JPH0695094A - Active matrix type liquid crystal display panel - Google Patents

Abstract

PURPOSE:To prevent light drop-out and to enable a high contrast with a high opening rate by providing projecting parts for forming gaps in the regions shielded with a black matrix near places where reverse tilt domains are generated. CONSTITUTION:The liquid crystal panel constituted by combining a TFT array side glass substrate 1 and a counter side glass substrate 13 having the black matrix 14 is provided with the the projecting parts for forming the gaps in the regions shielded with the black matrix 14 near the places where the reverse tilt domains are generated at the driving time. The surfaces of the projecting parts 22 for forming the gaps have no uniaxial orientability of the liquid crystal and therefore, the orientation state of the liquid crystal is considered to be different from the ambient near these parts. Discrimination lines are trapped and exist stably and do not spread into picture elements any more when the reverse tilt discrimination lines arrive at these parts. Then, the infiltration of the reverse tilt domains into the picture elements is prevented and simultaneously, the light drop-out occurring in space beads is prevented.

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 panel, and more particularly to improving the display quality thereof.

[0002]

2. Description of the Related Art A thin film transistor (TFT) for each pixel
The active matrix type liquid crystal display panel provided with a switching element such as a diode or a diode has been applied to various displays such as a liquid crystal TV, and recently, it has been greatly expected as an OA display and a projection TV.

At present, in the active matrix type liquid crystal display panel, a TN liquid crystal display mode in which liquid crystal is twisted 90 ° between upper and lower substrates is generally used. The TN display has a normally black display mode in which black display is performed when no voltage is applied and a normally white display mode in which black display is performed when voltage is applied, depending on the arrangement of upper and lower polarizing plates. Each display mode has advantages and disadvantages, but the normally white display mode is superior in terms of black uniformity and contrast.

The active matrix liquid crystal display panel is
In the trend of improving display quality, we are moving toward higher density and larger screens. Along with this, it has become difficult to uniformly align the liquid crystal.

The uniform alignment treatment of liquid crystal necessary for liquid crystal display is
The surface of the polyimide film formed as an alignment film is rubbed with a soft cloth. A liquid crystal panel is formed by filling a liquid crystal in a gap of several μm between two substrates whose surfaces are oriented. As a liquid crystal filling method, a vacuum injection method performed in a vacuum chamber is generally used. Since the orientation of the liquid crystal is apt to be disturbed by the flow at the time of injection, the temperature of the panel is once raised above the liquid crystal-isotropic liquid transition temperature, and then cooled to rearrange the liquid crystal to uniformly align it. It has been taken. But,
In an active matrix type liquid crystal display panel, since unevenness due to TFTs, sources and gate wirings are present on the surface of the substrate, it is difficult to uniformly perform rubbing treatment, and alignment defects easily occur.

There are two types of alignment defects that pose a problem in an active matrix type liquid crystal display panel. One is the reverse twist domain. This is a domain in which the twisting direction of the liquid crystal is opposite to the surrounding normal part, and the disclination line at the boundary with the normal part causes light scattering, and if this exists in the display area, it becomes a display defect. This defect is present even when no voltage is applied, and becomes a bright spot in a normally black display mode, which is a serious problem. Therefore, in order to normally define the twisting direction as one direction, a right-handed or left-handed chiral substance is added to prevent the occurrence of the reverse-twisted domain.

Conventionally, the panel gap for filling the liquid crystal has been formed by dispersing spheres (spacer beads) of resin or silica in the liquid crystal panel. However, as the pixel size becomes smaller, light leakage due to spacer beads existing in the pixel portion cannot be ignored.

[0008]

[Problems to be Solved by the Invention]
The alignment defect in the N-aligned active matrix liquid crystal panel is due to the reverse tilt domain induced near the gate wiring and the source wiring when a voltage is applied. The size of the reverse tilt domain changes depending on the potential relationship among the gate electrode, the source electrode, and the pixel electrode, and under normal driving conditions, this domain penetrates into the pixel electrode. In this case, the disclination line at the boundary with the normal portion causes light scattering as in the case of the reverse twist domain, resulting in a display defect. The influence of the light scattering due to the disclination line is remarkable in the normally white display mode in which black display is performed when a voltage is applied. The influence increases as the pixel size becomes smaller due to the higher pixel density, which causes a decrease in contrast. .

If the width of the black matrix is widened in order to prevent light leakage due to the disclination line, the aperture ratio is lowered and the display brightness is lowered. The reverse tilt domain can be suppressed to some extent by increasing the pretilt angle of the liquid crystal, but the effect of the pretilt angle cannot completely prevent the disclination line from entering the pixel.

Further, as the pixel size decreases, light leakage due to the influence of spacer beads existing in the pixel portion becomes a problem. The contrast is deteriorated due to light leakage from the beads and their surroundings during black display.

In view of the above points, the present invention prevents display defects that occur in a liquid crystal panel, in particular, pixels of a reverse tilt domain that occur in the vicinity of a source electrode and a gate electrode due to voltage application, and eliminates contrast deterioration due to the influence of spacers. Then, an object is to provide an active matrix type liquid crystal display panel having a high aperture ratio and a high quality.

[0012]

In a liquid crystal panel formed by combining a TFT array substrate and a counter substrate having a black matrix, a gap is formed in the vicinity of a place where a reverse tilt domain occurs during driving and in a region shielded by a black matrix. Protrusions are provided. This prevents the reverse tilt domain from penetrating into the pixel and at the same time prevents the light leakage due to the spacer beads, thereby obtaining an active matrix type liquid crystal display panel with a high aperture ratio and a high contrast.

Further, in the manufacturing process of the liquid crystal panel described above, the active matrix type liquid crystal display panel having no alignment defect can be obtained by forming the gap forming convex portion after performing the liquid crystal alignment treatment.

[0014]

The domain generated when the TFT liquid crystal display panel is driven is a reverse tilt domain in which the rise of the liquid crystal inside the domain is different from the surrounding normal part. The mechanism of generation of the reverse tilt domain is considered as follows. Due to the influence of the lateral electric field generated between the source / gate wiring and the pixel electrode, the liquid crystal molecules rise in the direction opposite to the direction defined by the pretilt. The boundary between the region that rises normally and the region that rises in the opposite direction becomes a disclination line, causing light leakage. The size and shape of the region in which the reverse tilt occurs changes depending on the orientation processing direction of the liquid crystal and the direction of the lateral electric field.

In the present invention, by providing the convex portion for forming the gap in the vicinity of the place where the reverse tilt domain occurs during driving and in the region shielded by the black matrix, the invasion of pixels in the reverse tilt region is prevented. The reason for this is unknown, but it is currently estimated as follows. Since the surface of the convex portion for forming the gap does not have the uniaxial orientation of the liquid crystal, it seems that the orientation state of the liquid crystal is different from that of the surrounding in this vicinity. When the reverse tilt disclination line reaches this portion, the disclination line is trapped, exists stably, and does not further spread inside the pixel. Further, in the present invention, since it is not necessary to dispose the spacer in the pixel, there is also an effect of preventing deterioration of contrast due to light leakage from the spacer portion and the abnormal alignment portion of the liquid crystal around the spacer.

Normally, the gap of a TN type liquid crystal panel is several μm. Therefore, the height of the convex portion for forming the gap needs to be several μm. However, when an alignment treatment is performed on a substrate having a step of several μm by rubbing, the vicinity of the step is less likely to be oriented and a display defect such as a reverse twist domain is likely to occur. Also, depending on the strength of the convex portion,
The rubbing process may destroy the shape. In the manufacturing process of the liquid crystal panel of the present invention, the above-mentioned problems of display defect and shape destruction can be avoided by forming the gap forming convex portion after performing the liquid crystal alignment treatment.

[0017]

EXAMPLES In the present invention, the convex portion for forming the gap is
Basically, it is desirable to provide them in the vicinity of all pixels.
However, depending on the driving method, there are cases where the invasion of pixels in the reverse tilt domain is a problem in the panel, and in that case, if there is no problem in forming the gap, only in the part where the reverse tilt domain is likely to occur. May be installed. The protrusion for forming the gap is provided near either or both of the source wiring and the gate wiring. When installing on the opposite substrate, in the area hidden by the black matrix,
Install in a position near the source or gate line when combined. The position where the convex portion for forming the gap is installed is near the source and the gate wiring, and even if it is in contact with the wiring,
You may be separated. The size of the convex portion is not particularly limited, but if it is too large, the aperture ratio decreases, and the light transmittance of the panel decreases, which is a problem.

As a method of providing the gap forming convex portion in the vicinity of the gate or source wiring and in the region shielded by the black matrix, a method by photolithography or a method by printing can be used.

The outline of the active matrix type liquid crystal panel used in Examples and Comparative Examples of the present invention will be described below. It has a TFT as an active element and has a screen diagonal 2.
8 inch size (aspect ratio 3: 4) horizontal gate line 479 x vertical source line 720, number of pixels 3448
Eighty matrix substrates were used. Pixel pitch is vertical 89μ
m, horizontal 79 μm. The step difference of the wiring portion is about 7,000 Å on the source wiring side and about 1000 Å on the gate wiring side, and the width of the wiring is 8 μm. Chrome (thickness 100
A substrate having a black matrix patterned with 0Å) was used. Although the counter substrate having no color filter layer is used in the specific example, naturally the same effect can be obtained by using a substrate with a color filter.

As the liquid crystal material, a PCH-based mixed liquid crystal having Δn of about 0.09 was used. Right-handed 4'- as a chiral agent
(S-2-methylbutyl) -4-cyanobiphenyl,
0.2% was added. The panel gap was about 5 μm.
A rubbing treatment film of a polyimide resin was used as the alignment film.
The pretilt angle of the resulting liquid crystal was about 2 ° as measured by the crystal rotation method.

The domain generated when an electric field was applied was observed under a polarizing microscope. (Comparative Example) (FIG. 5) is a sectional view showing a schematic structure of one pixel of the active matrix type liquid crystal panel used in (Comparative Example), and (FIG. 6) is a plan view thereof. The rubbing orientation treatment directions of the TFT array substrate and the counter substrate are as shown in the figure. The solid arrow 20 indicates the rubbing direction of the TFT array substrate, and the broken arrow 21 indicates the rubbing direction of the counter substrate. The panel gap was formed by dispersing resin beads having a diameter of about 5 μm at a density of 200 beads / mm ² . The aperture ratio of the black matrix pattern 19 is 40%. The polarizing plate 15 was placed in a normally white mode, and the panel temperature was evaluated at 50 ° C. This panel is displayed under a normal drive condition in which the gate is scanned from the upper part of the screen with the opposite potential kept constant and the polarity of the source signal is inverted every field, and the source signal level is 10V.
The appearance of the disclination line line at pp was observed. Then, at the bottom of the screen, 2 of (Fig. 5)
In the shape as shown in FIG. 4, the reverse tilt disclination line invaded into the pixel. When the transmitted light intensity of the panel was measured when the voltage was not applied and the source signal level was 10 Vp-p, and the contrast ratio was evaluated, it was 200: 1 at the upper part of the screen, whereas the discrepancy was found at the lower part of the screen. It decreased to 50: 1 due to the influence of the nation line.

(Embodiment 1) (FIG. 1) is a sectional view showing a schematic structure of one pixel of the active matrix type liquid crystal panel used in (embodiment 1), and (FIG. 2) is a plan view thereof. This is the structure of (Comparative Example)
A convex portion 22 for forming a gap is additionally formed in the vicinity of, and the shape of the convex portion is 5 μm □ and the height is about 5 μm. Although the convex portion 22 has a very elongated shape in the cross-sectional view, this is due to the difference in magnification between the vertical and horizontal directions, and the actual shape is a cubic shape with vertical, horizontal and height of 5 μm.
A panel gap of about 5 μm could be formed by these protrusions. This convex portion was formed by the following method. A polyamic acid solution was applied onto the TFT array substrate and baked to form a polyimide film having a thickness of 5 μm. Approximately 2000 Cr on the entire surface
A was vapor-deposited, and 5 μm square patterning was performed using a positive photoresist. Cr is removed by using a Cr etching solution except the place where the convex portion is formed, and reactive ion etching (RIE) is performed using Cr as a mask (condition: 100% oxygen,
The polyimide was patterned by 300 W for 5 minutes. After immersing in a Cr etching solution to remove Cr, it was washed with water and dried to form a protrusion having a size of 5 μm □ and a height of about 5 μm. An alignment film polyimide 700A was formed on this substrate, alignment treatment was performed by rubbing, and a gap was formed by combining with a black matrix substrate, and liquid crystal was vacuum-injected and then sealed.

The rubbing direction is the same as in (Comparative Example).
When this panel was driven and evaluated in the same manner as in (Comparative Example), no intrusion of disclination lines into the pixels was observed even in the lower part of the screen. The contrast was about 300: 1 at the top and bottom of the screen. The realization of such a high contrast is due to both the prevention of pixel intrusion of the reverse tilt disclination line and the absence of light leakage due to the influence of the spacer beads.

(Embodiment 2) (FIG. 3) is a sectional view showing a schematic structure of one pixel of the active matrix type liquid crystal panel used in (Embodiment 2), and (FIG. 4) is a plan view thereof. This is a structure in which a convex portion 23 for forming a gap is provided in the black matrix of the counter substrate of (Comparative Example). The convex portion is formed by patterning polyimide using a positive photoresist as in (Example 1).
The shape is 5 μm □ and the height is about 5 μm. The rubbing direction is the same as (Comparative Example). When this panel was driven and evaluated in the same manner as in (Comparative Example), no intrusion of disclination lines into the pixels was observed even in the lower part of the screen. The contrast was about 300: 1 at the top and bottom of the screen. The realization of such a high contrast is due to both the effect of preventing pixels from entering the reverse tilt disclination line and the absence of light leakage due to the influence of the spacer beads.

The protrusions for forming the gap may be formed on both the TFT array substrate side and the counter substrate side at the same time. Further, it is also possible to form the two substrates at a position where they overlap each other when the substrates are bonded to each other and to form a predetermined gap by combining them.

(Example 3) In the panel forming step of (Example 1), the rubbing orientation treatment on the TFT array substrate side was performed before the step of forming the convex portion for gap formation.

An alignment film of polyimide 700A was formed on the TFT array substrate and subjected to an alignment treatment by rubbing. About 2000 A of Cr was vapor-deposited on the entire surface, and a polyamic acid solution was applied onto it and baked to form a polyimide film with a thickness of about 5 μm. Further, about 2000 A of Cr was vapor-deposited on the entire surface, and patterning of 5 μm □ was performed using a positive photoresist. Cr is removed by using a Cr etching liquid except the place where the convex portion is formed, and reactive ion etching (RIE) is performed using Cr as a mask (conditions: oxygen 100%, 300 W, 5
Min) to pattern the polyimide. After immersion in a Cr etching solution to remove Cr, rinse with water and dry,
A convex part having a size of m □ and a height of about 5 μm was formed. In combination with a black matrix substrate, a gap was formed and liquid crystal was vacuum-injected and then sealed.

In the panel of Example 1 in which the rubbing treatment was performed after forming the convex portion, the reverse twist domain was observed in the pixel. On the other hand, after the rubbing treatment, in the panel in which the photoresist was patterned to form the convex portions, no reverse twist domain was observed, and a very good liquid crystal alignment state was obtained. From these results, it was found that the rubbing alignment treatment performed before the formation of the protrusions was superior in the uniformity of liquid crystal alignment.

[0029]

The active matrix type liquid crystal display panel of the present invention prevents a display defect generated in the liquid crystal panel, especially light leakage due to the influence of the reverse tilt domain and the spacer beads generated when a driving voltage is applied, and has a high aperture ratio. A high contrast active matrix liquid crystal display panel can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a schematic structure of an active matrix liquid crystal element of (Example 1) of the present invention.

FIG. 2 is a plan view showing a schematic structure of (Embodiment 1) of the present invention.

FIG. 3 is a cross-sectional view showing a schematic structure of an active matrix type liquid crystal element of (Example 2) of the present invention.

FIG. 4 is a plan view showing a schematic structure of (Example 2) of the present invention.

FIG. 5 is a sectional view showing a schematic structure of an active matrix type liquid crystal device of (Comparative example) of the present invention.

FIG. 6 is a plan view showing a schematic structure of (Comparative example) of the present invention.

[Explanation of symbols]

1 TFT Array Side Glass Substrate 2 SiO ₂ Film 3 SiNx Film 4 Polyimide Alignment Film 5 ITO Electrode 6 Pixel Electrode (ITO) 7 Gate 8 Amorphous Silicon Layer 9 Source 10 Drain 11 Liquid Crystal 12 Counter Electrode (ITO) 13 Counter Side Glass Substrate 14 Black matrix 15 Polarizing plate 16 Gate wiring 17 Source wiring 18 TFT 19 Black matrix pattern 20 TFT array substrate side rubbing direction 21 Opposing substrate side rubbing direction 22 Convex portion formed on TFT array substrate 23 Convex portion formed on opposing substrate 24 Reverse tilt Disclination line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaru Ishihara 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A liquid crystal panel comprising a combination of a TFT array substrate and a counter substrate having a black matrix, wherein a gap is formed in the vicinity of a position where an inverse tilt domain is generated during driving on the TFT array substrate side and in a region shielded by the black matrix. An active matrix type liquid crystal display panel, characterized in that a convex portion for forming is provided. 2. A liquid crystal panel comprising a combination of a TFT array substrate and a counter substrate having a black matrix, in the vicinity of a position where a reverse tilt domain is generated at the time of driving on the counter substrate side, and a convex for gap formation inside the black matrix region. An active matrix type liquid crystal display panel characterized by having a section. 3. A process for producing a liquid crystal panel comprising a combination of a TFT array substrate and a counter substrate having a black matrix, wherein a projection for gap formation is formed after a liquid crystal alignment process. Or 2
A method for manufacturing the active matrix type liquid crystal display panel described.