JP2002131781A - Active matrix type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active matrix type liquid crystal display device, which is a horizontal field type and adopts a chevron-like electrode structure, permitting to decrease discrimination near the apex of a chevron-like electrode. SOLUTION: To decrease discrimination areas which have conventionally occurred in the neighborhood of the apexes of the chevron-like electrodes, a transparent common auxiliary electrode 32 and a pixel auxiliary electrode 47 are formed so as to connect the apex parts of the chevrons of the common electrode 22 and the pixel electrode 27, and thus, it has become possible to decrease the discrimination and increase the opening ratio.

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 device, and more particularly to an in-plane switching (IPS).
g) The structure of the liquid crystal display device.

[0002]

2. Description of the Related Art In-plane switching (IPS: I
2. Description of the Related Art A display panel of an n-plane-switching type liquid crystal display device has a structure in which liquid crystal is sandwiched between a pair of transparent substrates at a predetermined interval, and an electric field that is effectively parallel to the substrates is applied to form a liquid crystal molecule. It has the feature that a wide viewing angle can be achieved by rotating horizontally in the plane of the substrate. Here, the electric field that is effectively parallel to the substrate can be generated by arranging the pixel electrode and the common electrode on one of the transparent substrates sandwiching the liquid crystal in a comb-tooth shape with a predetermined interval. Therefore, in the IPS type LCD, since the display display is always viewed only from the short axis direction of the liquid crystal molecules, there is an advantage that the viewing angle is very wide.

As described above, the IPS type LCD has an advantage that the viewing angle is very wide, but it is colored yellow or blue when the screen is tilted and viewed from the longitudinal direction of the comb-shaped electrode. It also has disadvantages. To solve this problem, Japanese Unexamined Patent Application Publication No. 10-148826 proposes a U-shaped electrode structure (multi-domain structure).

FIG. 4 shows this electrode structure. As shown in FIG. 4A, the common electrode 122 includes a U-shaped electrode portion and an electrode portion traversing the central portion and the periphery of the pixel, and a region above and below the electrode portion traversing the central portion of the pixel. When the liquid crystal corresponding to, when viewing the screen at an angle from the longitudinal direction of the U-shaped electrode when applying a voltage, the colors change with respect to the viewing angle because they are colored yellow and blue, respectively. No images can be obtained.

[0005]

Problems to be Solved by the Invention
In the case where the common electrode crossing the central portion of the pixel, which causes a decrease in light transmittance, is removed from the dogleg-shaped electrode structure disclosed in Japanese Patent Publication No. 26-26, and the electrode structure shown in FIG. When a voltage is applied, the electric field concentrates on the apex of the square of the pixel electrode 227, and the force for rotating the liquid crystal is applied to both the right and left rotations in a plane parallel to the substrate, so that the liquid crystal cannot be rotated. It causes religion. Further, when the pixel electrode 227 and the common electrode 222 are formed using the mask pattern by the divided exposure, the liquid crystal 218 shifts from a direction facing each other and shifts from a normal alignment direction. The position and area slightly change, and along the dividing exposure part boundary line,
Linear display unevenness occurs on the screen. In the left and right regions around the apex of the square of the common electrode 222, the driving directions of the liquid crystal 218 are opposite.
This is a very sensitive configuration in which the direction of the liquid crystal changes abruptly depending on the position of 8.

In order to alleviate the above problem, an electrode structure disclosed in Japanese Patent Application Laid-Open No. H10-148826 as shown in FIG. 4A is employed. If the common wiring is placed in the center of the pixel, the light transmittance is reduced from 8% to about 3 to 5%.

Further, as shown in the enlarged plan view of FIG. 4B, the liquid crystal 1 oriented parallel to the data line when no voltage is applied.
Reference numeral 18 denotes a pixel electrode 12 when a voltage is applied between the electrodes.
7 and the common electrode 122 change their directions uniformly in the direction in which they face each other. As shown in FIG. , The pixel electrode 127 and the common electrode 12
2 are not opposed to each other, and the same pixel electrode 127 or the same common electrode 122 sandwiches the region Y at an acute angle. Instead, the liquid crystal is the pixel electrode 127
In addition, the common electrode 122 does not face in a direction facing each other and shows a halfway direction, and disclination occurs in the region Y.

[0008] Further, in the case of forming a U-shaped electrode as shown in FIG. 2 (a), the exposure for forming an electrode pattern is usually limited because the exposure range of an exposure apparatus is limited when exposing a large monitor. This is performed by a division exposure method. For this reason,
The disclination does not appear at an arbitrary portion, and the display image quality becomes uneven uniformly at a boundary portion to be divided and exposed, that is, at a straight line portion connecting the vertices of the square, due to an exposure shift of the exposure device. As a result, a line appears on the divided exposure portion, resulting in a screen defect. The screen defect is caused by a pattern shift (about 1 μm) at a divided portion as shown in an enlarged plan view of the common electrode 222 and the pixel electrode 227 near the apex of the V-shape in FIG. 5B. appear. Figure 5
(A), an electrode pattern is formed, and disclination occurs vertically symmetrically in the vicinity of the apex of the pixel electrode 227 toward the paper surface. On the other hand, as shown in FIG. 5B, when the overlay shift of the divided exposure occurs downward toward the paper surface, the electric field strength depends on the distance between the electrodes, and the pattern overlay shift changes the electrode interval. So
The manner in which the electric field is applied becomes non-uniform only in the overlap deviation part, and in particular, disclination moves in the electric field region from the vertex of the square of the pixel electrode 227 where the electric field is concentrated to the part where the electrode interval of the common electrode 227 is widened. Occurs, and linear unevenness occurs on the display screen.

An object of the present invention is to reduce disclination near the apex of a U-shaped electrode in an active matrix type liquid crystal display device employing a horizontal electric field type and a U-shaped electrode structure. An object of the present invention is to provide an active matrix type liquid crystal display device.

[0010]

According to the present invention, there is provided an active matrix type liquid crystal display device comprising a common wiring and a source / drain wiring provided on a first substrate, and the common wiring provided on the first substrate. Having a TFT-side insulating film covering the source / drain wiring and an alignment film thereon
A T substrate; a color layer provided on the second substrate;
A color filter substrate having a color filter-side insulating film on the substrate and covering the color layer and an alignment film thereon; and a liquid crystal sandwiched between the TFT substrate and the color filter substrate. The wiring and the source / drain wiring have a common electrode and a pixel electrode each having a zigzag line shape including at least one L-shape parallel to each other at substantially equal intervals, and the common electrode and the pixel electrode An active matrix liquid crystal display device that rotates the liquid crystal in a plane substantially parallel to the surface of the first substrate by applying a voltage between the common electrode and the pixel electrode. Are provided at the apexes of the U-shape in a direction parallel to the electric field, and are connected to the common electrode and the pixel electrode, respectively. And it is constituted basically a configuration having a pixel auxiliary electrode. The active matrix type liquid crystal display device of the present invention employs the following application modes.

First, the pixel electrode is located in the insulating film on the TFT side and is located closer to the liquid crystal than the common electrode.
The common auxiliary electrode and the pixel auxiliary electrode are respectively provided through a first opening and a second opening provided by opening a TFT-side insulating film on the common electrode and the pixel electrode, respectively. Connected to pixel electrode.

The common auxiliary electrode and the pixel auxiliary electrode are provided so as to extend on the surface of the TFT-side insulating film in parallel with the electric field and in a direction in which the U-shape protrudes.
The common auxiliary electrode and the pixel auxiliary electrode are provided to partially overlap the pixel electrode and the common electrode, respectively.

The common electrode has a U-shaped pattern in a region not sandwiched between the pixel electrodes.

Further, the common electrode is provided so as to connect the V-shaped end of the common electrode sandwiched between the pixel electrodes in a direction parallel to the electric field.

Finally, both the common auxiliary electrode and the pixel auxiliary electrode are made of a transparent conductive film.

[0016]

Next, an active matrix liquid crystal display device according to a first embodiment of the present invention will be described with reference to FIG. Here, FIG. 1A is a plan view of the TFT substrate viewed from the liquid crystal side, and FIG.
TFT substrate, liquid crystal, CF (color filter) on a plane passing through the cutting line AA 'in FIG.
It is sectional drawing when cutting a board | substrate. The active matrix type liquid crystal display device of the present embodiment is a horizontal electric field type liquid crystal display device, and the configuration is the same as that used in the description of the conventional technology, so that the detailed description is omitted here, and the configuration is different from the conventional one. The description will focus on. Note that the same elements as those in the related art are denoted by numbers obtained by removing 1 from the numbers in the hundreds of the conventional illustrated numbers.

As shown in FIG. 1A, the feature of this embodiment is that a common auxiliary electrode 32 and a pixel auxiliary electrode 37 are provided at the tops of the U-shaped common electrode 22 and the pixel electrode 27, respectively. Are formed to be connected to the common electrode 22 and the pixel electrode 27, respectively, and extend in the protruding direction of the U-shape.
2 is formed.

Next, a method of forming the common auxiliary electrode 32 and the pixel auxiliary electrode 37 will be described mainly with reference to FIG.

The plane size is 360 × 465 and the thickness is 0.3 mm.
First, a gate wiring 2 and a common electrode 22 are formed on a first transparent substrate 1 made of a 7 (unit mm) glass substrate. The gate wiring 2 and the common electrode 22 are formed on the first transparent substrate 1.
A 200 nm Cr film is formed thereon by a sputtering device, and then a positive resist film is applied, and the film is exposed, developed, and etched.

Next, the first insulating films 3 and 100 having a thickness of 200 nm are formed.
a-Si (amorphous silicon) layer of nm
The a-Si layer is patterned to form an a-Si region 6. Subsequently, a metal such as Cr is deposited to a thickness of 200 nm on the first insulating film 3 so as to cover the a-Si region 6, and is patterned to form an SD electrode (source / drain electrode; A pixel electrode 27 and a data line 37 which are formed simultaneously with the SD electrode 7. Thereafter, the a-Si region 6 is formed using the SD electrode 7 as a mask.
Is partially etched from the surface to form a channel portion of the TFT. Here, the common electrode 22 and the pixel electrode 27
As shown in FIG. 1 (a), are formed in a V shape and are formed in parallel with each other.

Next, the first insulating film 3 covering the SD electrode 7 and the like is formed.
Protective film 8 made of silicon nitride (SiNx) or the like
Then, predetermined regions of the protective film 8 and the first insulating film 3 are opened to form a contact hole 9. At this time, the contact hole 9 is opened at the top of the square of the common electrode 22 and the pixel electrode 27.

Next, a 50 nm-thick ITO film is formed on the protective film 8 on which the contact hole 9 is formed, and is patterned to form the common auxiliary electrode 32 and the pixel auxiliary electrode 37. When the polarizing plate 10 is formed on the other surface of the first transparent substrate 1, a TFT substrate 40 is obtained.

On the CF substrate 50 opposed to the TFT substrate 40, a second transparent substrate 51 and a black matrix 61, a color layer 63, and a silicon nitride film (SiNx) on one surface of the second transparent substrate 51 are formed. The two insulating films 64, the conductive film 65 on the other surface of the second transparent substrate 51, and the polarizing plate 66 are formed.

The TFT substrate 40 and the CF substrate 50 are formed by printing an alignment film on the uppermost surface of each of the TFT substrate 40 and the CF substrate 50 obtained as described above by a method such as offset printing. Complete.

The alignment films of the TFT substrate 40 and the CF substrate 50 thus obtained are rubbed as an alignment film 17, and alignment film molecules are arranged in a predetermined direction, and the cell gap is set so that the two substrates have a predetermined interval. The liquid crystal 18 is sealed in the gap between the materials.

The liquid crystal panel obtained in this manner has a TFT in the alignment direction of the liquid crystal 18 defined by the rubbing method.
The transmission axis of the polarizing plate 10 of the substrate 40 is made coincident, and CF
A polarizing plate 66 whose absorption axis is orthogonal to that of the TFT substrate 40 is attached to the substrate 50, and light 56 is irradiated from the TFT substrate 40 side to freely give a potential difference between the pixel electrode 27 and the common electrode 22. Thus, full-color display from black display to white display can be performed.

Next, details of the difference between the present embodiment and the conventional example will be described. There are two different points from the conventional configuration.

First, an ITO film, which has conventionally been used to conduct the peripheral portion of the first transparent substrate 1 on the TFT substrate 40 side, is used inside the pixel, and the common electrode 22 and the pixel electrode 27 are formed. They are used as a common auxiliary electrode 32 as an auxiliary electrode and a pixel auxiliary electrode 37. Since the common auxiliary electrode 32 and the pixel auxiliary electrode 37 are used as auxiliary electrodes for the common electrode 22 and the pixel electrode 27, the electric field is disturbed in the vicinity of the top of the U-shaped common electrode 22 and the pixel electrode 27. Are corrected by the common auxiliary electrode 32 and the pixel auxiliary electrode 37 to prevent disturbance of the electric field. As a result, it has become possible to drive a portion where the liquid crystal cannot be driven in a normal direction due to disclination (abnormal liquid crystal alignment) in the conventional electrode structure.

Second, in the structure disclosed in Japanese Patent Application Laid-Open No. H10-148826, the common electrode 122 is passed through the center in a direction parallel to the direction of the electric field. Since the electric field is prevented from being disturbed by the common auxiliary electrode 32 and the pixel auxiliary electrode 37 made of a transparent conductive film, the common electrode 22 in the present embodiment has a structure in which the electric field in the vicinity of the top of the square of the pixel electrode 27 and the pixel electrode 27 is prevented. The wiring area can be moved to an area where the liquid crystal cannot be driven, and the conventional panel transmittance is 5% or less (light does not pass through because the lower wiring portion composed of the common electrode 22 is a Cr film).
It was improved to 8% or more.

When the electrode structure of the present invention is used, the state of driving the liquid crystal when the electric field between the electrodes is turned on and off is improved as shown in FIG. In other words, while a region X that cannot be rotated has conventionally been generated in the liquid crystal near the apex of a square when a voltage is applied as shown in FIG. 2A, the use of the electrode structure of the present invention. , As shown in FIG.
The liquid crystal in the regions X1 and X2 other than immediately above the pixel auxiliary electrode 32 (or the common auxiliary 47) can be driven. As a result, the display range is enlarged, the image can be clearly displayed, and the screen also has a high transmittance, and a bright screen can be displayed.

As a second effect, it is possible to compensate for a pattern shift occurring at the time of exposure, which is a problem in actual mass production. More specifically, the exposure range of a large monitor is limited. Therefore, the disclination does not appear in an arbitrary part because the exposure is performed in divisions, and is uniformly displayed on the boundary part of the divisional exposure, that is, the straight line part connecting the vertices of the square, due to the mask limit of the exposure device. Image quality is uneven. As a result, a line appears on the divided exposure portion and the screen becomes defective (currently, about 20% occurs). The screen defect is caused by a pattern shift (about 1 μm) at the divided portion. The ITO auxiliary electrode pattern of the present invention is
By using a wiring of 2 μm thicker than the divisional pattern shift (1 μm), the pattern shift can be covered, and the display defect can be prevented even if the pattern shift occurs at the boundary between the exposure divisions.

Further, as a third effect, the lower layer Cr
The common electrode composed of a film does not transmit light because it is composed of a Cr film having a reflectance of 95%. Therefore, the panel (TFT
The transmittance in the state of (substrate + liquid crystal material + CF substrate) is reduced. Therefore, the common electrode, which was conventionally wired across the center of the pixel, is moved from the center of the pixel to the periphery of the pixel,
The transmittance could be improved. Again, in the conventional structure, the electric field is prevented from being disturbed by traversing the common electrode in the center of the pixel, so that the common electrode in the center of the pixel cannot be removed. Is formed of a transparent electrode, the light-shielding common electrode can be removed.

Next, a second embodiment of the present invention will be described with reference to FIG. The cross-sectional structure in the present embodiment is the first structure.
Therefore, FIG. 3 shows only a plan view of the TFT substrate side.

As shown in FIG. 3, the features of this embodiment are as follows.
The common auxiliary electrode 82 and the pixel auxiliary electrode 8 are respectively provided on the tops of the U-shaped common electrode 72 and the pixel electrode 77.
7 is formed to extend in the direction in which the U-shape protrudes, and its ends are formed so as to overlap the pixel electrode 77 and the common electrode 72, respectively.

From the description of the first embodiment, if the U-shaped electrodes have substantially the same area, the transmittance does not change from that of the first embodiment. It may be provided. Therefore, the present invention can be applied to a configuration in which a large number of U-shaped portions are connected in one element and provided in a zigzag line shape to improve the visibility of dots by taking advantage of this advantage.

[0036]

In the active matrix type liquid crystal display device employing the horizontal electric field type U-shaped electrode structure according to the present invention, the area of the disclination which has conventionally occurred near the apex of the U-shaped electrode is reduced. In order to reduce the number, transparent auxiliary electrodes are formed so as to connect the vertices of the squares of the common electrode and the pixel electrode, so that disclination can be reduced and the aperture ratio can be increased. .

[Brief description of the drawings]

FIG. 1 is a plan view of a TFT substrate and a cross-sectional view of a liquid crystal panel of an active matrix liquid crystal display device for explaining a first embodiment of the present invention.

FIG. 2 is an enlarged plan view for explaining a state of improvement of disclination in the first embodiment of the present invention.

FIG. 3 is a plan view of an active matrix liquid crystal display device for explaining a second embodiment of the present invention.

FIG. 4 is a plan view and an enlarged plan view of a conventional active matrix liquid crystal display device.

FIG. 5 is an enlarged plan view for explaining a display defect due to misalignment of an electrode pattern of a conventional active matrix liquid crystal display device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 First transparent substrate 2, 52, 102 Gate electrode 3 First insulating film 6, 56, 106 a-Si region 7, 57, 107 SD electrode 8 Protective film 9 Contact hole 10, 66 Polarizing plate 17 Alignment film 18, 118 218 liquid crystal 22, 72, 122, 222 common electrode 27, 77, 127, 227 pixel electrode 32, 82 common auxiliary electrode 37, 87, 137 data line 40 TFT substrate 47, 97 pixel auxiliary electrode 50 CF substrate 51 second transparent Substrate 56 light 61 black matrix 63 color layer 64 second insulating film 65 conductive film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H090 JD10 KA18 LA04 MA02 MA06 MA15 MB01 2H092 GA14 JA26 JA29 JA33 JA35 JA38 JA39 JA42 JA43 JA46 JB13 JB22 JB27 JB32 JB36 JB51 JB57 JB63 JB69 KA05 KA16 KA18 MA18 MA05 MA08 MA19 MA20 MA27 MA35 MA37 MA41 NA04 NA25 NA27 PA02 QA18 5C094 AA02 AA03 AA10 AA55 BA03 BA43 CA19 CA23 EA03 EA04 EA07 EA10 ED02 FA01 FB12 GA10

Claims (7)

[Claims] 1. A common wiring and a source / drain wiring provided on a first substrate, and a TFT on the first substrate and covering the common wiring and the source / drain wiring.
A TFT substrate having a side insulating film and an alignment film thereon,
A color filter substrate having a color layer provided on a second substrate, a color filter side insulating film on the second substrate covering the color layer, and an alignment film thereon;
A liquid crystal sandwiched between a T substrate and the color filter substrate, wherein the common wiring and the source / drain wiring have a zigzag line shape including at least one dog-leg that runs parallel to each other at substantially equal intervals. Each has a common electrode and a pixel electrode, and by applying a voltage between the common electrode and the pixel electrode to generate an electric field, the liquid crystal is moved in a plane substantially parallel to the surface of the first substrate. An active matrix liquid crystal display device to be rotated,
The common electrode and the pixel electrode are provided at the apexes of the U-shape in a direction parallel to the electric field, and have a common auxiliary electrode and a pixel auxiliary electrode respectively connected to the common electrode and the pixel electrode. An active matrix type liquid crystal display device characterized by the above-mentioned. 2. The pixel electrode is located in the TFT-side insulating film and is located closer to the liquid crystal than the common electrode, and the common auxiliary electrode and the pixel auxiliary electrode are connected to the common electrode and the pixel electrode, respectively. 2. The active matrix type liquid crystal display device according to claim 1, wherein said common electrode and said pixel electrode are respectively connected through a first opening and a second opening provided by opening a TFT-side insulating film on said TFT. 3. The common auxiliary electrode and the pixel auxiliary electrode are provided so as to extend on the surface of the TFT-side insulating film in parallel with the electric field and in a direction in which a U-shaped projection is provided. 3. The active matrix liquid crystal display device according to 2. 4. The active matrix liquid crystal display device according to claim 3, wherein the common auxiliary electrode and the pixel auxiliary electrode are provided so as to partially overlap the pixel electrode and the common electrode, respectively. 5. The active matrix type liquid crystal display device according to claim 1, wherein the common electrode has a U-shaped pattern in a region not interposed between the pixel electrodes. 6. The active device according to claim 1, wherein the common electrode is provided so as to connect a square-shaped end of the common electrode sandwiched between the pixel electrodes in a direction parallel to the electric field. Matrix type liquid crystal display device. 7. The active matrix liquid crystal display device according to claim 1, wherein said common auxiliary electrode and said pixel auxiliary electrode are both formed of a transparent conductive film.