JPH05232441A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the degradation in the numerical aperture by excess light shielding films without degrading the contrast of the twisted nematic liquid crystal display device which divides orientation directions in order to widen a visual angle range. CONSTITUTION:All picture elements are classified to picture elements A, B 1, 2, varying in orientation direction by 180 deg., provided that the liquid crystal within one picture element is twisted nematic phases 3, 4 having the same orientation direction. The parts varying in the orientation direction match picture element boundary parts 5 and are shielded of light by inter-picture element light shielding films. The degradation in the contrast by the discrination at the time of voltage impression is, therefore, obviated and the degradation in the numerical aperture is prevented.

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.

[0002]

2. Description of the Related Art Twisted nematic (TN) structures are widely used in currently used liquid crystal display devices. However, this twisted nematic structure has a drawback that the viewing angle dependency is severe. In particular, as shown in FIG. 4A, the rubbing direction (9) 45 ° of the lower substrate to the rubbing direction (8) 135 ° of the upper substrate.
In the twisted nematic structure that twists inward, the viewing angle dependency in the 90 ° direction and the 180 ° direction is large. Therefore, in FIG.
As shown in (b), one pixel (10) is divided into two regions, a twisted nematic phase A3 and a twisted nematic phase B4, and the viewing angle dependences in the 90 ° direction and the 180 ° direction are averaged. It was (JP-A-63-10
It can be found in Japanese Patent No. 6634 and Japanese Patent Laid-Open No. 64-88520. )

At present, a twisted nematic structure between a pair of parallel polarizing plates (normally white mode) is used because a high contrast is easily obtained.
Has become widely used. In the normally white mode, white display is shown when no voltage is applied to the twisted nematic structure, and black display is shown when a voltage is applied.

However, when a voltage is applied to the twisted nematic structure in the pixel shown in FIG. 4B, the discontinuity of orientation occurs at the boundary (11) of the twisted nematic phase. Therefore, in the normally white mode, there is a problem that light leakage due to the discontinuity of the alignment is observed and the display contrast is lowered.

Further, as means for preventing this light leakage, in JP-A-63-106634, a strip spacer is provided at the center of one pixel. However, provision of such a band-shaped spacer significantly narrows the area of the pixel opening. Therefore, there is a problem that the display brightness is lowered.

An object of the present invention is to provide a liquid crystal display device that solves such a problem.

[0006]

A liquid crystal display device according to a first aspect of the invention comprises all two kinds of pixels each having a twisted nematic phase whose orientation directions are different from each other by 180 °, and one pixel has a single orientation direction. And a twisted nematic phase.

In the liquid crystal display device of the second invention, all pixels are composed of pixels having different color filters of three colors, and one pixel is a display unit driven by a single display signal having a single color filter. One pixel is made of a twisted nematic phase having a single orientation direction, and all pixels are made of two kinds of pixels having a twisted nematic phase having different orientation directions of 180 °.

[0008]

The first invention will be described with reference to FIG. Figure 1
1A is a sectional view, and FIG. 1B is a plan view. In the present invention, one pixel is defined by one unit on one display. Therefore, the display signal supplied to this one pixel must be unique among all pixels. Therefore, as long as the pixels are formally divided into two and driven by the same display signal, the two pixels are regarded as a single pixel.
In the present invention, as shown in FIG. 1 (b), all pixels are roughly classified into a group A and a group B having twisted nematic phases 3 and 4 whose orientation directions are different from each other by 180 °. The plane arrangement of the groups A and B is not limited to that shown in FIG.
An example such as The twisted nematic phases of the group A and the group B are different from each other in the orientation direction by 180 °. However, as shown in FIG. 1A, the twisted nematic phase in one pixel has a single orientation direction. Therefore, the boundary between the twisted nematic phases of the group A and the group B is always aligned with the pixel boundary portion (5). However,
Usually, the pixel boundary portion (5) is shielded from light by the light shielding film.
Therefore, the light leakage due to the disclination generated at the boundary of the twisted nematic phase is blocked, and high contrast display is possible. Moreover, the area of the opening is not reduced by using the present invention.

In FIG. 1A, 1 is a pixel A and 2 is a pixel A.
Indicates a pixel B.

In the present invention, the minimum combination that complements the viewing angle dependency is a combination of one pixel in the group A and one pixel in the group B, a total of two pixels. However, in the conventional method of dividing one pixel shown in FIG. 4, the viewing angle dependency is compensated for within one pixel. Therefore, when viewed obliquely, a maximum resolution of 1 pixel is obtained in FIG. 4, and a maximum resolution of 2 pixels is obtained in FIG. However, in the case of television display, an image that actually requires a resolution of 1 or 2 pixels is rarely displayed. Also, in the display of the computer terminal, an image which requires a resolution of 1 or 2 pixels is not displayed. In particular, when a character such as a character is displayed on a computer terminal, since a character image is formed by a set of several pixels, there is no practical problem even if the resolution is up to about 2 pixels. Further, when viewed from the front, the resolution of the present invention is 1 pixel at the maximum, which is no different from normal display.

The second invention will be described with reference to FIG. In the present invention, three different types of color filters (R,
The entire display screen is composed of pixels composed of G and B). This allows color display. Further, in the present invention, one pixel is defined by one unit on one display. Therefore, the display signal supplied to this one pixel is
It must be unique among all pixels including the distinction of color signals. Therefore, as long as the pixels are formally divided into two and driven by the same display signal of the same color, these two pixels are
Considered as a single pixel. Further, all the pixels are composed of two kinds of pixels of a group A and a group B having a twisted nematic phase whose orientation directions are different from each other by 180 °. For this reason,
The combination of two pixels, one pixel in the group A and one pixel in the group B, mutually compensates for the viewing angle dependency. Further, the boundary between the group A and the group B always matches the pixel boundary portion. Therefore, the boundary portion of the twisted nematic phase is always shielded by the light shielding film at the pixel boundary portion, and high contrast display is possible. Furthermore, a new light-shielding film is not provided corresponding to the boundary of the twisted nematic phase, and the area of the opening of the pixel is not reduced by using the present invention. Further, the reduction in resolution does not pose a practical problem as already described in the first aspect of the invention.

FIGS. 2A, 2B and 2C show examples of application of the present invention to well-known color filter arrangements such as stripe arrangement, diagonal arrangement and triangular arrangement. Focusing only on the types A and B of the orientation directions of the twisted nematic phase, it can be seen that checkered patterns are formed in FIGS. 2A and 2B. This is an arrangement that avoids the line-shaped display unevenness due to the continuation of only the group A or the group B when viewed obliquely. However, the present invention is not limited to these examples, but another example shown in FIG.
It can be applied to different stripe arrangements, diagonal arrangements, and triangular arrangements as shown in (b) and (c).

The first and second inventions can be applied to both the active matrix system and the simple matrix system.

[0014]

EXAMPLE A black and white liquid crystal display device according to an example of the first invention will be described with reference to the plan view of FIG. The active matrix substrate used in this example is an amorphous silicon thin film transistor array formed on a glass substrate. Amorphous silicon thin film transistor (14)
The structure of the reverse staggered structure was used. Further, a chromium thin film was used as the signal wiring (13) and the scanning wiring (15). Pixel size is 160μm x 120μm
Is. The counter substrate has a light-shielding film made of a chromium thin film corresponding to the pixel size, and a counter electrode made of an ITO (indium tin oxide) thin film. A polyimide thin film (A11051 manufactured by Japan Synthetic Rubber Co., Ltd.) is formed on both of the active matrix substrate and the counter substrate, and after applying a photoresist, a photolithography process is performed to form a thin film (FIG.
The region A (twisted nematic phase A) in the inside was opened. A rubbing treatment was applied to the polyimide thin film in this opening to give it an alignment regulating force. After removing the photoresist, a new photoresist was applied and a region B (twisted nematic phase B) in FIG. 5 was opened by a photolithography process. The polyimide thin film in this opening is 18
Rubbing treatments different in 0 ° direction were performed to give the alignment regulating force. After that, the counter substrate and the active matrix substrate were bonded together via a spacer having a diameter of 5.7 μm so that the light-shielding film and the pixel were aligned. Further, nematic liquid crystal (ZLI-4792) is injected into the gap between both substrates in a vacuum,
Sealed.

In the liquid crystal display device obtained after the above steps, the viewing angle dependency at the time of displaying 16 gradations was measured. The measurement result is shown in FIG. The horizontal axis of FIG. 6 is the zenith angle, and 0 ° means the direction vertical to the display surface. It can be seen that there is no inversion in gradation display up to a zenith angle of about 45 °. In the normal twisted nematic liquid crystal, 16 gradation display is guaranteed only up to a zenith angle of about 5 °. Further, the pixels at the time of black display were observed under a polarizing microscope with the polarization axes orthogonal to each other. As a result, no light leakage due to disclination could be observed in the pixel. When the display contrast was measured, a contrast ratio of 200 or more was confirmed.

A color liquid crystal display device according to an embodiment of the second invention will be described with reference to the plan view of FIG. The active matrix substrate used in this example is an amorphous silicon thin film transistor array formed in a glass substrate shape. Amorphous silicon thin film transistor (1
As the structure of 4), an inverted staggered structure was used. Further, a chromium thin film was used as the signal wiring (13) and the scanning wiring (15). Pixel size is 120μm × 90μm
Is. The counter substrate is a diagonally arranged color filter, a light shielding film made of a chromium thin film corresponding to the pixel size, and an IT.
It has a counter electrode made of an O (indium tin oxide) thin film. A polyimide thin film (A11051) was formed on both of the active matrix substrate and the counter substrate, and after coating the photoresist, a region A in FIG. 7 was opened by a photolithography process. A rubbing treatment was applied to the polyimide thin film in this opening to give it an alignment regulating force. After the photoresist was peeled off, a new photoresist was applied and a region B in FIG. 7 was opened by a photolithography process. The polyimide thin film in this opening is 180 °
Rubbing treatments in different directions were performed to give the alignment regulating force. The arrangement is selected so that the A area and the B area are adjacent to each other. After that, the counter substrate and the active matrix substrate were bonded together via a spacer having a diameter of 5.7 μm so that the light-shielding film and the pixel were aligned. Further, nematic liquid crystal (ZLI-4792) is injected into the gap between both substrates in a vacuum,
Sealed.

When the viewing angle dependency of the liquid crystal display device obtained after the above steps was measured, the same measurement results as those in the above-mentioned example were obtained. Further, when the pixel at the time of black display was observed under a polarization microscope with the polarization axes orthogonal to each other, no light leakage due to disclination could be observed in the pixel. When the display contrast was measured, a contrast ratio of 200 or more was confirmed.

[0018]

According to the present invention, the viewing angle characteristics are good,
Moreover, it is possible to obtain a high-contrast liquid crystal display device which does not leak light due to discontinuity of liquid crystal alignment.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of pixel arrangement for explaining the present invention.

FIG. 2 is a diagram showing an example of pixel arrangement for explaining the present invention.

FIG. 3 is a diagram showing an example of pixel arrangement for explaining the present invention.

FIG. 4 is a plan view for explaining a conventional technique.

FIG. 5 is a plan view for explaining an embodiment of the first invention.

FIG. 6 is a diagram showing a measurement result of viewing angle dependence of the example of the first invention.

FIG. 7 is a plan view for explaining an embodiment of the second invention.

[Explanation of symbols]

 1 Pixel A 2 Pixel B 3 Twisted nematic phase A 4 Twisted nematic phase B 5 Pixel boundary 8 Rubbing direction of upper substrate 9 Rubbing direction of lower substrate 10 1 pixel 11 Twisted nematic phase boundary 12 Pixel electrode 13 Signal wiring 14 Amorphous silicon Thin film transistor 15 Scan wiring

Claims (2)

[Claims] 1. A liquid crystal display characterized in that all pixels are composed of two kinds of pixels having twisted nematic phases having mutually different 180 ° alignment directions, and one pixel is composed of a twisted nematic phase having a single alignment direction. apparatus. 2. All pixels are composed of pixels having different color filters of three colors, and one pixel is a display unit driven by a single display signal having a single color filter,
A liquid crystal display device, wherein one pixel is composed of a twisted nematic phase having a single orientation direction, and all pixels are composed of two kinds of pixels having a twisted nematic phase having different orientation directions by 180 °.