JP3135689B2 - Active matrix type liquid crystal display - 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 display in which a liquid crystal layer composed of liquid crystal molecules is held between a pair of electrodes.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device in which a liquid crystal layer made of liquid crystal molecules is held between a pair of electrodes has been used as a computer display device or a television display device by utilizing the features of light weight and low power consumption. It is being used in the field.

[0003] For example, a projection type liquid crystal display device in which light transmitted through a liquid crystal layer is projected and displayed by an optical lens system will be described as an example. The projection type liquid crystal display device has a structure in which light from a light source is separated into three primary colors by a filter, and the light is transmitted through the liquid crystal display device, combined again, and projected.

FIG. 9 shows a conventional active matrix type liquid crystal display device (701) from a counter substrate (801) to an array substrate (711).
FIG. 10 is a schematic front view when viewed from FIG. 10, and FIG. 10 is a schematic sectional view taken along the line DD ′ in FIG.

A video signal line (715) for transmitting a video signal on a transparent insulating substrate (713) and a scanning signal line for transmitting a scanning signal for controlling on / off of a switch element (721) composed of a MOS transistor. (717) are arranged in a matrix through an interlayer insulating film (771), and a switch element (721) is provided in a region surrounded by a video signal line (715) and a scanning signal line (717).
The pixel electrode (731) connected to the pixel electrode is disposed. Then, an alignment film (78) rubbed in a predetermined direction is formed thereon.
1) is installed and the array substrate (711) is configured.

A counter electrode (813) is disposed on the entire surface of a transparent insulating substrate (811), and an alignment film (815) rubbed in a predetermined direction is provided thereon. It is configured. Then, the array substrate (711) and the opposite substrate
The active matrix type liquid crystal display device (701) is configured by holding the liquid crystal layer (901) between them at intervals of 5.0 microns.

In such a liquid crystal display device (701), in order to improve the contrast of the display pixel and to prevent the display quality from deteriorating due to the photocurrent caused by the light incident on the switch element (721), A light-shielding layer having an opening smaller than the pixel electrode (731) was provided on the array substrate (711) side or the counter substrate (801) side.

[0008]

In the above-mentioned liquid crystal display device (701), the alignment film (781) itself is poorly aligned due to a step in the pattern on the array substrate (711), and the image signal lines (715) and the scanning lines are not scanned. Due to the poor orientation of the liquid crystal molecules due to the influence of the horizontal electric field from the signal line (717), a display defect due to a region contrary to the normal pretilt, that is, a reverse tilt domain has occurred.

The reverse tilt domain has a transmittance different from that of a normal alignment region (no-multi tilt domain) depending on the display state, thereby causing display failure or causing a disc between the no-multi tilt domain and the reverse tilt domain. This causes the generation of a region that causes light leakage called a ligation line, which causes a decrease in contrast and the like.

[0010] As a method of preventing the contrast from being lowered by the reverse tilt domain, for example, Japanese Patent Laid-Open Publication No.
3-111820 discloses a technique for removing a part of a counter electrode so as to prevent a horizontal electric field. However, such patterning of the counter electrode is not preferable in terms of manufacturing because it makes it difficult to position the counter electrode with the array substrate.

Japanese Patent Application Laid-Open No. 3-243934 discloses a technique in which the distance between a pixel electrode and a video signal line is equal to or greater than the thickness of a liquid crystal layer. However, it is not possible to prevent poor alignment due to a substantial lateral electric field.

In recent years, the size of each display pixel constituting a liquid crystal display device has been steadily miniaturized. The inventors have confirmed in experiments that the reverse tilt domain is not reduced even when the display pixel size is reduced. Therefore, the influence of the reverse tilt domain increases as the display pixel size decreases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above technical problems, and has as its object to provide an active matrix type liquid crystal display device which can effectively prevent a decrease in contrast due to a reverse tilt domain. It is.

[0014]

According to the present invention, there is provided a pixel electrode which is arranged via a switch element in a region surrounded by a video signal line and a scanning signal line which are arranged in a matrix on a substrate. Array substrate having an alignment film arranged in the first direction and rubbed in a first direction, and an array substrate
And a counter substrate having a counter and rubbed alignment film in the second direction, in an active matrix type liquid crystal display device comprising a liquid crystal layer composed of liquid crystal molecules held between the array substrate and the counter substrate , Pixel electrodes are video signal lines and
And the pixel electrodes are arranged on the scanning signal lines via an insulating film.
Reversal tilt domain created by lateral electric field
There are more pixel electrodes on the side corresponding to the area where
This is characterized by overlapping with a video signal line or a scanning signal line .

Further, the array substrate includes a light shielding layer,
The optical layer is between the video signal line or scanning signal line and the pixel electrode
May be arranged.

Moreover, when further the A, B, C, and D from the first direction 4 points on the pixel electrode to be placed vector AB in the range of 0 to 45 degrees clockwise to clockwise ,
The openings of the light-shielding layer are closer to sides AB and BC than sides CD and DA.
May be arranged in close proximity.

[0017]

The reverse tilt domain is affected by the alignment state of the liquid crystal molecules and the lateral electric field generated between the pixel electrodes, and is generated by the following operation. As shown in FIG. 8, the liquid crystal molecules are oriented between the electrode substrates at a predetermined pretilt angle (θ1).

For this liquid crystal molecule, the pretilt angle (θ
When a gradient electric field in the direction A in the figure having an angle larger than 1) and smaller than the pretilt angle (θ1) +90 degrees, for example, an angle (θE), is applied, the liquid crystal molecules are shifted from the direction A following the electric field direction. Are oriented.

However, when an inclined electric field having an angle larger than the pretilt angle (θ1) +90 degrees and smaller than the pretilt angle (θ1) +180 degrees is applied to the liquid crystal molecules, the liquid crystal molecules follow the electric field direction. Since the liquid crystal molecules are oriented in a direction opposite to the pretilt direction, the liquid crystal molecules are reverse tilted according to the tilted electric field, and a reverse tilt domain is generated. From the above, according to the experiments of the present inventors, it has been found that the reverse tilt domain has the following characteristics. (1) The reverse tilt domain decreases as the pretilt angle increases. (2) The reverse tilt domain occurs only near one specific side or two adjacent sides of the pixel electrode. (3) The reverse tilt domain is generated in the same area on the pixel electrode regardless of the distance between each signal line and the end of the pixel electrode if the electric field strength in the horizontal direction is constant.

As described above, as in the active matrix type liquid crystal display device of the present invention, by providing a light-shielding layer having an opening closer to one side or two adjacent sides of the pixel electrode than the other sides, the reverse tilt can be achieved. Domains can be avoided and a sufficient aperture ratio can be secured.

From the experiments performed by the inventors, it has been found that the defective display area associated with the reverse tilt domain can be specified as follows. That is, as described above, the four points on the pixel electrode are moved clockwise A, A so that the vector AB is arranged in the range of 0 to 45 degrees clockwise from the first direction which is the rubbing direction of the alignment film. When B, C, and D, the side CD,
A reverse tilt domain occurs near DA.

Therefore, by providing the openings closer to the sides AB and BC than the sides CD and DA of the pixel electrode, it is possible to prevent a decrease in contrast due to the reverse tilt domain while maintaining a sufficient aperture ratio.

Furthermore, the reverse tilt domain occurs in the same area on the pixel electrode without depending on the distance between each signal line and the end of the pixel electrode if the electric field strength in the horizontal direction is constant. By arranging at least one of the side CD or the side DA so as to overlap the video signal line or the scanning signal line, a part of the reverse tilt domain can be shifted on each signal line, and the area surrounded by each signal line The effective reverse tilt domain in the inside can be reduced.

In particular, since the light-shielding layer is provided between the substrate of the array substrate and the pixel electrode to increase the pretilt angle of the liquid crystal molecules between the pixel electrodes, it is possible to reduce the pretilt due to the lateral electric field. The opposite orientation can be prevented. By preventing the reverse tilt domain by locally varying the pretilt angle in this way, it is possible to reduce the occurrence of the reverse tilt domain without deteriorating the display quality.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An active matrix type liquid crystal display (1) according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an arrangement of the active matrix type liquid crystal display device (1) of the present embodiment from the counter substrate (101) to the array substrate (1).
FIG. 2 is a schematic front view when viewing 1), and FIG.
It is the schematic sectional drawing cut | disconnected along the -A 'line.

Active matrix type liquid crystal display (1)
As shown in FIG. 2, an array substrate (11) is provided with a video signal driving circuit (not shown) and a scanning signal driving circuit (not shown) on a transparent insulating substrate (13). A plurality of video signal lines connected to a video signal drive circuit as shown in FIG.
(15) and a plurality of scanning signal lines (17) connected to the scanning signal drive circuit are arranged in a matrix.

At the intersection of each video signal line (15) and scanning signal line (17), a switching element composed of a MOS transistor
(21) through a substantially square I.D. T. O. A transparent conductive film made of is provided as a pixel electrode (31). That is, the video signal line (15) has a source region (21b) formed by adding impurities to polysilicon of the switch element (21), and the pixel electrode (31) has a drain region (2) formed by adding impurities to polysilicon.
1c), the scanning signal line (15) is integrally formed with the gate electrode (16), and is disposed on the active region (21a) made of polysilicon via the gate insulating film (23).

A second interlayer insulating film (73) and a third interlayer insulating film (75) are provided between the pixel electrode (31) and the video signal line (15) and the scanning signal line (17). An opaque conductive film having a substantially square opening (43) sandwiched therebetween is provided as a light shielding layer (41) so that the pixel pitch is 40 microns.

Further, on the pixel electrode (31), FIG.
As shown in (1), a uniform alignment film (51) is provided, rubbed in the first direction in FIG. 1 (an angle of 45 degrees clockwise from the video signal line (15)), and the array substrate (11) Is composed.

The opposing substrate (101) provided facing the array substrate (11) is a transparent insulating substrate (111) as shown in FIG.
I. T. O. A transparent conductive film consisting of a counter electrode (113)
A uniform alignment film (115) is provided thereon, and a second direction orthogonal to the first direction is provided as shown in FIG.
The rubbing process is performed in the direction of.

In this active matrix type liquid crystal display device (1), as shown in FIG. 2, an array substrate (11) and a counter substrate (101) are arranged facing each other at an interval of 5.0 microns.
Between these substrates (11) and (101), a liquid crystal layer (2
01) is held.

The features of this embodiment are characterized by the positional relationship between the pixel electrode (31) and the light shielding layer (41) and the light shielding layer (41).
This is the location of (41), which will be described with reference to FIGS. 3 to 6 in comparison with a comparative example. In each of the figures, the rubbing process was performed on the alignment films (51) and (751) of the array substrates (11) and (711) in the first direction at 45 degrees clockwise from the scanning signal lines (15) and (715). And the rubbing process is performed on the opposing substrates (101) and (801) in a second direction orthogonal to the first direction.

FIG. 5 shows a video signal line (715) and a scanning signal line (71).
7) Pixel electrodes (731) are arranged at equal intervals from the signal lines (715) and (717) in the area surrounded by
The smaller aperture (743) is from each signal line (715), (717) 5.
This shows a comparative example that is arranged at an interval (d2) of 0 microns.

Thus, the pixel electrode (731) and the opening (74
3), the pixel electrode (731) is arranged as shown in FIG.
In the vicinity of the side DA, the area where no liquid crystal molecules are oriented in the direction of the pretilt angle (A), the counter electrode (813)
A region (B) following the gradient electric field between the pixel electrode (731) and the counter-electrode (813) and a region (C) forming a reverse tilt following the gradient electric field between the counter electrode (813) and the pixel electrode (731)
And the interface with the regions (A) and (C) becomes the disclination line (791). Then, depending on the display state, the regions (B) and (C) constitute defective display regions having different transmittances. The same applies to the vicinity of the side CD of the pixel electrode (731).

In the structure described above, the interval (d1 ₄ ) between the display defective areas near the side DA of the pixel electrode (731) is 7.3 μm, and the display defective area near the side CD of the pixel electrode (731) is reduced. The spacing (d1 ₃ ) was 11.1 microns. Then, opening (743) from the disclination line (791)
The interval (d3) is the allowable amount of the defective display area.
In the above-described structure, the permissible amount (d3 ₄ ) of the pixel electrode (731) near the side DA is 2.7 μm, and the interval (d3) near the side CD is 2.7 μm.
3 ₃₎ is very small and 0.9 microns, depending on the degree of temperature rise opening (43) which may display defect region is formed inside.

On the other hand, according to the present embodiment, as shown in FIG. 3, the side CD of the pixel electrode (31) is connected to the scanning signal line (17-2).
In addition, the side DA is connected to the interlayer insulating films (71), (73), and the video signal line (15-1).
(75) (see FIG. 2). Further, the distance between the scanning signal line (17-1) and the opening (43) (d
2 ₁₎ and the spacing between the video signal line (15-2) and the opening (43) (d
2 ₂ ) is 2.0 μm each, and the distance (d 2 ₃ ) between the scanning signal line (17-2) and the opening (43) and the distance (d 2 ₄ ) between the video signal line (15-1) and the opening (43). Are each formed to 3.0 microns.

As described above, the opening (43) is connected to the side C of the pixel electrode (31).
By arranging closer to sides AB and BC than to D and DA, a sufficient opening (43) can be formed avoiding a defective display region, so that a sufficient opening ratio is ensured in addition to preventing display failure. be able to.

The features of this embodiment are as follows.
As described above, the side DA of the pixel electrode (31) is connected to the video signal line (15-
1) The side CD is arranged so as to overlap the scanning signal line (17-2).

The reverse tilt domain is provided on the pixel electrode (31) independently of the distance between each signal line (15), (17) and the end of the pixel electrode (31) if the horizontal electric field strength is constant. Since it occurs in the same area, the above-described configuration causes a display defect area to occur in an area surrounded by the signal lines (15) and (17) as shown in FIG. 4, that is, an area serving as a reverse tilt domain ( Part C) can be moved onto each of the signal lines (15-1) and (17-2). Therefore, each signal line (15), (17)
Can reduce the proportion of the display defective area in the area surrounded by.

As described above, the pixel electrode (31) and the opening (43)
, The opening (4) from each signal line (15), (17)
The opening ratio was 36% when the interval (d2) up to 3) was 5.0 microns, whereas the opening ratio was 51%. Moreover, according to the present embodiment, since the light-shielding layer (41) is disposed between the pixel electrode (31) and the alignment film (51), the light-shielding layer (41) is provided on the side of the counter substrate (101) or the like. As shown in FIG. 4, the inclination of the alignment film (51) between the adjacent pixel electrodes (31) is configured to be larger than that in the case where it is provided.

As a result, according to the present embodiment, the apparent pretilt angle of the liquid crystal molecules between the adjacent pixel electrodes (31) is increased, and the region (C) serving as the reverse tilt domain is further suppressed. Can be. In particular, according to the present embodiment, since the pretilt angle of the entire liquid crystal molecules is not increased, the display quality does not deteriorate.

According to the above-described operation, the aperture ratio is improved, and according to the liquid crystal display device (1) of this embodiment, the defective display area near the side DA of the pixel electrode (31) shown in FIG. The interval (d1 ₄ ) can be reduced to 4.2 microns, and the interval (d1 ₃ ) between the display defect areas near the side CD can be reduced to 7.0 microns, whereby the allowable amount (d3 ₄ ) can be reduced to 4.8 microns.
The allowable amount (d3 ₃ ) could be sufficiently increased to 2.0 microns. A case will be described in which the rubbing process is performed in the direction of the side AB of the pixel electrode (31) instead of the rubbing direction in the above-described embodiment. Even in the case where the rubbing process is performed in such a direction, a defective display area occurs near the sides CD and DA of the pixel electrode (31) as described above.

Therefore, as described above, the liquid crystal display device
By configuring (1), the region (C) itself serving as the reverse tilt domain is reduced, and the side DA of the pixel electrode (31) is reduced.
The distance (d1 ₄ ) between neighboring display defective areas is very small at 4.3 microns, and the allowable amount (d3 ₄ ) up to the opening (43) is 4.7.
It was possible to make it as large as a micron.

The same applies to the vicinity of the side CD of the pixel electrode (31).
₄₎ is as small as 5.9 microns, yet allowance to the opening (43) (d3 ₃₎ was as large as 3.1 microns.

As described above, the rubbing direction is changed to the pixel electrode (3
A specific pixel electrode (31) is also used as a direction along the AB direction of (1).
And the arrangement of the opening (43) with respect to the pixel electrode (31) achieves the elimination of display defects and the improvement of the aperture ratio with the reduction of the region (C) itself serving as the reverse tilt domain as in the above-described embodiment. We were able to. In addition, the increase in the allowable amount of the defective display area does not adversely affect the increase in the reverse tilt domain due to the decrease in the pretilt angle due to the temperature rise of the liquid crystal layer (201).

Next, another embodiment of the present invention will be described with reference to FIG. The difference of the active matrix type liquid crystal display device (1) of the present embodiment from the above-described embodiment is the structure between the pixel electrodes (31), and only different portions from the above-described embodiment will be described.

In this embodiment, each video signal line (1
5), interlayer insulating films (73), (74) on scanning signal lines (not shown)
A dummy layer (81) sandwiched between is provided. The dummy layer (81) has the same width as each signal line on the video signal line (15) and the scanning signal line side where the pixel electrode (31) overlaps, and the pixel electrode (31) does not overlap. The video signal line (15) and the scanning signal line side are wider than each signal line width.

By interposing such a dummy layer (81), the apparent pretilt angle of the liquid crystal molecules between the pixel electrodes (31) is increased, and the reverse tilt domain region (C ) Itself can be further reduced.

Referring to FIG. 3, the side DA of the pixel electrode (31)
The distance (d1 ₄ ) between the neighboring defective display areas was as small as 4.0 μm, and the allowable amount (d3 ₄ ) of the defective display area was sufficiently large as 5.0 μm. In addition, the pixel electrode (3
Similarly, also in the vicinity of the side CD of 1), the interval (d1 ₃ ) between the display defective areas is as small as 6.8 μm, and the allowable amount (d
3 ₃₎ was able to be increased with 2.2 microns.

As described in detail above, according to the present embodiment,
Compared with the above-described embodiment, the reverse tilt domain is further reduced, thereby preventing the display quality from deteriorating due to the reverse tilt domain, and ensuring a high aperture ratio and obtaining a liquid crystal display device having a large allowance (d3). Was.
Therefore, the active matrix type liquid crystal display device of this embodiment is most suitable for a liquid crystal display device such as a projection type liquid crystal display device in which the temperature of a liquid crystal layer rises.

In the liquid crystal display device of each of the above-described embodiments, a case where one pixel electrode is provided in a region surrounded by each signal line has been described. Needless to say, a configuration in which two or more pixel electrodes are arranged may be adopted.

[0053]

According to the active matrix type liquid crystal display device of the present invention, the reverse tilt domain can be reduced by the specific arrangement of the light-shielding layer and the pixel electrode, and the degradation of the display quality due to the reverse tilt domain can be prevented. Moreover, a high aperture ratio can be secured.

[Brief description of the drawings]

FIG. 1 is a schematic front view of an array substrate of an active matrix type liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of the active matrix type liquid crystal display device taken along the line AA ′ in FIG.

FIG. 3 is a schematic front view of one pixel electrode for explaining an operation of the active matrix type liquid crystal display device in FIG. 1;

FIG. 4 is a schematic sectional view taken along the line BB ′ in FIG.

FIG. 5 is a schematic front view of one pixel electrode of a comparative example for explaining the operation of the active matrix type liquid crystal display device of the present embodiment.

FIG. 6 is a schematic sectional view taken along the line CC ′ in FIG. 5;

FIG. 7 is a schematic sectional view of a main part of an active matrix type liquid crystal display device according to another embodiment of the present invention.

FIG. 8 is a diagram for explaining a reverse tilt domain in an active matrix liquid crystal display device.

FIG. 9 is a schematic front view of an array substrate of a conventional active matrix type liquid crystal display device.

FIG. 10 is a schematic cross-sectional view of the active matrix type liquid crystal display device cut along the line DD ′ in FIG. 9;

[Description of Signs] (1), (701) ... Active matrix type liquid crystal display device (11), (711) ... Array substrate (15), (715) ... Video signal line (17), (717) ... Scanning signal Lines (31), (731) ... Pixel electrode (41) ... Light shielding layer (43) ... Opening (101), (801) ... Counter substrate (201), (901) ... Liquid crystal layer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-1-266512 (JP, A) JP-A-4-166816 (JP, A) JP-A-4-188110 (JP, A) JP-A-4-266 323625 (JP, A) JP-A-5-313185 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1362 G02F 1/1343 G02F 1/1337 G02F 1/1335

Claims (5)

(57) [Claims] (1) Images arranged in a matrix on the substrate
The switch is located in the area surrounded by the signal lines and the scanning signal lines.
And a pixel electrode disposed via a switch element
The alignment film, which is disposed on the substrate and rubbed in the first direction,
An array substrate comprising:Facing the array substrateSecond person
A counter substrate having an alignment film rubbed in the opposite direction;
The liquid crystal component held between the array substrate and the counter substrate
Matrix type liquid having a liquid crystal layer composed of
Crystal display device,The pixel electrodes are separated from the video signal lines and the scanning signal lines.
Placed through the rim, Rivastilt due to lateral electric field to the pixel electrode
The pixel electrodes on the side corresponding to the region where the domain is generated
The poles overlap the video signal line or the scanning signal line more than others.
Duplicate Active matrix liquid
Crystal display device. 2. The array substrate according to claim 1, further comprising a light shielding layer.
Active matrix liquid crystal display device, wherein the free it. 3. The active matrix type liquid crystal display device according to claim 2, wherein the light shielding layer is disposed between the video signal line or the scanning signal line and the pixel electrode . Wherein said light-shielding layer of claim 3, wherein the said image signal
Signal line and the area surrounded by the scanning signal line.
An active matrix liquid crystal display device having a small opening . 5. The liquid crystal molecules of claim 1 wherein the said array group
Arranged at a predetermined pretilt angle with respect to the plate,
The step in the region where the rivastilt domain occurs.
The retilt angle is greater than the pretilt angle in other areas
An active matrix type liquid crystal display device characterized by being set large .