JPH10260646A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high aperture rate without causing any decrease in contrast by making the width of a black matrix narrower than wiring width. SOLUTION: Liquid crystal molecules 10 on a surface tilt part of an organic insulating film 3 with which a wire is coated are prevented from rising in the opposite direction from the normal direction and a reverse tilt domain is prevented from being formed by satisfying a relation of (θp-θi)/2>0 deg., where θp is the pretilt angle of the liquid crystal molecules 10 and θi is the maximum tilt angle to a flat part of the organic insulating film 3, and also satisfying a relation of Wb<Ws, where Ws is the width of a signal line and Wb is the width of a black matrix 5 provided on a counter substrate 19 to a 1st substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional liquid crystal display device using an array substrate. The conventional active matrix liquid crystal display device will be described with reference to FIG. FIG.
(a) and (b), 1 is a glass substrate, 2 is a glass substrate 1
The polarizing plate 3 disposed above is an organic insulating film made of, for example, an acrylic resin, 4 is a source electrode made of a plurality of metals such as Ti / Al, 5 is a black matrix, 6 is a color filter layer, 7 is A liquid crystal layer, 8 is ITO (transparent conductive film), 9 is an array substrate, 10 is a liquid crystal molecule tilted in a normal direction, 11 is a liquid crystal molecule tilted in a direction opposite to the normal direction,
12 is a reverse tilt domain. Here, after the source electrode 4 is formed on the lower glass substrate 1, an organic insulating film 3 made of an organic polymer is formed, and ITO 8 is formed on the organic insulating film 3; The glass substrate 1 is configured as an array substrate 9 through a contact hole formed in the organic insulating film 3 and connected to a drain electrode described later. Further, as shown in FIG. 4, the electrical isolation region of the pixel electrode formed of ITO 8 is above the data electrode. Such a conventional technique is disclosed, for example, in JP-A-62-112588.

[0003]

However, the conventional active matrix type liquid crystal display device has a problem that the array substrate 9
In FIG. 5, the pixel electrode is on the wiring,
Even if the organic insulating film 3 is coated as shown in (a) and (b), the organic insulating film 3 is actually completely coated with a coat of about 3 to 4 μm.
The inclination of the projection on the surface cannot be eliminated.
FIG. 5A is a cross-sectional view along the gate electrode when an organic insulating film is applied on the array substrate, and FIG. 5B is a cross-sectional view along the source electrode when the organic insulating film is applied on the array substrate. In FIG. 5A, reference numeral 13 denotes a gate electrode, 14 denotes a drain electrode, 15 denotes a gate insulating film, and 16 denotes an a-Si layer.
The ITO 8 on the organic insulating film 3 is connected to the drain electrode 14 through the contact hole 17 as shown in FIG. As is apparent from FIG.
Alternatively, the inclination θi of the cross section on the wiring formed by the source electrode 4
4B, the lines of electric force 18 between the gate electrode 13 and the pixel electrode are distorted as shown in FIG. 4B, so that the reverse tilt domains 12 having different pretilt angles are generated. Such a generation of the reverse tilt domain 12 results in a significant decrease in contrast. For this reason, conventionally, it was necessary to make the wiring thicker to hide this area, or to make the width of the black matrix 5 formed on the counter substrate 19 with respect to the array substrate 9 larger than the wiring width. As a result, there is a problem that the aperture ratio is reduced.

[0004] An object of the present invention is to solve the above-described problem even if the width of the black matrix is made smaller than the wiring width.
An object of the present invention is to provide a liquid crystal display device that can achieve a high aperture ratio without causing a decrease in contrast.

[0005]

In order to solve the above-mentioned problems, a liquid crystal display device of the present invention comprises a scanning line and a signal line made of a light-shielding substance on a first substrate and a non-linear element at an intersection thereof. An insulating film made of an organic polymer is formed on the first substrate on which the scanning lines, signal lines, and non-linear elements are formed, and a transparent conductive material electrically connected to a drain is formed on the insulating film. In a liquid crystal display device formed using an array substrate formed with a film, the pretilt angle of the liquid crystal molecules at the interface of the alignment film is θp, and the plane of the insulating film surface made of an organic polymer coated on the wiring is The maximum inclination angle is θ
When i, the relationship of (θp−θi) / 2 ≧ 0 ≧ is satisfied, the width of the signal line is Ws, and the width of the black matrix provided on the counter substrate with respect to the first substrate is W.
When b is satisfied, the relationship of Wb <Ws is satisfied.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention. Members corresponding to those described with reference to FIGS. 4 and 5 are denoted by the same reference numerals and description thereof is omitted. FIGS. 4A and 4B show the organic insulating film 3 along the source electrode 4 of the array substrate 9 coated with PC302 (trade name) manufactured by Japan Synthetic Rubber Co., Ltd. as an example of an organic polymer (acrylic). The cross section is schematically shown. As is clear from this figure, even if the organic insulating film 3 is applied, it is difficult to make the protrusions on the wiring sufficiently smooth. In particular, the wiring has a raised shape and the inclination θi remains.
FIG. 2 is a measurement diagram showing the relationship between the applied film thickness of the organic insulating film, the surface step after application, and the maximum surface inclination θi. As is apparent from FIG. 2, the organic insulating film 3 of the array substrate 9 is formed.
The maximum step before coating is 1.5 μm, and up to about 3 μm, the step tends to decrease with an increase in film thickness. It turns out that it is not so effective. FIG. 3 is a measurement diagram showing a relationship between a coating film thickness of an organic insulating film and a change in transmittance. Since the organic insulating film 3 is formed below the pixel electrode, FIG.
As is clear from FIG. 5, the transmittance decreases as the thickness of the organic insulating film 3 increases, which is not preferable as a characteristic of the liquid crystal display device. Generally, since the transmittance of the liquid crystal display device is preferably 90% or more, the thickness of the organic insulating film 3 needs to be 3.5 μm or less. From the above results, when the thickness of the organic insulating film 3 is set to about 3 μm in order to obtain good transmittance as a liquid crystal display device, the surface step after application of the organic insulating film 3 is about 0.4 μm, It was found that the inclination remained about 8 °.

[0007] Table 1 shows that, in the structure of the array substrate 9 of the present embodiment, the above-mentioned PC302 manufactured by Japan Synthetic Rubber Co., Ltd. was applied as the organic insulating film 3 by 3 µm and prebaked at 90 ° C. Exposure and development were performed using a mask with holes (not shown) to create contact holes 17 at 220 ° C.
After the post-baking, the pretilt angles θp and (θp−) when the pretilt angle is changed by changing the type of the alignment film applied on the array substrate 9 on which the ITO 8 is formed.
θi) / 2 and the presence or absence of the reverse tilt domain.

[0008]

[Table 1]

As an alignment film, AL1051 (trade name) manufactured by Japan Synthetic Rubber Co., Ltd., which is an alignment material having a pretilt angle θp = 1 °, and JALS-246 manufactured by Japan Synthetic Rubber Co., Ltd., as an alignment material having a pretilt angle θp = 7 °. -R1 was mixed to produce liquid crystal display devices with various pretilt angles. From this experimental result, (θp−θi) / 2
It was found that the generation of the reverse tilt domain 12 was suppressed when ≧ 0 °. This result will be considered considering the orientation of liquid crystal molecules.

FIG. 1 (a) shows the driving voltage in the liquid crystal display device of the present embodiment which satisfies the relationship (θp−θi) / 2 ≧ 0 ° when the inclination angle of the cross section is θi and the pretilt angle is θp. 3 schematically shows the alignment state of the liquid crystal molecules 10 when no voltage is applied. In FIG. On the other hand, FIG. 4A shows that the inclination angle θi and the pretilt angle θp are θp−
9 schematically shows the orientation state of liquid crystal molecules when a driving voltage is not applied in a conventional liquid crystal display device having a relationship of θi <0 °. Here, (θp−θi) / 2 indicates the tilt angle of the liquid crystal molecules at the center position in the thickness direction of the liquid crystal layer 7. This is defined as the pretilt angle θpm of the midbrain molecule 20.
Is defined.

In the liquid crystal display device of the present embodiment when no drive voltage is applied as shown in FIG. 1A, θpm ≧ 0. For this reason, even if a lateral electric field is applied by the electric lines of force 18 when the driving voltage is applied, the torque acting on the liquid crystal molecules is reduced, so that the liquid crystal on the inclined surface of the organic insulating film 3 is reduced as shown in FIG. The rising direction of the molecule is the normal direction. On the other hand, when the driving voltage is not applied as shown in FIG.
In the conventional liquid crystal display device which becomes 0, θpm <0, and the liquid crystal molecules 11 slightly stand in the direction opposite to the normal tilt direction from the initial state. The torque acting on the liquid crystal molecules increases. Therefore, as shown in FIG. 4B, the liquid crystal molecules 11 on the inclined surface of the organic insulating film 3 rise in the direction opposite to the normal direction, and the reverse tilt domain 12 is generated. Therefore, in the conventional liquid crystal display device, the reverse tilt domain 12
In order to hide the influence of the above, it is necessary to make the width of the black matrix 5 of the counter substrate 19 wider than the width of the signal line formed by the source electrode 4 as shown in FIG.

In contrast to the conventional liquid crystal display device, according to the liquid crystal display device of this embodiment, the pretilt angle θp of the alignment film is set to 4 ° or more under the conditions shown in (Table 1). Since the occurrence of the tilt domain 12 can be prevented, it is not necessary to hide the influence of the reverse tilt domain 12 in the black matrix 5 of the counter substrate 19. Therefore, in the liquid crystal display device of the present embodiment, the width of the signal line formed by the gate electrode 13 is 9 μm, and the width of the black matrix 5 is 6 μm.
If the wiring metal of the black matrix 5 is exposed on the display surface, the reflectance there will be large, so it is important to suppress this. As a material of such a black matrix 5, a material having a lower reflectance than a wiring metal such as low-reflection chromium oxide or resin is particularly preferable.

When the display characteristics of the liquid crystal display device of this embodiment in which the screen size and the number of pixels are 12.1 inches and 1280 trios * 768 dots are measured, the aperture ratio is 78%, and the transmittance is 78%. A measured value of 8.5% and a contrast of ≧ 300 were obtained, showing excellent display characteristics as a liquid crystal display device. On the other hand, the measured values of the conventional liquid crystal display device described with reference to FIG. 4 were 70% in aperture ratio, 7.6% in transmittance, and 300 in contrast, respectively.

[0014]

As described above, according to the liquid crystal display device of the present invention, the pretilt angle of the liquid crystal molecules at the interface of the alignment film is θp, and the plane of the surface of the insulating film made of the organic polymer coated on the wiring is When the maximum inclination angle with respect to the portion is θi, the relationship of (θp−θi) / 2 ≧ 0 ° is satisfied, the width of the signal line is Ws, and the black matrix provided on the counter substrate with respect to the first substrate. When the width is Wb, Wb
By satisfying the relationship of <Ws, the liquid crystal molecules on the inclined surface of the organic insulating film can be prevented from rising in the direction opposite to the normal direction, and the generation of the reverse tilt domain can be prevented. The width of the black matrix can be made smaller than the width of the wiring of the array substrate. As a result, a liquid crystal display device having a high aperture ratio and high transmittance can be easily realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a measurement diagram showing a relationship between a coating film thickness of an organic insulating film, a surface step after coating, and a maximum surface inclination in the liquid crystal display device of the present embodiment.

FIG. 3 is a measurement diagram showing a relationship between a coating film thickness of an organic insulating film and a change in transmittance in the liquid crystal display device of the present embodiment.

FIG. 4 is a configuration diagram of a conventional liquid crystal display device using an array substrate.

FIG. 5 is a sectional view of an array substrate in a conventional liquid crystal display device.

[Explanation of symbols]

1: glass substrate, 2: polarizing plate, 3: organic insulating film,
4: Source electrode, 5: Black matrix, 6: Color filter, 7: Liquid crystal layer, 8: ITO (transparent conductive film), 10, 11: Liquid crystal molecule, 12: Reverse tilt domain,
13 ... gate electrode, 14 ... drain electrode, 15 ... gate insulating film, 16 ... a-Si layer, 17 ... contact hole, 1
8 ... electric lines of force, 19 ... counter substrate, 20 ... midplane molecule.

Claims (1)

[Claims] A non-linear element is formed on a first substrate at a scanning line and a signal line made of a light-shielding substance and at an intersection thereof, and the first line formed with the scanning line, the signal line and the non-linear element is formed. A liquid crystal display device formed using an array substrate formed by forming an insulating film made of an organic polymer on the substrate of above, and forming a transparent conductive film electrically connected to the drain on the insulating film, When the pretilt angle of the molecule at the interface of the alignment film is θp and the maximum inclination angle of the surface of the insulating film made of the organic polymer coated on the wiring with respect to the plane portion is θi, (θp−θi) / 2 ≧ 0 ° Where Wb is the width of the signal line and Wb is the width of the black matrix provided on the counter substrate with respect to the first substrate, the relationship Wb <Ws is satisfied. Liquid crystal display device.