JPH07248498A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device which has good display characteristics according to applications and has an improved effective visual field angle as well. CONSTITUTION:This liquid crystal display device has a liquid crystal panel packed with liquid crystals between substrates and is provided with plural twist oriented regions varying in the rising directions of liquid crystal molecules within the display plane. The rising directions of the liquid crystal molecules in each of the plural twist oriented regions are set at any of plural kinds of the specific directions. The threshold voltages of the device set at the same rising directions of the liquid crystal molecules among the twist oriented regions are set nearly at the same voltages. The threshold voltages of the twist oriented regions varying in the rising directions of the liquid crystal molecules are set at the values different from each other. In such a case, the value obtd. by subtracting the min. value from the max. value among the respective threshold voltages of the plural twist oriented regions is set in a range from a value exceeding 5mV to a value of <=100mV.

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 having an improved effective viewing angle and display characteristics.

[0002]

2. Description of the Related Art Liquid crystal display devices are widely used as display devices for wrist watches, calculators and the like because they are thin and can be driven at a low voltage. In particular, the twisted nematic (TN) type liquid crystal display system can have display characteristics similar to that of a CRT by incorporating an active switch element such as a TFT, and the STN type liquid crystal display system enables high duty multiplex driving. As a result, both came to be used for displays of word processors and personal computers.

However, the TN type liquid crystal display system has drawbacks that the viewing angle is narrow and the light utilization efficiency is low. In particular, the problem that the viewing angle is narrow is caused by the essential structure that the TN type liquid crystal display has a rising direction of liquid crystal molecules, and therefore there is no fundamental solution.

The influence of the existence of the rising direction of the liquid crystal molecules becomes particularly remarkable in the halftone display, and the rising direction of the liquid crystal molecules uniquely determines the direction in which the contrast decreases and the direction in which color inversion occurs. Therefore, as a method of displaying a halftone only with binary display that allows a relatively wide viewing angle, a method has been proposed in which a region within a pixel is finely divided and a writing area is controlled according to a halftone display state. There is. However, this method is not preferable in practice because a very small area such as a pixel must be divided into smaller areas, and the number of gray scales that can be displayed is determined according to the number of divisions.

On the other hand, attempts have been made to widen the viewing angle by changing the rising direction of the liquid crystal molecules on the alignment film within the pixel to mutually compensate for the difference in the viewing angle in the in-plane direction. However, in this method, the part where the contrast is lowered spreads, and on the contrary, it becomes difficult to see as a display for a word processor or a personal computer which often has a binary display. On the other hand, halftone display is the most difficult cause of grayscale inversion in television displays, and it is required to suppress grayscale inversion as much as possible.

[0006]

As described above, the conventional method applying the method of mutually compensating for the difference in the viewing angle in the in-plane direction by changing the rising direction of the liquid crystal molecules on the alignment film within the pixel. In the liquid crystal display device, mutual compensation was simply performed uniformly, so there was a certain improvement in the viewing angle, but the contrast deteriorated in the display for word processors and personal computers, which often display binary images, and There is a problem that display characteristics are impaired, such as gradation inversion being conspicuous on most television displays that display tones.

The present invention has been made in consideration of the above circumstances, and has good display characteristics according to the application and
An object of the present invention is to provide a liquid crystal display device having an improved effective viewing angle.

[0008]

A means for solving the problems in the present invention comprises a liquid crystal panel in which liquid crystals are filled between substrates, and a liquid crystal in which a plurality of twist alignment regions having different rising directions of liquid crystal molecules are provided in a display surface. In the display device,
A twist in which the rising direction of the liquid crystal molecules in each of the twist alignment regions is set to any one of a plurality of specific directions, and the rising directions of the liquid crystal molecules in the twist alignment regions are set to be the same. The threshold voltages of the alignment regions are set to substantially the same value, and the threshold voltages of the twist alignment regions in which the rising directions of the liquid crystal molecules are different are set to different values.

Further, preferably, a value obtained by subtracting the minimum value from the maximum value of the threshold voltage of each of the twist orientation regions is set within a range from a value exceeding 5 mV to a value less than 100 mV. It is effective. It should be noted that it is desirable to set the specific plural types of directions according to the application of the liquid crystal display device.

[0010]

As a result, depending on the application, a region having desired characteristics (high contrast, good halftone display) is located at a viewing angle that is often used. It is possible to evacuate a region with deteriorated characteristics to a small viewing angle. Therefore, there is a practical advantage that a good display characteristic according to the application can be obtained while securing a wide viewing angle which is an effect of the mutual compensation method.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the liquid crystal display device according to the embodiment of the present invention, the rising direction of the liquid crystal molecules on the alignment film is changed within the pixel to mutually compensate for the difference in the viewing angle in the in-plane direction and to widen the viewing angle. The liquid crystal molecules in each twist region and the magnitude relation of the threshold value between the twist alignment regions having different rise directions are used for the liquid crystal display device (personal application).・ Computer, TV, etc.).

That is, the conventional mutual compensation system is
A plurality of twist alignment regions (for example, two types) having different pretilt directions are provided in each pixel of the liquid crystal display device, and the twist alignment regions mutually compensate for the difference in display characteristics due to the in-plane visual field determined by the pretilt direction of the liquid crystal. This improves the viewing angle by suppressing the light-dark reversal in the halftone state.However, since the characteristics related to the display required for the liquid crystal display device differ depending on the application, a uniform average value is required as in the past. Only compensation would give a bad impression. Therefore, the present inventors focused on the fact that the required display characteristics differ depending on the application, and as a result of examining the method of setting the display characteristics according to the application in the above mutual compensation method, the rising direction of liquid crystal molecules was determined. It is possible to achieve desired display characteristics by setting a specific direction according to the application and by setting the magnitude relationship of the threshold voltage of the liquid crystal between the alignment regions according to the application. Do you get it. In order to change the threshold voltage, it is effective to change the pretilt angle or change the effective voltage. In this embodiment, a case where the threshold voltage is changed will be described.

First, a liquid crystal display device suitable for use as a display of a personal computer mainly using binary display will be specifically described. Figure 1
FIG. 4 is a top view of a part (4 pixels) of the display screen of the liquid crystal display device of the present embodiment. This display screen has a plurality of pixels 1
Composed of. Further, this liquid crystal display device adopts a TN type liquid crystal display system, and each pixel 1 is provided with two twist alignment regions 2 and 3 in which rising directions of liquid crystal molecules are different from each other by 180 degrees. In the twist alignment region 2, 6 indicates the rising direction of the lower liquid crystal,
Reference numeral 4 indicates the rising direction of the upper liquid crystal. Similarly, in the twist alignment region 3, 7 indicates the rising direction of the lower liquid crystal and 5 indicates the rising direction of the upper liquid crystal.

FIG. 2 shows another configuration example of the pixel. Instead of vertically dividing the pixel into two as in FIG. 1, the pixel may be horizontally divided into two. 1 and 2, the positions of the twist alignment regions 2 and 3 and the positions of the twist alignment regions 12 and 13 may be replaced with each other.

Here, in FIGS. 1 and 2, the rising directions of the liquid crystals in the two twist alignment regions are set so that the grayscale inversion directions are located in two vertical directions. Moreover, the threshold voltage of the twist alignment region which causes gradation inversion in the upward direction of the viewing angle is set lower than that of the other twist alignment region.

In FIG. 3, the pixel 2 alignment division structure as described above is provided, and 10 pixels are provided between two twist alignment regions.
FIG. 3 shows display characteristics when viewed from each direction in the visual field using a liquid crystal display device having a difference of 0 mV. Note that FIG.
Is displayed in the spherical coordinate system.

As shown in FIG. 3, the gradation inversion region (region where a large contrast can be obtained) is set in the upper visual field, and the contrast lowering region in the upper visual field is suppressed to a small value. On the other hand, the wide contrast lowering region is located in the lower visual field. That is, in general, the display on a personal computer is almost a binary display, and since the display for a personal computer is rarely seen from below, the contrast is emphasized and the tone reversal is suppressed to the extent that it is not a concern. As described above, the gradation reversal region side where a large contrast can be obtained is set as the upper visual field, and the visual field is widened to the upper side to widen the effective visual field. Further, the area where the contrast is lowered is rendered harmless by bringing it to a lower visual field which is not normally used in a display for a personal computer.

Next, a liquid crystal display device suitable for use as a display of a television or the like which mainly uses halftone display will be described. When the liquid crystal display device is used as a display for a television or the like, it is effective to avoid grayscale inversion in the upper visual field, and therefore, it is desirable to bring the grayscale inversion area downward, contrary to FIG. . A liquid crystal display device having such a display characteristic adopts, for example, the configuration of FIG. 1 or FIG. 2 and sets the threshold voltage of the twist alignment region that causes gradation inversion downward in the viewing angle to the other twist alignment. It can be realized by setting the area low. Further, the display characteristics in this case are obtained by vertically inverting the characteristics shown in FIG.

Thus, by setting the rising direction and the threshold voltage of the liquid crystal molecules in each twist alignment region provided in the pixel according to the use of the display,
Good display characteristics and a wide effective viewing angle can be realized.

Here, the maximum difference (absolute value) in the threshold voltage of each twist alignment region in which the rising direction of the liquid crystal is different.
Is preferably set within a range from a value exceeding 5 mV to a value below 100 mV. If a potential difference exceeding 100 mV is provided as the maximum threshold voltage difference, the originally intended compensation effect due to the difference in the pretilt direction is lost. When the maximum difference in threshold voltage is 5 mv or less, the grayscale inversion region and the contrast lowering region have the same extent, and for example, the grayscale inversion region is widened in the upper visual field as shown in FIG. On the other hand, it is not possible to take such a structure as to reduce the contrast reduction area.
The configuration of the present invention cannot be applied.

When the threshold voltage is changed according to the pretilt angle as in this embodiment, the pretilt angle is set to 25.
If the value is set to exceed the value, the contrast cannot be sufficiently obtained and the effective viewing angle becomes narrow. Therefore, it is desirable to set the pretilt angle within 25 degrees.

Next, an example of the manufacturing process of the liquid crystal display device according to the present invention will be described. FIG. 4 shows schematic cross-sectional views of the liquid crystal display device in the manufacturing process. In this manufacturing process, first, a TFT switch element (not shown) is provided on one of the two transparent substrates 23, and the 200 μm square pixel electrode 22 formed of the transparent electrode is used as a signal line or a gate line (not shown). On the other hand, it is provided in a matrix. On the other substrate 23, an entirely transparent electrode 22 and a black matrix (not shown) corresponding to each wiring are provided.

On one of the substrates 23, a solvent-soluble ring-closing type medium pretilt angle polyimide 24 is applied, and 180
C. Post-baking is performed for 1 hour to fix it on the substrate. On the other substrate 22, a thermal ring-closing type high pretilt angle polyimide 24 is applied and post-baked at 280 ° C., and a solvent-soluble ring-closing type low pretilt angle polyimide 25 is applied continuously on this film 24. Then, post bake is performed at 180 ° C. (FIG. 4A).

Using a positive photoresist (for example, OFPR-5000, manufactured by Tokyo Ohka Kogyo Co., Ltd.) on the two alignment films 24 and 25, the low pretilt alignment film is formed in a half region corresponding to a pixel. 25 is removed, and the high pretilt alignment film 2
4 is exposed (FIG. 4 (b)).

After rubbing both substrates 23, they were combined at 90 ° TN and Np liquid crystal 29 having a twist in the direction opposite to the cell orientation direction was sandwiched to produce a liquid crystal display cell with an interelectrode distance of 6 μm. (FIG. 4 (c)).

This liquid crystal display cell has a threshold voltage difference of 50 mV between the two regions, exhibits a good alignment state, and has a good contrast upward setting so that the viewing angle in a halftone display suitable for a personal computer can be improved. The inversion of the light and darkness due to was not conspicuous, and good display with high contrast was able to be made.

Next, another example of the manufacturing process of the liquid crystal display device according to the present invention will be described. FIG. 5 shows schematic cross-sectional views of the liquid crystal display device in the manufacturing process. First, a TFT switch element (not shown) is provided on one of the two transparent substrates 23, and 200 μm square pixel electrodes 22 formed of transparent electrodes are provided in a matrix with respect to signal lines and gate lines (not shown). . On the other substrate 23, an entirely transparent electrode 22 and a black matrix (not shown) corresponding to each wiring are provided.

Solvent-soluble ring-closure type polyimide 31 is applied to each of the two substrates 23 and post-baked at 180 ° C. for 1 hour to fix them on the substrates, followed by the first rubbing treatment (FIG. 5A). .

A negative photoresist layer (for example, OFPR-85, manufactured by Tokyo Ohka Kogyo Co., Ltd.) 800 nm is applied to half of the portion of the alignment film 31 corresponding to the pixel, exposed, and developed with a dedicated developer to form a photoresist. Is patterned to form a mask 32 that covers half of the pixels (FIG. 5B).

Next, after the second rubbing treatment is performed in the direction opposite to the rubbing direction of the first rubbing (FIG. 5B), the mask layer 32 is removed by a dedicated stripping solution. The rubbing direction is a direction in which liquid crystal molecules rise toward the TFT element.

Then, the portions of the two alignment-treated substrates 23 provided with the resist layer 32 and the portions subjected to the second rubbing treatment are made to face each other, and 9
Combined with 0 ° TN and sandwiching the Np liquid crystal 30, a liquid crystal display cell with a distance between electrodes of 6 μm is manufactured (FIG. 5).
(C)).

This liquid crystal display cell has a threshold voltage difference of 10 mV in two regions, exhibits a good alignment state, and has a good contrast upward setting so that the viewing angle in a halftone display suitable for a personal computer can be improved. The inversion of the light and darkness due to was not conspicuous, and good display with high contrast was able to be made.

Although the case where the pretilt angle is changed to change the threshold value has been described above, it can be realized by changing the effective voltage instead.
In this case, it is conceivable to provide a capacitor having a different capacitance for each divided pixel.

The display system used in the liquid crystal display device of the present invention is a twisted nematic display (TN).
It can be used for all displays whose viewing angle is limited due to the difference from the rising direction of liquid crystal molecules such as STN, SBE, and ECB when an electric field is applied.

Further, a TFT is provided for the liquid crystal display device of the present invention.
By incorporating the equal active switch element, a better display is possible. Further, the present invention is not limited to the above-described embodiments, and various modifications can be carried out without departing from the scope of the invention.

[0036]

As described above in detail, in the liquid crystal display device of the present invention, when the twist alignment regions having different rising directions of the liquid crystal molecules are provided in the display surface, the threshold voltage between the alignment regions is positively set. By setting different values for, the effective viewing angle is wide, and good display characteristics without abnormality can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an example of a subpixel structure in a pixel forming a display screen of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining another example of a sub-pixel structure in a pixel forming a display screen of a liquid crystal display device according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of screen display characteristics of a liquid crystal display device according to an embodiment of the present invention.

FIG. 4 is a diagram for explaining a main part of a manufacturing process example of the liquid crystal display device of the present invention.

FIG. 5 is a view for explaining a main part of another example of the manufacturing process of the liquid crystal display device of the present invention.

[Explanation of symbols]

1, 11 ... Pixel, 2, 3, 12, 13 ... Twist alignment region, 4, 5, 14, 15 ... Pretilt direction of upper liquid crystal,
6, 7, 16, 17, ... Pretilt direction of lower liquid crystal, 22
... Pixel electrode, 23 ... Substrate, 24 ... High pretilt angle polyimide, 25 ... Low pretilt angle polyimide, 26 ... Medium pretilt angle polyimide, 30 ... Resist mask, 29,
30 ... Liquid crystal, 31 ... Alignment film, 32 ... Resist mask

Claims (2)

[Claims] 1. A liquid crystal display device comprising a liquid crystal panel filled with liquid crystal between substrates, wherein a plurality of twist alignment regions having different rising directions of liquid crystal molecules are provided in a display surface, wherein the liquid crystal in each of the twist alignment regions is provided. The rising direction of the molecule is set to any one of a plurality of specific directions, and the threshold voltage of the twist alignment region in which the rising directions of the liquid crystal molecules in the twist alignment region are set to be the same. A liquid crystal display device, wherein the threshold voltages of the twist alignment regions in which the rising directions of the liquid crystal molecules are different from each other are set to substantially the same value. 2. A value obtained by subtracting the minimum value from the maximum value of the threshold voltages of the twist alignment regions is 5 m.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device is set in a range from a value exceeding V to a value not exceeding 100 mV.