JPH05224210A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the degradation in the contrast of the liquid crystal display device having a twisted nematic liquid crystal varying in orientation direction within one picture element. CONSTITUTION:The twisted nematic layer on one picture element is divided into the two regions 2, 3 varying in the orientation direction by 180 deg.. Further, the light leakage from a boundary 4 of the twisted nematic layer at the time of a normal white and black display is prevented by using a light shielding film 5, by which the high contrast is attained.

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. 3A, the rubbing direction (1
0) 135 from 45 ° in the rubbing direction (11) of the upper substrate
In the twisted nematic structure that twists to 90 °, the viewing angle dependency in the 90 ° direction and the 180 ° direction is large. In the figure, (1
2) shows the twist of the nematic layer. Therefore, in FIG.
As shown in (b), one pixel (13) has a twisted nematic layer A (12) and a twisted nematic layer B.
It is divided into two areas of (12), and the 90 ° direction and 180
The viewing angle dependence in the ° direction has been averaged (Japanese Patent Laid-Open Nos. 63-106634 and 64-88).
See 520. )

At the present time, a twisted nematic structure (normally white mode) between orthogonal polarizing plates has been widely used because a high contrast can be easily obtained. 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. 3B, discontinuity of alignment occurs at the boundary (4) of the twisted nematic layer. 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.

An object of the present invention is to provide a liquid crystal display device which solves the above problems.

[0005]

In a liquid crystal display device according to a first aspect of the invention, a nematic layer on one pixel electrode is divided into regions having different 180 ° alignment directions, and the light shielding film is aligned with the boundaries of the regions. On at least one of the substrates.

The liquid crystal display device of the second invention is characterized in that it has two pixel electrodes driven by the same signal, and the nematic liquid crystal layers on the respective pixel electrodes have different 180 ° alignment directions.

[0007]

The first invention will be described with reference to FIGS. 1 (a) and 1 (b). In the present invention, two pixels are formed on one pixel electrode (1).
Twisted nematic layers A and B divided into two areas
(2,3) exists. The orientation directions of the both are different by 180 °, and the tilt directions of the liquid crystal molecules are opposite to each other when a voltage is applied. Further, a light shielding film (5) is formed at a position corresponding to the boundary (4) of the twisted nematic layer. This light-shielding film is used as an active matrix substrate (6) as shown in FIG.
It may be contained in any of the above layer structures. Further, the light shielding film (5) may be formed on the counter substrate (7) side as shown in FIG. 1 (b).

With this structure, the twisted nematic layer A,
When a voltage is applied to B (2,3), orientation discontinuity occurs at the boundary (4) between the two twisted nematic layers.
Therefore, in the normally white mode, light leakage occurs despite the black display, but the black display is maintained because the light shielding film (5) is provided. As described above, it is possible to reduce the amount of transmitted light during black display and maintain high contrast. In FIG. 2, (8) indicates the pixel electrode A,
(9) shows the pixel electrode B.

When the present invention is applied to a color liquid crystal display device, it can be used in combination with a plane arrangement of color filters. FIG. 4A shows a stripe arrangement that is commonly used, in which R, G, and B color filters are arranged vertically. As an example of applying the present invention to this stripe arrangement, it is also possible to horizontally divide each one pixel into two and arrange them as shown in FIG. Here, the division 25 indicated by a line means that one pixel is divided. Therefore, in the present invention, this division 25
A light-shielding film corresponding to is required. Also, each pixel can be vertically divided into two, as in the example shown in FIG. In FIGS. 4B and 4C, A and B of each pixel correspond to the twisted nematic layers A and B in FIG. 1, and their orientation directions are different from each other by 180 °. Whether each pixel is A or B does not have to be limited to the examples of FIGS. 4B and 4C, and the arrangements of the examples of FIGS. 5D and 5E are also possible. Further, not limited to the examples of FIGS. 4B, 4C, 5D, and 5E, pixel division and stripe arrangement can be combined.

In addition to the stripe arrangement, FIG.
It is also possible to apply to the diagonal arrangement shown in (a). In this case also, as some examples, FIGS.
Pixel arrangements such as (d) and (e) can be mentioned.
Not limited to these examples, pixel division and diagonal array can be combined.

Further, it can also be applied to the triangular array shown in FIG. As an example, FIG. 8 (b), (c), and FIG.
(D) and (e) can be mentioned. Not limited to these examples, pixel division and triangular arrangement can be combined.

The present invention can be applied not only to the stripe arrangement, the diagonal arrangement, and the triangular arrangement but also to various color filter arrangements to perform color liquid crystal display.

The second invention will be described with reference to FIGS. 2 (a) and 2 (b). In the present invention, the two pixel electrodes A and B
(8,9) exists. These pixel electrodes A, B (8,
It is sufficient that the same signal is supplied to 9) at the same timing. Therefore, the pixel electrodes A and B may be connected to the same active matrix element. Also,
Even if the pixel electrodes A and B are connected to two different active matrix elements, the connected two active matrix elements may be supplied with the same signal at the same timing. In any case, more flexible pixel arrangement is possible as compared with the case where only a single pixel electrode is used.

In the present invention, the twisted nematic layers A and B (2, 3) are formed on the two pixel electrodes A and B (8, 9), respectively. The twisted nematic layers A and B (2,3) have orientation directions different from each other by 180 °. Further, as shown in FIG. 2A, a light shielding film (5) may be provided on the active matrix substrate (6) side. Further, as shown in FIG. 2B, a light shielding film (5) may be provided on the counter substrate (7) side. In either case, the tilt directions of the liquid crystal molecules in the twisted nematic layers A and B are different when a voltage is applied. However, since the orientation is continuously changed in the pixel electrodes A and B, light leakage such as the above-mentioned disclination does not occur.

Further, there is a light shielding film at a position corresponding to the boundary (4) of the twisted nematic layer. Therefore, even if a bus line for supplying a scan or a signal is arranged between the pixel electrodes A and B (8, 9) to apply a voltage, the light shielding film (5) prevents light leakage. Is possible.

When the present invention is applied to a color liquid crystal display device, it can be used in combination with a planar arrangement of color filters. In this case, two pixels that are driven by the same signal are prepared. Moreover, the two pixels driven by the same signal must be incorporated in the color filter arrangement. Therefore, it can be described with reference to FIGS. 4 and 5 as in the case of the first invention. In this case, pixels of the same color that are adjacent to each other across the section 25 are driven by the same signal. When the color filters are arranged in stripes, as shown in FIG. 4 (b), (c),
The arrangements shown in (d) and (e) are possible. At this time, A and B in the parentheses in the drawing represent the types of orientation directions of the twisted nematic layer, and the orientation directions are different from each other by 180 °. Furthermore, when the color filters are arranged in a diagonal arrangement, as an example, FIG. 6 (b), (c), FIG. 7 (d), (e)
You can think of the arrangement. In addition, when the color filters are arranged in a triangle, similarly, as an example, FIGS.
The arrangements shown in FIGS. 9D and 9E can be given.
Not limited to these stripe arrangement, diagonal arrangement, and triangular arrangement,
The present invention can be applied to various color filter arrangements.

The first and second inventions can be applied not only to the active matrix system but also to the simple matrix system.

[0018]

EXAMPLE An example of the first invention will be described with reference to FIG. 10 which is a sectional view and FIG. 11 which is a plan view. In this embodiment, amorphous Si having an inverted staggered structure is used.
An active matrix substrate made of TFT was used. In the present embodiment shown in FIG. 10, the light shielding film A (1
4) and a light-shielding film B (15) for the boundary (4) of the twisted nematic layer on the active matrix substrate side.
Is equipped with. These light shielding films are made of a chromium thin film. Further, since there is no color filter layer on the counter substrate side, black and white display is possible. The pixel electrode (1) is IT
It is composed of an O (indium oxide-tin oxide) thin film.
Since the shape of one pixel (120 μm × 200 μm) is a vertically long rectangle, the boundary of the twisted nematic layer (4)
Are arranged in the short side direction of the pixel. Therefore, the light shielding film B
It is possible to minimize the decrease in aperture ratio due to (15). The twisted nematic layers A and B (2, 3) were separately formed in the same pixel by the following method. After applying the alignment film (17) (AL1051 manufactured by Nippon Synthetic Rubber Co., Ltd.), it was heated and baked at 180 degrees. Then, the twisted nematic layer A is exposed to the counter substrate and the active matrix substrate by an exposure process using a photoresist.
The region corresponding to (2) was selectively rubbed. After that, a region corresponding to the twisted nematic layer B (3) was similarly selectively rubbed on both substrates. Both substrates, which had been subjected to the alignment treatment as described above, were bonded to each other via a spacer of 5 μm. At this time, the rubbing treatment areas A of both substrates or the rubbing treatment areas of both substrates were aligned and bonded so as to overlap each other. Then, in a vacuum, nematic liquid crystal (ZLI-479 manufactured by Merck Japan Ltd.)
2) was injected. As a result, twisted nematic layers A and B (2,3) were formed between both substrates. When a scanning signal was applied to the scanning line and a signal for displaying black in the normally white mode was applied to the signal line, it was confirmed that the pixel responded to black under a polarizing microscope. At this time, no light leakage due to the discontinuity of alignment was observed in the pixel. In addition, a signal voltage corresponding to 16 gradation display is applied to change the rubbing direction to 4
The angle dependence of the transmittance in the direction of 5 ° was measured. The result is shown in FIG. It was found that there was no inversion in gradation display up to about 40 °. In a general twisted nematic structure, 16 gradation display is guaranteed only within 5 °.

Next, the color liquid crystal display device of the first embodiment of the second invention will be described with reference to FIG. 13 which is a sectional view and FIG. 14 which is a plan view. The amorphous Si TFT in FIG. 14 has an inverted staggered structure. The size of one pixel is 120 μm × 120 μm. This amorphous Si TFT array is composed of two amorphous Si TFTs driven by the same scanning electrode or signal electrode.
The TFTs A and B (22, 21) drive the respective pixel electrodes A and B (8, 9). The pair of pixel electrodes A and B includes a symbol electrode (19) or a scanning electrode (1
6) are adjacent to each other. In this way, the pixel electrodes on the entire display surface are roughly classified into the group A and the group B. Further, in order to prevent vertical lines or horizontal lines from appearing on the display screen, the A group is not arranged in a vertical example or a horizontal example, but A and B are arranged in a checkered pattern. The color filters are arranged in a triangle, and the pixel electrodes in FIG. 14 are shown in parentheses to indicate which of the R, G, and B color filters they correspond to. Further, as shown in FIG. 13, the light shielding film (5) is arranged so as to be aligned with the boundary (4) of the twisted nematic layer, and the scanning electrode (1
6) or the signal electrode (19). In this way, the light shielding film (5) can be used for the dual purpose of light shielding, and the reduction of the aperture ratio is suppressed.

The twisted nematic layers A and B were formed in the same manner as in the first embodiment of the invention. When observed under a polarizing microscope when black was displayed in a normally white mode by supplying a signal voltage, light leakage due to disclination could not be observed. In addition, the viewing angle dependence was measured in the same manner, and it was confirmed that the visibility was excellent in a wider viewing angle range than the usual twisted nematic structure. Also, when the contrast was measured, a value contrast ratio of 200 equivalent to that of a normal twisted nematic structure was obtained.

A color liquid crystal display device of the second embodiment of the second invention using a polycrystalline Si TFT will be described. Figure 15
FIG. 16 is a cross-sectional view of this example, and FIG. 16 is a polycrystalline Si TF.
It is a top view of a T array. In this embodiment, one polycrystalline Si TFT (24) has two pixel electrodes A and B.
Driving (8, 9). The size of one pixel is 65 × 6
It is 5 μm. All pixel electrodes are roughly divided into groups A and B, and are arranged in a checkered pattern. Further, in FIG. 16, the letters written in parentheses on the pixel electrodes correspond to the colors (R, G, B) of the color filter layer (23). As shown in FIG. 16, stripe arrangement is adopted for the arrangement of the color filters. The two pixel electrodes are arranged across the scan electrode (16). After forming the polycrystalline Si TFT array, the alignment film (17) was selectively rubbed with a counter substrate in a resist process. The boundary between the two rubbing steps was provided around each pixel electrode. Further, also on the counter substrate side, the light shielding film (17) was used as the boundary of the rubbing process. After that, both substrates were bonded to each other through a spacer in the same manner so that the boundaries of the rubbing process of both substrates were aligned, and nematic liquid crystal was injected into the gap. Twisted nematic layers A and B (2, 3) were formed in the gap between both substrates. The twisted nematic layers A and B were formed in the same manner as in the first embodiment of the invention. No disclination could be observed when displaying black in normally white mode.
Similarly, it was confirmed that the visibility was excellent in a wider viewing angle range than the twisted nematic structure. Further, a value contrast ratio of 200 equivalent to that of a normal twisted nematic structure was obtained.

[0022]

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 cross-sectional view illustrating a liquid crystal display device of a first invention.

FIG. 2 is a cross-sectional view illustrating the liquid crystal display device of the first invention.

FIG. 3 is an explanatory diagram of a conventional liquid crystal display device.

FIG. 4 is a plan view illustrating an example of a combination of the present invention and a stripe arrangement of color filters.

FIG. 5 is a plan view illustrating a combination example of the present invention and a stripe arrangement of color filters.

FIG. 6 is a plan view illustrating a combination example of the present invention and a diagonal arrangement of color filters.

FIG. 7 is a plan view illustrating a combination example of the present invention and a diagonal arrangement of color filters.

FIG. 8 is a plan view illustrating an example of a combination of the present invention and a triangular arrangement of color filters.

FIG. 9 is a plan view illustrating an example of a combination of the present invention and a triangular arrangement of color filters.

FIG. 10 is a sectional view illustrating an embodiment of the first invention.

FIG. 11 is a plan view illustrating an embodiment of the first invention.

FIG. 12 is a diagram showing measurement results of viewing angle dependence of the example of the first invention.

FIG. 13 is a sectional view illustrating a first embodiment of the second invention.

FIG. 14 is a plan view illustrating the first embodiment of the second invention.

FIG. 15 is a sectional view for explaining the second embodiment of the second invention.

FIG. 16 is a plan view illustrating a second embodiment of the second invention.

[Explanation of symbols]

 1 pixel electrode 2 twisted nematic layer A 3 twisted nematic layer B 4 boundary of twisted nematic layer 5 light-shielding film 6 active matrix substrate 7 counter substrate 8 pixel electrode A 9 pixel electrode B 10 rubbing direction of lower substrate 11 rubbing direction of upper substrate 12 Twisting of nematic layer 13 Pixel 14 Light-shielding film A 15 Light-shielding film B 16 Scan electrode 17 Alignment film 18 Counter electrode 19 Signal electrode 20 Amorphous Si TFT 21 Amorphous Si TFT A 22 Amorphous Si TFT B 23 Color filter layer 24 Polycrystalline Si TFT 25 Division

Claims (2)

[Claims] 1. A nematic layer on one pixel electrode is 180
A liquid crystal display device characterized by being divided into regions having different orientation directions and having a light-shielding film on at least one substrate in alignment with the boundaries of the regions. 2. A liquid crystal display device having two pixel electrodes driven by the same signal, wherein nematic liquid crystal layers on the respective pixel electrodes have different 180 ° alignment directions.