JPH08146425A - Liquid crystal display element - Google Patents

Abstract

PURPOSE: To provide a liquid crystal display element having excellent display performance. CONSTITUTION: This liquid crystal display element has an active element substrate 14, a counter substrate 17 arranged to face this active element substrate 14 and a liquid crystal compsn. 21 held between the active element substrate 14 and the counter substrate 17. The main surfaces on one side of the active element substrate 14 and the counter substrate 17 are respectively subjected to the orientation treatments in such a manner that the axes of orientation thereof attain approximately 90 deg. with each other and that prescribed pretilt angles are imparted on the liquid crystal molecules. The liquid crystal display element has light shielding parts 19 for shielding the light of the pixel electrodes of regions where the transverse electric fields between the pixel electrodes 12 and wirings 13 counter the pretilt of the liquid crystal molecules more than the light in the other regions.

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, and more particularly to a black matrix and array structure of an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art As a display element using liquid crystal, an active matrix type display element having a large capacity and a high density directed to a television display, a graphic display or the like has been developed and put into practical use. In such a display element, a semiconductor switch is used as a means for driving and controlling each pixel so that high-contrast display without crosstalk can be performed. As the semiconductor switch, a thin film transistor (TFT) formed on a transparent insulating substrate, a MIM element, or the like is usually used because it can be used for a transmissive display and can be easily enlarged.

In general, as an active matrix type liquid crystal display element, two substrates each subjected to a uniaxial alignment treatment by rubbing have their alignment directions mutually.
Twisted nematic (TN) type devices, which are arranged parallel to each other so as to form 90 ° and in which a nematic type liquid crystal composition is sandwiched, are widely used.

In this type of liquid crystal display device, the liquid crystal molecules usually have a pretilt angle in relation to the rubbing direction, and in the case of alignment using polyimide, the pretilt angle is about 2 °.

[0005]

However, among the above-mentioned liquid crystal display elements, for example, the type using a TFT as a switching element for directly driving individual pixels has the following problems in display. That is, for example, when normally white display is performed (the transmission axes of the polarizing plates attached to the two substrates are made orthogonal to each other), the black level is not sufficiently lowered, and the contrast is lowered. In addition, even when normally black display (the transmission axes of the polarizing plates attached to the two substrates are made parallel to each other),
The appearance of the display was different depending on the viewing angle.

The present invention has been made in view of such conventional circumstances, and an object thereof is to provide a liquid crystal display element having excellent display performance.

[0007]

According to the present invention, a plurality of active elements and pixel electrodes connected to the active elements are arranged on one main surface, and wirings are provided around the active elements and the pixel electrodes. A liquid crystal molecule sandwiched between the active element substrate and the counter substrate, the counter substrate having a common electrode on one main surface, which is arranged to face the active element substrate, A liquid crystal display device having a liquid crystal composition, and having an alignment axis of about 90 ° on one main surface of an active device substrate and a counter substrate and being subjected to an alignment treatment so as to impart a predetermined pretilt to liquid crystal molecules. The present invention is characterized by including a light-shielding portion that shields the pixel electrode in a region where the lateral electric field between the pixel electrode and the wiring opposes the pretilt of the liquid crystal molecules more than other regions.

Further, as in the present invention, a plurality of active elements and pixel electrodes connected to the active elements are arranged on one main surface, and wirings are formed around the active elements and the pixel electrodes. A liquid crystal composition containing an active element substrate, a counter substrate having a common electrode arranged to face the active element substrate on one main surface, and liquid crystal molecules sandwiched between the active element substrate and the counter substrate. Related to a liquid crystal display element having an active element substrate and a counter substrate with alignment axes of approximately 90 ° on each other and having been subjected to an alignment treatment so as to impart a predetermined pretilt to liquid crystal molecules. In addition, the distance between the pixel electrode and the wiring in the region where the lateral electric field between the pixel electrode and the wiring opposes the pretilt of the liquid crystal molecules is larger than the distance between the wiring and the pixel electrode in other regions. It is characterized by being set.

The present invention is the liquid crystal display device according to claim 2, characterized in that the distance between the wiring and the pixel electrode in the region is at least 15 μm or more.

[0010]

[Function] In the active matrix type liquid crystal display device,
Matrix-like wirings are provided on the active element substrate in the vertical and horizontal directions.
A pixel electrode made of O (Indium Tin Oxide) is formed. Then, a strong electric field is generated between the matrix-shaped wiring and the pixel electrode, which disturbs the alignment of the liquid crystal molecules. The phenomenon related to the misalignment of the liquid crystal molecules is called “tilt reverse at the pixel end”.

The present invention takes advantage of the fact that "tilt reverse at the pixel edge" appears only in a limited area,
To suppress the occurrence of "tilt reverse at the pixel edge" by devising the arrangement of the light shielding part within a range that does not affect other display performance, or by widening the interval between the matrix wiring and the pixel electrode. As a result, the influence of “tilt reverse at the pixel end” on the optical characteristics is reduced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the invention described in claim 1. In FIG. Among these, FIG. 1A shows a schematic sectional view of this embodiment. In FIG. 1A, a plurality of TFTs as active elements (11) and a pixel electrode (12) having a substantially rectangular shape connected to the TFTs are provided on a glass substrate (10). And active element (1
The active element substrate (14) is configured by forming a matrix-shaped wiring (13) including gate lines and signal lines around the pixel electrode (12) and the pixel electrode (12). On the other hand, a common electrode (16) made of, for example, ITO is formed on the entire surface of the glass substrate (15) to form a counter substrate (17). Then, on the main surface of the active element substrate (14) on which the active elements (11) and the like are formed, an alignment film (1) made of, for example, low temperature cure type polyimide (PI) is further formed.
8) is formed on the main surface of the counter substrate (17) on which the common electrode (16) is formed.
A light-shielding portion (19), which is a black matrix on the lattice of Cr (chrome) of m, and an alignment film (20) made of, for example, a low temperature cure type polymide, are sequentially formed on the entire surface so as to cover the light-shielding portion (19). Then, on the main surfaces of the active element substrate (14) and the counter substrate (17), respective alignment films (18) and (20) are formed.
By rubbing with a cloth or the like in a predetermined direction, the alignment treatment by rubbing such that the mutual alignment axes form approximately 90 ° is performed. Further, the active element substrate (14) and the counter substrate (17) are arranged such that their main surface sides face each other and their alignment axes form approximately 90 °, and they are made of, for example, a nematic liquid crystal. The liquid crystal composition (21) is sandwiched. Here, when the active element substrate (14) and the counter substrate (17) are combined, the rubbing directions of the alignment films (18) and (20) are set so that the good viewing angle direction is the front direction. Polarizing plates (22) and (23) are provided on the other principal surface sides of the active element substrate (14) and the counter substrate (17), respectively.
The active element substrate (14) and the counter substrate (1
7) Illumination is performed from the other main surface side on one side.

FIG. 1B is a schematic plan view showing a state in which the active element substrate (14) and the light shielding portion (19) are opposed to each other in this embodiment. As can be seen from FIG. 1B, in the active element substrate (14), the gate line (24) shown by the dotted line and the signal line (25) shown by the solid line are orthogonal to each other, which form the matrix-like wiring (13). The area surrounded by the matrix-shaped wiring (13) constitutes one pixel, and the active element (11) and the pixel electrode (12) are arranged therein. Here, the gate line (24) is, for example, a wiring for applying a gate scanning signal to the active element (11), while the signal line (25) is, for example, an image signal to the drain (or source) of the active element (11). Is a wiring for giving. And
The shading portion (19) not only overlaps with the active element (11) and the matrix-shaped wiring (13), but also the rubbing start side of the pixel electrode (12) in the rubbing direction (26) on the active element substrate (14) side. The corner portion (27) located at is also shaped so as to cover the corner portion (27). Specifically, the length from the L-shaped corner (28) of the signal line (25) to the end of the light shielding part (19) overlapping the pixel electrode (12) is 30 μm.

FIG. 2 is a diagram showing the mechanism of occurrence of a phenomenon called "tilt reverse at pixel end" (alignment irregularity of liquid crystal molecules) in this embodiment. This “tilt reverse at the pixel edge” is because an electric field is applied to the portion (30) on the active element substrate (14) corresponding to the rubbing start direction in the direction against the pretilt of the liquid crystal molecule (31) in FIG. It is thought to occur. More specifically, regarding this point, first, during operation, a liquid crystal molecule is generated by a lateral electric field (32) substantially parallel to the glass substrate (10) between the matrix wiring (13) and the pixel electrode (12). (31) is forced to have an orientation different from the original orientation. Then, distortion occurs here, and elastic energy concentrates. Further, due to the interaction between the liquid crystal molecules (31), the energy due to the strain may reach the inside of the pixel, so that a portion different from most of the arrangement in the pixel occurs. This phenomenon is "tilt reverse at the pixel end", and the boundary between this area and a normal area becomes a disclination line, and a bright line is generated.

FIG. 3 is a schematic plan view showing a region where the above-mentioned "tilt reverse at the pixel end portion" occurs in one pixel portion of this embodiment. As can be seen from the figure, the "tilt reverse at the pixel end" hardly spreads over the entire pixel electrode (12) and occurs only in a very limited region (33). This size depends on the material of the alignment film (18), but in the case of low temperature cure PI, the signal line (25)
It is about 20 μm from the corner (28) bent in the L-shape, and it is extremely rare that it extends beyond this. On the other hand, the "tilt reverse at the pixel end" region also depends on the distance between the end of the signal line (25) and the pixel electrode (12). This is natural considering that the "tilt reverse at the pixel end" is caused by the electric field between the signal line (25) and the pixel electrode (12). According to an experiment conducted by the present inventor, when the distance is 10 μm or more, the magnitude of “tilt reverse at the pixel end” becomes small.

The "tilt reverse at the pixel end" occurs because of the correlation between the alignment direction of the liquid crystal molecules (31) and the electric field between the matrix wiring (13) and the pixel electrode (12). , The rubbing direction on the active element substrate (14) side has a strong relation, and the rubbing direction on the pixel electrode (12) side increases. In this portion, the orientation direction of the liquid crystal molecules (31) and the electric field direction between the matrix-shaped wiring (13) and the pixel electrode (12) have the largest angle, that is, the strain of elastic energy becomes the largest. Because it is a part. Therefore,
In this embodiment, when the light shielding part (19) is arranged, it is largely provided in this direction. As a result, even if the signal voltage is changed from 1V to 5V corresponding to white to black, "tilt reverse at pixel end" is not observed in the display area at all, and the contrast ratio is 80: 1 to 100: 1. Within the range and a viewing angle of ± 45 °, we obtained extremely excellent display performance.

In this embodiment, the light shield (1
Although 9) is provided on the counter substrate (17) side, it goes without saying that the same applies if it is provided on the active element substrate (14) side via the insulating layer (40) as shown in FIG. Further, when the light shielding portion (19) is arranged, the edge of the portion of the light shielding portion (19) that covers the corner portion (27) does not decrease the aperture ratio so much as shown in FIG. It is desirable to make it substantially orthogonal to the rubbing direction (26) as shown in FIG.

FIG. 5 is a diagram showing an embodiment of the invention described in claim 2, and the portions corresponding to those in FIG. 1 are designated by the same reference numerals. In this embodiment, the shape of the pixel electrode (12) is different from that in the embodiment shown in FIG. This point will be described with reference to FIG. 5, which is a plan view showing a state where the active element substrate (14) and the light shielding part (19) face each other. That is, although the pixel electrode (12) has a substantially rectangular shape, it is located on the rubbing start side of the pixel electrode (12) in the rubbing direction (26) on the active element substrate (14) side in FIG. The part corresponding to the corner (27) has a chipped shape. As a result, specifically, the distance from the L-shaped corner (28) of the signal line (25) to the pixel electrode (12) with the above-mentioned corner dropped is 15
μm.

In this embodiment, instead of covering the area where "tilt reverse at the pixel end" occurs with the light-shielding portion (19) on the display, the corner (28) in the rubbing direction (26) is used.
The distance from to the pixel electrode (12) is 15 μm or more. That is, since the electric field applied by the signal line (25) and the pixel electrode (12) is reduced in the area where "tilt reverse at the pixel edge" has been generated conventionally, the occurrence of "tilt reverse at the pixel edge" occurs. Is suppressed to an extremely small value, and "tilt reverse at the pixel end" cannot be seen on the display as in the embodiment shown in FIG. In fact, in this embodiment, the "tilt reverse at the pixel edge" invades the display area within 1 μm, the display characteristics are not effectively degraded, and the excellent display with a wide viewing angle is provided with a contrast ratio of about 100: 1. I was able to get

Even if the size of the pixel electrode (12) itself is reduced as a whole, the angle (2
The distance from 8) to the pixel electrode (12) can be set to 15 μm or more, but in this case, the aperture ratio is drastically reduced, which is not practical. It goes without saying that it is desirable to have a shape in which only the portion corresponding to the portion (27) is dropped.

[0022]

According to the present invention, the "tilt reverse at the pixel end" region is overlapped by the light-shielding portion or the occurrence of the "tilt reverse at the pixel end" situation is suppressed to be small in display. It is possible to obtain an active matrix type liquid crystal display device having a high contrast ratio and a wide viewing angle, in which “tilt reverse” in the above is inconspicuous.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the invention described in claim 1.

FIG. 2 is a diagram for explaining a phenomenon called “tilt reverse at a pixel end”.

FIG. 3 is a diagram for explaining a region where “tilt reverse at a pixel end” occurs.

FIG. 4 is a diagram for explaining another embodiment of the invention according to claim 1;

FIG. 5 is a diagram for explaining an embodiment of the invention according to claim 2;

[Brief description of reference numerals]

 (11) …… Active element (12) …… Pixel electrode (13) …… Wiring (14) …… Active element substrate (16) …… Common electrode (17) …… Counter substrate (19) …… Shading part ( 26) …… Rubbing direction (27) …… Corner

Claims (3)

[Claims] 1. An active element substrate in which a plurality of active elements and pixel electrodes connected to the active elements are provided on one main surface, and wiring is formed around the active elements and the pixel electrodes. A counter substrate having a common electrode disposed on one main surface facing the active element substrate, and a liquid crystal composition containing liquid crystal molecules sandwiched between the active element substrate and the counter substrate. In the liquid crystal display element, wherein the active element substrate and the counter substrate have alignment axes of approximately 90 ° on one main surface, and each of which is subjected to an alignment treatment so as to impart a predetermined pretilt to the liquid crystal molecules, A liquid crystal display device, comprising: a light-shielding portion that shields the pixel electrode in a region where a lateral electric field between the pixel electrode and the wiring opposes the pretilt of the liquid crystal molecule more than in other regions. 2. An active element substrate in which a plurality of active elements and pixel electrodes connected to the active elements are respectively disposed on one main surface, and wiring is formed around the active elements and the pixel electrodes. A counter substrate having a common electrode disposed on one main surface facing the active element substrate, and a liquid crystal composition containing liquid crystal molecules sandwiched between the active element substrate and the counter substrate. In the liquid crystal display element, wherein the active element substrate and the counter substrate have alignment axes of approximately 90 ° on one main surface, and each of which is subjected to an alignment treatment so as to impart a predetermined pretilt to the liquid crystal molecules, A distance between the wiring and the pixel electrode in a region where a lateral electric field between the pixel electrode and the wiring opposes the pretilt of the liquid crystal molecule is a distance between the wiring and the pixel electrode in another region. Is set larger than A liquid crystal display device characterized by 3. The liquid crystal display element according to claim 2, wherein the distance between the wiring and the pixel electrode in the region is at least 15 μm or more.