JP2932817B2 - Active matrix type liquid crystal panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal panel applied to a liquid crystal display or the like.

[0002]

2. Description of the Related Art Among display elements using a liquid crystal panel,
2. Description of the Related Art A display element using an active matrix liquid crystal panel in which a transistor is arranged for each pixel has excellent features such as being thin, low power consumption, high contrast and high quality display. For this reason, in recent years, development has been actively pursued as a substitute for a television or the like using a cathode ray tube.

Hereinafter, a structure of a conventional active matrix type liquid crystal panel will be briefly described. FIG. 2 is a schematic diagram of one pixel of the active matrix type liquid crystal panel. A transistor driving wiring 22 (hereinafter, referred to as a gate line) and a pixel voltage applying wiring 23 (hereinafter, referred to as a source line) exist around the periphery of the pixel electrode 21. By turning on / off the transistor 24 by a signal from the gate line 22, the voltage of the source line 23 is applied to the pixel electrode 21 to perform display.

FIG. 3 is a part of a sectional view of one pixel of an active matrix type liquid crystal panel. This shows a part of the panel cross section along a line parallel to the gate line and orthogonal to the source line in the schematic diagram of FIG.

[0005] 31 is a glass substrate, 32 is a pixel electrode, 33
Is a cross section of the source line, 35 is a passivation film, 36 is a liquid crystal, 37 is a polyimide alignment film, 38 is a counter electrode, 39 is a counter substrate, 40 is a color filter, and 41 and 42 are polarizing plates. When the transistor is turned on and the potential of the source line 33 is applied to the pixel electrode 32, the pixel electrode 32 and the counter electrode 3
A voltage between 8 is applied to the liquid crystal 36 to perform display.

[0006] In order to perform good display on an active matrix type liquid crystal panel, it is important that the liquid crystal on the pixel uniformly respond to a uniform initial alignment of liquid crystal molecules and a vertical electric field between the substrates.

As can be seen from FIG. 3, in a normal active matrix type liquid crystal panel, a source line 33 or a gate line exists near a pixel electrode 32.
Further, since the potential of the source line 33 is constantly changing, a potential difference occurs between the pixel electrode 32 and the source line 33.
Therefore, the liquid crystal in the pixel includes the pixel electrode 32 and the counter electrode 3
An electric field between the pixel electrode 32 and the source line 33 is applied to the pixel electrode 32 in a lateral direction in addition to the electric field between the pixel electrodes 32. This latter electric field is hereinafter referred to as a horizontal electric field.

The rubbing direction in a conventional active matrix type display is shown in FIG. As can be seen, the orientation direction of the liquid crystal molecules on the pixel electrode side is 45 degrees from the source line. For this reason, the arrangement distortion of the liquid crystal molecules in the pixel due to the lateral electric field is increased, and there is a defect that display defects such as light leakage or the like occur as reverse tilt disclination lines.

Further, in order to reduce the influence of such a lateral electric field, a display has been put to practical use in which an alignment process of an organic alignment film on a pixel substrate side is performed along a source line.

However, when displaying in the TN mode,
In this method, about 2
The liquid crystal molecules have a twist angle in a region within a micron, and it is inevitable that an alignment distortion due to a lateral electric field occurs.

[0011]

Since such an area of the reverse tilt disclination line in the pixel plane cannot be used for display, the domain area of the pixel is usually masked so that the domain cannot be seen. ing. For this reason, the pixel aperture ratio was reduced, and it was difficult to obtain a high-luminance panel.

An object of the present invention is to provide an active matrix type panel capable of suppressing the occurrence of reverse tilt disclination lines in a pixel plane due to the above-mentioned lateral electric field and obtaining a good display and a high pixel aperture ratio. With the goal.

[0013]

In order to achieve the above object, an active matrix type liquid crystal panel according to the present invention comprises a director for liquid crystal molecules at a position where the electric field intensity is maximized temporally and spatially in the panel. Is parallel to the source line, and in particular, the alignment processing direction of the alignment film on the pixel substrate side (hereinafter, referred to as an array-side rubbing direction) is at least 1 degree or more and 30 degrees or less from the source line direction, The rubbing direction of the alignment film on the opposing substrate is orthogonal or almost orthogonal to the rubbing direction on the array side , and the twisting direction of the liquid crystal
In the area closer to the pixel substrate than the middle between the pixel substrate and the counter substrate.
Where the director of the liquid crystal molecules is parallel to the source line.
It is characterized by having a twisting direction as having.

[0014]

The mechanism of the generation of the reverse tilt disclination line in the pixel plane by the lateral electric field will be described below by taking the source line and the pixel electrode as examples.

It is considered that the reverse tilt disclination line in the pixel is basically generated in the process of relaxing the alignment distortion of the liquid crystal molecules due to the lateral electric field between the source line and the pixel electrode. When the horizontal electric field is weak, the liquid crystal molecules near the edge of the pixel electrode are in a no-multi tilt state, but when the horizontal electric field is strong, the liquid crystal molecules are in a reverse tilt state. At this time, a reverse tilt disclination line is generated at the boundary between the reverse tilt and the no multiple tilt. The driving of the active matrix type panel is such that the horizontal electric field strength repeats the strength. Therefore, the liquid crystal molecules near the edge of the pixel electrode alternately repeat no-multi tilt and reverse tilt according to the strength of the horizontal electric field.

In order to alleviate the reverse tilt disclination line formed at this time, the reverse tilt disclination line enters the pixel in the process of rearranging the liquid crystal molecules on the pixel. This is considered to be the mechanism for generating the reverse tilt disclination line in the pixel plane.

In order to prevent a reverse tilt disclination line from being formed in a pixel, it is necessary to set the alignment direction of liquid crystal molecules in a direction that is less responsive to a lateral electric field.

In general, liquid crystal molecules have dielectric anisotropy. Therefore, in the case of a liquid crystal having positive anisotropy, directors of liquid crystal molecules are aligned along the direction of the electric field. Ease of movement of liquid crystal molecules with respect to an electric field largely depends on the angle between the direction of the electric field and the liquid crystal molecules.

A liquid crystal having a positive dielectric anisotropy hardly responds to an electric field perpendicular to the director of liquid crystal molecules. Therefore, if the direction of the horizontal electric field is perpendicular to the director of the liquid crystal molecules, the liquid crystal molecules are unlikely to respond even in the presence of the horizontal electric field, and the occurrence of the reverse tilt disclination line can be suppressed.

In a TN panel having a structure in which liquid crystal molecules are twisted by 90 degrees between the upper and lower substrates, the liquid crystal molecules have a twist angle. Therefore, it is difficult to arrange the liquid crystal molecules so that the director of the molecules is perpendicular to the horizontal electric field in all the regions where the horizontal electric field exists.

Therefore, when a lateral electric field is present, it is important in which region in the panel the director of the liquid crystal molecules is perpendicular to the lateral electric field. Horizontal with normal panel drive
The electric field is large in a region within about 2 μm on the pixel.
The panel gap is usually about 5 μm. Accordingly
As shown in FIG.
In the region close to the substrate, the liquid crystal director
If there is a row, the director of the liquid crystal molecules is
At the position where the horizontal electric field is strongest,
Disclination within pixels due to reduced effect of electric field
The line is eliminated. Also, the configuration shown in FIG.
In order for the liquid crystal twist direction to be
Left or right depending on the combination of the rubbing directions
Direction is uniquely determined.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized in that directors of liquid crystal molecules are arranged along a source line at a position where the intensity of a transverse electric field is highest temporally and spatially in a panel.

In normal panel driving, the strength of the lateral electric field is considered to be large in a region of about 2 μm or less on a pixel. If the panel gap is 5 microns,
To align the major axes of liquid crystal molecules along the source line within 2 microns, the rubbing direction on the array side should be at least 1 degree or more and 30 degrees or less from the direction of the source line, and the rubbing direction of the opposing substrate should be the same as the rubbing direction on the array side. What is necessary is just to make it orthogonal.

FIG. 1 shows an embodiment of the active matrix type liquid crystal panel of the present invention. Although the embodiment describes a panel compatible with a direct-view display, the same applies to a panel compatible with a projection display.

A pixel electrode 2, a source line 3 and the like were formed on a glass substrate 1 by using a technique of vapor deposition and etching. Further, a passivation film 4 was deposited. A color filter 6 and a counter electrode 7 were provided on the counter substrate 5. Further, a polyimide alignment film 8 is formed on the passivation film 4 and the counter electrode 7.
And 9 were printed.

The rubbing directions of the upper and lower substrates need to be determined in consideration of the distribution of the electric field intensity in the panel. The distribution of the electric field intensity in the panel is determined by the electric potential of the pixel, the source line, and the like, and the three-dimensional structure of the source line, the pixel electrode, and the like.

In order to determine the rubbing directions of the upper and lower substrates, an experiment was conducted by changing the rubbing direction of the panel.
With a normal panel drive voltage, in the case of a TN panel, it was found that there was an angle at which the reverse tilt disclination line was suppressed in the rubbing direction within 30 ° from the source line.

The angle at this time is related to the panel drive voltage and the panel configuration. Rubbing treatment was performed on the polyimide alignment films 8 and 9 using a nylon cloth. The direction of the rubbing treatment was a direction at an angle of 18 degrees from the source line on the array side. The rubbing direction on the counter substrate side was made orthogonal to the array side. The rubbing direction was such that the long axis of the liquid crystal molecules was parallel to the source line at a position 1 micron above the pixel substrate surface when the panel gap was set to 5 microns. FIG. 5 shows the rubbing direction of this embodiment. still,
The array-side rubbing direction may be any angle other than the above-mentioned 18 degrees and at least 1 degree or more and 30 degrees or less.

Hereinafter, a panel was prepared by an ordinary method. When a voltage of +4 V was applied to the pixel electrode from the source line, and then a 4 V AC waveform was applied to the source line, and the panel was observed in normally white mode, the reverse tilt disk which had conventionally appeared largely in the center of the pixel was observed. A ligation line appears near the edge of the pixel electrode.
Good display was obtained. In addition, the pixel aperture ratio could be made higher than before because the reverse tilt disclination area became smaller.

[0030]

According to the present invention, in an active matrix type liquid crystal panel, the angle of the rubbing direction on the array side is at least 1 degree and within 30 degrees from the source line direction, and the rubbing direction on the counter electrode side is orthogonal to the array side. Alternatively, they are substantially orthogonal. At this time, in the region where the horizontal electric field intensity is large, the liquid crystal molecules are arranged almost parallel to the source line,
The effect of the lateral electric field is reduced. Therefore, the reverse tilt disclination line in the pixel is eliminated, and a good display display and a high pixel aperture ratio can be realized.

In the present invention, like a normal TN panel,
This naturally includes not only the case where the rubbing directions of the upper and lower substrates are orthogonal and the twist angle is 90 degrees, but also the case where the twist angle is almost close to 90 degrees.

Further, although polyimide is used as the alignment film, an organic alignment film capable of performing TN type alignment processing is almost allowed.

The same applies even if the passivation film in the embodiment is not provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of an active matrix type liquid crystal panel according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of one pixel of an active matrix type liquid crystal panel.

FIG. 3 is a sectional view of a conventional active matrix type liquid crystal panel.

FIG. 4 is a schematic diagram of one pixel showing a rubbing direction of a conventional active matrix type liquid crystal panel.

FIG. 5 is a schematic diagram of one pixel showing a rubbing direction of the active matrix type liquid crystal panel according to the embodiment of the present invention.

[Explanation of symbols]

2 pixel electrode 3 source line 7 counter electrode 8, 9 polyimide alignment film 10 liquid crystal

Claims (2)

(57) [Claims] A liquid crystal between a first substrate and a second substrate, at least a pixel electrode, a transistor driving wiring, a pixel potential applying wiring, and an organic alignment film on the first substrate;
In an active matrix type liquid crystal panel having at least an electrode and an organic alignment film on a second substrate, as an alignment process for the organic alignment film, a time period between the first substrate and the second substrate is reduced by driving the panel. and in spatially the electric field intensity becomes the maximum position, orientation treatment as director of the liquid crystal molecules is parallel to the <br/> pixel potential applying wiring subjected
The active matrix type liquid crystal panel, characterized by being. 2. An alignment process for an organic alignment film on an organic alignment film on a first substrate, wherein the direction of alignment processing on the organic alignment film is at least 1 degree or more and 30 degrees or less from a pixel potential application wiring direction.
An inner alignment treatment direction for the second organic alignment film on the substrate is near the perpendicular or perpendicular to the alignment treatment direction for the first organic alignment film on the substrate, further first substrate and the second
Direction of director of liquid crystal molecules between different substrates
Is closer to the first substrate than the middle between the first substrate and the second substrate.
In the near area, the director of the liquid crystal molecules is the wiring for applying the pixel potential
2. The active matrix type liquid crystal panel according to claim 1, wherein the liquid crystal panel has a twist direction having a portion parallel to the liquid crystal panel.