JPH06265905A - Liquid crystal display element - Google Patents

Abstract

(57) [Summary] [Structure] Two substrates 11, 1 having electrodes 13 to 16
The present invention relates to a liquid crystal display device in which a liquid crystal layer 23 made of a nematic liquid crystal having a positive dielectric anisotropy and having a twisted molecular arrangement is sandwiched. This liquid crystal display device has at least two regions A and B having different molecular alignment states, and is characterized in that the twist angle (TW) of the liquid crystal is 90 ° <(TW) ≦ 110 °. [Effect] It is possible to realize a liquid crystal display device having an extremely wide viewing angle, which is easily stable and has almost no inversion phenomenon.

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 liquid crystal display device in which the contrast ratio and the viewing angle dependency during gradation display are controlled.

[0002]

2. Description of the Related Art In recent years, liquid crystal display elements, which have the great advantages of thinness, light weight, and low power consumption, have been actively used as display devices for personal OA equipment such as Japanese word processors and desktop personal computers. Liquid crystal display devices currently commercialized (hereinafter abbreviated as LCD)
Can be roughly classified into two types, TN type and STN type.

The STN type LCD has a sharply twisted molecular arrangement of, for example, 240 ° and has steep electro-optical characteristics. Therefore, even if there is no switching element for each pixel, a simple matrix-like electrode structure has a large capacity. Is displayed.

On the other hand, the TN type LCD has a molecular arrangement twisted by 90 ° and exhibits a high contrast ratio at a low voltage, so that it is widely used not only for displays of watches and calculators but also for displays of liquid crystal televisions and OA equipment. Has been. Especially for LCD TVs and OA equipment displays,
Since large-capacity display and high-speed operation are required, an active matrix system in which a switching element such as a thin film transistor (TFT) or a diode is formed in a portion corresponding to each display pixel is applied (TFT-LCD).

In recent years, this TFT-LCD performs gradation display and, in combination with three color filters,
It realizes multicolor display (for example, 512 colors for 8 gradations).
These gradations are displayed by changing the applied voltage. Here, an example of the applied voltage-transmittance characteristic of the TN method is shown in FIG. As is apparent from the figure, the curve (f ₁ ) has a monotonous decreasing curve in the front, but the curve (f ₂ ) when observed obliquely has an extreme value.
Therefore, in the TN method, when the driving voltage for performing gradation display is determined based on the applied voltage-transmittance characteristic on the front surface, when observed obliquely, display inversion, blackout, and blank areas occur. .

As described above, the liquid crystal display element has a viewing angle dependency in which a display color and a contrast ratio change depending on a viewing angle and an azimuth, and the display performance of a CRT (Cathode Ray Tube) cannot be completely exceeded. As a method of improving the viewing angle dependency of such a liquid crystal display element, a method of dividing one pixel into two regions having different molecular arrangements and canceling the extreme value of the VT curve has been recently proposed. KHYa
ng (1991, IDRC, p68) A method of providing two regions in which the rising directions of liquid crystal molecules are different by 180 ° within one pixel (TWO DOMAIN TN: TDTN), or different pretilt within one pixel Domain Divided TN (Y.
Koike, et.al 1992, SID, p798) and so on. However, this method of dividing the orientation into two parts also has some problems, and one of them is left-right inversion at the time of display. It is thought that this left-right reversal problem can be solved by dividing the orientation into four, but this method is difficult to manufacture in an LCD with high definition, that is, with a small pixel area. ) Often appears, which is not preferable in display characteristics.

[0007]

At present, the liquid crystal display element does not have a characteristic such as a CRT that shows a substantially uniform contrast ratio from any position, but the contrast ratio greatly changes depending on the viewing angle and orientation. That is, the liquid crystal display element has a viewing angle dependency. As a method of improving the viewing angle dependency, there is a method of dividing one pixel into two regions having different molecular arrangements, but there is a problem of left and right inversion at the time of display.

The present invention solves the above-mentioned inconvenience, and an object of the present invention is to realize a liquid crystal display element in which viewing angle characteristics such as inversion of display hardly occur even if the liquid crystal molecule arrangement is divided into only two. .

[0009]

Means for Solving the Problems As a means for solving the problems, the present invention comprises a twisted molecular arrangement having a helical axis in the substrate radial direction between two substrates having electrodes between two polarizing plates. In a liquid crystal display device in which a liquid crystal cell sandwiching a nematic liquid crystal having a positive dielectric anisotropy is arranged, the liquid crystal cell has two or more kinds of molecular alignment states, and the twist angle (TW) of the liquid crystal composition is 90. It is characterized in that ° <(TW) ≦ 110 °.

Further, it is characterized in that the liquid crystal molecule array constituting one pixel of the liquid crystal cell is composed of two or more kinds of arrays which are different when no voltage is applied.

Further, it is characterized in that two or more kinds of arrays have orientation processing directions opposite to each other by 180 ° on the same substrate.

[0012]

The present invention achieves the above object, and the principle and method for achieving the object will be described below.

FIG. 5 shows the transmittance-applied voltage (VT) characteristics of a liquid crystal display element in the alignment two-division method.
A characteristic obtained by combining two VT characteristics in which the difference in the azimuth angle of the LCD is 180 ° is shown. That is, in the vertical direction of the display screen, the VT characteristic (c) is a combination of the upward characteristic (a) and the downward characteristic (b) of the TN-LCD. In the left and right azimuth, a characteristic (c) obtained by combining the left azimuth characteristic (a) and the right azimuth characteristic (b) of the TN-LCD shown in FIG. 6 is shown. This measurement was performed using the measurement coordinate system shown in FIG. That is, with the normal direction of the rectangular display screen as the front, the inclination from the normal line z to the observation point is the incident angle θ, and the right azimuth of the screen long axis k is 0 ° as the reference, and angles such as on the screen and directly below the observation point are azimuth angles. φ
In the vertical VT characteristic (c) (FIG. 5), the extreme values seen in the characteristics (a) and (b) of the figure are eliminated. On the other hand, in the left-right direction, the characteristics a and b (FIG. 6) of the left azimuth and the right azimuth of the TN-LCD show almost the same characteristics, so the combined VT characteristics (c) (FIG. 6) shows the vertical azimuth. No significant improvement is seen, and inversion (a phenomenon in which the VT characteristic jumps to the upper right on the high voltage side) remains.

Therefore, it is effective to reduce the left-right inversion of the conventional TN-LCD in order to improve the left-right azimuth inversion in the orientation division method.

80, 90, respectively in FIGS. 7, 8 and 9.
The transmittance-applied voltage characteristics of the characteristic a in the front (θ = 0 °) of the TN-LCD with a twist of 100 ° and 100 ° and the characteristic b in the case of the left azimuth (φ = 180 °, θ = 60 °) Show. (T in FIG.
As the twist angle increases from (W) = 80 ° to (TW) = 100 ° in FIG. 9, the VT characteristic curve in the front becomes steeper and the saturation voltage decreases, but the threshold voltage twists 80 °, twists 90 °, 100
The twist is almost the same and is about 2 (v). Also, the greater the twist angle, the greater the transmittance of the minimum value in the oblique direction (θ = 60 °) at the observation point, but the voltage that causes the minimum value is almost 80 ° twist, 90 ° twist, and 100 ° twist. The same is about 3.4 (v). In order to realize the gradation display of 8 gradations shown by level 1 to level 8 in FIGS. 7 to 9, a constant relative transmittance between 0 (v) and the saturation voltage in the front characteristic (a). 8 from level 1 to level 8
Determines one grayscale voltage level. The gradation voltage levels in the case of 80 ° twist, 90 ° twist, and 100 ° twist are as shown in FIGS. 7, 8 and 9. As shown in the figure, the level 8 voltages of 80 ° twist, 90 ° twist, and 100 ° twist are about 5 (v), about 4.2 (v), and about 3.5 (v), respectively, and the twist angle (TW) of the liquid crystal. Becomes larger, becomes smaller. The voltage that causes the extreme value is 3.4 (v), which is almost the same for all three characteristics.
It can be seen that the larger the twist angle, the less the inversion that occurs at the oblique viewing angle. However, the twist angle is 110
If it becomes larger than 0 °, coloring occurs, so it is appropriate that the twist angle of the liquid crystal be 110 ° or less. That is, the twist angle (T
It is necessary that W) is in the range of more than 90 ° and 110 ° or less.

As described above, according to the present invention, the orientation 2
It is possible to reduce the lateral inversion of the liquid crystal display element using the division method.

[0017]

EXAMPLES Examples of the present invention will be described in detail below.

(Embodiment 1) FIGS. 1 and 2 show an embodiment of the present invention. Two transparent substrates 11 and 12 made of glass
Then, the transparent electrodes 13, 14, 15, 16 made of ITO are formed in a two-letter pattern of C and D as codes to be displayed. The electrodes 13 and 14 of the upper substrate 11 are the electrodes 15 and 16 of the lower substrate 12.
The patterns of the characters C and D are made to overlap each other when they are opposed to each other. Figure 1
(B) The electrodes of the upper substrate 11 are arranged as seen from the back surface of the substrate.

Next, an alignment film of polyimide (AL-1051, made by Japan Synthetic Rubber) is formed on the entire surface of the electrodes 11 and 12 on which the electrodes are formed.
17 and 18 are formed by coating (see FIG. 2B).

Next, as shown in FIG. 1B, two regions, that is, a region A divided by boundary lines 19 and 20 passing through the center of the width of the character electrode and a remaining region B are formed, and the mask rubbing method is applied. Using the upper substrate 11, in the region A in the direction of the arrow 21A,
In the area B, rubbing is performed in the direction of arrow 21B, which is shifted by 180 °. Similarly, the lower substrate 12 is rubbed in the area A in the direction of arrow 22A and in the area B in the direction of arrow 22B shifted by 180 °.

The direction of these rubbing treatments is shown in FIG.
As shown in, when the upper and lower substrates 11 and 12 are opposed to each other at a constant interval, they intersect at 100 °. As a result, the liquid crystal is aligned so that the twist angle (TW) is 100 °. A nematic liquid crystal having a positive dielectric anisotropy (ZL1-229) having a twisted molecular arrangement having a helix axis between the substrates in the substrate normal direction with a gap between the upper and lower substrates of 4 μm.
3, a Merck Japan product) was sandwiched between layers 23 to prepare a liquid crystal display device of the present invention. When gradation display was performed by controlling the voltage applied to the electrodes 13 to 16 of this element,
Almost no inversion of the display occurred in any viewing direction.

(Embodiment 2) In this embodiment, a large number of pixel electrodes are used.
In a display element arranged in a matrix, a substrate having an electrode structure of one pixel as shown in FIG. 10 was prepared, and 110 μm × 330 μm electrodes were formed by the same method as in Example 1.
24 was divided into area A and area B. That is, liquid crystal molecular alignments 25A, 26A, 25 similar to the alignment regions A, B in FIG.
A liquid crystal display element was prepared in which each pixel was provided with two types of liquid crystal molecular arrangements (B, 26B (100 ° crossing)) (no voltage application, etc.). Transmissivity-viewing angle characteristics (T-θ), in which the change in θ of the horizontal direction (φ = 0 °, 180 °) is plotted on the horizontal axis and the change in the transmittance of light having a wavelength of 550 nm with respect to θ is plotted on the vertical axis. (Characteristics) was measured and the result was as shown in Fig. 11. Curves 1 to 8 in the figure are T- when voltages of 1 to 8 gradations are applied.
The θ characteristic is shown. The transmittance is a standard value. 1 in the figure
Even if the curve of ~ 8 changes θ, if the order of θ = 0 ° is maintained, ideal gradation display can be performed.

FIG. 12 shows T-.theta. Characteristics in the left-right direction of the conventional element having a twist angle of 90.degree. In FIG. The left-right inversion is clearly reduced in FIG. 11 compared to FIG. Further, when the twist angle became 115 °, coloring was observed.

[0024]

According to the present invention, it is possible to easily and stably realize an LCD having an extremely wide viewing angle in which the inversion phenomenon hardly occurs.

Although not described in the embodiments, it is needless to say that the present invention can obtain the same effect by using a switching element other than the TFT such as MIM.

[Brief description of drawings]

1A and 1B are explanatory views of an electrode pattern according to a first embodiment of the present invention, in which FIG. 1A is a plan view and FIG. 1B is an exploded view.

2A and 2B are views for explaining the molecular arrangement of Example 1 of the present invention, in which FIG. 2A is a plan view, and FIG. 2B is a cross-sectional view taken along the line I-I of FIG.

FIG. 3 is a diagram illustrating applied voltage-transmittance characteristics of a conventional TN-LCD.

FIG. 4 is a diagram illustrating a measurement coordinate system.

FIG. 5 is a graph showing an applied voltage-transmittance characteristic in an upper (lower) direction of a liquid crystal display device using an alignment two-division method for explaining the operation of the present invention.

FIG. 6 is a graph showing applied voltage-transmittance characteristics in the left (right) direction of a liquid crystal display device using an alignment two-division method for explaining the operation of the present invention.

FIG. 7 is a view for explaining the operation of the present invention, in which an 80 ° twist T
The applied voltage-transmissivity characteristic figure of (theta) = 0 degree and 60 degree in (phi) = 180 degree of N-LCD.

FIG. 8 is a view for explaining the operation of the present invention, in which a 90 ° twist T
The applied voltage-transmissivity characteristic figure of (theta) = 0 degree and 60 degree in (phi) = 180 degree of N-LCD.

FIG. 9 is a characteristic graph of applied voltage-transmittance at θ = 0 ° and 60 ° at φ = 180 ° of a 100 ° twisted TN-LCD for explaining the operation of the present invention.

FIG. 10 is a schematic diagram illustrating an electrode of Example 2 of the present invention.

FIG. 11 is a diagram illustrating T-θ characteristics in the horizontal direction according to the second embodiment of the present invention.

FIG. 12 is a diagram for explaining the T-θ characteristic of the conventional element in the lateral direction.

[Explanation of symbols]

 11 ... Upper substrate 12 ... Lower substrate 13, 14, 15, 16 ... Electrodes 17, 18 ... Alignment films A, B ... Alignment regions 21A, 21B, 22A, 22B ... Alignment treatment direction

Claims (3)

[Claims] 1. A liquid crystal display device comprising a liquid crystal layer made of nematic liquid crystal having a positive dielectric anisotropy, which is composed of twisted molecular arrangements, and sandwiched between two substrates having electrodes. A liquid crystal display device comprising regions having different molecular alignment states, wherein the twist angle (TW) of the liquid crystal is 90 ° <(TW) ≦ 110 °. 2. The liquid crystal display element according to claim 1, wherein the liquid crystal molecule array forming one pixel is composed of two or more kinds of arrays which are different when no voltage is applied. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device has at least two kinds of arrangements in which the alignment treatment directions on the same substrate are 180 ° opposite to each other.