JPH07159810A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce the occurrence of reverse tilt and domain and to prevent faulty display and the lowering of contrast without lowering numerical aperture by providing an area in which the value of an interval between a scanning line and a holding capacitance line is equal to or below a specified value between one picture element electrode and the other picture element electrode adjacent along the extending direction of a scanning line. CONSTITUTION:The area 213a constituted of one scanning line 113a and one picture element potential holding capacitance 211 arranged in accordance with the one picture element electrode 151a connected to the scanning line 113a through a TFT 121a keeps the interval of <=20mu, for example, 10mu. In the same way, the area 231b constituted of the scanning line 113b and one picture element potential holding capacitance line 211 arranged in accordance with the one picture element electrode 151b keeps the interval of <=20mu, for example, 10mu. Thus, even though the picture element electrodes 151a and 151b are proximately arranged with respect to a video signal line 111, an electric field perpendicular to the electric field in a horizontal direction generated between the video signal line 111 and the respective picture element electrodes 151a and 151b is generated between the scanning lines 113a and 113b and the picture element electrode holding capacitance line 211.

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 in which a liquid crystal layer is held between a pair of electrode substrates, and more particularly to an active matrix type liquid crystal display device in which a switch element is provided for each display pixel. .

[0002]

2. Description of the Related Art A liquid crystal display device has been attracting attention as a flat panel display which achieves light weight and low power consumption. Above all, an active matrix type liquid crystal display device in which a switching element such as a thin film transistor (hereinafter abbreviated as TFT) is provided for each display pixel is capable of obtaining a high-definition display image without crosstalk.
It is used as various displays such as TV applications and OA applications.

In recent years, due to the demand for larger display screens,
Attempts have been made to use such a liquid crystal display device as a projection type. When using a liquid crystal display device as a projection type,
In order to achieve small size and low power consumption, downsizing of the optical system is essential, and accordingly, it is necessary to form the liquid crystal display device itself into a small size of about 3 inches. For this purpose, the following is required. It is necessary to solve technical problems.

First, even if the liquid crystal display device itself is formed in a small size, its display image is enlarged and projected, so that it is necessary to make the display pixel pitch finer than in the prior art. Secondly, even if the liquid crystal display device itself is formed in a small size, it is necessary to improve the light utilization efficiency while maintaining the switch element characteristics. Therefore, the aperture ratio can be made larger than before without making a large change in the switch element size. Need to raise.

Under such circumstances, a liquid crystal display device which achieves both a fine pitch and a high aperture ratio is, for example, SID 90 DIGES.
T P.315-P.318; New Technologies for Compact TFT LCD
s with High Aperture Ratio. In this liquid crystal display device, a liquid crystal layer is held between a matrix array substrate integrally formed with a drive circuit section and a counter substrate via an alignment film.

As shown in FIG. 6, a matrix array substrate
(701) is a plurality of scanning lines (7) on an insulating substrate (not shown).
13a), (713b) and a plurality of video signal lines (711) are arranged in a matrix form, and pixel electrodes ((a), (721b), (721b) are arranged at each intersection as switching elements). 7
51a) and (751b) are provided. And two scan lines
(713a) and (713b) are closely arranged as one set, and scanning lines (713
A pixel potential holding capacitance line (821) common to the pixel electrodes (751a) and (751b) adjacent to each other is provided along the video signal line (711) without passing through a) and (713b).

By adopting such a configuration, firstly, the number of pixel potential holding capacitance lines (821) can be reduced to about half that of the conventional one, and secondly, the pixel potential holding capacitance lines (821) are connected to one set of scanning lines arranged close to each other. Since the number of contact holes (730) between the TFTs (751a) and (751b) and the video signal line (711) can be reduced to about half that in the conventional case, a fine pitch can be achieved without impairing the aperture ratio.

[0008]

By the way, in the active matrix type liquid crystal display device, a portion of the alignment film where the alignment treatment is insufficient is partially formed due to a step on the substrate formed by various wirings. This may lead to poor alignment of liquid crystal molecules. Further, due to the influence of the lateral electric field generated between the video signal line or the scanning line and the pixel electrode, the alignment failure of the liquid crystal molecules is caused, which is a region contrary to the normal pretilt, that is, a normal alignment region (hereinafter, normal tilt・ A reverse tilt domain having a different transmittance from that of a domain) is generated, resulting in display failure.

Further, since there is a region called a disclination line which causes light leakage between the normal tilt domain and the reverse tilt domain, a display defect due to an afterimage and a reduction in contrast are caused.

The deterioration of the display quality due to such a reverse tilt domain occurs in a substantially wide area even if the display pixel is miniaturized. Therefore, it is more remarkable as the display pixel is miniaturized. Become.

As a method of preventing the deterioration of display quality due to such a reverse tilt domain, for example, Japanese Patent Laid-Open No. 3-118820 discloses a technique of removing a part of a counter electrode so as to prevent a lateral electric field. It is disclosed. But,
Such patterning of the counter electrode makes positioning of the matrix array substrate and the counter electrode substrate difficult, and is not a preferable method in manufacturing. In addition, JP-A-3-2439
In No. 34, the distance between the pixel electrode and the video signal line is made equal to or larger than the thickness of the liquid crystal layer to reduce the electric field in the lateral direction,
As a result, a technique for preventing the occurrence of reverse tilt / domain is disclosed. However, increasing the distance between the pixel electrode and the video signal line not only causes a reduction in the aperture ratio, but also cannot substantially eliminate the influence of the electric field in the lateral direction, which is not an effective method.

The present invention has been made in response to the above-mentioned technical problem, and sufficiently reduces the occurrence of reverse tilt domains without inviting a reduction in the aperture ratio, which results in a display defect and a reduction in contrast. It is an object of the present invention to provide a liquid crystal display device that can be effectively prevented.

[0013]

According to a first aspect of the present invention, a plurality of video signal lines and scanning lines arranged in a matrix and a plurality of pixel potentials arranged substantially in parallel with the scanning lines. A matrix array substrate having a storage capacitor line, a pixel electrode arranged on the video signal line and the scanning line via a switch element on the substrate, and a counter electrode arranged so as to face the pixel electrode. A counter substrate, and a liquid crystal display device including a liquid crystal layer disposed between the matrix array substrate and the counter substrate, wherein one pixel electrode,
A region in which a distance between the scanning line and the pixel potential holding capacitance line is 20 μm or less is provided between the one pixel electrode and another pixel electrode adjacent to each other along the extension direction of the scanning line. There is.

According to a second aspect of the invention, the region of the first aspect is arranged corresponding to one scanning line and one pixel electrode arranged on the one scanning line via a switch element. And the pixel potential holding capacitance line. The invention described in claim 3 is characterized in that the potential difference between the scanning line and the pixel potential holding capacitance line according to claim 1 is 0.5 V or more.

[0015]

[Function] According to the study by the present inventors, the reverse tilt /
It was found that the domain is affected by the alignment state of liquid crystal molecules and the lateral electric field generated between the pixel electrodes, and is mainly generated by the following action.

As shown in FIG. 5, the liquid crystal molecules (LC) are aligned between the electrode substrates (SUB) with a predetermined pretilt angle (θ1). For this liquid crystal molecule (LC),
An angle larger than the pretilt angle (θ1) and smaller than [pretilt angle (θ1) + 90 °], for example, the angle (θ
When a gradient electric field A indicated by a dotted line A having E) is applied, the liquid crystal molecules are aligned from the direction of the gradient electric field A.

However, [pretilt angle (θ1) +90
[Pretilt angle (θ1) +180
When a tilted electric field having a smaller angle than [°] is applied to the liquid crystal molecules (LC), the liquid crystal molecules (LC) follow the direction of the tilted electric field B opposite to the pretilt direction. As a result, the liquid crystal molecules (LC) are aligned, so that a reverse tilt domain is generated.

Further, according to the experiments by the present inventors,
The reverse tilt domain has a positive correlation between the generated amount and the lateral electric field strength, and depends on the polar angle of the lateral electric field.
It has been found that the higher the pretilt angle is, the more it is reduced.

According to the liquid crystal display device of the present invention, as described above, the scanning line and the pixel are provided between the one pixel electrode and another pixel electrode adjacent to the one pixel electrode along the extension direction of the scanning line. A region with a distance of 20 μm or less from the potential holding capacitance line is provided. Therefore, an electric field that crosses the lateral electric field from the pixel electrode is generated between the scanning line and the pixel potential holding capacitance line, which can effectively prevent the reverse tilt domain near the pixel electrode.

In particular, by forming the above-mentioned region with one scanning line and one pixel potential holding capacitance line arranged corresponding to one pixel electrode arranged on the one scanning line via the switch element, the opening is formed. It can be effectively achieved without incurring a decrease in the rate.

Incidentally, if the potential difference between the scanning line and the pixel potential holding capacitance line is 0.5 V or more, the occurrence of reverse tilt domains can be reduced, and particularly when it exceeds 5 V, it can be sufficiently prevented. The display quality can be improved.

[0022]

EXAMPLE Hereinafter, a liquid crystal display device according to an example of the present invention (50
1) will be described in detail with reference to the drawings. This liquid crystal display device (501) is used for a projection type high-definition TV and has a display area (281) having a diagonal of 3.3 inches as shown in FIG.

As shown in FIG. 3, this liquid crystal display device (501) has a matrix array substrate (101) and a counter substrate (301) with alignment films (333) and (271) made of polyimide interposed therebetween.
An N-type liquid crystal layer (401) is held and configured.

As shown in FIG. 1, a matrix array substrate
(101) is a video signal line driving circuit (291), a scanning line driving circuit (293) and a counter electrode driving circuit (in the periphery of the display area (281) on a transparent quartz substrate (103) (see FIG. 3). 295) are integrated. In the display area (281), m video signal lines Xi (i = 1,2, ..., m) connected to the video signal line drive circuit (291) and arranged substantially in parallel with each other at a predetermined interval. ,
The n scanning lines Yj (j = 1, 2, ..., N) (113a, which are connected to the scanning line driving circuit and are arranged in close proximity to each other as a set, and are arranged substantially orthogonal to the video signal line (111). ) And (113b) are arranged.

A TFT (121a) is arranged at the intersection of one scanning line (113a) and a video signal line (111).
1st consisting of ITO (Indium Tin Oxide) via 21a)
The pixel electrode (151a) of is arranged. In addition, the TFT (12) is also provided at the intersection of the other scanning line (113b) and the video signal line (111).
1b) is arranged, and the second pixel electrode (151b) made of ITO is arranged through the TFT (121b). A pair of adjacent TFTs (121a) and (121b) is connected to the video signal line (111) through a commonly formed contact hole (112).

Further, the pixel electrodes adjacent to each other along the video signal line (111) without passing through the pair of scanning lines (113a) and (113b).
Between (151a) and (151b), a pixel potential holding capacitance line (211) connected to a predetermined potential is commonly parallel to the scanning line (113) with respect to each pixel electrode (151a) and (151b). It is located in.

As shown in FIG. 3, the counter substrate (301) comprises a transparent quartz substrate (303) and a counter electrode (321) made of ITO on a transparent quartz substrate (303).
An alignment film (331) arranged on this is provided. Although not shown, a stripe-shaped light shielding layer made of a metal such as chromium (Cr) extending substantially parallel to the scanning lines (113a) and (113b) constitutes a set of scanning lines (113a) and (113b) and a TFT (121).
It is arranged so that the above (a) and (121b) are shielded from light.

The liquid crystal display device (5
Each display pixel of (01) will be described in more detail. Figure 2
As shown in FIG. 3 and FIG. 3, the first polycrystalline silicon layer (131) is arranged on the quartz substrate (103) and the scanning lines (113a), (11)
The region intersecting with 3b) acts as the channel region. The first polycrystalline silicon layer (131) has pixel electrodes (151a), (151).
It has extended regions (133a), (133b) for forming the pixel potential holding capacitance (Cs) while being guided to the contact holes (152a), (152b) connected to b).

A first insulating film (141) functioning as a gate insulating film and a pixel potential holding capacitor insulating film is arranged on the first polycrystalline silicon layer (131). Further, on the first insulating film (141), the scanning lines (113a) and (113b) which also serve as the gate electrodes of the TFTs (121a) and (121b) and the pixel potential holding capacitance line (211) are formed on the second insulating film (141). It has a two-layer structure of a polycrystalline silicon layer and a metal silicide. In this embodiment, the extension regions (133a), (13a) of the first polycrystalline silicon layer (131) are mainly used.
3b) and the pixel potential holding capacitance line (211) mainly form the pixel potential holding capacitance (Cs), and each pixel electrode (151a), (15)
The pixel potential holding capacitance (Cs) is also formed between 1b) and the pixel potential holding capacitance line (21 1). One scanning line (113a)
The area (231a) between the scanning line (113a) and one pixel potential holding capacitance line (211) arranged corresponding to the pixel electrode (151a) arranged via the TFT (121a) is 10 It is composed of micron. Also, one scanning line (113b), one scanning line (113b)
Similarly, the area (231b) between the one pixel potential holding capacitance line (211) arranged corresponding to the one pixel electrode (151b) arranged via the TFT (121b) is also 10 μm. It is configured.

Then, a video signal line (111) is arranged on this via a second insulating film (161). In addition, the pixel electrodes (151a) and (151b) are formed on top of this via the third insulating film (171).
Are arranged.

As described above, according to the liquid crystal display device (501) of this embodiment, one scanning line (113a) and one scanning line (113a)
A region (231a) constituted by one pixel potential holding capacitor line (211) arranged corresponding to one pixel electrode (151a) connected to the TFT (121a) maintains a 10 micron interval. , One scanning line (113b) and one scanning line (113b) TFT (1
The area (231b) formed by the one-pixel potential holding capacitance line (211) arranged corresponding to the one-pixel electrode (151b) connected via 21b) maintains the interval of 10 microns. , Pixel electrodes (151a), (151b) for the video signal line (111)
The video signal line (111) and each pixel electrode
An electric field perpendicular to the lateral electric field generated between (151a) and (151b) is generated by the scanning lines (113a) and (113b) and the pixel potential holding capacitance line (2
11), which relaxes the lateral electric field,
Also, in combination with the shield effect, the occurrence of reverse tilt domains could be reduced.

The reverse tilt domain is particularly problematic in a transitional state in which the display state is changed from white to black, and the reverse tilted main is gradually reduced at intervals of several seconds so that it appears as an afterimage. . However,
According to this liquid crystal display device (501), the reverse tilt length in the transient state can be suppressed to 1 micron or less by the above configuration.

By the way, when the regions (231a) and (231b) between the scanning lines (113a) and (113b) and the pixel potential holding capacitance line (211) were made different, an experiment was carried out. It was found that the above effect was remarkable.

Further, in the above-mentioned structure, the scanning line (113
By setting the potential difference between a) and (113b) and the pixel potential holding capacitance line (211) to 0.5 V or more in effective value, the reverse tilt length can be expected to decrease, especially when it exceeds 5 V and is large. It can be understood from FIG. 5 that the reverse tilt length can be surely suppressed to 1 micron or less. The scanning lines (113a), (113
The potential difference between b) and the pixel potential holding capacitance line (211) is based on the non-selection period of the scanning lines (113a) and (113b).

Further, according to the liquid crystal display device (501) of this embodiment, the video signal line (111) and the pair of pixel electrodes (151a) or pixel electrodes (adjacently arranged on both sides of the video signal line (111) are arranged. 151b) As shown in FIGS. 2 and 3, the pixel potential holding capacitance line (211) is arranged via the second and third insulating films (161) and (171). Therefore, the video signal line (1
11) through a pair of pixel electrodes (151a) or pixel electrodes (1
Even if 51b) are arranged sufficiently close to each other, the pixel potential holding capacitance line (to suppress the horizontal electric field generated between the video signal line (111) and the pixel electrode (151a) or the pixel electrode (151b) ( 211)
Acts as a shield layer. This allows the video signal line
Generation of the rebus tilt domain due to the lateral electric field between (111) and each pixel electrode (151a), (151b) is suppressed,
In addition, it is possible to reduce the coupling capacitance between the video signal line (111) and each pixel electrode (151a), (151b) and to secure a good display image.

Further, as can be seen from FIG. 3, the pixel electrode
Set the position of (151a) to the counter electrode (321) rather than the video signal line (111).
By arranging them in close proximity to each other, the inclination of the alignment plane between the pixel electrodes (151a) arranged via the video signal line (111) is relaxed, and the pretilt angle of the liquid crystal molecules on the alignment plane is increased. Can be operated.

As a result, the video signal line (111) and the pixel electrode
It is possible to reduce the influence exerted on the liquid crystal molecules by the lateral electric field generated between (151a). According to the liquid crystal display device (501) of this embodiment, the video signal line (1
Since the pixel electrodes (151a) and (151b) can be arranged sufficiently close to (11), the reverse tilt length can be secured while maintaining the aperture ratio of 38% while having a fine display pixel shape such as a 40 micron pitch. Could be suppressed to 1 micron or less.

[0038]

According to the liquid crystal display device of the present invention, a scanning line and a storage capacitor line are formed between one pixel electrode and another pixel electrode adjacent to the one pixel electrode along the extension direction of the scanning line. Since it is configured with areas with a spacing of 20 microns or less,
Even if the pixel electrode is placed sufficiently close to the video signal line, the reverse tilt domain can be effectively reduced, and as a result, both a fine pitch and a high aperture ratio can be achieved and high display quality can be achieved. Can be secured.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an active matrix type liquid crystal display device according to an embodiment of the present invention.

2 is a partial schematic front view of the matrix array substrate in FIG.

FIG. 3 is a schematic cross-sectional view of the liquid crystal display device taken along the line AA ′ in FIG.

FIG. 4 is a diagram showing a principle of generation of a reverse tilt domain.

FIG. 5 is a diagram showing voltage dependence of edge reverse length.

FIG. 6 is a partial schematic front view of a matrix array substrate of a conventional active matrix type liquid crystal display device.

[Explanation of symbols]

 (111) ... video signal lines (113a), (113b) ... scanning lines (121a) (121b) ... TFTs (151a), (151b) ... pixel electrodes (211) ... pixel potential holding capacitance lines (231a), (231b) ) Area (501) Liquid crystal display device

Claims (3)

[Claims] 1. A plurality of video signal lines and scanning lines arranged in a matrix, a plurality of pixel potential holding capacitance lines arranged substantially parallel to the scanning lines, the video signal lines and the scanning lines. And a matrix array substrate having a pixel electrode disposed on the substrate via a switch element, a counter substrate having a counter electrode disposed so as to face the pixel electrode, the matrix array substrate and the counter substrate. In a liquid crystal display device including a liquid crystal layer disposed between a substrate, one pixel electrode, and between the one pixel electrode and another pixel electrode adjacent along the extension direction of the scanning line, A liquid crystal display device comprising a region in which a distance between the scanning line and the pixel potential holding capacitance line is 20 μm or less. 2. The region according to claim 1, wherein one pixel line holding capacitor is arranged corresponding to one scanning line and one pixel electrode arranged on the one scanning line via the switch element. A liquid crystal display device characterized by being composed of lines. 3. A liquid crystal display device according to claim 1, wherein a potential difference between the scanning line and the pixel potential holding capacitance line is 0.5 V or more.