JP2506328B2 - LCD display panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] According to the present invention, the thickness of an alignment film or a color filter is changed stepwise without changing the thickness of a liquid crystal layer constituting a pixel, or the alignment film and the transparent electrode are provided between the alignment film and a transparent electrode. By either interposing a dielectric layer on the substrate or forming the alignment film by changing the pretilt angle in a strip shape, the voltage-transmittance characteristic is moderated and multi-gradation display is realized. Liquid crystal display panel.

[Industrial applications]

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

Various image processing apparatuses have been developed with the progress of information processing apparatuses, and contribute to speeding up information processing as terminal devices.

There is a liquid crystal display panel as well as a cathode ray tube (CRT), a plasma display panel, etc. as an image processing device, but when it comes to liquid crystal display panels, it is possible to display from a segment type that displays only numbers and English characters to a graphic display. Is progressing to a possible dot matrix type,
LCD TVs are also being put to practical use.

In this way, as the use progresses toward higher capacity and color, gradation display is required, and a display method capable of realizing this is desired.

[Conventional technology]

Liquid crystal display panels are classified into a simple matrix type and an active matrix type. The latter can drive a large number of pixels independently of each other, and therefore, in principle, large-capacity display is possible.

Next, the twisted nematic effect (Tw
There is a TN display method using isted Nematic Effect) and a DSM display method using Dynamic Scattering Mode, but with these two methods, multi-gradation display is difficult until then.

In other words, the TN display is a display in which a liquid crystal is placed between two orthogonal deflection plates and the twisting of the liquid crystal is controlled by an electric field. When the electric field is OFF, the twisted state is maintained while the electric field is ON. In the case of, the phenomenon in which the incident light is blocked from passing through the deflector by changing the direction of the liquid crystal molecules in the direction of the electric field is used. It is difficult to perform multi-gradation display because there is a slight difference.

The DSM display utilizes light scattering caused by collisions with liquid crystal molecules that occur when impurity ions move in the liquid crystal due to an electric field. In principle, the voltage should control the degree of light scattering. However, in actuality, the migration of ions occurs only at a voltage value equal to or higher than a certain threshold value, and then the ion current rapidly increases, so that gradation display is difficult.

As described above, multi-gradation display is difficult with the conventional display technology, and in order to make this possible, research is being conducted from the aspects of liquid crystal composition and liquid crystal panel configuration.

That is, when a cholesteric-nematic phase transition type liquid crystal is used, conventionally, a liquid crystal composition which causes a rapid phase transition at a threshold voltage or more and has a sharp rise or a fall in light transmittance is used. Liquid crystal compositions that slowly change are studied.

However, sufficient multi-gradation display has not been realized on any of the surfaces.

[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 it is necessary to solve this not only in terms of liquid crystal composition, but also in terms of liquid crystal panels.
The challenge is to put the device configuration into practical use in which the light transmittance changes gently with respect to the applied voltage.

[Means for solving problems]

The above problem does not change the thickness of the liquid crystal layer forming the pixel,
Whether the film thickness of the alignment film or the color filter is changed stepwise, the dielectric layer is partially interposed between the alignment film and the transparent electrode, or the alignment film is formed in a band shape by changing the pretilt angle. It is possible to solve the problem by grading the voltage-transmittance characteristic and realizing gradation display by using any one of the means.

[Action]

The present invention realizes gradation display by partially changing the electric field strength with respect to the liquid crystal without changing the thickness of the liquid crystal layer in each pixel which constitutes the active matrix type liquid crystal display device by using the TN liquid crystal. is there.

Here, the display electrodes and the transparent electrodes, which are patterned to face each other across the liquid crystal layer on the glass substrate and form the pixels, are circuit-connected to the data bus line and the scan bus line, respectively. The liquid crystal display is performed by changing the light transmittance of the pixel synchronized with the voltage pulse applied to one bus line.

FIG. 2 shows the light transmittance characteristics when an applied voltage is applied to these pixels. Conventionally, a signal voltage of V _{1 to} V ₂ is applied between the display electrode and the transparent electrode of each pixel, Indicates the light transmittance corresponding to this voltage value.

However, as shown in FIG. 2, the applied voltage-light transmittance characteristics are steep, which makes it difficult to perform multi-gradation display.

Therefore, in the present invention, the change in the light transmittance with respect to the applied voltage in each pixel is constant over the entire area of the pixel (in this case, indicated by A) as shown in FIG. Divided into multiple areas (in this case, two areas B and C),
By making the light transmittance with respect to the applied voltage different for each region, the light transmittance-applied voltage characteristic is made gentle.

That is, the light transmittance of the B region is V _{1 to} V _{2 as} shown by the solid line 1.
When the C region is formed such that the transmittance of the region C shifts from V ₁ ′ to V ₂ ′ as indicated by the broken line 2, the light transmittance-applied voltage characteristic of the pixel as a whole is 3 It becomes gentle as shown in.

The present invention realizes multi-gradation display by such a method, and the following method can be considered for realizing this.

The thickness of the alignment film forming each pixel is changed stepwise.

The film thickness of the color filter forming each pixel is changed stepwise.

It is formed by partially interposing a dielectric layer between the alignment film and the transparent electrode forming each pixel.

The alignment film forming each pixel is formed stepwise with the pretilt angle changed.

Therefore, the present invention proposes a configuration in which the pixel is divided into a plurality of regions without changing the thickness of the liquid crystal layer forming the pixel and the light transmittance and the applied voltage characteristic are gradually obtained.

〔Example〕

Example 1: (Corresponding to the case where the thickness of the alignment film is changed) The size of each of the two 200 × 150 mm glass substrates for forming a liquid crystal display element was 200
A display electrode pattern and a transparent electrode pattern of square μm were formed.

Pixels are formed with the respective display electrode patterns and transparent electrode patterns facing each other. In this example, the number of pixels is 640 × 400.

FIG. 3 is a sectional view of a unit pixel for explaining the method of implementing the present invention.

First, an area where unit pixels are to be formed on the second glass substrate 6 is divided into a plurality of areas (in this case, two areas), and a polyimide layer 5 having a thickness of 5 μm is patterned in this area.

In this method, the polyimide layer 5 is coated over the entire surface of the second glass substrate 6 by a spin coating method, and then a resist is selectively coated using a photolithography technique (photolithography), and plasma etching is performed. By performing the above step, the polyimide layer 5 is formed in a pattern in a half area of each pixel.

Then, in the same manner as in the conventional method, an indium-tin alloy film (abbreviated as ITO film) 7 is formed on the first glass substrate 4 and the second glass substrate 6.
Is formed to a thickness of about 400 Å by a sputtering method, and then an alignment film 8 made of polyimide is formed to a thickness of 3 μm by a spin coating method.
Formed to a thickness of. Next, the first glass substrate 4 has a thickness of about 800 Å in a region facing the polyimide layer 5 of the second glass substrate 6 and the second glass substrate 6 has a region adjacent to the polyimide layer 5 in a thickness of about 800 Å. The alignment film 8 was formed by performing plasma etching until the film was formed.

Then, the first glass substrate 4 and the second glass substrate 6 were accurately aligned, and they were opposed to each other with a spacer kept at a distance of 10 μm, and TN liquid crystal was sealed between them to form a liquid crystal display panel.

In this case, since the dielectric constant of TN liquid crystal is about 10 and the dielectric constant of polyimide is 3, the voltage related to the left half of FIG. 3 is 1/2 of the right half, and as a result, the solid line in FIG. The applied voltage-light transmission amount characteristic as shown in 13 was realized.

The broken line 14 shows the characteristic shown in the right half region in FIG. 4, and the dashed line 15 shows the characteristic shown in the left half region.

The reason why the voltage related to the left half of FIG. 3 becomes 1/2 of the right half will be described below.

Assuming that the voltage applied between the transparent electrodes (ITO film) of the pixel is V, the voltage V ₁ applied to the right half of the pixel is regarded as V ≈ V ₁ (1) because the thickness of the alignment film is thin. On the other hand, since the voltage applied to the left half of the pixel is the sum of the voltage V ₂ applied to the liquid crystal layer and the voltage V ₃ applied to the alignment film, V = V ₂ + V ₃ (2).

Here, the capacitance of the liquid crystal layer on the left half of the pixel is C ₂ ,
Also, the electrostatic capacity of the alignment film is C _3, and the electrostatic capacity is proportional to the ratio of the dielectric constant ε of the material used to the thickness d, so it can be expressed by the following relational expression: ₂ / V ₃ = C ₃ / C ₂ (3) After replacing this capacitance relationship with the dielectric constant-thickness relationship, the alignment film has ε = 3, d = 3 μm, and the liquid crystal has ε = 10, d = 10μ
Substituting m, V ₂ / V ₃ = 1 (4), and from the relationship between equations (2) and (4), V ₂ = 1/2 · V (5) Therefore, V ₁ : V ₂ = 1: 1/2 (6)

Example 2 (corresponding to the case where the film thickness of the color filter is changed) The color filter is provided with any one of red, blue and green filters for each pixel, thereby realizing color display. Made by mixing dye in polyvinyl alcohol (abbreviated as PVA).

FIG. 4 is a sectional view of this embodiment, showing the second glass substrate 6
After spin coating with gelatin mixed with a dye, a color filter layer 16 having a thickness of about 5 μm is formed in a half region of the pixel by a plasma etching method. An ITO film 7 and an alignment film 8 were layered on top.

In addition, after the ITO film 7 is formed on the first glass substrate 4, a color filter layer 17 is formed to a thickness of 4 μm in the left half region, and then an alignment film 8 made of polyimide is formed thereon.
Is formed.

 The liquid crystal layer 9 has a thickness of 10 μm.

 In this way, a liquid crystal display panel was formed.

In this case, since the liquid crystal has a dielectric constant of about 10 and the color filter has a dielectric constant of about 5, the voltage applied to the liquid crystal layer 9 in the left half is the same as that applied to the liquid crystal layer 9 in the right half in FIG. From the same calculation as in Example 1, the value was halved, and the applied voltage-light transmission amount characteristic similar to that in FIG. 7 was realized.

Example 3 (corresponding to the case where a dielectric layer is interposed) FIG. 5 shows this example, and ITO is formed on the first glass substrate 4 and the second glass substrate 6 in the same manner as in Example 1. After forming the film 7, tantalum pentoxide (Ta ₂ O ₅ ) having a thickness of 3 μm is formed on the first glass substrate 4 by a sputtering method, and this is plasma-etched by a photo-etching method. ,
The dielectric layer 18 was formed only in the half region of each pixel.

Then, a polyimide layer was applied thereon by a spin coating method so that the thickness of the alignment film 8 was about 800 Å as in the conventional case, and pattern formation was performed.

In this case, the alignment film 8 in the left half region without the dielectric layer 18
Is thicker.

Next, the first and second glass substrates 4 and 6 are set to 10 μm.
A liquid crystal display panel was formed by facing each other with a space of m and enclosing TN liquid crystal between them.

Here, Ta ₂ O _{5 has} a dielectric constant of 25, polyimide is about 3 and liquid crystal is about 10. Therefore, when V voltage is applied to the pixel, 0.5 V is applied to the left half region and 0.5 V is applied to the right half region. Area is 0.
A voltage of 9 V was applied, and the same applied voltage-light transmission amount characteristic as described above with reference to FIG. 7 was realized.

Example 4 (corresponding to the case where the pretilt angle is changed) FIG. 6 is a cross-sectional view of a unit pixel in which the present invention is carried out. In the right half region, an ITO film 7 and an alignment film 8 are formed as in the conventional case. I'm standing.

That is, after the alignment film 8 made of polyimide was patterned to a thickness of about 800Å, rubbing treatment was performed to form an alignment film. The pretilt angle at this time was 0.5 to 2.0 degrees was investigated using a separate investigation cell.

Next, silicon oxide (SiO) is formed by about 1000Å oblique vapor deposition with the right half region covered with a resist film, and then the resist is stripped using a resist stripper, leaving SiO only in the left half. I did it.

It should be noted that the oblique vapor deposition is performed from a direction of about 85 degrees with respect to the normal direction of the substrate, and it was separately investigated that the pretilt at this time is about 35 degrees.

The first glass substrate 4 and the second glass substrate 6
Liquid crystal display panels were made by facing each other with a space of 10 μm, and enclosing TN liquid crystal between them.

The solid line 22 in FIG. 8 is the applied voltage-light transmission amount characteristic of the liquid crystal display panel thus manufactured. The characteristic that the slope is much gentler is realized.

〔The invention's effect〕

As described above, the present invention realizes multi-gradation display by smoothing the applied voltage-light transmittance characteristics without changing the thickness of the liquid crystal layer, and by implementing the present invention, 16 or more levels Key display is possible.

[Brief description of drawings]

1 is a light transmittance-applied voltage characteristic showing the principle of the present invention, FIG. 2 is a conventional light transmittance-applied voltage characteristic, FIG. 3 is a sectional view of a pixel for explaining the first embodiment, FIG. Is a sectional view of a pixel for explaining the second embodiment, FIG. 5 is a sectional view of a pixel for explaining the third embodiment, FIG. 6 is a sectional view of a pixel for explaining the fourth embodiment, and FIGS. It is a characteristic view of an example. In the figure, 4 ... First glass substrate 5 ... Polyimide layer 6 ... Second glass substrate 7 ... ITO film 8, 19 ... Alignment film, 9 ... Liquid crystal layer, 16, 17 ... Color filter The layers are.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Oki, 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, inside Fujitsu Limited (72) Inventor Jun Inoue 1015, Ueda-anaka, Nakahara-ku, Kawasaki, within Fujitsu Limited (56) References JP-A-52-148151 (JP, A) JP-A-56-1017 (JP, A) JP-A-55-50219 (JP, A) JP-A-58-123587 (JP, A) JP-A-56-88193 (JP, A) JP 61-166590 (JP, A) JP 49-45748 (JP, Y2)

Claims (4)

(57) [Claims] 1. A pair of glass substrates facing each other, a liquid crystal layer injected between the pair of glass substrates, and a glass substrate on the glass substrate.
A liquid crystal display panel comprising an alignment film provided at an interface with the liquid crystal layer, and an electrode film provided between the glass substrate and the alignment film, wherein a plurality of pixels are arranged in a matrix. The liquid crystal layer has substantially the same thickness in each pixel, and the alignment film is provided in each pixel so as to have a step on the electrode film on one substrate. The liquid crystal display panel, wherein the other substrate is provided on the electrode film provided with a step. 2. A pair of glass substrates facing each other, a liquid crystal layer injected between the pair of glass substrates, and a glass substrate on the glass substrate.
An alignment film provided at the interface with the liquid crystal layer, an electrode film and a color filter layer provided between the glass substrate and the alignment film, and a plurality of pixels arranged in a matrix. In the liquid crystal display panel, the liquid crystal layer has substantially the same thickness in each pixel, the color filter layer, in each pixel, in one substrate of the electrode film and the alignment film A liquid crystal display panel, wherein the liquid crystal display panel is provided with a step between them, and the other substrate is provided with a step between the glass substrate and the electrode film. 3. A pair of glass substrates facing each other, a liquid crystal layer injected between the pair of glass substrates, and on the glass substrate,
A liquid crystal display panel comprising an alignment film provided at an interface with the liquid crystal layer, and an electrode film provided between the glass substrate and the alignment film, wherein a plurality of pixels are arranged in a matrix. The liquid crystal layer has substantially the same thickness in each pixel, and a dielectric film is provided in each pixel so that a step is formed between the alignment film and the electrode film. A liquid crystal display panel characterized by being a thing. 4. A pair of glass substrates facing each other, a liquid crystal layer injected between the pair of glass substrates, and a glass substrate on the glass substrate.
A liquid crystal display panel comprising an alignment film provided at an interface with the liquid crystal layer, and an electrode film provided between the glass substrate and the alignment film, wherein a plurality of pixels are arranged in a matrix. The liquid crystal layer has substantially the same thickness in each pixel, and the alignment film has a pretilt angle that changes in a strip shape in each pixel. Display panel.