JP2000162599A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent pixels from becoming irregular in the place where disclination is caused and to prevent an image from becoming rough and flickering by providing a common electrode with an alignment control window which is open opposite a pixel electrode and making the alignment control window thin nearby the center of its long extension part, and thus causing disclination concentrically here. SOLUTION: The common electrode is equipped with the alignment control window 60 and an alignment film which is not rubbed is used. The alignment control window 60 has the long extension part 60c which is parallel to the long side of the pixel electrode 53 and peripheral parts 60b which extend from both the ends of the long extension part 60c to the four corners and is so shaped that a Y shape and an inverted Y shape are connected together. The center part of the long extension part 60c is formed to width w2 and both the end parts of the long extension part 60c are formed to width w1; and the long extension part is thinner nearby the center than at other parts. Consequently, disclination occurs concentrically at the point of the width w2 in the center to prevent respective pixels from becoming irregular in the place where disclination occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display (LCD) that performs display by utilizing the electro-optical anisotropy of liquid crystal.
Liquid Crystal Display), especially viewing angle characteristics,
The present invention relates to a liquid crystal display device having improved luminance.

[0002]

2. Description of the Related Art Heretofore, a vertical alignment type liquid crystal display device using a liquid crystal having a negative dielectric anisotropy and a vertical alignment film has been developed. There are two types separately.

First, the first type uses a rubbed vertical alignment film, and its structure is shown in FIG. A TFT 5 covered with an interlayer insulating film 51 is formed on a substrate 50.
2 are formed for each pixel. On top of this, TFT5
2 connected via a contact hole to the pixel electrode 53
Then, the alignment film 54 subjected to the rubbing treatment is formed.

On a substrate 55 arranged opposite to the substrate 50, a common electrode 56 common to each pixel and an alignment film 57 subjected to a rubbing process are formed. These substrates 50,
55, a liquid crystal 58 is filled, and the pixel electrode 53
The orientation of the liquid crystal molecules 59 is controlled according to the electric field strength formed by the voltage applied between the common electrode 56 and the common electrode 56. As a result, the polarization characteristics of the liquid crystal layer 58 change, and the transmittance of light linearly polarized by a polarizing plate (not shown) is controlled.

In the case of a vertical alignment type LCD, the liquid crystal has a negative dielectric anisotropy, that is, has a property of being oriented in a direction perpendicular to the electric field direction. The alignment films 54 and 57 are vertical alignment films in which the initial alignment of the liquid crystal when no voltage is applied is controlled in the normal direction of the substrate.
Is set between 85 ° and 99 ° with respect to the substrate surface. By applying the pretilt θ, the liquid crystal molecules 59 are caused to incline in the pretilt θ direction by applying a voltage. For this reason, the inclination directions of the liquid crystal molecules 59 are aligned, and the orientation of the liquid crystal is prevented from varying with respect to the planar direction, thereby preventing the display quality from deteriorating.

Another type is a vertical alignment type liquid crystal display device in which an alignment control window is provided in the common electrode 56 and has no alignment film, and is proposed in, for example, Japanese Patent Application No. 5-84696. FIG. 5 is a sectional view showing the structure of an LCD having such an alignment control window. The LCD shown in FIG.
Above are the TFT 52 and the pixel electrode 5 connected to the TFT 52.
3 is formed, and the liquid crystal 58 is sealed together with the substrate 55. However, the common electrode 56 is opened to form an alignment control window 60, and the alignment film 61, 62 is greatly different in that no rubbing treatment is performed. The same structures as those of the LCD of FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. In this configuration, when a voltage is applied between the pixel electrode 53 and the common electrode 56, the electric field 6
3, 64 are formed, and the liquid crystal molecules 59 are inclined. At the end of the pixel electrode 53, the electric field 63 has a shape obliquely inclined from the pixel electrode 53 toward the common electrode 56. Similarly, since no electrode is present at the end of the alignment control window 60, the electric field 64 has a shape inclined toward the pixel electrode 53. Therefore, the liquid crystal molecules 59 are inclined toward the inside of the pixel electrode 53 regardless of the pretilt angle.

In the orientation control window 60, the common electrode 56
Is not present, an electric field is not formed even by applying a voltage, and the liquid crystal molecules 59 are fixed in the initial alignment state, that is, in the vertical direction in the region of the alignment control window 60. by this,
Due to the continuity of the liquid crystal, the alignment directions of the liquid crystal oppose each other across the alignment control window 60, and a wider viewing angle than that of the LCD shown in FIG. 4 can be obtained.

Although various shapes of the alignment control window 60 are conceivable, FIG. 6 is a plan view showing one pixel in a liquid crystal display device having the alignment control window 60. FIG. Pixel electrode 53
An alignment control window 60 is formed in the common electrode above the pixel region defined by the pixel. The orientation control window 60 has a centrally extending elongated portion 60a extending longitudinally in the drawing and an elongated portion 60a.
A peripheral portion 60 extending from the end toward the four corners of the pixel region
b. The alignment of the liquid crystal molecules 59 is indicated by a double circle and an arrow.

The liquid crystal molecules 5 located immediately below the alignment control window 60
As described above, 9a has no electrodes, and thus is vertically oriented regardless of the presence or absence of voltage application.

On the other hand, the orientation control window 60 on the pixel area
The liquid crystal molecules 59b, 59c, 59d, 59e not underneath are:
By voltage application, they are respectively oriented so as to be perpendicular to the orientation control window 60, 59b is directed to the left of the drawing, 59c is directed to the right of the drawing, 59d is directed substantially below the drawing, and 59e is directed substantially upward of the drawing.

[0011]

As described above, since the alignment control window 60 has no electrodes, it is a dark area that does not always transmit light irrespective of the presence or absence of a voltage while being in the pixel area. The region of the alignment control window 60 on the pixel is shown in FIG.
A dark line as shown in the pixel 70 of FIG. This causes a reduction in the brightness of the liquid crystal display device.

Therefore, the present applicant has made an attempt to form the liquid crystal display window as thin as possible, and found the following problems.

FIG. 8 shows a pixel gap of 5 μm and a pixel region 1.
In a 70 μm × 60 μm LCD, the alignment control window 60
FIG. 4 is a plan view of each pixel when the width of each pixel is uniformly set to 4 μm.
In the pixel 71, the pixel region is entirely dark. In the pixel 72, the dark line is doubled even though the elongated portion of the alignment control window 60 has a straight shape.
The intersection of the double dark line is different for each pixel.

The occurrence of the dark pixels 71 causes the brightness of each pixel to fluctuate, causing unevenness in display and making the image appear grainy. In addition, the occurrence of the pixel 72 in which the dark line is doubled causes the alignment direction of the liquid crystal to lose its balance,
That is, the number balance between the leftwardly directed liquid crystal molecules 59b and the rightwardly directed molecules 59c is lost, so that the viewing angle dependence of the liquid crystal display device varies from pixel to pixel. Furthermore, since which pixel becomes the dark pixel 71 and at which pixel the intersection of the double line occurs changes every time a voltage is applied, there is a problem that the image of the liquid crystal display device flickers.

[0015]

The cause of the above problem will be described with reference to the following model.

FIG. 7 is a sectional view taken along the line AA 'of FIG. As shown in FIG. 7A, since the liquid crystal has a property of alignment continuity, the alignment direction does not change from just below the end 60a of the alignment control window 60, and the liquid crystal molecules within a certain distance d are not changed. , Under the influence of the liquid crystal molecules below the electrode 56. Therefore, even if the liquid crystal molecules are below the alignment control window 60, the liquid crystal molecules 59a 'within a range of a distance d from the alignment control window 60 are aligned by the electric field.

When the width of the alignment control window 60 is reduced to less than twice the distance d, the liquid crystal molecules at the center of the alignment control window 60 are affected by both liquid crystal molecules, as shown in FIG. As a result, the orientation direction becomes unstable. In addition, since there is no vertically aligned molecule 59a, so-called disclination occurs, in which left and right liquid crystal molecules are in contact with each other. This causes the pixel 72 of the double line. When the disclination occurs, the area where the display of the pixel is most visible, that is, the center of the viewing angle (the front in the case of a normal pixel) faces obliquely,
The front of the screen is shifted from the center of the viewing angle. As a result, the pixel looks dark from the front of the screen, which causes the dark pixel 71.

From the above considerations, it is considered that discontinuity and disclination of molecules are likely to occur at the narrowest position of the orientation control window 60.

In order to solve the above-mentioned problems, the present invention provides a liquid crystal display device having an alignment control window having a long elongated portion in one direction, wherein the vicinity of the center of the elongated portion is different from that of the alignment control window. A liquid crystal display device characterized by being formed thinner than a part.

Further, both ends of the elongated portion are set at a distance d of 2 above.
Even if it is thinner than twice, it has been experimentally revealed that if the center of the elongated portion is wider than 2d, disclination hardly occurs. This is considered to be due to the fact that vertically oriented molecules remain in the thick region, which plays a so-called "wall" role, and prevents disclination. Therefore, the present invention is a liquid crystal display device in which the vicinity of the center of the elongated portion is formed thick.

In addition, disclination tends to be induced by liquid crystal molecules in a region defined by a peripheral portion of the alignment control window. Therefore, the present invention is a liquid crystal display device having, at both ends of the elongated portion, ends having sides forming a predetermined angle with respect to the elongated portion.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the disclination is caused by the fact that the elongated portion of the orientation control window 60 has a certain limit width w2.
It is easy to happen when: For example, when an alignment control window 60 having a long extension of 100 μm is formed on an LCD having a pixel electrode size of 170 μm × 60 μm and a cell gap of 5 μm, disclination occurs when the width of the long extension becomes 4 μm or less. It is easy to get up. Similar L
When the orientation control window 60 having a long extension of 6 μm in width was formed on the CD, disclination was difficult. When the width of the elongated portion is smaller than the cell gap, disclination is likely to occur.

It is assumed that the width at which disclination is likely to occur is w2 (4 μm in the above example), and the minimum width at which disclination does not easily occur is w1 (6 μm in the above example).

First, a first embodiment of the present invention will be described. FIG. 1 is a plan view of a single cell of the liquid crystal display device of the present embodiment. In the present embodiment, the common electrode is provided with an alignment control window, and an alignment film that has not been subjected to a rubbing process is used. Its cross-sectional structure is exactly the same as the structure shown in FIG. The alignment control window 60 has an elongated portion 60c parallel to the long side of the pixel electrode 53, and peripheral portions 60b extending from both ends of the elongated portion 60c toward the four corners. The shape is connected. The central portion of the elongated portion 60c is formed to have a width w2, and both end portions of the elongated portion 60c are formed to have a width w1, and the vicinity of the center of the elongated portion is formed thinner than other portions.

According to the present embodiment, disclination occurs intensively at the central point of the width w2. Therefore, it is possible to prevent the location where disclination occurs from varying for each pixel. As a result, the luminance does not differ for each pixel, so that it is possible to prevent image flickering and flickering. In addition, since disclination can occur at the center of the pixel, the balance between rightward and leftward liquid crystal molecules is not lost, and variation in viewing angle dependence can be prevented. Further, since the area of the alignment control window 60 is reduced as compared with the linear elongated portion 60a having the width w1, the aperture ratio of the entire pixel is improved, and the brightness of the LCD is improved.

In FIG. 1, the shape of the elongated portion 60b is drawn as a straight line, but it may be a smooth curve having a width w2 at the center and a width w1 at both ends, or a discrete curve at the center. Any shape can be used as long as it is easy for the nation to occur.

Next, a second embodiment of the present invention will be described. FIG. 2 is a plan view of a single cell of the liquid crystal display device of the present embodiment. In the present embodiment, the common electrode is provided with an alignment control window, and an alignment film that has not been subjected to a rubbing process is used. Its cross-sectional structure is exactly the same as the structure shown in FIG. The alignment control window 60 has an elongated portion 60d parallel to the long side of the pixel electrode 53, and peripheral portions 60b extending from both ends of the elongated portion 60d toward the four corners. The shape is connected. The central portion of the elongated portion 60d has a width w1 and both end portions of the elongated portion 60d have a width w2, and the vicinity of the center of the elongated portion is formed thicker than other portions.

According to the present embodiment, as described above, the vicinity of the center is thick, and the liquid crystal molecules aligned vertically remain here, so that disclination hardly occurs. Therefore, it is possible to prevent the image from being flickered and flickered due to the disclination, and the variation in the viewing angle dependency. Also,
The area of the orientation control window 60 is smaller than that of the linear elongated part 60a having the width w1, and the elongated part 60d of the orientation control window has the maximum width w1 even though the maximum width is w1. Since the dark line has a width of about w2, the aperture ratio of the entire pixel is improved, and the luminance of the LCD is improved.

In FIG. 2, the shape of the elongated portion 60b is drawn as a straight line, but it may be a smooth curve having, for example, a width w1 at the center and a width w2 at both ends.

Next, a third embodiment of the present invention will be described. FIG. 3 is a plan view of a single cell of the liquid crystal display device of the present embodiment. In the present embodiment, the common electrode is provided with an alignment control window, and an alignment film that has not been subjected to a rubbing process is used. Its cross-sectional structure is exactly the same as the structure shown in FIG. The alignment control window 60 has a linear elongated portion 60e having a width w2 parallel to the long side of the pixel electrode 53, and at both ends thereof,
It has an end portion 60f having a side that forms an angle wider than 45 ° with the elongated portion 60e, and has an I-shape. End 60
f may be a triangular shape having the above sides, or a shape obtained by cutting both ends of the triangular shape as shown in the figure.

For example, in FIG. 6, if the peripheral portion 60b is not formed, the elongated portion 60a and the pixel electrode 53 are orthogonal to each other, and the orientation direction of the liquid crystal molecules changes rapidly, so that the liquid crystal molecules at the intersection cannot follow. Here, disclination occurs. This is one of the reasons why the peripheral portion 60b was formed in the first and second embodiments. However, due to the peripheral portion 60b, the liquid crystal molecules aligned in the vertical direction in the drawing trigger the disclination of the central portion of the pixel. Therefore, as shown in FIG. 3, the present invention eliminates the peripheral portion 60b in order to prevent disclination in the central portion of the pixel, and removes the peripheral portion 60b in order to prevent disclination in the pixel peripheral portion. Instead, an end portion 60f having a side having the same angle as the direction in which the peripheral portion b extends is formed. In other words, the end 60f is a region defined by the peripheral portion 60b as an opening control window. End 6
By setting it to 0f, there is no trigger for disclination, so that disclination hardly occurs in the elongated portion 60e even if it has a small width w2.

According to the present embodiment, since there are few liquid crystal molecules aligned in the vertical direction in the drawing, disclination hardly occurs. Therefore, it is possible to prevent the image from being flickered and flickered due to the disclination, and the variation in the viewing angle dependency. Further, since the elongated portion 60e is linear in width w2, the aperture ratio of the entire pixel is improved, and the brightness of the LCD is improved.

In FIG. 3, the elongated portion 60e and the end 60
Although the shape of f is drawn as a straight line, it may be a smooth curve.

[0034]

As described above, claims 1 and 2 have been described.
In the invention described in (1), since the vicinity of the center of the elongated portion of the alignment control window is formed narrow, disclination occurs intensively here. Therefore, it is possible to prevent the portion where the disclination occurs from being varied for each pixel, and to prevent the image from being rough or flickering. In addition, since disclination can occur at the center of a pixel, variation in viewing angle dependence can be prevented. Furthermore, since a part of the elongated portion is thinned, the area of the alignment control window is reduced, so that the aperture ratio of the entire pixel is improved and the brightness of the LCD is improved.

Further, according to the third and fourth aspects of the present invention, the vicinity of the center of the elongated portion is formed thick, so that disclination can be prevented, resulting in image flickering, flickering, and visual field. Variation in angle dependence can be prevented. In addition, since the area of the alignment control window is reduced and the dark line caused by the area is narrow, the aperture ratio of the entire pixel is improved, and the brightness of the LCD is improved.

According to the fifth aspect of the present invention, since there is an elongated portion substantially parallel to the side of the pixel electrode and an end having a side forming a predetermined angle with the elongated portion, disclination is achieved. Can be prevented, resulting in image roughness,
It is possible to prevent flicker and variation in viewing angle dependency. Further, since the elongated portion has a linear shape with a width w2, the aperture ratio of the entire pixel is improved, and the brightness of the LCD is improved.

[Brief description of the drawings]

FIG. 1 is a plan view of a first embodiment of the present invention.

FIG. 2 is a plan view of a second embodiment of the present invention.

FIG. 3 is a plan view of a third embodiment of the present invention.

FIG. 4 is a sectional view of a conventional liquid crystal display device.

FIG. 5 is a cross-sectional view of a conventional liquid crystal display device having an alignment control window.

FIG. 6 is a plan view of a conventional liquid crystal display device having an alignment control window.

FIG. 7 is a cross-sectional view for explaining a problem of a conventional liquid crystal display device having an alignment control window.

FIG. 8 is a plan view for explaining a problem of a conventional liquid crystal display device having an alignment control window.

[Explanation of symbols]

 50, 55 Substrate 51 Insulating film 52 TFT 53 Pixel electrode 54, 57 Alignment film 56 Common electrode 58 Liquid crystal 59 Liquid crystal molecule 60 Alignment control window 61, 62 Alignment film not subjected to rubbing 63, 64 Electric field 70 Normal pixel 71 Dark pixel 72 Pixel where double line appeared

Claims (5)

[Claims] A first substrate on which a plurality of pixel electrodes for driving liquid crystal are formed; a second substrate on which a common electrode facing the pixel electrodes is formed; and a first substrate and a second substrate on which a common electrode is formed.
A liquid crystal display device having a liquid crystal layer in which liquid crystal is sealed between the substrates, wherein the common electrode has an alignment control window that is opened at a portion facing the pixel electrode; A liquid crystal display device having a long extension in one direction, wherein a portion near the center of the long portion of the alignment control window is formed narrower than other portions of the alignment control window. 2. A first substrate on which a plurality of pixel electrodes for driving a liquid crystal are formed; a second substrate on which a common electrode facing the pixel electrodes is formed;
A liquid crystal display device having a liquid crystal layer in which liquid crystal is sealed between the substrates, wherein the common electrode has an alignment control window opened at a portion opposed to the pixel electrode, and the alignment control window is A long part extending in one direction, and a peripheral part extending in four directions at a predetermined angle from the one direction from both ends of the long part, and the vicinity of the center of the long part is A liquid crystal display device characterized by being formed thinner than other parts. 3. A first substrate on which a plurality of pixel electrodes for driving liquid crystal are formed, a second substrate on which a common electrode opposed to the pixel electrodes is formed, and the first substrate and the second substrate.
A liquid crystal display device having a liquid crystal layer in which liquid crystal is sealed between the substrates, wherein the common electrode has an alignment control window that is opened at a portion facing the pixel electrode; A liquid crystal display device having a long elongated portion in one direction, wherein a portion near the center of the elongated portion of the alignment control window is formed thicker than other portions of the alignment control window. 4. A first substrate on which a plurality of pixel electrodes for driving liquid crystal are formed, a second substrate on which a common electrode opposed to the pixel electrodes is formed, the first substrate and the second substrate.
A liquid crystal display device having a liquid crystal layer in which liquid crystal is sealed between the substrates, wherein the common electrode has an alignment control window opened at a portion opposed to the pixel electrode, and the alignment control window is A long part extending in one direction, and a peripheral part extending in four directions at a predetermined angle from the one direction from both ends of the long part, and a part of the long part is a part of the long part. A liquid crystal display device characterized by being formed thicker than other parts. 5. A first substrate on which a plurality of pixel electrodes each having a side for driving liquid crystal is formed, a second substrate on which a common electrode facing the pixel electrodes is formed, and the first substrate. And a liquid crystal layer having liquid crystal sealed between the second substrate, wherein the common electrode has an alignment control window opened at a portion facing the pixel electrode; The control window has an elongated portion substantially parallel to a side of the pixel electrode, and the alignment control window has, at both ends of the elongated portion, ends having sides forming a predetermined angle with respect to the elongated portion. A liquid crystal display device comprising: