JPH07248497A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To expand an effective visual field angle by setting the value obtd. by subtracting the min. value from the max. value among the respective threshold voltages of plural twist oriented regions at a specific value or below. CONSTITUTION:The display surface of a liquid crystal panel is provided with the plural twist oriented regions varying in the rising directions of liquid crystal molecules within this plane. 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 at <=5mV. The display characteristics at the corresponding visual field angle between the respective twist oriented regions are then made nearly uniform. Then, the effect of crosscompensation is enhanced and the gradation inversion regions and the regions where the contrast decreases are suppressed to a smaller level. The good display of the wide effective visual field angle is thus executed.

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.

[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 fine area such as a pixel must be divided into smaller areas, and the number of gradations that can be displayed is determined according to the number of divisions.

On the other hand, an attempt has been made to widen the viewing angle by 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. However, in this method, since the alignment process of each pixel is different, the display characteristics in the corresponding viewing angles between the twist alignment regions are slightly different, and there is a problem that the mutual compensation effect is small.

[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. The liquid crystal display device has a problem that the display characteristics in the corresponding viewing angles between the twist alignment regions are slightly different from each other, and a sufficient mutual compensation effect cannot be obtained. The present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid crystal display device having a wide effective viewing angle.

[0007]

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 value obtained by subtracting the minimum one from the maximum ones of the threshold voltages of the plurality of twist alignment regions is set to 5 mV or less.

[0008]

As a result, according to the liquid crystal display device of the present invention, since the threshold values of the twist alignment regions provided in the display surface are set within substantially the same range, the twist alignment regions between the twist alignment regions can be The display characteristics at corresponding viewing angles are almost the same.

Therefore, since the effect of mutual compensation is enhanced, the gradation inversion region and the region in which the contrast is reduced can be suppressed to a small size, and good display with a wide effective viewing angle can be performed.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. A liquid crystal display device according to an embodiment of the present invention employs a mutual compensation method in which the rising direction of liquid crystal molecules on an alignment film is changed within a pixel. In this mutual compensation method, in order to mutually compensate for the difference in display characteristics depending on the in-plane visual field determined by the pretilt direction, a portion having different pretilt directions is provided, and the pretilt direction is changed within the pixel to perform mutual compensation, thereby obtaining a halftone state. Brightness / darkness inversion is further suppressed, and the contrast is suppressed to improve the viewing angle. In the liquid crystal display device to which the conventional mutual compensation method is applied, the present inventors have different pretilt angles and effective voltages because the number of alignment treatments is different in each alignment region or the alignment film material is different. It was confirmed that there was a difference in the threshold voltage, which caused the mutual compensation to be incomplete. In view of this, the present invention is characterized in that the threshold values of the twist alignment regions are set to the same value in order to further enhance the effect of the mutual compensation method.

FIG. 1 is a top view of a part (4 pixels) of the display screen of the liquid crystal display device of this embodiment. This display screen is composed of a plurality of pixels 1. Further, this liquid crystal display device adopts the TN type liquid crystal display system, and the rising directions of the liquid crystal molecules in each pixel 1 are 18 degrees relative to each other.
Two twist orientation regions 2 and 3 which are different by 0 degrees are provided. In the twist alignment region 2, 6 indicates the rising direction of the lower liquid crystal and 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 example of the configuration 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 twist alignment regions 12 and 13 may be replaced with each other. Moreover, various rising directions can be considered in addition to those shown in FIGS. 1 and 2, and the present invention can be applied to any case. The number of divisions is not limited to two.

In FIG. 1 and FIG. 2, the threshold value of each twist orientation region is set to the same value by adopting the manufacturing process described later. FIG. 3 shows display characteristics as seen from each direction in the visual field using the liquid crystal display device having the above-mentioned configuration and having the threshold voltage difference between the two twist alignment regions set to 5 mV. On the other hand, in FIG. 6, in addition to having the above configuration in FIG.
The difference between the threshold voltages of the two twist orientation regions is 100
The display characteristic using the liquid crystal display device set to mV is shown.
3 and 6 are displayed in the spherical coordinate system.

Comparing FIG. 3 and FIG. 6, in FIG. 3, both the gradation inversion area and the area in which the contrast is reduced are suppressed small, whereas in FIG. 6, the gradation inversion area or the contrast is reduced in a specific direction. One of the areas of decline is widely distributed. That is, as can be seen from this result, the effective viewing angle becomes wider when the difference (absolute value) between the threshold voltages of the twist alignment regions is reduced, that is, when the threshold voltages are aligned. There is. This is because it is better to perform the mutual compensation by setting the respective twist orientation regions to the same rising state as much as possible, and it means that the compensation cannot be completely performed in the case of the twist orientation regions having different rising states as in the conventional case. There is.

Here, the threshold voltage difference (absolute value) is 5
It was found that it is desirable to set it within mV, and it is found that substantially the same effect can be obtained within 5 mV. Also,
If the threshold voltage difference (absolute value) exceeds 5 mV, as shown in FIG. 6, either the gradation reversal region or the contrast lowering region widens in a specific direction and the field of view becomes narrow, which is not preferable.

As described above, according to this embodiment, the effect of mutual compensation is enhanced, so that the gradation reversal region and the region where the contrast is reduced are suppressed to a small level, and good display characteristics with a wide effective viewing angle can be obtained. You can

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. First, a TFT switch element (not shown) is provided on one of the two transparent substrates 23,
The 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). Note that the auxiliary capacitance line (not shown) is provided in the center of the pixel (not shown). On the other substrate 23,
A black matrix (not shown) corresponding to the whole-surface transparent electrode 22 and each wiring is provided.

Solvent-soluble ring-closing polyimide 21 is applied on both substrates 23. After 180 ° C. post-baking for 1 hour to fix it on the substrate 23, half of the portion corresponding to the pixel on the alignment film 21 (that is, gate line, signal line
A negative photoresist layer (for example, OFPR-85, manufactured by Tokyo Ohka Kogyo Co., Ltd.) 8000 is applied to the portion surrounded by the auxiliary capacitance line), exposed, and developed with a dedicated developer to form a mask 24 covering half of the pixels. Are formed (FIG. 4A).

After the first rubbing process, the mask layer 24 is removed with a dedicated stripping solution. Next, after masking the portions other than the previous mask portion (FIG. 4B), the second rubbing is performed from the direction opposite to the rubbing direction of the first time, and then the mask layer 24 is removed by a dedicated stripping solution.

The two portions of the two orientation-treated substrates 23, which have been subjected to the first rubbing treatment, and the portions which have been subjected to the second rubbing treatment, are made to face each other, and 90 ° T
Combined with N, the Np liquid crystal 30 is sandwiched, and a liquid crystal display cell having a distance between electrodes of 6 μm is manufactured (FIG. 4C).

This liquid crystal display cell had a threshold voltage difference of ± 2 mV in the two regions, exhibited a good alignment state, and was able to perform a good display in which half-tone anti-region shift depending on the viewing angle was small in halftone display.

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. Two transparent substrates 23
A TFT switch element (not shown) is provided on one side of the above, and a 200 μm square pixel electrode 22 formed of a transparent electrode is provided in a matrix with respect to a signal line and a gate line (not shown).
The auxiliary capacitance line is provided in the center of the pixel (not shown). On the other substrate 23, a totally transparent electrode 22 and a black matrix (not shown) corresponding to each wiring are provided.

Solvent-soluble ring-closing polyimide 21 is applied onto both substrates 23. After 180 ° C. post-baking for 1 hour to fix it on the substrate, the first rubbing treatment is performed, and the second rubbing treatment is performed again from the opposite direction (FIG. 5).
(A)).

A negative photoresist layer (for example, OFPR-85, manufactured by Tokyo Ohka Kogyo Co., Ltd.) of 800 nm is applied to half of a portion of the alignment film 21 corresponding to a pixel, exposed, and developed with a special developer to obtain a photo. The resist was patterned to form a mask 24 that covers half of the pixels (FIG. 5B).

After the third rubbing treatment is performed in the direction opposite to the second rubbing direction, the mask layer 24 is removed with a dedicated stripping solution. The two orientation-treated substrates 23 were made to face each other at 90 ° with the portions provided with the resist layer 24 and the portions subjected to the third rubbing treatment facing each other.
In combination with TN, Np liquid crystal 30 was sandwiched, and a liquid crystal display cell with a distance between electrodes of 6 μm was produced (FIG. 5C).

This liquid crystal display cell had a threshold voltage difference of ± 5 mV in the two regions, exhibited a good alignment state, and was able to perform a good display in which half-tone anti-region shift depending on the viewing angle was small in halftone display.

Next, still another example of the manufacturing process of the liquid crystal display device according to the present invention will be described. Note that a schematic cross-sectional view of the liquid crystal display device in the manufacturing process is obvious to a person skilled in the art, and is omitted here.

A TFT switch element is provided on one of the two transparent substrates, and pixel electrodes of 200 μm square formed of transparent electrodes are provided in a matrix with respect to the wiring. The auxiliary capacitance line is
It is provided in the center of the pixel. On the other substrate, a black matrix corresponding to the entire transparent electrode and wiring is provided.

A positive photoresist (for example, OFPR-5000, manufactured by Tokyo Ohka Kogyo Co., Ltd.) 1000 nm is exposed to half of a portion corresponding to a pixel on this alignment film, and an alkaline developer (for example, NM) is used.
D-3, manufactured by Tokyo Ohka Co., Ltd.) for 30 seconds, patterning the photoresist to form a mask covering half of the pixels.

After the first 90-degree oblique vapor deposition of SiO, the mask layer is removed with a dedicated stripping solution. Next, after masking the portions other than the above-mentioned mask portion and performing the second SiO oblique vapor deposition rubbing from the same direction as the first rubbing direction from the same angle, the mask layer is removed by a dedicated stripping solution.

The two orientation-treated substrates were made to face each other at the portions subjected to the first oblique vapor deposition, and were combined at 90 ° TN to sandwich the Np liquid crystal, A liquid crystal display cell with an electrode distance of 6 μm is produced.

This liquid crystal display cell had a threshold voltage difference of ± 3 mV in the two regions, exhibited a good alignment state, and was able to perform a good display in which the light-dark reversal region depending on the viewing angle was small in the halftone display.

Next, two comparative examples will be described with respect to the example of the manufacturing process of the liquid crystal display device according to the present invention. Since a schematic cross-sectional view of the liquid crystal display device in the manufacturing process of the comparative example is obvious to those skilled in the art, it is omitted here.

In the first comparative example, first, a heat-closing polyimide is applied onto a transparent substrate having two transparent electrodes formed thereon. After the post-baking at 280 ° C. for 1 hour to fix it on the substrate, the first rubbing process is performed. A positive photoresist layer (for example, OFPR-5000, manufactured by Tokyo Ohka Co., Ltd.) of 800 nm is exposed on half of a portion corresponding to pixels on this film, and developed with an alkaline developer (for example, NMD-3, Tokyo Ohka Co., Ltd.) for 30 seconds. Then, the photoresist is patterned to form a mask covering half of the pixels.

After the second rubbing treatment is performed in the direction opposite to the rubbing direction of the first rubbing, the mask layer is removed with a dedicated stripping solution. A liquid crystal display cell with a distance of 6 μm between electrodes, where two portions of the orientation-treated substrates were provided with a resist layer and the portions subjected to the second rubbing treatment were made to face each other, and were combined at 90 ° TN to sandwich Np liquid crystal. To make.

This liquid crystal display cell has a threshold voltage difference of ±
A good alignment state was exhibited at 20 mV, but a wide light-dark reversal region appeared at a specific viewing angle in halftone display. Next, a second comparative example will be described.

In this comparative example, first, a TFT switch element is provided on one of two transparent substrates, and 200 μm square pixel electrodes formed of transparent electrodes are provided in a matrix with respect to the wiring. On the other substrate, a black matrix corresponding to the entire transparent electrode and wiring is provided.

On one of the substrates, a solvent-soluble closed ring type medium pretilt angle polyimide is applied. Post-baking at 180 ° C. is performed for 1 hour to fix it on the substrate. On the other substrate, a thermal ring-closing type high pretilt angle polyimide is applied and post-baked at 280 ° C., then a solvent-soluble ring-closing type low pretilt angle polyimide is applied, and 180 ° C. post-baking is performed.

Using a positive photoresist (for example, OFPR-5000, manufactured by Tokyo Ohka Kogyo Co., Ltd.) on the two superposed alignment films, the low pretilt alignment film corresponding to half of the portion corresponding to the pixel is removed to obtain the high pretilt film. The alignment film is exposed.

After rubbing both substrates, 2
Combined with 70 ° TN, Np liquid crystal having a twist opposite to the cell orientation direction is sandwiched, and the distance between electrodes is 6 μm.
A liquid crystal display cell is manufactured.

This liquid crystal display cell had a threshold voltage difference of ± 50 mV in the two regions and showed a good alignment state, but a wide bright-dark reversal region appeared at a specific viewing angle in the halftone display, and the voltage was changed. Due to the application, flicker was severe and the display quality was significantly reduced.

Here, as a display system used in the liquid crystal display device of the present invention, a twisted nematic display (T
N) and STN, SBE, ECB, etc. can be used for all displays in which the viewing angle is limited due to the difference from the rising direction of liquid crystal molecules in an electric field applied state.

Further, in the liquid crystal display device of the present invention, the TFT
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.

[0044]

As described above in detail, according to the liquid crystal display device of the present invention, the threshold values of the twist alignment regions provided in the display surface are set within substantially the same range, and gradation inversion is performed. By suppressing the area and the area in which the contrast is reduced to be small, it is possible to obtain good display characteristics with a wide effective viewing angle.

[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.

FIG. 6 is a diagram showing screen display characteristics of a liquid crystal display device according to a comparative example.

[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, 21
... Alignment film, 22 ... Pixel electrode, 23 ... Substrate, 24 ... Resist mask, 30 ... Liquid crystal

Claims (1)

[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 each of the plurality of twist alignment regions is provided. A liquid crystal display device, wherein a value obtained by subtracting the minimum threshold voltage from the maximum threshold voltage is set to 5 mV or less.