JP2000098410A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which uses vertical orientation liquid crystal of negative permittivity anisotropy by a horizontal electric field system, and which uses a rubbing-less system of super wide visual field, high contrast, and high speed response in which a visual field angle is more improved than an orientation bi-sected type. SOLUTION: In a liquid crystal display device provided with a first substrate 1 in which one or more common electrodes 23 being formed in parallel with a pixel electrode keeping a fixed distance are arranged in pixels having a switching element 20 coupled with at least one or more pixel electrodes 24, a second substrate 2 opposed to the substrate 1 holding a gap, vertical orientation films 25, 26 provided on an electrode surface of the substrate 2, and a nematic liquid crystal layer 27 which is almost vertically oriented between substrates and in which permittivity anisotrophy is negative, the pixel electrodes 24 and the common electrode 24 are formed by being bent into almost right angle at least one time or more while holding parallel in pixels and arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device driven by a lateral electric field, which has high productivity and has a wide field of view and fast response.

[0002]

2. Description of the Related Art In a conventional active matrix type liquid crystal display device, a transparent electrode is used as an electrode for driving a liquid crystal layer, at least one of which is formed on two substrate surfaces and opposed to each other. This is operated by making the direction of the electric field applied to the liquid crystal substantially perpendicular to the substrate surface, and twisted nematic (TN) using a nematic liquid crystal having a positive dielectric anisotropy that has been conventionally aligned by rubbing. It has been used in many liquid crystal display devices such as notebook personal computers.

[0003] However, its viewing angle characteristics are narrow, its response is slow, and the rubbing process has the drawbacks of reduced yield.

On the other hand, as a method in which the direction of the electric field applied to the liquid crystal is made substantially parallel to the interface between the substrates, switching (I) by in-plane horizontal operation of liquid crystal molecules by a lateral electric field driving method is employed.
Japanese Patent Application Laid-Open No. 7-36058, which uses the PS method, has been proposed and partially put into practical use.

[0005]

The viewing angle characteristic has a characteristic close to 160 degrees vertically, horizontally and horizontally, but the response speed is slower than that of the TN mode, and defects such as display unevenness appear because alignment processing is generally performed by rubbing. Cheap. Further, due to the different orientation around the spacer for maintaining the gap, light leakage occurs, causing a decrease in contrast.

[0006] In addition, a literature SI in which an alignment bisected region is formed by using a vertical alignment liquid crystal having a negative dielectric anisotropy by driving a lateral electric field.
The DDVA system based on D'98 and P-91 has been proposed. As shown in the plan view of the conventional configuration in FIG. 1, the orientation can be divided into two, the field of view is wider, the response is faster, and the rubbing-less process is used. However, orientation 2
Because of the division, the viewing angle is 120 degrees vertically and horizontally, and the viewing angle characteristics are still insufficient.

The present invention is directed to a liquid crystal display device using a vertically aligned liquid crystal having a negative dielectric anisotropy by the above-mentioned lateral electric field method, and has a super wide field of view, a high contrast, and a high speed which has a further improved viewing angle than the above-mentioned two-divided type. An object of the present invention is to provide a rubbingless liquid crystal display device having a response.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is to provide a pixel having a switching element connected to at least one or more pixel electrodes at a predetermined distance from the pixel electrodes. A first substrate on which at least one common electrode formed in parallel is disposed, a second substrate opposed to the first substrate with a gap therebetween, and a vertical alignment film provided on the substrate and the electrode surface, respectively And a liquid crystal display device having a nematic liquid crystal layer having a negative dielectric anisotropy that is substantially vertically aligned between the substrates, wherein the pixel electrode and the common electrode are held at least once while maintaining parallelism in the pixel. As described above, the means is formed by being bent at substantially a right angle and arranged.

[0009] More specifically, the present invention is a means comprising an insulating layer interposed between the pixel electrode and the common electrode. Further, a polarizing plate having a polarization axis direction substantially 45 degrees with respect to the pixel electrode and the common electrode direction and at least a negative biaxial retardation film are disposed outside the opposed substrate. is there.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 2 is a conceptual cross-sectional view of a liquid crystal display device according to a first embodiment of the present invention.
FIG.

FIG. 2 is a conceptual diagram of the configuration of the liquid crystal display device in an operating state when a voltage is applied, and does not show a non-operating state. In FIG. 2, a pair of transparent glass substrates 1 and 2 facing each other are aligned with polarizing plates 21 and 22 and biaxial film retarders 211 and 212 having a negative refractive index phase difference in a predetermined axial direction. And place it outside. The substrate 1
On the inner surface, in the drawing, a representative example is shown in one pixel 200, which is described as being 10 μm bent once at a substantially right angle in the pixel.
A common electrode 23 made of a single piece of Al metal or the like is formed.

Next, in order to reduce the number of masks in the thin film process, the insulating layer 241 on the switching element is used as it is to form the insulating layer 241 into the common electrode 2.
3 is formed. Next, on the insulating layer 241,
10 μm bent once at a right angle within the same pixel 200
A pixel electrode 24 made of Al metal or the like having a width
Are formed and arranged while maintaining a spacing of about 30 μm, and a switching element 20 composed of a TFT is formed and arranged in connection therewith.

The transparent glass substrate 2 is spaced apart from the substrate 1 formed as described above by a spacer of about 3.5 μm.
Are arranged facing each other. Polyimide-based vertical alignment films 25 and 26 are applied and baked on the inner surfaces of the substrates 1 and 2 and on the electrode surfaces, respectively. A nematic liquid crystal having a negative dielectric anisotropy, for example, MJ-951152 manufactured by Merck, is injected between the substrates 1 and 2, and a liquid crystal layer 27 oriented substantially perpendicular to the substrate surface is inserted and arranged. The polarization axes of the polarizing plates 21 and 22 are orthogonal to each other so as to make an angle of approximately 45 degrees with the pixel electrode line and the common electrode line formed side by side, that is, arranged in the X and Y axis directions in the figure. . The X and Y axis directions in the drawing indicate the left and right viewing angle directions and the up and down viewing angle directions of the display device. A driving circuit (not shown) is connected to the switching element 20, the common electrode 23, and the like, and a driving voltage is applied to the liquid crystal panel thus formed. At a driving voltage of 2.5 V, the liquid crystal molecules 29 are almost still in a vertically aligned state, indicating an off state in a non-light transmitting state. Due to the vertical alignment, there was almost no light leakage near the spacer, so that the light characteristics were extremely black. Next, when a drive voltage higher than about 2.5 V is applied, a strong horizontal electric field generated between the pixel electrode 24 and the common electrode 23 provided on the same substrate causes a strong horizontal electric field in FIG. The liquid crystal molecules 29 vertically aligned between the substrates except for the liquid crystal molecules 28 and 28 ′ near the substrate interface have the pixel electrode 24 and the common electrode 2.
With the intermediate line of No. 3 as a boundary, the liquid crystal molecules were obliquely oriented in directions opposite to each other to form different alignment regions A and B, indicating a light transmitting state of an intermediate state. Similarly, the pixel electrode 24 and the common electrode 2
In the opposite direction at right angles to No. 3, different orientation regions C and D were also formed. In one pixel 200, alignment regions A, B, C,
D can be formed automatically by a simple method of merely changing the shape of the electrode without performing an alignment process such as rubbing or optical alignment on the alignment quadrants having different viewing angle characteristics from each other by exactly 90 degrees. . When a driving voltage of about 8.5 V is applied, the light transmission is almost saturated, indicating a complete ON state. After measuring the characteristics of the liquid crystal display device thus manufactured, FIG.
With a very wide viewing angle characteristic of 170 degrees up and down in the Y direction and 170 degrees left and right in the X direction, there is almost no black and white inversion area when viewed from any direction, and there is little change in hue in the oblique direction and good image quality is obtained. Was done. The front contrast in the normal direction of the substrate was about 300, and a very high contrast was obtained.
The response speed was about 25 ms, which was a high-speed response. Since there was no process such as rubbing, there was almost no alignment defect, and the production yield was improved compared to the conventional case.

In the conventional DDVA method, the viewing angle characteristics were low only by forming the two-divided alignment regions. However, a liquid crystal display having an extremely wide viewing angle characteristic can be automatically formed by the extremely simple method according to the present invention. The device was obtained. Further, the response was fast, the color change in the oblique direction was small, and there was no rubbing process.

In the above description, the pixel electrode and the common electrode are arranged in parallel in the pixel and bent and formed once at a right angle. However, as shown in a plan view of FIG.

In the above description, one pixel electrode is provided in one pixel.
Although two common electrodes and two common electrodes are formed to generate a horizontal electric field, a plurality of common electrodes may be further increased and arranged. However, if the value is excessively increased, the pixel aperture ratio decreases. Therefore, the pixel aperture ratio is determined in consideration of the balance between the above characteristics and the aperture ratio.

Although the pixel shape is formed along the bending of the electrode line in FIG. 2, it can also be formed in an ordinary rectangular pixel shape by devising the electrode shape. The position of the switching element can also be arranged at the optimum position.

In the above description, one of the substrates has no electrode, but a transparent electrode may be provided for preventing static electricity.

Further, the electrode width, the spacing interval, the value of the substrate gap, the type of the liquid crystal material and the type of the alignment film material used above may be appropriately changed for optimization.

In the above description, a negative biaxial film retardation plate is inserted for optical compensation in order to improve the viewing angle characteristics in the vertical alignment mode. However, without this, the viewing angle characteristics are vertically asymmetric. The viewing angle characteristics are lower than the above viewing angle characteristics, and the viewing angle characteristics and contrast can be further improved by inserting another uniaxial film phase difference plate or the like.

Due to the insulating layer between the electrodes, a short circuit between the electrodes,
Defects such as alignment unevenness were reduced, and a liquid crystal display device having a higher yield and a lower process cost was obtained.

In the present invention, a reflective liquid crystal display device can be obtained by using a reflective substrate as one of the substrates. Further, the present invention provides a TFT having a switching element,
The present invention can be similarly applied to any active matrix type liquid crystal display device such as MIM.

[0024]

As described above, according to the present invention, the conventional I
The disadvantages of the liquid crystal display devices of the PS system and the DDVA system are improved, and the alignment quadrant can be automatically formed by an extremely simple method. A liquid crystal display device having a fast response can be obtained, and a liquid crystal display device with a high yield can be obtained because processes such as rubbing treatment and optical alignment treatment are not required at all.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a configuration of a conventional liquid crystal display device.

FIG. 2 is a configuration conceptual diagram of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 3 is a more specific configuration conceptual diagram of the liquid crystal display device according to the first embodiment of the present invention.

[Explanation of symbols]

 1, 2 Substrate A, B, C, D Alignment region 28, 28 ', 29 Liquid crystal molecule 21, 22 Polarizer 23 Common electrode 24 Pixel electrode 25, 26 Alignment film 27 Liquid crystal layer 20 Switching element 211, 212 Phase difference plate P1 , P2 Polarizing plate polarization axis

Claims (3)

[Claims] A pixel having a switching element connected to at least one pixel electrode, at least one common electrode formed parallel to the pixel electrode at a fixed distance from the pixel electrode. A first substrate, a second substrate facing the first substrate with a gap therebetween, a vertical alignment film provided on the substrate and the electrode surface, and a dielectric anisotropy substantially vertically aligned between the substrates. A liquid crystal display device comprising a negative nematic liquid crystal layer, wherein the pixel electrode and the common electrode are formed and arranged at least once at substantially right angles while maintaining parallelism within the pixel. . 2. The liquid crystal display device according to claim 1, wherein an insulating layer is interposed between said pixel electrode and said common electrode. 3. A polarizing plate having a polarization axis direction substantially 45 degrees with respect to the pixel electrode and the common electrode direction and at least a negative biaxial retardation film are disposed outside the opposing substrate. Liquid crystal display device.