transparent substrate so that rubbing in the opposite direction is performed on adjacent pixels. FIG. 4 is a cross-sectional view showing an alignment division structure according to another embodiment of the present invention, and illustrating the alignment process of the liquid crystal display device in order. The substrate 31 shown in FIG. 4A has, for example, a source wiring (not shown) and a gate wiring (not shown) arranged in a matrix, and ITO or the like for each region surrounded by the source wiring and the gate wiring. Are provided, and a thin film transistor (not shown) as a switching element is connected to each of the pixel electrodes 32, 32,.... The surface of the pixel electrode 32 is covered with an alignment film 33 made of a material such as polyimide. In the figure, reference numeral 34 denotes a black matrix that covers a non-display area around the pixel electrode, and reference numeral 35 denotes an insulating film.

A rubbing process is performed on the substrate 31 in a direction indicated by an arrow G as shown in FIG. This rubbing treatment can be performed, for example, by rubbing the surface of the alignment film 33 with a roller around which a rubbing cloth is wound. Next, as shown in FIG. 4B, after a photoresist film 36 is formed every other pixel, as shown in FIG. 4C, an arrow opposite to the arrow G shown in FIG. A rubbing process is performed in the direction of H. Thereafter, as shown in FIG. 4D, when the photoresist film 36 is peeled off, the second rubbing treatment is not performed on the surface of the alignment film 33 in the region covered by the photoresist film 36, The rubbing direction is the direction of arrow G. On the other hand, in the region not covered by the photoresist film 36, the second rubbing treatment is performed on the surface of the alignment film 33. Orientation. In this way, two regions in which alignment processing in different directions is performed between adjacent pixels are formed. As shown in FIG. 4E, the substrates 31 and 37 thus processed are combined, and a liquid crystal is interposed therebetween. By injecting the liquid crystal 38, it is possible to realize an alignment division structure in which the liquid crystal molecules 39 are inclined in the opposite direction between adjacent pixels.

[0022]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. (Embodiment) As shown in FIG.
The rubbing directions were reversed between arrows 0 and 40 (arrows D and E), pixel size 40 μm × 70 μm,
A transparent electrode having a black matrix width of 5 μm was manufactured. (Comparative Example) As shown in FIG. 5B, the inside of the pixel 41, 41 was divided into four, and the rubbing directions were opposite between the adjacent divided regions (arrows D and E). Size 40μm × 70μm, Black matrix width 5μm
Was manufactured. The aperture ratio and transmittance were measured for each of the examples and comparative examples. Table 1 shows the results.

[0023]

[Table 1]

In the transparent electrode of the embodiment, the aperture ratio is 4
On the other hand, in the transparent electrode of the comparative example,
Disclination occurred in the center of the pixel, and a black matrix had to be provided for the purpose of preventing light leakage, so the aperture ratio was 23%. When the transmittance of the transparent electrode of the example was set to 100%, the transmittance of the transparent electrode of the comparative example remained at 60% for the same reason as described above. That is,
It is concluded that the liquid crystal display device of the present invention has very excellent aperture ratio and transmittance as compared with the conventional liquid crystal display device having an in-pixel alignment division structure.

[0025]

As described above in detail, in the liquid crystal display device of the present invention, the rubbing process in the opposite direction is performed on the adjacent pixels, so that the liquid crystal molecules are reversed in every other pixel. You will stand up leaning.
As a result, asymmetric contrast due to the alignment direction of the liquid crystal is averaged between two adjacent pixels, and the viewing angle can be increased as a whole liquid crystal display device. Further, in the configuration of the present invention, since rubbing processing in the opposite direction is performed in adjacent pixels, disclination does not occur in pixels as in a liquid crystal display device having an intra-pixel alignment division structure. Therefore, since there is no need to provide a black mask to prevent light leakage, there is no problem that the aperture ratio is reduced.

Further, in the configuration of the present invention, when two pixels adjacent in the lateral direction are colored by the same color filter and the contrast is averaged, the two pixels are recognized as one dot. However, by setting the width in the lateral direction of each pixel to 50 μm or less, a liquid crystal display device having a resolution comparable to that of a conventional liquid crystal display device can be obtained. This makes it possible to provide a liquid crystal display device that has little viewing angle dependence and has good visibility regardless of the viewing direction.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example in which the alignment direction is different in the alignment division structure according to the present embodiment.

FIG. 3 is a cross-sectional view showing, in order, steps of an alignment treatment of a liquid crystal display device in the alignment division structure of the present embodiment.

FIG. 4 is a cross-sectional view sequentially showing steps of an alignment treatment of a liquid crystal display device in an alignment division structure according to another embodiment of the present invention.

FIG. 5 is a plan view showing an example of a transparent electrode having an orientation-divided structure according to the present embodiment and an example of a transparent electrode having a conventional in-pixel orientation-divided structure.

FIG. 6 is a sectional view sequentially showing an alignment processing step of a conventional liquid crystal display device having an intra-pixel alignment division structure.

FIG. 7 is a view showing general viewing angle dependence of a TN mode liquid crystal display device.

[Explanation of symbols]

 10, 11 Transparent substrate 12 Liquid crystal layer 17 Common electrode 18, 20 Alignment film 18a, 20a First alignment film 18b, 20b Second alignment film 23 Photoresist film 25 Liquid crystal molecules 31, 37 Transparent substrate 33 Alignment film 36 Photoresist Film 39 liquid crystal molecules

Claims (2)

[Claims] 1. A pair of substrates each having an alignment film are opposed to each other, a liquid crystal layer is provided between these substrates, and each of the alignment films is subjected to a rubbing process in an opposite direction in an adjacent pixel. Liquid crystal display device. 2. The liquid crystal display device according to claim 1, wherein each pixel has a width in a lateral direction of 50 μm or less.