JPS62159119A - Liquid crystal display panel - Google Patents

Abstract

PURPOSE:To realize gradational display by forming a liquid crystal display element by using different kinds of materials or materials in different shapes partially to constitute respective picture elements. CONSTITUTION:Picture elements are divided into plural areas (two areas B and C in this case), which are different in light transmissivity to an applied voltage. Namely, the light transmissivity of the area B varies with V1-V2 as shown by a and the transmissivity of the area C varies with V1'-V2' as shown by broken line 2 so that their variation start voltages are different. Consequently, the light transmissivity-applied voltage characteristic of the whole picture elements is gentle as shown by a solid line 3. For the purpose, the thickness of a liquid crystal layer constituting the respective picture elements, the film thickness of an oriented film, and the film thickness of a color filter are varied stepwise. Then, a dielectric layer is interposed locally between the oriented film and an constituting each picture element and a transparent electrode, and the oriented film constituting each picture element is formed varying in pre-tilt angle stepwise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to the structure of a liquid crystal display panel that achieves multi-gradation display by smoothing voltage-transmittance characteristics.

[Industrial application field]

The present invention relates to an element configuration of a liquid crystal display panel that realizes multi-gradation display.

Various image processing devices have been developed along with advances in information processing devices, and are contributing to speeding up information processing as terminal devices.

Here, along with cathode ray tubes (CRTs) and plasma display panels, there are liquid crystal display panels as image processing devices.As for liquid crystal display panels, they range from segment types that display only numbers and alphabetic characters to graphic ink displays. It has progressed to a don-to-matrix type that allows for
Furthermore, the practical use of LCD televisions is progressing.

As usage progresses toward larger capacity and color, gradation display becomes necessary, and a display method that can achieve this is desired.

[Conventional technology]

There are two types of liquid crystal display panels: a simple matrix type and an active matrix type. The latter allows a large number of pixels to be driven independently, and is therefore theoretically capable of large-capacity display.

Furthermore, when using the same type of liquid crystal, the contrast is high and the viewing angle is wide.

Next, as a method for liquid crystal display, the deflection nematic effect (Tw
The TN display method using the static nematic effect and the dynamic scattering mode
There is a DSM display method using a tttering mode), but it is difficult to display multiple gradations using these two methods as they are.

In other words, in a TN display, a liquid crystal is placed between two orthogonal polarizing plates, and the display is performed by controlling the twist of the liquid crystal using an electric field.When the electric field is off, the liquid crystal remains twisted, but when the electric field is on, the liquid crystal remains twisted. This method takes advantage of the phenomenon in which the incident light is blocked from passing through the polarizing plate by changing the direction of the liquid crystal molecules in the direction of the electric field. Multi-gradation display is difficult because the difference between the two is small.

r) SM display utilizes the light scattering caused by collisions with liquid crystal molecules that occur when impurity ions move through the liquid crystal due to an electric field, and in principle, the degree of light scattering should be able to be controlled by voltage. However, in reality, ion movement occurs only at a voltage value higher than the dark value, and then the ion current increases rapidly, making it difficult to display gradations.

As described above, it is difficult to display multiple gradations using conventional display technology, and in order to make this possible, research is being conducted in terms of liquid crystal composition and liquid crystal panel configuration.

In other words, when using a cholesteritter nematic phase transition type liquid crystal, a liquid crystal composition that rapidly undergoes a phase transition above the dark value voltage and exhibits a sharp rise or fall in light transmittance is conventionally used. Liquid crystal compositions that change slowly are being studied.

However, sufficient multi-gradation display has not been achieved on any surface.

[Problems to be solved by the invention] In order to put liquid crystal color televisions into practical use, it is necessary to be able to perform gradation display, and this can be solved not only from the perspective of the liquid crystal composition but also from the perspective of the liquid crystal panel. The challenge is to put into practical use an element configuration in which the light transmittance gradually changes to i with respect to the applied voltage.

[Means for solving problems]

The above problem can be solved by a liquid crystal display panel in which each pixel of the liquid crystal display element is formed by partially changing the material, shape, or type of material.

[Effect]

The present invention realizes multi-gradation display by using TN liquid crystal and forming each pixel of an active matrix liquid crystal display device by partially changing the material, shape, or type of material. .

Here, the display electrodes and transparent electrodes forming pixels, which are patterned to face each other on a glass substrate with a liquid crystal layer in between, are connected to the data bus line and the scan path line, respectively. The voltage pulse applied to the pass line is 3IIH.

The light transmittance of each pixel changes and a liquid crystal display is performed.

Figure 2 shows the light transmittance characteristics when an applied voltage is applied to these pixels. Conventionally, a signal voltage of V1 to ■2 is applied between the display electrode and the transparent electrode of each pixel, and the pixel is The light transmittance corresponding to this voltage value was shown.

However, as shown in FIG. 2, the applied voltage-light transmittance characteristic is steep, making multi-gradation display difficult.

Therefore, in the present invention, the change in light transmittance with respect to the applied voltage in each pixel is as shown in the same figure.
(as shown in Figure 1), and divide it into multiple regions (in this case, three regions B and C) as shown in Figure 1.
By configuring each region to have a different light transmittance with respect to the applied voltage, the light transmittance-applied voltage characteristic is made gentler.

That is, the light transmittance of region B is V, ~■ as shown by solid line 1.
2, and on the other hand, if the transmittance of the C region is formed so that the change start voltage is shifted from V, to 2' as shown by the broken line 2, the light transmittance-applied voltage characteristic of the entire pixel will be as shown by the solid line 3.
As shown in , it is gradual.

The present invention realizes multi-gradation display using such a method, and the following methods can be considered to realize this.

■ Change the thickness of the liquid crystal layer that makes up each pixel in a stepwise manner.

(2) The thickness of the alignment film constituting each pixel is changed stepwise.

■ The thickness of the color filter that makes up each pixel is changed stepwise.

(2) A dielectric layer is partially interposed between the alignment film and the transparent electrode that constitute each pixel.

■ The alignment film that constitutes each pixel is formed in a stepwise manner with different pretilt angles.

〔Example〕

Example 1 (Changing the thickness of the liquid crystal layer) A display electrode pattern of 200 μm square and a transparent pattern were formed on two glass substrates of 200 x 150 +n to form a liquid crystal display element using a method similar to the conventional method. An electrode pattern was formed.

Pixels are formed by making each display electrode pattern and transparent electrode pattern face each other, and in this example, the number of pixels is 640 x 400.

FIG. 3 is a cross-sectional view of a unit pixel for explaining the present invention in detail.

First, a region on the first glass substrate 4 where a unit pixel was to be formed was divided into a plurality of regions (in this case, two regions), and a polyimide layer 5 having a thickness of 5 μm was patterned in this region.

In this method, polyimide layers 5 are coated over the entire surface of the first glass substrate 4 using a spin code method, and then resist is selectively coated using photolithography, and then plasma etching is performed. By doing this, the polyimide layer 5 was patterned in a half area of each pixel.

Next, in the same manner as before, an indium-tin alloy film (abbreviated as ITO film) 7 is sputtered onto the first glass substrate 4 and the second glass substrate 6 to a thickness of approximately 400 mm, and an oriented film made of polyimide is applied. After forming the film 8 to a thickness of approximately 800 mm using a spin code method, plasma etching was performed to form an electrode pattern.

Then, a liquid crystal display panel is formed by accurately aligning the first glass substrate 4 and the second glass substrate 6, making them face each other with a gap of 10 μm maintained through a separator, and sealing TN liquid crystal between them. .

In this case, the thickness of the liquid crystal layer 9 in 172 areas of each pixel is 5
μm, and the other 172 regions are 10 μm.

FIG. 8 shows the relationship between the amount of light transmission and the applied voltage, and the amount of light transmission when no voltage is applied is taken as 100%.

In this figure, a broken line 10 indicates an interval of 5 between the liquid crystal layers 9 of pixels.
Transmittance characteristics in the case of μm, and the dot-dashed line 1) has an interval of 1
In the case of 0 μm, the characteristic 12 corresponds to that shown in FIG. 3, and it can be seen that the characteristic has a gentle slope.

Example 2 (When the thickness of the alignment film was changed) Figure 4 shows the thickness of the liquid crystal layer unchanged (in this example, it was 10 μm).
1Yl), this is an example in which the electric field strength was changed by changing the thickness of the alignment film 8.

That is, on the second glass substrate 6, a polyimide layer 5 having a thickness of about 3 μm is formed in the region 172 of the pixel.

Next, as in Example 1, the IT including the first glass substrate 4 is
A pattern is formed by forming a layer with the OTlO2-directing film 8.
Only the alignment film 8 of the first glass substrate 4 was formed to a thickness of 3 μm, and only the portion facing the polyimide layer 5, which had been patterned first, was etched to a thickness of approximately 800 μm by plasma etching. A pixel with the structure shown in the figure was formed.

In this case, the dielectric constant of the TN liquid crystal is approximately 10. Polyimide 8
'f, the electric rate is 3, so the voltage on the left half of Figure 4 is 1/2 of the right half, and as a result, the applied voltage - amount of light transmission is as shown by the solid line 13 in Figure 9. characteristics have been realized.

In FIG. 4, the broken line 14 indicates the characteristic shown in the left half region, and the dotted line 15 indicates the characteristic shown in the right half region.

Example 3 (When the thickness of the color filter is changed) The color filter is red and blue for each pixel.

A green filter is provided to achieve color display, and it is made by mixing a dye into gelatin or polyvinyl alcohol (abbreviated as PVA).

FIG. 5 is a cross-sectional view of this embodiment, in which gelatin mixed with a dye is spin-coded onto the second glass substrate 6, and then a color filter J'ff1) 6 is applied to the 172 area of the pixel using a plasma etching method. The first layer is formed to a thickness of about 5 μm.
Including the glass substrate 4, ITOTlO2 and an alignment film 8 were formed thereon.

Note that after the ITOTlO2 formation is completed, the color filter layer 17 in the left half area of the first glass substrate 4 is 4 μm thick.
After forming the alignment film 8 to a thickness of , an alignment film 8 made of polyimide is formed thereon.

Note that the thickness of the liquid crystal layer 9 is 10 μm.

A liquid crystal display panel was thus formed.

In this case, since the dielectric constant of the liquid crystal is about 10 and the dielectric constant of the color filter is about 5, in FIG. /2, and the applied voltage-light transmission amount characteristic similar to that shown in FIG. 9 was realized.

Example 4 (When a dielectric layer is interposed) FIG.
After forming the second glass substrate 4, tantalum pentoxide (
Ta205) was formed to a thickness of 3 ttm using a sputtering method, and then plasma etched using a photolithography method to form a dielectric layer 18 only in half of each pixel.

Next, a polyimide layer was applied thereon by a spin code method so that the thickness of the alignment film 8 was approximately 800 nm, as in the conventional method, and a pattern was formed.

In this case, the alignment film 8 in the left half region where there is no dielectric layer 18
becomes thicker.

Next, the first and second glass substrates 4°6 were
A liquid crystal display panel was formed by facing each other with an interval of μm and sealing a TN liquid crystal between them.

Here, the dielectric constant of Ta205 is 25. Polyimide is about 3
Also, since the liquid crystal is approximately 10, if a voltage of ■ is applied to a pixel, a voltage of 0.5 ■ will be applied to the left half area, and a voltage of 0.9 ■ will be applied to the right half area. Thus, the applied voltage-light transmission amount characteristic similar to that previously explained in FIG. 9 was realized.

Example 5 (Case where the pretilt angle is changed) FIG. 7 is a cross-sectional view of a unit pixel implementing the present invention,
In the right half region, an ITOTlO2 directed film 8 is formed as in the conventional case.

That is, after patterning the alignment film 8 made of polyimide to a thickness of approximately 800 mm, a rubbing process is performed to form a pattern of 0.5 mm.
A pretilt angle of ~2 degrees has been achieved.

On the other hand, the left half region is oriented with a pretilt angle of up to about 35 degrees by performing oblique evaporation of silicon oxide (StO) to a thickness of about 1,000 degrees while the right half region is covered with a resist film. A film 19 was formed.

The first glass substrate 4 and the second glass substrate 6 are combined into one
They faced each other with an interval of 0 μm, and a TN liquid crystal was sealed between them to produce a liquid crystal display panel.

The solid line 22 in FIG. 10 is the applied voltage-light transmission amount characteristic of the liquid crystal display panel made in this way, and the broken line 21. is the pretilt angle of ~35 degrees. Compared to the dot-dashed line 20 where the pretilt angle is ~1 degree, a characteristic is realized in which the inclination is gentler.

〔Effect of the invention〕

As described above, the present invention realizes multi-gradation display by smoothing the applied voltage-light transmission amount characteristic, and by implementing the present invention, it becomes possible to display 16 or more gradations.

[Brief explanation of drawings]

Figure 1 is a light transmittance-applied voltage characteristic showing the principle of the present invention, Figure 2 is a conventional light transmittance-applied voltage characteristic, Figure 3 is a cross-sectional view of a pixel explaining Example 1, and Figure 4 is a cross-sectional view of a pixel explaining Example 1. 5 is a cross-sectional view of a pixel explaining Example 2, FIG. 5 is a cross-sectional view of a pixel explaining Example 3, FIG. 6 is a cross-sectional view of a pixel explaining Example 4, and FIG. Cross-sectional views of pixels to be explained, Figures 8 to 1
Figure 0 is a characteristic diagram of the example. In the figure, 4 is a first glass substrate, 5 is a polyimide layer, 6 is a second glass substrate, 7 is a [TO film, 8.19 is an alignment film,
9 is a liquid crystal layer, and 16 and 17 are color filter layers. Many/Figures

Claims (6)

[Claims] (1) A liquid crystal display panel characterized in that each pixel of the liquid crystal display element is formed by partially changing any one of the thickness, shape, or type of material within each pixel. (2) The liquid crystal display panel according to claim 1, wherein the thickness of the liquid crystal layer constituting each pixel of the liquid crystal display element is changed stepwise. (3) The liquid crystal display panel according to claim 1, wherein the thickness of the alignment film constituting each pixel of the liquid crystal display element is changed stepwise. (4) The liquid crystal display panel according to claim 1, characterized in that the thickness of the color filter constituting each pixel of the liquid crystal display element is changed stepwise. (5) A liquid crystal display panel according to claim 1, characterized in that a dielectric layer is interposed between an alignment film and a transparent electrode constituting each pixel of the liquid crystal display element. (6) The liquid crystal display panel according to claim 1, wherein the alignment film constituting each pixel of the liquid crystal display element is formed by changing the pretilt angle in a stepwise manner.