JP2002303890A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that an OCB type liquid crystal display element has a bright point defect when transition is not certain. SOLUTION: Display is made by applying a voltage to liquid crystal in a bend alignment state and the liquid crystal display element has a transition means which causes transition from an alignment state wherein no voltage is applied to the bend alignment state. The liquid crystal display element further has a means which generates a disclination line when the transition means is in operation and a bending means which bends the disclination line. This disclination line is the border of a maldistributed splay alignment state and the bending is actualized by varying the growth speed of the line. To actualize that, an area is formed in which the cell thickness is different, a pyramid body is arranged, or an electrode absence part is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device used for a liquid crystal television, a liquid crystal monitor and the like.

[0002]

2. Description of the Related Art Conventionally, a TN type liquid crystal display device has been generally used as a liquid crystal display device.

As a liquid crystal display element characterized by a high-speed response, an OCB type display element has been studied. The OCB-type liquid crystal display element is described in "IEICE Technical Report EDI9"
8-144 page 199 ".

In this OCB type liquid crystal display device, liquid crystal is sandwiched between substrates, and a transparent electrode is formed on the substrate as a voltage applying means. Before the power is turned on, the alignment state of the liquid crystal is in a state called splay alignment. When the power of the device is turned on, a relatively large voltage is applied to the voltage applying means in a short time to change the orientation of the liquid crystal to a bend orientation state. Displaying using this bend alignment state is a feature of the OCB type liquid crystal display mode.

[0005]

In the OCB type liquid crystal display device, this transition is not reliable, and there is a problem that if a pixel which remains in splay alignment remains, it looks like a bright spot defect.

[0006]

A liquid crystal display device according to the present invention, which solves the above-mentioned problems, performs display by applying a voltage to a liquid crystal having a bend alignment, and performs a bend alignment from an alignment state where no voltage is applied. A liquid crystal display device having a transition means for transitioning to a state, comprising: means for generating a disclination line when the transition means operates; and bending means for bending the disclination line.

The disclination line is located at a boundary between two liquid crystal alignment states, and at least one of the two liquid crystal alignment states is preferably in a splay alignment state.

The liquid crystal display element has two substrates, and the splay alignment state is preferably a splay alignment in which liquid crystal molecules arranged substantially parallel to the substrate plane are unevenly distributed on one substrate side in the cell thickness direction.

It is preferable that the refracting means makes the moving speed of the disclination line different.

It is preferable that the bending means is a step forming regions having different cell thicknesses.

The height of the step is preferably 0.1 μm or more.

Preferably, the height of the step is 1 μm or less.

It is preferable that the liquid crystal display element has a substrate, and a black matrix is formed on at least one of the substrates, and the step is a black matrix.

It is preferable that the liquid crystal display element has a substrate, and an active matrix element is formed on at least one of the substrates, and the step is preferably formed simultaneously with the formation of the active matrix element.

Preferably, the width of the step is not less than 4 micrometers and not more than 50 micrometers.

In another embodiment, the bending means may be a column.

This columnar body is preferably substantially equal to the layer thickness of the liquid crystal.

It is preferable that the columnar body is formed in a region other than the display area.

As still another embodiment, it is preferable that the bending means is an electrode defective portion for limiting a region to which an electric field is applied.

It is preferable that the bending means is a different pretilt region in which regions having different pretilts are formed.

Preferably, the bending means for bending the disclination line is disposed in the rubbing direction or in the direction opposite to the rubbing direction with respect to the means for generating the disclination line.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a display device according to an embodiment of the present invention will be described with reference to the drawings.

The basic structure of the OCB type liquid crystal display element is to perform a rubbing process on the upper and lower substrates and make the directions parallel. In this element, when no initial voltage is applied, the liquid crystal molecules are in a splay alignment state in which the liquid crystal molecules are arranged substantially in parallel (FIG. 1A). FIG. 1 is a conceptual diagram showing the configuration of the present liquid crystal display element. A liquid crystal 101 is sandwiched between substrates 102, and has a retardation plate 103 and a polarizing plate 104 outside the substrate.

When no voltage is applied, the liquid crystal is in splay alignment (FIG. 1A). Here, the substrate is subjected to an alignment process, which is a parallel alignment process so that the liquid crystal molecules are arranged as shown in the figure. The orientation of the liquid crystal is changed to a bend orientation state used for display (FIG. 1B). In order to perform this transition, a relatively large transition voltage, for example, about 10 V to 25 V was applied to the liquid crystal layer.

We have previously disclosed the concept of forming a transition nucleus in Japanese Patent Application Laid-Open No. 10-20284, and further disclosed in Japanese Patent Application Nos. 11-68149 and 11-24934.
7. In Japanese Patent Application No. 2000-69501, two splay alignment states, in particular, an alignment state in which liquid crystal molecules are arranged substantially parallel to a substrate plane, form a localized splay alignment which is unevenly distributed on one substrate side in the cell thickness direction. Has been disclosed. When forming this uneven splay alignment, a disclination line is generated. Also, Japanese Patent Application 2000-2
No. 95756 discloses that a bend transition occurs when a high-order twist rotated by 180 degrees or more is formed.

The present invention is characterized in that the transfer is further ensured by providing a bending means for bending the disclination line.

We have found that when a transition waveform is applied, two splay alignments, in particular, an alignment state in which liquid crystal molecules are arranged substantially in parallel to the substrate plane, cause an unevenly distributed splay alignment that is unevenly distributed on one substrate side in the cell thickness direction. It has been shown that forming is important.

Prior to the application of the transition waveform, the state is as shown in FIG. When a transition voltage is applied thereto, an unevenly distributed spray region which is unevenly distributed on one substrate side (shown in the upper side in the figure) as shown in FIG.
A disclination line occurs between the unevenly distributed spray area and a moderate spray state where a sufficient response has not yet been made. Also, when an eccentric splay state eccentric to the upper substrate side and an eccentric splay state eccentric to the lower substrate side occur and are adjacent to each other, a disclination line is generated at this boundary (FIG. 2C). In either case,
It has been found that bend transition easily occurs from this disclination line, but particularly when this disclination line is bent in a plan view, bend transition occurs from this bending point.

According to our observation, liquid crystal molecules are microscopically rotated in the in-plane direction within the disclination line,
Even where the disclination is running straight,
The microscopic liquid crystal molecules were found to rotate 180 degrees.

Further, when a structure in which the disclination line is bent in a plan view is formed, the molecules are rotated further by this bending angle, thereby generating a higher-order twist locally twisted by 180 degrees or more. . This was found to be a nucleus causing bend alignment.

As described above, it is important to form a high-order twist in which liquid crystal molecules are rotated by 180 degrees or more in order to form a transition nucleus. In order to realize this, a disclination line is formed. It is effective to have both of the bending of the disclination line.

(Embodiment 1) In this embodiment, a disclination line is generated by a lateral electric field, and the disclination line is bent by a step structure.

The structure of the active matrix substrate used in the first embodiment will be described with reference to FIG. Figure 3
This is an enlarged description of one pixel. A plurality of pixel electrodes 304 were formed on the liquid crystal display element, and a TFT transistor 303 was formed on the pixel electrodes 304. Gate line 302 for operating this transistor
The source lines 303 for supplying data to be written to the pixel electrodes were formed in a matrix in the vertical direction of the panel.

In the present embodiment, the TFT 303 is formed in a U-shaped source shape, and a voltage is applied between the TFT 303 and the gate line 302 so that a horizontal electric field 3 oblique in the cross-sectional direction is obtained.
07 was generated. This oblique horizontal electric field 307
As a result, the direction of the liquid crystal molecules was controlled, and as a result, an unevenly distributed splay state was formed. Specifically, FIGS. 3 and 4
The pixel structure shown in FIG. FIG. 3 is a plan view, FIG.
Is a sectional view. In the transition period for performing the transition, first, −20 V was applied to the counter electrode 301 as the transition voltage.
At this time, +10 V was applied to the gate line 302 and -5 V was applied to the source line 303. At this time, source line 3
The source line 303 is drawn out from the intersection of the gate line 302 and the gate line 302 in the horizontal direction, and a source line lead-out portion 303a overlapping the gate line 302 is provided. Due to the oblique horizontal electric field 307, the liquid crystal molecules b and c near the center of the liquid crystal layer change to the right as shown in FIG. On the other hand, the liquid crystal molecules a in the liquid crystal layer in the vicinity of the substrate 101 maintain a state of being directed to the lower right direction by rubbing. Therefore, between the liquid crystal molecules a and c, there are liquid crystal molecules oriented in a direction parallel to the substrate, and the TFT
An uneven splay state 305 was formed on the substrate side on which the array was formed. The unevenly distributed spray region 305 grows gradually. A disclination line 308 occurred at the boundary between the unevenly distributed splay state and another moderate splay state.

In order to bend the disclination line 308, the disclination line 30
If an area for changing the moving speed of 8 is formed, bending occurs at a boundary between a fast area and a slow area. Since this disclination line is the boundary between the alignment regions of the liquid crystal,
What is necessary is just to form regions in which the growth rates of the liquid crystal alignment regions are different. In this embodiment, in particular, the growth rate in the unevenly distributed splay state may be locally controlled.

In particular, it has been found that this growth rate depends on the cell thickness, and the higher the growth rate, the faster. Here, the cell thickness is the thickness of the liquid crystal layer. In order to change the cell thickness, irregularities or steps may be formed on the substrate.

Therefore, in this embodiment, regions having different cell thicknesses are formed in the vicinity of the location where the unevenly distributed splay state occurs. As a result, as shown at 308 in FIG. 3, the disclination line was bent, and a bend orientation was generated from the bending point 306.

In order to form regions having different cell thicknesses,
An insulating film 309 was formed on the pixel electrode 304. The thickness of the insulating film 309 is determined by using a process for forming a TFT array (for example, a photolithographic etching method). For this purpose, the insulating film 309 may be partially left or may be partially removed. Since there is a lot of freedom in the pattern for forming the insulating film outside the region where the TFT is formed, this was used. Further, the material used for the metal wiring may be selectively left. Increasing these layers can increase the level difference.

An effect was obtained when the step due to the insulating film 309 (that is, the thickness of the insulating film 309) was 0.1 μm or more. Alternatively, the steps may be separately formed using a resin resist or the like. Further, the pixel electrode 304 may be above or below the insulating film 309 forming the step.
However, if this step is too large, there is a problem that bend transition on the step is difficult and sometimes the spray remains stably. This occurred when the height of the step was 1 μm or more. At this time, the region with the smallest cell thickness was 4 μm.

The present invention is not limited to this. A step may be formed on the color filter side. In this case, it may be formed on a counter substrate other than the substrate on which the TFT is formed. At this time, the step may use a color filter or a black matrix. In the present invention, a black matrix is used, and a step of 0.5 μm is formed using the black matrix.

If the width of the step structure is too small, the effect of the step cannot be exerted, and if it is too wide, the curvature becomes wide, so that there is no effect. In our study, it was effective that the width of the region where the cell thickness of the step was relatively thick was 4 μm or more and 50 μm or less. 6 is best
It was the condition of not less than micrometer and not more than 10 micrometers.

(Embodiment 2) In this embodiment, a pillar is used to bend the disclination line. This columnar body also served as a column spacer. As shown in FIG. 5, a resist spacer 401 having a height so as to have a predetermined cell thickness was formed at this time. At this time, the disclination line is bent by the column spacer 401,
This caused a bend orientation. At this time, the column spacer 401 was made light-blocking. The surrounding area was shielded from light by a black matrix. Since the column spacer 401 causes light leakage, it must be formed on a black matrix instead of being formed in the display area.

In order to form a column spacer, it is necessary that the cell thickness, that is, the liquid crystal layer thickness and the column height are substantially the same.

Also in this embodiment, a local electric field is applied at the intersection of the source line and the gate line, thereby forming a localized splay alignment. The feature is that the location where the localized splay orientation occurs and the location where the column spacer is arranged are brought close to each other.

(Embodiment 3) In this embodiment, a region where no electric field is applied is formed in order to bend the disclination line. As shown in FIG. 6, a defective region 501 was formed in the pixel electrode. In the area where the electric field is applied, the localized spray area also grows, but the area 5 where the electric field is not applied.
01 does not grow this domain. It is possible to bend using this phenomenon.

The feature is that the region 501 where the electrode is lost is formed close to the location where the localized splay alignment occurs.

Since the growth of the localized splay orientation is mainly performed in the rubbing direction or the direction opposite to the rubbing direction,
It was favorable to form the bending means at a location slightly separated from the location of occurrence in the rubbing direction or the opposite direction. The growth was slow in the direction perpendicular to the rubbing direction, and even when the bending means was formed in the direction perpendicular to the rubbing direction at the point of occurrence, the degree of occurrence of bend transition was relatively low.

The gist of the present invention is to form an unevenly distributed splay state and to bend a disclination line generated at that time. Therefore, the method for generating this is not limited. For example, in addition to the above-described example, it was confirmed that when a region having a different pretilt was formed, the growth rate of the region changed and the region was bent. There was also an effect when the rubbing direction was changed.

Further, there are various methods for forming the unevenly distributed splay state. In addition to the application of the horizontal electric field, a method of making the pretilt angles of the upper and lower substrates asymmetric and a method of changing the inclination angle of the substrates have been effective.

[0050]

As described above, according to the present invention, it is possible to provide a liquid crystal display device in which the transition is reliable and the number of bright spot defects is small.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a liquid crystal display device of the present invention.

FIG. 2A is a cross-sectional view showing a transition behavior in an initial state of the liquid crystal display element of the present invention. FIG. 2B shows a case where a disclination line is formed in one eccentric splay alignment state and a target splay alignment state. Sectional view showing the transition behavior of the liquid crystal display element of the present invention. (C) Sectional view showing the transition behavior of the liquid crystal display element of the present invention when a disclination line is formed between two unevenly distributed splay alignment states. FIG. 4 is a cross-sectional view showing the transition behavior of the liquid crystal display element of the present invention in a bend alignment state.

FIG. 3 is a plan view showing a pixel structure of the liquid crystal display element according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing the behavior of the liquid crystal of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 5 is a plan view showing a pixel structure of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 6 is a plan view showing a pixel structure of a liquid crystal display device according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 101 liquid crystal 102 substrate 103 retardation plate 104 polarizing plate 301 counter electrode 302 gate line 303 source line 304 pixel electrode 305 unevenly distributed spray region 306 bend transition occurrence point 307 lateral electric field 308 disclination line 309 different cell thickness region 310 insulating film 401 columnar shape Body (pillar spacer) 501 Electrode missing part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H088 FA02 HA08 HA12 HA14 HA16 HA18 JA05 JA28 MA01 2H090 KA05 KA18 LA02 LA04 LA06 LA09 LA15 MA02 MA17 MB01 2H091 FA02Y FA08X FA08Z FA11X FA11Z FA35Y GA08 GA13 HA07 HA18 LA30

Claims (16)

[Claims] 1. A liquid crystal display element having a transition means for performing a display by applying a voltage to a liquid crystal having a bend orientation and transitioning from an orientation state in which no voltage is applied to a bend orientation state. A liquid crystal display device comprising: means for generating a disclination line in some cases; and bending means for bending the disclination line. 2. A liquid crystal display device according to claim 1, wherein said disclination line is located at a boundary between two liquid crystal alignment states, and at least one of said two liquid crystal alignment states is in a splay alignment state. . 3. The liquid crystal display element has two substrates, and the splay alignment state is an uneven splay alignment in which liquid crystal molecules arranged substantially parallel to a substrate plane are unevenly distributed on one substrate side in a cell thickness direction. The liquid crystal display device according to claim 2, wherein: 4. The liquid crystal display device according to claim 1, wherein said refracting means changes the moving speed of the disclination line. 5. The liquid crystal display device according to claim 4, wherein said bending means is a step forming regions having different cell thicknesses. 6. The liquid crystal display device according to claim 5, wherein the height of the step is 0.1 μm or more. 7. The liquid crystal display device according to claim 5, wherein the height of the step is 1 μm or less. 8. The liquid crystal display device according to claim 5, wherein the liquid crystal display device has a substrate, and a black matrix is formed on at least one of the substrates, and the step is the black matrix. 9. The liquid crystal display device according to claim 5, further comprising a substrate, wherein at least one of the substrates has an active matrix element formed thereon, and the step is formed simultaneously with the formation of the active matrix element. Liquid crystal display element. 10. The liquid crystal display device according to claim 5, wherein the width of the step is 4 μm or more and 50 μm or less. 11. The liquid crystal display device according to claim 1, wherein said bending means is a columnar body. 12. The liquid crystal display device according to claim 11, wherein said columnar body has a thickness substantially equal to a layer thickness of said liquid crystal. 13. A liquid crystal display device according to claim 12, wherein said columnar body is formed outside of a display area. 14. The liquid crystal display device according to claim 1, wherein said bending means is an electrode defective portion for limiting a region to which an electric field is applied. 15. The liquid crystal display device according to claim 4, wherein said bending means is a different pretilt region in which regions having different pretilts are formed. 16. A rubbing direction or a direction opposite to a rubbing direction with respect to a means for generating a disclination line, wherein the bending means for bending the disclination line is disposed. The liquid crystal display element as described in the above.