KR100623986B1 - a liquid crystal display - Google Patents

Abstract

In the thin film transistor substrate, a pixel electrode is formed in a pixel region formed by an intersection of a gate line and a data line, and a common electrode is formed in a color filter substrate corresponding thereto. The two substrates are provided with an alignment film which is rubbed in a direction parallel to the gate lines, so that the liquid crystal layer between the two substrates is arranged in a bent structure. In this case, the pixel area has a horizontal length equal to or greater than the vertical length, thereby reducing an area where the alignment of the liquid crystal molecules is broken, thereby improving image quality. In addition, the alignment film is rubbed in parallel with the gate line, so that the viewing angle is maximized. The viewing angle is maximized by the stretching axis of the compensating plate support body coinciding with the transmission axis of the adjacent polarizing plate, and the excellent black state can be obtained by the stretching axis of the WV plate support body coinciding with the transmission axis or absorption axis of the adjacent polarizing plate. .

Alignment film, rubbing, bending, compensation plate, WV plate, polarizing plate, viewing angle

Description

Liquid crystal display {a liquid crystal display}

1 is a schematic view of a thin film transistor substrate of a liquid crystal display according to a first exemplary embodiment of the present invention.

FIG. 2A is a cross-sectional view showing the color filter substrate facing the Q portion in FIG. 1, illustrating an arrangement of liquid crystal molecules before applying an electric field. FIG.

FIG. 2B is a diagram illustrating an arrangement state of liquid crystal molecules after applying an electric field in FIG. 2A;

3A to 3C are diagrams illustrating the shape of a pixel electrode;

4 is a schematic view of a thin film transistor substrate of a liquid crystal display according to a second exemplary embodiment of the present invention.

5 is a graph illustrating a contrast ratio with respect to a viewing angle on a screen of a liquid crystal display device;

6A is a graph showing a change in luminance with respect to a change in viewing angle in the rubbing direction,

6B is a graph showing a change in luminance with respect to a change in viewing angle in a direction perpendicular to the rubbing direction,

FIG. 7 is a view illustrating a polarizer, a compensation plate, and a WV plate attached to an outer side of a substrate in the liquid crystal display according to the first and second embodiments of the present invention.

The present invention relates to a liquid crystal display device and to a liquid crystal display device for maximizing the viewing angle and improving image quality.

The liquid crystal display is one of the most widely used flat panel display devices. The liquid crystal display includes two glass substrates on which electrodes are formed and a liquid crystal layer interposed therebetween. It is a device that displays a screen by controlling the amount of light transmitted by changing the arrangement of liquid crystal molecules.

Various methods have been proposed to improve the response speed and the viewing angle among the liquid crystal displays, and examples thereof include an OCB (optically compensated bend) type liquid crystal display.

The OCB type liquid crystal display device includes an electrode formed on two opposite substrates, a liquid crystal layer injected between the substrates, and formed on two substrates, respectively, and an alignment layer for aligning liquid crystal molecules horizontally with the substrate. In the OCB type liquid crystal display device, when an electric field is applied to two substrates, the liquid crystal molecules are symmetrical with respect to the center plane of the two substrates and take a vertical arrangement in a horizontal arrangement from the substrate to the center plane, thereby obtaining a wide viewing angle. In order to obtain such an arrangement of liquid crystal molecules, the alignment layers of the two substrates are rubbed in the same direction, and a high voltage is first applied to form a bend array.

In the liquid crystal display having such a bent arrangement, an electric field is formed between the common electrode formed on the front surface of the upper plate and the pixel electrode formed for each pixel region of the lower plate, and a fringe field is formed in the curved region between the pixel electrodes. . In this case, the fringe field is in a direction opposite to the bending of the liquid crystal molecules at the portion where the alignment of the pixel region begins, affecting the bending arrangement of the liquid crystal molecules, and is similar to the bending of the liquid crystal molecules at the end of the alignment of the pixel region. It does not significantly affect the bending arrangement of the liquid crystal molecules. Therefore, the bent alignment of the liquid crystal molecules is broken at the portion where the alignment of the pixel region starts due to the influence of the fringe field, resulting in a poor screen (see FIGS. 2B and 3A).

The technical problem to be achieved by the present invention is to minimize the area where the bending arrangement of the liquid crystal is broken to improve the poor image quality.

In order to achieve this problem, in the present invention, the horizontal length of the pixel region is equal to or larger than the vertical length, and the alignment film on the substrate is rubbed in a direction parallel to the gate line.

According to the present invention, a gate line is formed in a first direction, a data line is formed insulated from and crosses the gate line, and is formed in a second direction, and a plurality of gate lines and data lines are defined to intersect. A plurality of first electrodes are formed in the pixel region of. On the second substrate facing the first substrate, a second electrode is formed on the entire surface. A liquid crystal molecule that is horizontally aligned between the first substrate and the second substrate, and the liquid crystal molecules are symmetrically aligned with respect to the center plane of the first and second substrates when a voltage is applied between the first and second electrodes. The liquid crystal layer forming the bending arrangement in the direction is injected. At this time, it is preferable that the orientation of a liquid crystal layer is a 1st direction, and the ratio of the length of a 2nd direction with respect to the length of a 1st direction of a 1st electrode is 1 or more.

The thin film transistor may be connected to the gate line, the data line, and the first electrode, and an alignment layer may be further formed on the first and second substrates.

First and second polarizing plates having transmission axes or absorption axes perpendicular to each other are attached to the outer side of the first substrate and the second substrate, respectively, between the first substrate and the first polarizing plate, and between the second substrate and the second polarizing plate. First and second WV plates are attached therebetween. At this time, it is preferable that the alignment axis of the first WV plate is 0 ° with the rubbing direction of the first substrate, and the alignment axis of the second WV substrate is 0 ° with the rubbing direction of the second substrate.

The first and second WV plates are attached to the first and second supports, and the stretching axes of the first and second supports preferably coincide with the transmission axes of the first and second polarizing plates, respectively.

First and second compensation plates are attached between the first polarizing plate and the first WV plate and between the second polarizing plate and the second WV plate, respectively, wherein the stretching axes of the first and second compensation plates are the first and second polarizing plates. It is preferable to be parallel to the transmission axis or absorption axis of.

In the present invention, the horizontal length of the pixel area is equal to or larger than the vertical length, and the alignment layer is rubbed in a direction parallel to the gate line, thereby reducing the area where the alignment of the liquid crystal molecules is broken and the viewing angle is maximized. In addition, the viewing angle is maximized by the stretching axis of the compensating plate supporter coinciding with the transmission axis of the adjacent polarizing plate, and the excellent black state is obtained by the stretching axis of the WV plate supporter coinciding with the transmission axis or absorption axis of the adjacent polarizing plate. Can be.

Next, a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the same.

FIG. 1 is a schematic view of a thin film transistor substrate of a liquid crystal display according to a first exemplary embodiment of the present invention, and FIG. 2A is a cross-sectional view showing a color filter substrate facing a Q portion in FIG. 1 to apply an electric field. FIG. 2B is a view showing the arrangement state of the liquid crystal molecules before, and FIG. 2B is a view showing the arrangement state of the liquid crystal molecules after applying an electric field in FIG. 2A. At this time, the arrow direction in Figures 2a and 2b indicates the rubbing direction.

As shown in FIGS. 1 and 2A, the liquid crystal display includes a lower substrate 11 and an upper substrate 12 facing each other, the lower substrate 11 is called a thin film transistor substrate, and the upper substrate 12 is a color filter. It is called a substrate.

First, wirings for transmitting a signal applied from the outside are formed in the horizontal and vertical directions in the thin film transistor substrate 11. The wiring in the horizontal direction is the gate line 1 and the wiring in the vertical direction is the data line 2. . In addition, a thin film transistor 31 connected to the wirings 1 and 2 to control a signal applied from the outside is formed, and a plurality of pixel regions P1 formed by crossing the wirings 1 and 2 are formed in the thin film transistor ( A pixel electrode 21 electrically connected to 31 receives a signal. Here, the pixel region P1 has a ratio of the horizontal length to the vertical length of 1: 1 or more, and the horizontal length is equal to or longer than the vertical length, and the pixel regions P1 are formed by gathering three pixel regions P1 as shown in FIG. 1. The area is displayed in one color on the screen.

A color filter (not shown) and a black matrix (not shown) are formed on the color filter substrate 12, and a common electrode 22 covering them is formed on the entire surface of the substrate 12.

A horizontal alignment film (not shown) is formed on the pixel electrode 21 and the common electrode 22, respectively, and the alignment film is rubbed in a direction parallel to the gate line 1 as shown by the arrow direction. This will be described in detail later with reference to FIGS. 5 to 6B.

A nematic liquid crystal material layer 41 having positive dielectric anisotropy is inserted between the thin film transistor substrate 11 and the color filter substrate 12 having such a structure. In the state in which no voltage is applied, the liquid crystal molecules 42 are horizontally aligned with respect to the substrates 11 and 12 with a pretilt angle having one end lined up toward the rubbing direction as shown in FIG. 2A, Therefore, the arrangement of the liquid crystal molecules 42 is symmetrical with respect to the plane parallel to the substrates 11 and 12 about the center between the two substrates 11 and 12.

When a voltage is applied to the two electrodes 21 and 22 in the liquid crystal display, the liquid crystal molecules exhibit an arrangement having a bent structure as shown in FIG. 2B. That is, when a voltage of sufficient magnitude is applied to the two electrodes 21 and 22, an electric field (c line) perpendicular to the substrates 11 and 12 is formed, and since the liquid crystal molecules 42 have positive dielectric anisotropy, Attempts are arranged parallel to the electric field, ie perpendicular to the two substrates 11, 12. At this time, in the portion adjacent to the alignment layer, since the alignment force by the alignment layer is stronger than the force due to the applied electric field, the long axis tries to maintain the state parallel to the substrates 11 and 12 even when a voltage is applied. The liquid crystal molecules 42 between the two alignment layers form a bent structure. However, the electric field is not formed perpendicular to the two substrates 11 and 12 between the pixel electrodes 21, but the electric field is formed in a bent shape like the a and b lines. In this case, the bending of the electric field a has a similar direction to the bending of the liquid crystal molecules, and thus the bending of the electric field a does not have a significant effect on the bending arrangement of the liquid crystal molecules. As a result, the alignment of the liquid crystal molecules is broken. This portion becomes left hatched portions c1, c2, c3 of the pixel region P1 as shown in FIG. 3B.

Next, the portions c1, c2, and c3 where the alignment of the liquid crystal molecules are broken will be described with reference to FIGS. 3A and 3B as compared with the conventional pixel region P2. When the alignment layer is rubbed from left to right as in the direction of the arrow, the portion where the alignment of the liquid crystal molecules is broken becomes the left hatched portions c1, c2, c3, c4, c5 and c6 of the pixel regions P1 and P2. At this time, since the vertical length of the conventional pixel area P2 is longer than the horizontal length, the proportion of the portions c4, c5, and c6 where the alignment is broken with respect to the pixel area P2 is large. On the other hand, as in the present invention, when the horizontal length of the pixel area P1 is longer than the vertical length, the portions c1, c2, and c3 whose orientation is broken may be reduced than in the conventional case, thereby improving image quality.

As described above, in the liquid crystal display device including the pixel area P1 having the same or larger horizontal length than the vertical length, the resolution may be increased by adjusting the number of wirings 1 and 2. For example, a conventional liquid crystal display having a resolution of SXGA level is composed of 1024 gate lines 1 and 3840 data lines 2, which reduces the vertical length of the pixel region P1 by 30%. If the number of gate lines 1 is increased and the width is increased by 100% to reduce the number of data lines 2 slightly, resolution 1.5 times higher than in the related art can be obtained.

Meanwhile, the structure of the pixel region P1 may also be applied to a three-color driving scheme that implements color by applying three image signals of red, green, and blue to one pixel electrode. The three-color driving method requires a faster response speed than a liquid crystal display device that displays one color in three pixel areas, thereby minimizing a portion where the alignment of the liquid crystal is broken. The liquid crystal display of the three-color driving method will be described as a second embodiment of the present invention with reference to FIGS. 3C and 4. In FIG. 3C, the arrow direction indicates the rubbing direction.

Here, it is preferable to make the shape of the pixel area P3 square. In this way, the portion where the alignment of the liquid crystal molecules is broken in the display of one color is conventionally hatched (c4, c5, c6) and in the present invention can be reduced to the hatched portion (c7) to reduce the pixel defects It can also increase resolution.

Next, a rubbing direction for improving image quality in such a liquid crystal display will be described with reference to FIGS. 5 to 6B. Here, in general, the elements for determining the image quality should include not only the viewing angle but also the angle at which gray level reversal occurs, so that both of them will be described. FIG. 5 is a graph showing a contrast ratio with respect to a viewing angle on a screen of a liquid crystal display, FIG. 6A is a graph showing a change in luminance with respect to a viewing angle change in a rubbing direction, and FIG. 6B is a direction perpendicular to the rubbing direction. Is a graph showing a change in luminance with respect to a change in viewing angle.

In FIG. 5, the color is displayed differently according to the contrast ratio in the circle 100, and the contrast ratio value decreases from the center of the circle 100 to the edge. Circles 10, 20, 30, 40, 50, 60, 70, and 80 in dotted lines within the circle 100 are respectively 10 °, 20 °, 30 °, 40 °, 50 °, 60 °, 70 °, 80 °, and the viewing angle refers to the case where the contrast ratio value is 10 or more. The number outside the circle 100 represents the angle, and the 135 ° to 315 ° direction (arrow direction) represents the rubbing direction. 6A and 6B, the transverse direction and the longitudinal direction respectively show the viewing angle and the luminance, and each graph shows the gray scale change. Here, each graph is measured by dividing the 64 gray scales by 8 ° intervals.

As shown in FIG. 5, in the rubbing direction, the contrast ratio value is the largest at the center (near 0 °) and the contrast ratio value decreases toward the outside from the center, and becomes smaller than 10 at 60 °. On the other hand, in the direction perpendicular to the rubbing direction, that is, 45 ° to 225 ° in the direction similar to the rubbing direction, the contrast ratio value of 10 or less is about 80 ° or more than in the rubbing direction. Therefore, it can be seen that the viewing angle in the rubbing direction is narrower than in the direction perpendicular to the rubbing direction.

On the other hand, as shown in the graph according to the change in the gray, as shown in Figures 6a and 6b, the grayscale inversion in the rubbing direction does not occur, but the grayscale inversion occurs near 50 ° in the direction perpendicular to the rubbing direction. Accordingly, it can be seen that the viewing angle becomes narrower in the direction perpendicular to the rubbing direction from the viewpoint of gray level inversion.

As described above, the viewing angle is narrow in the rubbing direction from the contrast ratio viewpoint, and the viewing angle in the direction perpendicular to the rubbing direction is narrow from the gray level inversion viewpoint. However, narrowing the viewing angle in view of the contrast ratio has room for improvement through the process, and it is preferable that the narrower viewing angle is disposed above and below the substrate, so that the rubbing direction is in a direction parallel to the gate line 1. .

In such a liquid crystal display, in addition to the thin film transistor substrate and the color filter substrate, a polarizer, a compensation plate, and a wide viewing (WV) plate are attached. Their structures for widening the viewing angle and improving image quality will be described with reference to FIG. 7. FIG. 7 is a view illustrating a polarizer, a compensation plate, and a WV plate attached to the outside of the thin film transistor substrate and the color filter substrate in the liquid crystal display according to the first and second embodiments of the present invention.

As shown in FIG. 7, in the thin film transistor substrate 11 and the color filter substrate 12, the alignment layer is rubbed from left to right as shown by the arrow directions 53 and 54, and a liquid crystal layer (B) between the substrates 11 and 12. 41), and the liquid crystal molecules 42 in the liquid crystal layer 41 have a bent arrangement structure. On the outside of the substrates 11 and 12, there are WV plates 61 and 62, respectively, and the WV plates 61 and 62 each have an orientation axis 63 on a support (not shown) made of triacetyl cellulose (TAC). 64, the liquid crystal layers 65 and 66 are aligned. Here, the alignment axes 63 and 64 represent the average optical axis directions, and the alignment axes 63 and 64 of the WV plates 61 and 62 are 0 ° with the orientation directions 53 and 54 of the adjacent substrates 11 and 12. To achieve. Accordingly, the liquid crystal layer 65 is twisted in the opposite direction to the liquid crystal molecules 43 adjacent to the thin film transistor substrate 11, and the liquid crystal layer 66 is adjacent to the color filter substrate 12. ) Is reversed in the opposite direction so that the luminance can be increased by compensating with each other. Compensation plates 71 and 72 are attached to the outer side of each of the WV plates 61 and 62, and the compensation plates 71 and 72 are made of a support (not shown) made of TAC. Outside the compensation plates 71 and 72, there are polarizing plates 81 and 82 in which the transmission axes 83 and 84 (or absorption axes) are perpendicular to each other.

At this time, in order to maximize the viewing angle, it is preferable that the slow axes 73 and 74 of the support plates 71 and 72 coincide with the transmission axes 83 and 84 of the polarizing plates 81 and 82, respectively. Do.

In addition, the alignment axes 63 and 64 of the WV plates 61 and 62 form an angle of 45 ° with the transmission axes 83. 84 of the polarizing plates 81 and 82, but the WV plates 61 and 62 are supported. When the stretching axis (not shown) coincides with the alignment axes 63 and 64, the light is emitted in the black state at 45 ° with the transmission axes 83 and 84 (or absorption axis) of the polarizing plates 81 and 82. In order to prevent such light leakage, an excellent black state is obtained by matching the stretching axes of the WV plates 61 and 62 support with the transmission axes 83 and 84 (or absorption axes) of the polarizing plates 81 and 82.

As described above, in the present invention, the alignment layer is rubbed in parallel with the gate line to maximize the viewing angle, and the horizontal length of the pixel region is equal to or greater than the vertical length, thereby minimizing the region where the alignment of the liquid crystal molecules is broken, thereby improving image quality. You can. In addition, the viewing axis of the compensating plate support body coincides with the transmission axis of the adjacent polarizing plate to maximize the viewing angle, and the stretching axis of the WV plate supporting body coincides with the transmission axis or the absorption axis of the adjoining polarizing plate. You can get it.

Claims (7)

A plurality of first electrodes formed in a plurality of pixel regions defined by crossing gate lines formed in a first direction and insulated from and intersecting the gate lines and formed in a second direction; A first substrate comprising a, A second substrate facing the first substrate and having a second electrode formed on a front surface thereof; And liquid crystal molecules injected and horizontally aligned between the first substrate and the second substrate, wherein the liquid crystal molecules are the centers of the first and second substrates when a voltage is applied between the first and second electrodes. The liquid crystal layer symmetrical with respect to the surface and arranged in a bend in the alignment direction Including; An orientation of the liquid crystal layer is a first direction, and the ratio of the length in the second direction to the length in the first direction of the first electrode is 1 or more. In claim 1, And a thin film transistor connected to the gate line, the data line, and the first electrode. In claim 1, And an alignment layer formed on each of the first and second substrates. In claim 1, And first and second polarizing plates attached to the outer side of the first substrate and the second substrate, respectively, and having a transmission axis or an absorption axis perpendicular to each other. In claim 4, Further comprising first and second WV plates attached between the first substrate and the first polarizing plate and between the second substrate and the second polarizing plate, respectively. The alignment axis of the first WV plate is 0 ° to the rubbing direction of the first substrate, and the alignment axis of the second WV substrate is 0 ° to the rubbing direction of the second substrate. In claim 5, Further comprising first and second supports attached to the first and second WV plates, The stretching axes of the first and second supports are respectively aligned with the transmission axis or absorption axis of the first and second polarizing plates. In claim 5, Further comprising first and second compensation plates attached between the first polarizing plate and the first WV plate and between the second polarizing plate and the second WV plate, respectively. The stretching axis of the first and second compensation plates coincide with the transmission axes of the first and second polarizing plates.

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