KR100686230B1 - liquid crystal display - Google Patents

Abstract

A liquid crystal layer having positive dielectric anisotropy is injected between the thin film transistor substrate on which the thin film transistor and the pixel electrode are formed and the color filter substrate on which the common electrode is formed. A horizontal alignment layer is formed on each substrate so that the liquid crystal molecules are horizontally aligned before applying voltage to the two electrodes, and when the voltage is applied, the liquid crystal molecules are aligned perpendicularly to the substrate and have a bent structure. In this case, openings are provided between the pixel electrodes and the common electrode, respectively. In this case, the fringe field formed between the pixel electrode and the common electrode is formed to be weaker than the intensity of the fringe field when the common electrode is formed on the entire surface, thereby stabilizing the bending arrangement of the liquid crystal molecules.

Dielectric constant anisotropy, horizontal alignment layer, bent array, fringe field

Description

Liquid crystal display

1 is a diagram illustrating an arrangement state of liquid crystal molecules before applying a voltage in a liquid crystal display according to an exemplary embodiment of the present invention.

2 is a diagram illustrating an arrangement state of liquid crystal molecules after voltage is applied in the liquid crystal display according to the first exemplary embodiment of the present invention.

3 is a diagram illustrating an arrangement state of liquid crystal molecules after voltage is applied in the liquid crystal display according to the second exemplary embodiment of the present invention.

The present invention relates to a liquid crystal display device and a liquid crystal display device having a structure for stabilizing the arrangement of liquid crystals.

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 response speed and viewing angle among the liquid crystal display devices, and examples thereof include an OCB (optically compensated bend) type liquid crystal display device.

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 processed in the same direction, and a high voltage is first applied to form a bend array.

However, among the two substrates, a common electrode is formed on the front surface of the upper substrate, and pixel electrodes separated by pixel regions are formed on the lower substrate, so that a fringe field is formed at the edge of the pixel region. Due to the fringe field, the bending arrangement of the liquid crystal molecules is changed at the edges of the pixel area, thereby causing a problem of poor image quality.

An object of the present invention is to provide a liquid crystal display device which improves image quality by stabilizing the bending arrangement of liquid crystal molecules.

According to the present invention, a plurality of pixel electrodes are formed in each pixel region on the first insulating substrate, and a common electrode corresponding to the pixel electrode is formed on the second insulating substrate facing the first substrate. The liquid crystal molecules are horizontally aligned between the first substrate and the second substrate, and the liquid crystal molecules are symmetric with respect to the center plane of the first and second substrates when a voltage is applied between the pixel electrode and the common electrode, and is aligned in the alignment direction. The liquid crystal layer forming the bending arrangement is injected. In this case, the pixel electrode may be separately formed for each pixel area so that a first opening exists between the pixel electrodes, the common electrode has a second opening, and the first opening and the second opening are positioned to be offset from each other.

Here, first and second alignment films for horizontally aligning the liquid crystal layer may be formed on the first substrate and the second substrate, respectively, and the liquid crystal layer preferably has positive dielectric anisotropy. In addition, a color filter may be formed between the second substrate and the common electrode.

Meanwhile, a thin film transistor electrically connected to the pixel electrode may be formed on the first substrate.

According to another embodiment of the present invention, a plurality of pixel electrodes are formed in each pixel region on the first insulating substrate, and are formed on the front surface corresponding to the pixel electrodes on the second insulating substrate facing the first substrate and are recessed. The common electrode including a part is formed. The liquid crystal molecules are horizontally aligned between the first substrate and the second substrate, and the liquid crystal molecules are symmetric with respect to the center plane of the first and second substrates when a voltage is applied between the pixel electrode and the common electrode, and is aligned in the alignment direction. The liquid crystal layer forming the bending arrangement is injected. Here, it is preferable that the opening portion, which is the boundary region of the pixel electrode, and the recessed portion of the common electrode are shifted from each other.

In this case, a color filter may be further formed between the second substrate and the common electrode, and the depression is formed by the color filter.

On the other hand, first and second alignment films for horizontally aligning the liquid crystal layer may be further formed on the first substrate and the second substrate, respectively, and the liquid crystal layer preferably has positive dielectric anisotropy.

In addition, a black matrix may be further formed between the second substrate and the common electrode.

In the present invention, since the bending arrangement of the liquid crystal is stabilized, screen defects can be reduced.

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.

A liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3.

1 is a diagram illustrating an arrangement state of liquid crystal molecules before applying a voltage in a liquid crystal display according to an exemplary embodiment of the present invention, and FIGS. 2 and 3 are liquid crystal displays according to first and second embodiments of the present invention. It is a figure which shows the arrangement state of the liquid crystal molecules after applying a voltage in an apparatus.

First, as shown in FIG. 1, the liquid crystal display according to the present invention includes a lower substrate 11 and an upper substrate 12 facing each other. Here, the lower substrate 11 is called a thin film transistor substrate, and the upper substrate 12 is called a color filter substrate.

The thin film transistor substrate 11 is formed with a thin film transistor 31 for controlling a signal applied from the outside. The thin film transistor 31 includes a gate electrode which is a part of a gate line (not shown) to which a scan signal is applied from the outside, a semiconductor layer (not shown) formed on the gate electrode to form a channel, and an image signal is applied from the outside A source electrode which is part of a receiving data line (not shown) and a drain electrode (not shown) which are separated from the source electrode are formed. In addition, the thin film transistor substrate 11 is electrically connected to the thin film transistor 31 and includes a pixel electrode 21 made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO) or an opaque conductive material. It is formed for each pixel area. In this case, since the pixel electrode 21 is separately formed for each pixel region, an opening 25 exists between each pixel electrode 21.

The color filter substrate 12 is provided with a color filter (not shown) and a black matrix (not shown). A common electrode 22 is formed on the color filter and the black matrix and covers them and has an opening 26.

Horizontal alignment layers (not shown) are formed on the pixel electrode 21 and the common electrode 22, respectively. The alignment film is rubbed from left to right. The arrow direction in the figure indicates the rubbing direction.

When the thin film transistor substrate 11 and the color filter substrate 12 are aligned and arranged, the positions of the openings 25 and 26 are shifted from each other. In detail, when the line A is drawn perpendicularly to the substrates 11 and 12 at the left end of the opening 25 between the pixel electrodes 21, the common electrode 22 moves from the line A to the right. When the line B is drawn perpendicular to the substrates 11 and 12 at the right end of the opening 25, the common electrode 22 enters to the right side from the line B. Therefore, as shown in the drawing, the opening 26 of the common electrode 22 is moved to the right with respect to the opening 25 between the pixel electrodes 21.

A nematic liquid crystal material layer 40 having positive dielectric anisotropy is inserted between the thin film transistor substrate and the color filter substrates 11 and 12 having such a structure. In the state in which no voltage is applied, the liquid crystal molecules 41 are horizontally oriented with respect to the substrates 11 and 12 with a pretilt angle in which one end thereof faces in the rubbing direction, and thus the liquid crystal molecules 41 The array of symmetry is symmetric with respect to the plane parallel to the substrates 11 and 12 about the center between the two substrates 11 and 12.

Next, the arrangement of the liquid crystal molecules when the electric field is applied in the liquid crystal display will be described with reference to FIG. 2.

In a liquid crystal display having a liquid crystal molecule array horizontal to the substrates 11 and 12 when no electric field is applied as shown in FIG. 1, when a voltage having a sufficient magnitude is applied to the two electrodes 21 and 22, the substrates 11 and 12 are applied. An electric field (line c) perpendicular to) is formed. Then, since the liquid crystal molecules 41 have positive dielectric anisotropy, they are arranged such that their major axes are parallel to the electric field, that is, perpendicular to the two substrates 11 and 12. At this time, in the portion adjacent to the alignment layer, the alignment force by the alignment layer is stronger than the force due to the applied electric field, so the long axis tries to maintain the state parallel to the substrates 11 and 12 even when a voltage is applied. As a result, the liquid crystal molecules 41 between the two alignment layers form a bent structure. That is, the inclination angle of the liquid crystal molecules 41 increases toward the central portion between the substrates 11 and 12 as compared to the inclination angles of the liquid crystal molecules 41 adjacent to the substrates 11 and 12, thereby connecting the long axes of the liquid crystal molecules 41. One shape represents a curved structure.

Meanwhile, as described above, since the openings 25 and 26 between the pixel electrodes 21 and the common electrode 22 are disposed to be offset from each other, the fringe field at the end of the pixel electrode 21 or the common electrode 22 is It bends like the a and b lines so that the bending of the liquid crystal molecules in this part is different from the bending arrangement in the electric field c lines. In this case, since the fringe field a line shows a direction similar to the bend of the liquid crystal, the fringe field a line does not have a significant influence on the bend arrangement of the liquid crystal. Since the degree of bending is smaller, it hardly affects the bending arrangement of the liquid crystal.

Therefore, in the liquid crystal display having the structure of the electrode as described above, since the bending arrangement of the liquid crystal is stabilized, screen defects can be reduced.

On the other hand, the color filter 32 may be formed on the color filter substrate 12. This will be described with reference to FIG. 3 as a second embodiment of the present invention. The second embodiment of the present invention has a structure similar to that of the first embodiment, except that the common electrode 22 is formed on the entire surface of the substrate 12 and does not have an opening.                     

Since the structure of the thin film transistor substrate 11 of the present invention is the same as that of the first embodiment, only the color filter substrate 12 will be described. The color filter 32 is formed in the position corresponding to the pixel electrode 21 on the color filter substrate 12, and the common electrode 22 is formed in the whole surface on it. In such a structure, the heights of the common electrode 22 formed between the color filters 32 and the common electrode 22 formed on the color filter 32 are different, so that the common electrodes 22 between the color filters 32 are different. This recessed depression 26 is made. On the other hand, a black matrix (not shown) may be formed between the color filters 32. Since the black matrix is thinner than the color filter 32, depressions are made at this time.

At this time, the opening part 25 and the depression part 26 are shifted | deviated, and the depression part 26 is moved to the right from the position of the opening part 25 between the pixel electrodes 21. FIG. That is, when the line D is vertically drawn at the left end of the opening 25 between the pixel electrodes 21, the color filter 32 is shown to the right at the line D, and the right end of the opening 25 is shown. When the line E is drawn vertically at, the color filter 32 enters to the right on the line E.

In the liquid crystal display including the color filter substrate 12 and the thin film transistor substrate 11, the liquid crystal 40 is injected between the two substrates 11 and 12. When a voltage is applied to the two electrodes 21 and 22, an electric field (c line) is formed between the two electrodes 21 and 22, and between the end portion of the pixel electrode 21 and the side surface of the recess 26. Fringe fields such as the d and e lines are formed to show a bent structure in which the liquid crystal molecules are arranged perpendicular to the substrates 11 and 12. This can achieve the same effect of stabilizing the bending arrangement of the liquid crystal molecules between the pixel electrodes 21 as in the first embodiment, and can reduce the number of processes since the pixel electrode 21 is not patterned.

As described above, in the present invention, the electrodes between the two substrates may be offset to stabilize the bending arrangement of the liquid crystal molecules between the two electrodes, thereby improving image quality.

Claims (11)

First insulating substrate, A plurality of pixel electrodes formed in each pixel region on the first substrate, A second insulating substrate facing the first substrate, A common electrode formed on the second substrate and corresponding to the pixel electrode; And a liquid crystal molecule which is injected between the first substrate and the second substrate and is horizontally aligned, and the liquid crystal molecules are formed on the center planes of the first and second substrates when a voltage is applied between the pixel electrode and the common electrode. A liquid crystal layer symmetric with respect to the long axis of the liquid crystal molecules oriented in a direction parallel to the first and second substrates to form a bent arrangement, Wherein the pixel electrode is separately formed in each of the pixel regions, a first opening is present between the pixel electrodes, the common electrode has a second opening, and the first opening and the second opening are positioned to be offset from each other. In claim 1, And first and second alignment layers formed on the first substrate and the second substrate, respectively, for horizontally aligning the liquid crystal layer. In claim 1, The liquid crystal layer has a positive dielectric anisotropy. In claim 1, And a color filter formed between the second substrate and the common electrode. In claim 1, And a thin film transistor formed on the first substrate and electrically connected to the pixel electrode. First insulating substrate, A plurality of pixel electrodes formed in each pixel region on the first substrate, A second insulating substrate facing the first substrate, A common electrode formed on a front surface of the second substrate corresponding to the pixel electrode and including a depression; And a liquid crystal molecule which is injected between the first substrate and the second substrate and is horizontally aligned, and the liquid crystal molecules are formed on the center planes of the first and second substrates when a voltage is applied between the pixel electrode and the common electrode. A liquid crystal layer symmetric with respect to the long axis of the liquid crystal molecules oriented in a direction parallel to the first and second substrates to form a bent arrangement, And an opening that is a boundary region of the pixel electrode and the recessed portion of the common electrode are shifted from each other. In claim 6, And a color filter formed between the second substrate and the common electrode, wherein the depression is formed by the color filter. In claim 6, And first and second alignment layers formed on the first substrate and the second substrate, respectively, for horizontally aligning the liquid crystal layer. In claim 6, And a black matrix formed between the second substrate and the common electrode. In claim 6, The liquid crystal layer has a positive dielectric anisotropy. In claim 6, And a thin film transistor formed on the first substrate and electrically connected to the pixel electrode.

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