JPH10301140A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which generates no domain, has no unevenness in grittiness, and is excellent in display quality, in a wide temperature range. SOLUTION: Gate bus lines 12 formed in a matrix, a gate insulating film 20, a source bus line 11, TFTs 13, picture element electrodes 14 are provided on a transparent insulating substrate 10 like glass, etc., and a voltage is applied to these picture element electrodes 14 via TFTs 13. On the part where domain is generated, additional electrodes 25a, 25b branched from the source bus lines 11a, 11b are provided between the gate bus line 12 and the picture element electrode 14 in parallel with the gate bus line 11. Thus, by providing an additional electrode 25, it is possible to shield the picture element electrode 14 against a lateral electric field from the gate bus line 12. Therefore, there is no turbulence in orientation of liquid crystal molecules, and no domain is observed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an active matrix type liquid crystal display device having a switching element such as a thin film transistor for each pixel.

[0002]

2. Description of the Related Art FIG. 5 is a plan view of an active matrix substrate of a conventional liquid crystal display device, and FIG.
FIG.

In FIG. 5 and FIG. 6, a gate bus line 32, a gate insulating film 40, a source bus line 31, and a thin film transistor (a thin film transistor as a switching element) formed in a matrix on a transparent insulating substrate 30 such as glass. Hereinafter, this is abbreviated as TFT.) 33 and a pixel electrode 34 are provided, and a voltage is applied to the pixel electrode 34 from the source bus line 31 via the TFT 33. Further, an alignment film 38 made of polyimide is formed on the pixel electrode 34, and the alignment is performed by rubbing. Thus, the active matrix substrate 45 is manufactured.

On a transparent insulating substrate 30 such as glass, a light-shielding film 36 for shielding light from the TFT 33 and light from the pixel electrode 34 is provided, and a counter electrode 37 is formed thereon. ing. An alignment film 38 made of polyimide is formed on the counter electrode 37, and is subjected to an alignment process by rubbing. Thus, the counter substrate 35 is manufactured.

[0005] The active matrix substrate 45 and the opposing substrate 35 are bonded to each other, and a liquid crystal layer 39 filled with liquid crystal is provided between the substrates to manufacture a liquid crystal display device.

In the liquid crystal display device, a voltage is applied through a TFT 33 to a liquid crystal layer 39 filled with liquid crystal between a pixel electrode 34 and a counter electrode 37, and the liquid crystal molecules are uniformly tilted in the vertical direction to thereby perform optical modulation. And the light transmittance is controlled for each pixel electrode.

In order to uniformly tilt the liquid crystal molecules on the pixel electrode in the vertical direction as described above, when no voltage is applied, the liquid crystal molecules slightly tilt in the vertical direction to the substrate surface depending on the rubbing direction. . This angle is called the pretilt angle.

In accordance with the voltage applied to the liquid crystal layer, each liquid crystal molecule uniformly rotates in the vertical direction according to the tilt rotation direction of the pretilt angle.

[0009]

However, the active matrix substrate 45 has a gate bus line 32 and a source bus line 31 around a pixel electrode 34 for applying a voltage to the liquid crystal layer 39. A lateral electric field is generated around the periphery of the. It is known that, due to the degree of the electric field in the horizontal direction, unevenness in transmittance occurs in the pixel electrode due to disorder in the alignment of liquid crystal molecules around the pixel electrode 34. Such a region is generally called a domain.

[0010] As described above, when an image is displayed on a liquid crystal display device in which domains are generated and the image quality is observed, unevenness of roughness is recognized, which causes a significant decrease in display quality.

As a result of confirming the dependence on temperature, it was found that even when almost no domains were generated at room temperature, 40 to 50
Domains are generated from about ° C., and as the temperature increases, the display quality is significantly reduced by the domains.

Microscopic observation of the location where the domain occurs in the liquid crystal display device shows that, as shown in FIG.
It is confirmed that the domain extends to the inside of the pixel electrode 34 at the portion where is parallel to the gate bus line 32 (domain generation location 6). on the other hand,
It was confirmed that almost no domains were generated in the horizontal electric field between the pixel electrode 34 and the source bus line 31.

FIG. 8 is a conceptual diagram for explaining a horizontal electric field between the pixel electrode 34 and the gate bus line 32 in the active matrix substrate 45 in the BB sectional view of FIG. Since the voltage of the pixel electrode 34 and the voltage of the gate bus line 32 are different from each other, a horizontal electric field is generated between the pixel electrode 34 and the gate bus line 32.
Disorder in the alignment of liquid crystal molecules occurs, and domains are observed.

Therefore, in order to prevent domains, it is necessary to reduce the electric field in the horizontal direction between the pixel electrode 34 and the gate bus line 32 shown in FIG.

Although the liquid crystal display device is usually used at room temperature, the brightness of the backlight is increased to obtain a bright screen, and the heat generated by the backlight causes a rise in the temperature of the liquid crystal display device.

When mounted on a car or the like, 80
It is required that good display quality can be obtained even in an environment of about ° C or higher.

As described above, preventing deterioration of display quality not only at normal temperature but also at high temperature is an important issue for expanding the application range of the liquid crystal display device.

The present invention has been made in order to solve the above problems, and provides a liquid crystal display device which is free from domains over a wide temperature range, has no unevenness in roughness, and has excellent display quality. is there.

[0019]

According to the present invention, there is provided a scanning wiring,
An active matrix substrate on which a signal wiring, a switching element, a pixel electrode to which a potential is applied via the switching element is formed, and a counter substrate on which a counter electrode is formed are arranged to face each other via a liquid crystal layer. In the liquid crystal display device, an additional electrode branched from the signal wiring is formed between the scanning wiring and the pixel electrode.

The operation of the above configuration will be described. By disposing an electrode electrically connected to the source bus line between the pixel electrode and the gate bus line, a horizontal electric field from the gate bus line can be shielded.

As a result, a domain can be prevented from being generated in the pixel electrode, and a domain can be prevented from being generated over a wide temperature range, and a liquid crystal display device having excellent display quality without roughness can be provided.

[0022]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a plan view of an active matrix substrate of a liquid crystal display device according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view of the liquid crystal display device taken along the line AA in FIG.

In FIG. 1 and FIG. 2, a gate bus line 12 and a gate insulating film 2 which are scanning wirings formed in a matrix are formed on a transparent insulating substrate 10 such as glass.
0, source bus lines 11a, 11b,
A TFT 13 and a pixel electrode 14 are provided as switching elements, and a voltage is applied to the pixel electrode 14 from the source bus line 11 via the TFT 13.

At the domain occurrence location 6 shown in FIG.
An additional electrode 25 branched from the source bus line 11 is provided between the gate bus line 12 and the pixel electrode 14 in parallel with the gate bus line 11. Specifically, the additional electrode 25
a branches off from the source bus line 11a,
b branches off from the source bus line 11b.

In the first embodiment, the additional electrodes 25a, 25b
Is longer than the width of the pixel electrode 14 and the additional electrode 25
a, 25b, pixel electrode 14 and gate bus line 12
Was set to 3 μm, and each electrode was set so as not to overlap.

Further, an alignment film 18 made of polyimide is formed on the pixel electrode 14 and is subjected to an alignment process by rubbing. Thus, the active matrix substrate 5 is manufactured.

On a transparent insulating substrate 10 such as glass, a light-shielding film 16 for shielding light from the TFT 13 and light from the pixel electrode 14 is provided, and a counter electrode 17 is formed thereon. ing. An alignment film 18 made of polyimide is formed on the counter electrode 17 and subjected to an alignment process by rubbing. Thus, the counter substrate 15 is manufactured.

The active matrix substrate 5 and the counter substrate 15 are bonded to each other, and a liquid crystal layer 19 filled with liquid crystal is provided between the substrates to manufacture a liquid crystal display device.

FIG. 3 shows the pixel electrode 14 and the additional electrode 2 on the active matrix substrate 5 in the sectional view taken on line A--A in FIG.
FIG. 5 is a conceptual diagram for explaining a relationship between a horizontal electric field between the gate bus line and a gate bus line. Gate bus line 12
And the additional electrode 25 branched from the source bus line 11b.
Since the voltage differs between the gate bus line 12 and the additional electrode 25b, a horizontal electric field is generated between the gate bus line 12 and the additional electrode 25b. On the other hand, between the pixel electrode 14 and the additional electrode 25b branched from the source bus line 11a, as described in the related art, there is almost no influence of the horizontal electric field. The additional electrode 25a is the same as the additional electrode 25b.

As described above, the provision of the additional electrode 25 enables the pixel electrode 14 to shield a horizontal electric field from the gate bus line 12. Accordingly, there is no disturbance in the alignment of the liquid crystal molecules, and no domains are observed.

In the first embodiment, as a result of observing the generation of the domain, no generation of the domain was found even in an environment of 80 ° C.

Therefore, even in a wide temperature range, a liquid crystal display device having no display domain, no unevenness of roughness, and excellent display quality can be realized.

(Embodiment 2) FIG. 4 is a plan view of an active matrix substrate of a liquid crystal display device of Embodiment 2.

The second embodiment is different from the first embodiment in the shape, the branch form, and the location of the additional electrode 25 branched from the source bus line 11. Otherwise, the configuration is the same as that of the first embodiment, and the description is omitted.

In FIG. 4, the source bus lines 11c,
11d and pixel electrode 14 surrounded by gate bus line 12
On the other hand, the additional electrode 25 includes an additional electrode 25c branched from the source bus line 11c and a source bus line 11d.
And additional electrodes 25d and 25e branched from.

By providing the additional electrode 25 as described above, the pixel electrode 14 can shield a horizontal electric field from the gate bus line 12. Accordingly, there is no disturbance in the alignment of the liquid crystal molecules, and no domains are observed.

As for the second embodiment, as a result of observing the generation of the domain, no generation of the domain was found even under the environment of 80 ° C.

Accordingly, even in a wide temperature range, a liquid crystal display device having no display domains, no unevenness in roughness, and excellent display quality can be realized.

Note that the pattern of the additional electrode 25 is not limited to the embodiment, since various patterns are conceivable besides the first and second embodiments.

[0041]

By arranging an additional electrode electrically connected to a source bus line between a pixel electrode and a gate bus line, a horizontal electric field from the gate bus line can be shielded.

As a result, it is possible to prevent a domain from being generated in the pixel electrode, and to provide a liquid crystal display device which has no domain generation over a wide temperature range and has excellent display quality without roughness.

[Brief description of the drawings]

FIG. 1 is a plan view of an active matrix substrate of a liquid crystal display device according to a first embodiment.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a conceptual diagram for explaining a relationship of a horizontal electric field between an additional electrode 25 and a gate bus line 12;

FIG. 4 is a plan view of an active matrix substrate of the liquid crystal display device according to the second embodiment.

FIG. 5 is a plan view of an active matrix substrate of a conventional liquid crystal display device.

FIG. 6 is a sectional view taken along line BB of FIG. 5;

FIG. 7 is a diagram showing locations where domains occur.

FIG. 8 is a conceptual diagram for explaining a relationship of a horizontal electric field between a pixel electrode and a gate bus line.

[Explanation of symbols]

 5 45 Active matrix substrate 6 Domain generation location 10 30 Substrate 11 31 Source bus line 12 32 Gate bus line 13 33 TFT 14 34 Pixel electrode 15 35 Opposite substrate 16 36 Light shielding film 17 37 Opposite electrode 18 38 Alignment film 19 39 Liquid crystal layer 20 40 gate insulating film 25 additional electrode

Claims (1)

[Claims] An active matrix substrate on which a scanning wiring, a signal wiring, a switching element, and a pixel electrode to which a potential is applied via the switching element are formed;
In a liquid crystal display device in which a counter substrate on which a counter electrode is formed is disposed to face through a liquid crystal layer, an additional electrode branched from the signal wiring is formed between the scanning wiring and the pixel electrode. A liquid crystal display device characterized by the above-mentioned.