JP3847403B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to an improvement of a so-called alignment-divided liquid crystal display device in which a plurality of alignment films having different alignment states are provided in one pixel region in order to expand a viewing angle.
[0002]
[Prior art]
Hereinafter, an alignment-divided liquid crystal display device according to a conventional example will be described with reference to the drawings. This alignment-divided liquid crystal display device is a TN (Twisted Nematic) mode liquid crystal display device. As shown in FIG. 4, a plurality of gate bus lines 1 and drain bus lines 2 are arranged orthogonally, and their intersections. A pixel electrode 4 made of an ITO (Indium Tin Oxide) film is connected to a nearby portion via a TFT (Thin Film Transistor) 3, and the TFT 3 and the pixel electrode 4 are arranged in a matrix.
[0003]
Each pixel electrode 4 substantially coincides with the display area, but the area is divided into first and second pixel areas 4A and 4B as shown in FIG. The pixel electrode 4 is not divided in this region, but the alignment state of an alignment film (not shown) formed thereon is changed for each of the first and second pixel regions 4A and 4B. In this way, a structure intended to enlarge the viewing angle by intentionally changing the alignment state of the liquid crystal molecules within one pixel is adopted (hereinafter, this structure is referred to as an alignment division type structure).
[0004]
The structure of this alignment-divided liquid crystal display device will be described in more detail below with reference to FIGS. 5A and 5B are top views focusing on one pixel of the alignment-divided liquid crystal display device. FIG. 6A is a cross-sectional view taken along line AA in FIG. 5, and FIG. 5B is a line taken along line BB in FIG. It is sectional drawing.
In this liquid crystal display device, as shown in FIGS. 6A and 6B, a transparent lower substrate 6 and an upper substrate 7 made of glass or the like are disposed to face each other, and liquid crystal is sealed between them. Consists of. On the lower substrate 6, gate bus lines 1A and 1B, a drain bus line 2, a ring Cs5 described later, and the like are formed, and a pixel electrode 4 made of an ITO film is formed through an insulating film 8. A common electrode 9 made of an ITO film is also formed on the upper substrate 7. By applying a voltage between the common electrode 9 and the pixel electrode 4, the direction of the liquid crystal molecules 10 enclosed therebetween is changed. It drives by changing.
[0005]
Although not shown in the drawing, an alignment film for defining the alignment state (particularly, the pretilt angle) of the liquid crystal molecules 10 is provided at a portion in contact with the liquid crystal molecules 10. As shown in FIG. 6A, on the lower substrate 6 side, the pretilt angle of the first pixel region 4A is α, and the pretilt angle of the second pixel region 4B is β (α> β). Conversely, on the upper substrate 7 side, the pretilt angle of the first pixel region 4A is β and the pretilt angle of the second pixel region 4B is α, so that the pretilt angle on the upper substrate side and the lower substrate side Since the pretilt angle is a combination of large and small, the alignment state of the liquid crystal molecules 10 is reversed in the first and second pixel regions 4A and 4B as shown in FIG. . By doing so, it is possible to prevent the alignment direction of the liquid crystal from being biased in one direction and to enlarge the viewing angle.
[0006]
Further, in this liquid crystal display device, in order to improve the aperture ratio, an auxiliary capacitor electrode that is usually formed so as to cross the pixel electrode is formed in an annular shape and arranged along the periphery of the pixel electrode of each pixel. (This is referred to as ring Cs below). This ring Cs is a gate bus line connected to a pixel next to a gate bus line connected to the selected pixel as shown in FIG. 5 (in FIG. 5, this is the nth gate bus line 1A). (In FIG. 5, this is the (n + 1) th gate bus line 1B). When a pixel connected to the nth gate bus line 1A is selected, the potential of the nth gate bus line 1A fluctuates to turn on / off the TFT 3, but the n + 1th gate bus line Since the potential of 1B is constant during this period, at this moment, the ring Cs5 connected to the (n + 1) th gate bus line 1B is also at a constant potential and can function as an auxiliary capacitor. In this way, by configuring the gate bus line of the next stage and the ring Cs to be connected, it becomes possible to improve the aperture ratio of the pixel.
[0007]
[Problems to be solved by the invention]
However, when manufacturing an alignment-divided liquid crystal display device as described above, if the pretilt angle on the upper substrate side and the pretilt angle on the lower substrate side have a combination of large and small, It is very difficult to avoid misalignment between the substrate and the lower substrate.
[0008]
In such a case, as shown in FIG. 7A, the pretilt angle of the upper substrate and the pretilt angle of the lower substrate coincide with each other in the same pixel region, and the pretilt angle is large—large, small— The combination of small arises. For example, in the second pixel region 4B in FIG. 7A, the large pretilt angle α is opposed to the upper substrate and the lower substrate.
[0009]
In such a case, the TN mode liquid crystal molecules are not only in the twisted state as expected, but also in a state in which the splay state is added due to the liquid crystal molecules receiving pressure at a large pretilt angle α from above and below. The energy state becomes higher than the twisted liquid crystal molecules, and the alignment state of the liquid crystal molecules becomes unstable. In a severe case, there is a defect that the direction of rotation of the liquid crystal is reversed from the normal direction (hereinafter referred to as a reverse twist domain defect).
[0010]
This phenomenon is more likely to occur as the applied voltage is higher.
In the conventional structure, as shown in FIGS. 5, 6, 7, etc., the ring Cs <b> 5 is disposed so as to slightly protrude from the formation region of the pixel electrode 4. This is to improve the aperture ratio by reducing the region overlapping with the pixel electrode 5 as much as possible while securing the area used as the auxiliary capacitor.
[0011]
The ring Cs is connected to the gate bus line, and a voltage higher than the applied voltage of the liquid crystal is applied to the gate bus line in order to control ON / OFF of the TFT (the applied voltage to the liquid crystal is 2 to 2). The voltage is about 3V, but a voltage of about ± 12V is applied to the gate bus line).
[0012]
In such a case, as shown in FIG. 7B, a high electric field E is generated between the ring Cs protruding from the pixel electrode formation region and the common electrode facing the ring Cs. The liquid crystal molecules are sometimes affected by the high electric field E and become different from the original alignment state. Since this abnormality propagates to the liquid crystal molecules in the center of the pixel, the orientation of the liquid crystal molecules in the entire pixel is thereby changed.
[0013]
In particular, this abnormality occurs in the liquid crystal molecules in the vicinity of the ring CS of the boundary region (hereinafter referred to as the alignment division region) between the first and second pixel regions 4A and 4B where the alignment state of the liquid crystal molecules is unstable even within the pixel. It was remarkable.
This instability spreads to the center of the pixel area, and thus a reverse twist domain defect occurs and disclination occurs, resulting in a problem that the display screen of the liquid crystal display device becomes rough.
[0014]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and includes a plurality of gate bus lines, a plurality of drain bus lines arranged to be orthogonal to the gate bus lines, the gate bus lines, and the drain bus lines. the surrounded by pixel regions in the gate bus lines and said drain bus pixel electrodes arranged so as not to overlap the line is arranged near the intersecting region of the gate bus lines and said drain bus line, the gate The TFT, which is a liquid crystal driving element connected to the bus line, the drain bus line, and the pixel electrode, is arranged along the periphery of the arrangement area of the pixel electrode, and is formed below the pixel electrode, A first transparent substrate having an auxiliary capacitance electrode connected to the gate bus line on the main surface, and a second transparent substrate having a common electrode on the main surface A bright substrate, the first transparent substrate and the second transparent substrate are arranged to face each other, a liquid crystal is sealed between them, and the pixel region is divided into a plurality of regions, In the liquid crystal display device in which the alignment state of the liquid crystal is different, the auxiliary capacitance electrode is arranged on the inner side so as not to protrude from the arrangement region of the pixel electrode at least at a boundary portion of the plurality of regions. The above-described problems are solved by the liquid crystal display device.
[0015]
Subsequently, the effects of the present invention will be described below.
According to the liquid crystal display device according to the present invention , the auxiliary capacitance electrode is arranged at least at the boundary portion of the plurality of regions so as not to protrude from the pixel electrode arrangement region, and is thus connected to the gate bus line. Therefore, the auxiliary capacitance electrode to which a high voltage is applied is electrically shielded by the pixel electrode.
[0016]
Therefore, as shown in FIG. 7B, the high electric field E between the auxiliary capacitance electrode and the common electrode facing the conventional electrode is not generated as shown in FIG. 7B. It is possible to suppress the occurrence of an anomaly that liquid crystal molecules in the vicinity of are affected by the high electric field E and deviate from the intended orientation direction.
As a result, it is possible to suppress as much as possible the disclination that has occurred in the conventional apparatus and the roughness of the display image caused by this.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings. This liquid crystal display device is a TN (Twisted Nematic) mode liquid crystal display device and has an alignment division type structure. Moreover, as shown in FIG. 1, it is the same as that of the prior art in that the aperture ratio is improved by having the ring Cs.
[0018]
The liquid crystal display device according to this embodiment will be described in more detail below with reference to FIGS. 1A and 1B are top views illustrating one pixel of an alignment-divided liquid crystal display device. FIG. 2A is a cross-sectional view taken along line XX in FIG. 1, and FIG. 1B is a cross-sectional view taken along line Y-Y in FIG. FIG.
In this liquid crystal display device, as shown in FIG. 2A and FIG. 2B, a first transparent substrate 16 and a second transparent substrate 17 made of glass or the like are arranged to face each other, and liquid crystal is enclosed therebetween. It is composed by being done. On the first transparent substrate 16, gate bus lines 11A and 11B, a drain bus line 12, a ring Cs15, and the like are formed, and a pixel electrode 14 made of an ITO film is formed through an insulating film 18. Further, a common electrode 19 made of an ITO film is formed on the second transparent substrate 17, and a liquid crystal molecule 20 sealed between the common electrode 19 and the pixel electrode 14 is applied by applying a voltage between the common electrode 19 and the pixel electrode 14. Is driven by changing the direction.
[0019]
Although not shown in the drawing, an alignment film for defining the alignment state (particularly, the pretilt angle) of the liquid crystal molecules 20 is provided at a portion in contact with the liquid crystal molecules 20. As shown in FIG. 2A, on the first transparent substrate 16 side, the pretilt angle of the first pixel region 14A is α, and the pretilt angle of the second pixel region 14B is β (α> β). . On the other hand, on the second transparent substrate 17 side, the pretilt angle of the first pixel region 14A is β, and the pretilt angle of the second pixel region 4B is α, so that the pretilt angle on the first transparent substrate side is α. And the pretilt angle on the second transparent substrate side have a combination of large and small so as to increase the viewing angle.
[0020]
Further, in this liquid crystal display device, in order to improve the aperture ratio, an auxiliary capacitor electrode that is usually formed so as to cross the pixel electrode is formed in an annular shape and arranged along the periphery of the pixel electrode of each pixel. (This is referred to as ring Cs below). The ring Cs15 is connected to the (n + 1) th gate bus line 11B connected to the pixel next to the nth gate bus line 11A connected to the selected pixel as shown in FIG. The ring Cs is an example of an auxiliary capacitance electrode.
[0021]
As shown in FIG. 1, the liquid crystal display device according to the present embodiment has the above-described ring Cs15 formation region within the pixel electrode 14 formation region in all regions including the alignment division region. The ring Cs is arranged so as not to protrude from the electrode formation region.
For this reason, since the ring Cs15 is completely electrically shielded by the upper pixel electrode 14, even if a high voltage for driving the TFT is applied to the gate bus line, the ring Cs15 is shown in FIG. The high electric field E generated between the ring Cs and the common electrode as in the prior art is not generated.
[0022]
As a result, it is possible to suppress the occurrence of an abnormality in which liquid crystal molecules in the vicinity are affected by the high electric field E and deviate from the orientation direction that should be originally formed.
Accordingly, it is possible to suppress disclination that has occurred in the conventional apparatus and image roughness caused by this.
Further, in this embodiment, the ring Cs is completely shielded by using the pixel electrode in the entire region, but the liquid crystal molecule abnormality is mostly generated in the vicinity of the alignment division region, so that the alignment is performed as shown in FIG. Even if only the ring Cs in the part of the divided region is shielded so as not to protrude from the pixel electrode formation region, the abnormal alignment state of the liquid crystal molecules in this region can be suppressed. The effect of.
[0023]
【The invention's effect】
As described above, according to the present invention, the annular auxiliary capacitance electrode is arranged on the inner side so as not to protrude from the arrangement area of the pixel electrode at least at the boundary between the plural areas. It is possible to suppress the occurrence of an abnormality in which the liquid crystal molecules in the vicinity of the boundary between the plurality of regions where the alignment state is unstable deviate from the alignment direction that should be originally formed.
[0024]
As a result, it is possible to suppress as much as possible the disclination that has occurred in the conventional apparatus and the roughness of the display image caused by this.
[Brief description of the drawings]
FIG. 1 is a top view illustrating a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a liquid crystal display device according to an embodiment of the present invention.
FIG. 3 is a top view illustrating a liquid crystal display device according to another embodiment of the present invention.
FIG. 4 is a diagram illustrating a configuration of an alignment-divided liquid crystal display device.
FIG. 5 is a top view illustrating a liquid crystal display device according to a conventional example.
FIG. 6 is a cross-sectional view illustrating a liquid crystal display device according to a conventional example.
FIG. 7 is a cross-sectional view illustrating a problem of a liquid crystal display device according to a conventional example.
[Explanation of symbols]
11A nth gate bus line 11B n + 1th gate bus line 12 drain bus line 13 TFT
14 pixel electrode 14A first pixel region 14B second pixel region 15 ring Cs (auxiliary capacitance electrode)
16 First transparent substrate 17 Second transparent substrate 18 Insulating film 19 Common electrode 20 Liquid crystal molecules

Claims (4)

A plurality of gate bus lines; a plurality of drain bus lines arranged orthogonal to the gate bus lines; and the gate bus lines and the drains within a pixel region surrounded by the gate bus lines and the drain bus lines. and pixel electrodes arranged so as not to overlap the bus lines are arranged in the region near the intersection of the gate bus lines and said drain bus line, the gate bus line, a liquid crystal to be connected to the drain bus line and the pixel electrode The main surface includes a TFT which is a driving element and an auxiliary capacitance electrode which is arranged along the periphery of the pixel electrode arrangement region, is formed below the pixel electrode, and is connected to the gate bus line. A first transparent substrate;
A second transparent substrate having a common electrode on the main surface,
The first transparent substrate and the second transparent substrate are disposed to face each other, liquid crystal is sealed therebetween, and the pixel region is divided into a plurality of regions, and the alignment state of the liquid crystal is different in each region. In liquid crystal display devices,
2. The liquid crystal display device according to claim 1, wherein the auxiliary capacitance electrode is arranged on the inner side so as not to protrude from the arrangement area of the pixel electrode at least at a boundary portion between the plurality of areas.   2. The liquid crystal display device according to claim 1, wherein the auxiliary capacitance electrode is disposed on the inner side so as not to protrude from the arrangement region of the pixel electrode.   3. The pixel region according to claim 1, wherein the pixel region is divided into a plurality of regions, and an alignment film having a different alignment state for each of the plurality of regions is provided in contact with the liquid crystal. Liquid crystal display device. 4. The liquid crystal according to claim 3 , wherein the alignment films having different alignment states for each of the plurality of regions are provided such that a pretilt angle of liquid crystal molecules in contact with the alignment film is different for each of the plurality of regions. Display device.

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