KR20040062117A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: An LCD(liquid crystal display) is provided to compensate a delay of light generated in all liquid crystal cells using a single compensation film. CONSTITUTION: An LCD includes the first and second substrates(111,112), a liquid crystal layer(130) interposed between the first and second substrates, and a compensation film(142) formed on at least one side of the first and second substrates. The compensation film has a multi-domain. The LCD further includes the first and second alignment films(121,122) that are respectively formed on the faces of the first and second substrates, which face each other. One of the alignment film is formed on the compensation film. The first substrate includes a thin film transistor array and a pixel electrode formed thereon. The pixel electrode is formed on the compensation film. The second substrate includes a color filter and a common electrode. The common electrode is formed on the compensation film.

Description

Liquid crystal display device {LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a liquid crystal display device, and more particularly, to a wide viewing angle liquid crystal display device using a compensation film to improve viewing angle characteristics.

Liquid crystal display devices are mainly used as flat panel display devices having high quality and low power. The liquid crystal display device is bonded so that the thin film transistor array substrate and the color filter substrate face each other at uniform intervals, and a liquid crystal layer is formed between the thin film transistor array substrate and the color filter substrate.

In the thin film transistor array substrate, pixels are arranged in a matrix form, and a thin film transistor, a pixel electrode, and a capacitor are formed in a unit pixel, and the color filter substrate is a common electrode and an actual color for applying an electric field to the liquid crystal layer together with the pixel electrode. An RGB color filter and a black matrix are implemented to implement the.

On the other hand, an alignment layer is formed on the opposite surface of the thin film transistor array substrate and the color filter substrate, and rubbing is performed so that the liquid crystal layer is arranged in a constant direction. In this case, the liquid crystal is rotated by dielectric anisotropy when an electric field is applied between the pixel electrode formed for each unit pixel of the thin film transistor array substrate and the common electrode formed on the front surface of the color filter substrate, thereby passing or blocking light per unit pixel. Characters or images are displayed. However, such a twisted nematic mode liquid crystal display device has a disadvantage in that the viewing angle is narrow. This is due to the refractive anisotropy of the liquid crystal molecules. In the TN mode, light transmittance is symmetrically distributed in the left and right viewing angles, but light transmittance is asymmetrically distributed in the vertical direction. In the viewing angle, an inverted range is generated so that the viewing angle is narrowed.

In order to solve the viewing angle problem, a film compensation mode for compensating the viewing angle with a compensation film, a multi-domain mode for compensating the viewing angle by dividing a pixel into multiple domains and changing the viewing angle of each domain, and two on the same substrate BACKGROUND ART Liquid crystal display devices such as a horizontal electric field mode in which electrodes are formed to form a horizontal electric field have been proposed.

1 illustrates a liquid crystal display device having an improved viewing angle using a conventional compensation film. As shown in the figure, the liquid crystal display device includes a lower substrate and an upper substrate 11 and 12 having the alignment layers 21 and 22 coated thereon, and a liquid crystal layer formed between the two substrates 11 and 12. 30 and polarizers 51 and 52 attached to the lower surfaces of the lower and upper substrates 110 and 120, respectively, and polarizing plates 51 and 52 attached to outer surfaces of the compensation films 41 and 42 to polarize light. It is composed of

When a voltage is applied to the common electrode and the pixel electrode (not shown) formed on the lower substrate and the upper substrates 11 and 12 of the liquid crystal display device configured as described above, as shown in FIG. Although 31 is standing vertically, even if a sufficient voltage is applied, the liquid crystal molecules 32a and 32b near the substrate are rubbed by the liquid crystal molecules due to the alignment control force of the alignment films 21 and 22 applied to the substrates 11 and 12. It is twisted in the direction and is inclined with respect to the substrates 11 and 12. Therefore, in this case, the optical axis is positive uniaxial optically anisotropic body in the normal direction of the substrate in the central portion 31 of the liquid crystal cell, but in the vicinity of the substrate 32a and 32b, the optical axis is inclined and twisted with respect to the substrate. The amount of uniaxial optical anisotropes inclined to the normal direction can be considered to be twisted. Therefore, in this case, using a compensation film made of negative uniaxial optically anisotropic body is not completely compensated. To compensate for these optically, negative uniaxial optically anisotropic bodies having optical axes in the same direction as the optical axes of the respective positive uniaxial optically anisotropic bodies should be used.

In the compensation films 41 and 42, disk-shaped molecules of a material, which is a negative uniaxial optical anisotropic body, are arranged such that the optical axis of the molecules has a progressively larger angle with respect to the normal of the liquid crystal display device substrate. The azimuth angle of the optical axis is twisted in a direction opposite to the direction of twisting the liquid crystal molecules in the cell about the normal of the substrate of the liquid crystal display device.

In order to compensate for retardation of light by liquid crystal molecules arranged differently in each region of the liquid crystal cell, the compensation films 41 and 42 are composed of two parts. That is, the second compensation layers 41b and 42b having a twisted splay arrangement are coated on the first compensation layers 41a and 42a made of a material that is a negative uniaxial optical anisotropy, and the first compensation layers 41a and 42a are coated. The liquid crystal layer 31 in the center of the liquid crystal cell is compensated for, and the liquid crystal layers 32a and 32b near the alignment layers 121 and 122 are compensated by the second compensation layers 41b and 42b having a twisted display arrangement. . In addition, the compensation films 41 and 42 are attached to both sides of the two substrates 11 and 12 so that the upper compensation film 42 attached to the upper substrate 12 is part of the upper liquid crystal layer 32b from the center of the liquid crystal cell. The lower compensation film 41 attached to the lower substrate 11 compensates for the lower liquid crystal layer 32b from the center of the liquid crystal cell.

As described above, the viewing angle of the TN liquid crystal display device can be improved by using the compensation films 41 and 42. However, in the related art, there is a disadvantage in terms of material ratio because the upper and lower compensation films must be attached to the back and upper substrates, respectively.

Accordingly, the present invention is to solve the above problems, by attaching a compensation film having a multi-domain liquid crystal alignment direction in each unit pixel region formed on one side of the substrate, by using a single compensation film Accordingly, an object of the present invention is to provide a liquid crystal display device that can accurately compensate for the delay of light occurring in all parts of the liquid crystal cell.

Other objects and features of the present invention will be described in detail in the configuration and claims of the following invention.

1 is a cross-sectional view showing a wide viewing angle liquid crystal display device using a conventional compensation film.

2 is a cross-sectional view showing a liquid crystal display device according to a first embodiment of the present invention.

3 is a view showing the alignment direction of the alignment film of the present invention.

Figure 4 is a process flow chart showing a manufacturing method of a compensation film according to the present invention.

5 is a view comparing the viewing angle characteristics of the TN liquid crystal display device when the compensation film is not used and the compensation film is used.

6 is a cross-sectional view showing a liquid crystal display device according to a second embodiment of the present invention.

*** Explanation of symbols for main parts of drawing ***

121: first alignment film 122: second alignment film

130: liquid crystal layer 142,342: compensation film

151: first polarizing plate 152: second and plate

Liquid crystal display device of the present invention for achieving the above object and the first and second substrate; A liquid crystal layer formed between the first and second substrates; It is formed on at least one side of the first and second substrates, and comprises a compensation film having a multi-domain. In this case, first and second alignment layers are formed on opposite surfaces of the first and second substrates, and the alignment layer is formed on the compensation film.

The thin film transistor array and the pixel electrode are formed on the first substrate, and the pixel electrode is formed on the compensation film. A color filter and a common electrode are formed on the second substrate, and the common electrode is also formed on the compensation film.

The first and second polarizing plates are attached to the rear surfaces of the first and second substrates, and the compensation film forms two domains having the first and second alignment directions. In this case, the first alignment direction of the compensation film coincides with the polarization axis direction of the first polarizing plate, and the second alignment direction is formed to coincide with the polarization axis direction of the second polarizing plate.

In addition, the liquid crystal display device according to the present invention comprises a first substrate comprising a thin film transistor array; A second substrate including a color filter; A liquid crystal layer formed between the first and second substrates; First and second compensation films formed on opposite surfaces of the first and second substrates and having a multi-domain; A pixel electrode and a first alignment layer formed on the first compensation film formed on the first substrate; A common electrode and a second alignment layer formed on the second compensation film formed on the second substrate; It comprises a first and a second polarizing plate formed on the back surface of the first and second substrate. In this case, the first and second compensation films are made of two domains having first and second alignment directions, and the first and second alignment films have directions perpendicular to each other.

In addition, the alignment direction of the first compensation film has a direction perpendicular to the alignment direction of the second compensation film.

In addition, the liquid crystal display device according to the present invention comprises a first substrate comprising a thin film transistor array; A second substrate including a color filter; A liquid crystal layer formed between the first and second substrates; A compensation film formed on opposite surfaces of any one of the first and second substrates and forming two domains having first and second mutually perpendicular directions; And first and second polarizing plates attached to the rear surfaces of the first and second substrates, the polarization axes of which are perpendicular to each other, wherein the first and second alignment directions of the compensation film are polarization axes of the first and second polarizing plates. Matches

Hereinafter, a liquid crystal display device according to the present invention will be described in detail with reference to the accompanying drawings.

2 illustrates a liquid crystal display device according to a first embodiment of the present invention. As shown in the drawing, the liquid crystal display device according to the first embodiment of the present invention includes a lower substrate 111 and the lower substrate 11. ) And an upper substrate 112 including a compensation film 142 on the opposite surface thereof, a liquid crystal layer 130 formed between the lower substrate 111 and the upper substrate 112, the lower substrate and The first and second polarizing plates 151 and 152 are attached to the rear surfaces of the upper substrates 111 and 112 to polarize light.

Although not shown in detail in the drawing, the lower substrate 111 includes a thin film transistor for switching the light transmittance of the liquid crystal layer 130 and a pixel electrode for applying a voltage to the liquid crystal layer 130, and the upper substrate 112. ), A common filter for applying a voltage to the liquid crystal layer 130 together with a color filter for realizing a color and the pixel electrode is formed. In addition, first and second alignment layers 121 and 122 are formed on opposite surfaces of the lower substrate 111 and the upper substrate 112, that is, the pixel electrode and the common electrode, and the first and second alignment layers 121 and 122 may be formed. As shown in FIG. 3A, the inclination directions of the first alignment layer 121 and the second alignment layer 122 are perpendicular to each other by 45 ° with respect to the horizontal direction of the substrate. The polarization axis of the first polarizing plate 151 coincides with the alignment direction of the first alignment layer 121, and the polarization axis of the second polarization plate 152 coincides with the alignment direction of the second alignment layer 122.

On the other hand, the compensation film 142 is a polarization axis of the first region 242a and the second polarizing plate 152 in which the negative liquid crystal molecules in the area of the unit pixel has the same alignment direction as the polarization axis of the first polarizing plate 151. It is divided into a second region 242b having the same orientation direction as to form a two domain.

When voltage is applied to the common electrode and the pixel electrode (not shown) formed on the lower and upper substrates 111 and 112 of the liquid crystal display device configured as described above, as shown in FIG. 2, the liquid crystal molecules 131 and 131 at the center of the liquid crystal cell. ') Stands vertically, even if sufficient voltage is applied, the liquid crystal molecules 132a, 132b, 132a', and 132b 'near the alignment layers 121 and 122 are not formed due to the alignment control force of the alignment layers 121 and 122 applied to the substrates 111 and 112. Liquid crystal molecules are twisted toward the rubbing direction and are inclined with respect to the substrates 111 and 112. Therefore, in this case, the optical axis is positive uniaxial optically anisotropic body in the normal direction of the substrate in the central portions 131 and 131 'of the liquid crystal cell. It can be said that the positive uniaxial optical anisotropes inclined with respect to the normal direction are twisted. Therefore, in this case, using a compensation film made of negative uniaxial optically anisotropic body is not completely compensated. Therefore, as mentioned in the prior art, in order to optically compensate for these, negative uniaxial optically anisotropic bodies having optical axes in the same direction as those of the respective positive uniaxial optically anisotropic bodies should be used. Accordingly, in the compensation film 142, disk-shaped molecules of a material, which is a negative uniaxial optical anisotropic body, are arranged so that the optical axis of the molecules has an increasingly larger angle with respect to the normal of the liquid crystal display device substrate. The azimuth angle of the optical axis is twisted in a direction opposite to the direction of twisting the liquid crystal molecules in the liquid crystal cell about the normal of the substrate of the liquid crystal display device.

In order to compensate for retardation of light caused by liquid crystal molecules arranged differently in each region of the liquid crystal cell, the compensation film 142 may include first compensation layers 141a and 142a made of a material that is a negative uniaxial optically anisotropic body. And second compensation layers 141b and 142b having a splay arrangement are coated on the first compensation layers 141a and 142a. The liquid crystal layers 131 and 131 'at the center of the liquid crystal cell are compensated by the first compensation layers 141a and 142a, and the liquid crystal near the alignment layers 121 and 122 by the second compensation layers 141b and 142b having a splay arrangement. Layers 132a, 132b, 132a 'and 132b' are compensated for. In more detail, the first region 242a of the compensation film 142 compensates the upper liquid crystal layer 132b from the center of the liquid crystal cell corresponding to the first region 242a, and the second region ( 242b improves the viewing angle of the liquid crystal display by compensating the lower liquid crystal layer 132a 'from the center of the liquid crystal cell corresponding to the second region 242b.

Meanwhile, the compensation film 142 may be formed on the lower substrate 121 as well as the upper substrate 111, and may be formed on the rear surface of the substrate as well as inside the liquid crystal cell. However, since the viewing angle compensation region of the liquid crystal cell is distorted due to the refractive indices of the substrates 111 and 121, the viewing angle compensation effect of the compensation film may be deteriorated.

4 is a view illustrating a method of manufacturing a compensation film according to the present invention. First, as shown in FIG. 4A, a substrate 200 is prepared through a thin film transistor array process or a color filter process, and then shown in FIG. 4B. As described above, an alignment layer 210 having a uniform thickness is coated on the entire surface of the substrate 200 using the plurality of rolls 205. Subsequently, as shown in FIG. 4C, after the rubbing cloth 207 is brought into contact with the alignment layer 210, the rubbing cloth 207 is moved to form fine grooves in the alignment layer 210 according to the moving direction of the rubbing cloth 207. The above process is repeated by changing the moving direction of the rubbing cloth to form a multi-domain. Next, as shown in FIG. 4D, a retarder material 230 is coated on the rubbed alignment layer 210 ′. The retarder material is shaped like a reactive mesogen, which is similar to the nematic liquid crystal form and has a double bond at the end so that the reaction occurs easily. As described above, after coating the lidder material, as shown in FIG. 4E, the compensation film 240 is completed through UV curing.

When the compensation film 240 is completed through the above process, a transparent electrode such as a pixel electrode or a common electrode is formed thereon, and an alignment layer for arranging liquid crystal molecules in the liquid crystal cell is formed. In this case, an adhesion between the compensation film and the transparent electrode may be improved between the compensation film 240 and the transparent electrode, and an overcoat layer may be formed to planarize the compensation film.

As described above, according to the first embodiment of the present invention, a compensation film is formed on one side of the liquid crystal cell, which is divided into the first and second regions and has the same polarization axis as the upper and lower polarizing films, each having an orientation direction attached to the rear surface of the substrate. As a result, since the entire liquid crystal layer in the liquid crystal cell is compensated, the manufacturing cost of the TN liquid crystal display device for improving the viewing angle can be reduced.

5 compares the viewing angle characteristics of the TN liquid crystal display device, respectively, when the compensation film is not used and when the compensation film according to the present invention is used. Here, each of the lines is an isoluminance curve drawn along a point where the luminance is the same, which means that the luminance is lowered from the center to the outside. As shown in the figure, when the compensation film is not used, the difference in the brightness of the screen appears large according to the viewing angle, whereas when using the compensation film of the present invention, it is confirmed that the brightness of the screen is almost unchanged according to the viewing angle. can do.

However, in the first embodiment of the present invention as described above, the lower liquid crystal layer 132a and the upper liquid crystal layer 132b 'corresponding to the first region 242a and the second region 242b are not compensated. Therefore, there was a limit to improving the viewing angle characteristics.

6 illustrates a liquid crystal capable of compensating for both the lower liquid crystal layer 132a and the upper liquid crystal layer 132b 'corresponding to the first region 242a and the second region 242b, respectively. The display element is shown. Compared to the first embodiment (FIG. 2), the second embodiment of the present invention has all the same components except for the second compensation film 324 added to the lower substrate 121, and the same reference numerals refer to the same components. It will be used only to explain the difference from the previous drawing (Fig. 2). As shown in the figure, the second embodiment of the present invention is divided into first and second regions, and the compensation films 142 and 342 having the same polarization axis as the upper and lower polarization films attached to the rear surface of the substrate are respectively arranged in the liquid crystal cell. It is formed on both sides.

As mentioned in the first embodiment of the present invention, the first region 242a of the first compensation film 142 compensates the upper liquid crystal layer 132b of the liquid crystal cell corresponding to the first region, and the second The region 242b compensates for the lower liquid crystal layer 132a ′ of the liquid crystal cell corresponding to the second region. In addition, according to the same principle as that of the first compensation film 142, the second compensation film 342 has a liquid crystal cell corresponding to the first area 341a of the first area 442a of the second compensation film 342. The lower liquid crystal layer 132a is compensated for, and the second region 442b compensates for the upper liquid crystal layer 132b 'of the liquid crystal cell corresponding to the second region 442b.

According to the second embodiment of the present invention as described above, by forming the compensation film is divided into the first and second regions inside both sides of the liquid crystal cell, each orientation direction is the same as the polarization axis of the upper and lower polarizing film attached to the back of the substrate All liquid crystal layers in the liquid crystal cell can be compensated for to further improve the viewing angle characteristics.

The present invention provides a liquid crystal display device having improved viewing angle characteristics using a compensation film. In particular, the compensation film of the present invention is formed together in the thin film transistor process or the color filter process in the liquid crystal cell without separately attaching to the outside of the substrate, and in the liquid crystal cell as a single compensation film by forming a multi-domain with different orientation directions. The viewing angle characteristics of all liquid crystal layers can be compensated. In addition, a compensation film may be formed on opposite surfaces of the lower and upper substrates, respectively, to further improve the viewing angle.

As described above, the present invention provides a compensation film having a multi-domain in a liquid crystal cell during a thin film transistor array process or a color filter process, thereby improving the viewing angle of a TN liquid crystal display device and manufacturing a compensation film as compared with the prior art. The cost of preparation can be reduced.

Claims (16)

First and second substrates; A liquid crystal layer formed between the first and second substrates; And a compensation film formed on at least one surface of the first and second substrates and having a multi-domain. 2. A liquid crystal display device as claimed in claim 1, further comprising first and second alignment films formed on opposite surfaces of said first and second substrates. The liquid crystal display device according to claim 2, wherein the alignment layer is formed on a compensation film. The liquid crystal display of claim 1, wherein a thin film transistor array and a pixel electrode are formed on the first substrate. The liquid crystal display device according to claim 4, wherein the pixel electrode is formed on a compensation film. The liquid crystal display device of claim 1, wherein a color filter and a common electrode are formed on the second substrate. The liquid crystal display of claim 6, wherein the common electrode is formed on a compensation film. The liquid crystal display device of claim 1, further comprising first and second polarizing plates attached to rear surfaces of the first and second substrates. The liquid crystal display of claim 1, wherein the compensation film forms two domains having first and second alignment directions. The liquid crystal display device according to claim 8 or 9, wherein the first alignment direction of the compensation film coincides with a polarization axis direction of the first polarizing plate. 10. The liquid crystal display device according to claim 8 or 9, wherein the second alignment direction of the compensation film coincides with the polarization axis direction of the second polarizing plate. A first substrate comprising a thin film transistor array; A second substrate including a color filter; A liquid crystal layer formed between the first and second substrates; First and second compensation films formed on opposite surfaces of the first and second substrates and having a multi-domain; A pixel electrode and a first alignment layer formed on the first compensation film formed on the first substrate; A common electrode and a second alignment layer formed on the second compensation film formed on the second substrate; And a first polarizing plate formed on a rear surface of the first and second substrates. 13. The liquid crystal display device according to claim 12, wherein the first and second compensation films are made of two domains having first and second alignment directions, and the first and second alignment directions are perpendicular to each other. The liquid crystal display device of claim 12, wherein the alignment direction of the first compensation film is perpendicular to the alignment direction of the second compensation film. A first substrate comprising a thin film transistor array; A second substrate including a color filter; A liquid crystal layer formed between the first and second substrates; A compensation film formed on opposite surfaces of any one of the first and second substrates and forming two domains having first and second mutually perpendicular directions; And first and second polarizing plates attached to the rear surfaces of the first and second substrates and having polarization axes perpendicular to each other. The liquid crystal display of claim 15, wherein the first and second alignment directions of the compensation film coincide with the polarization axes of the first and second polarizing plates.