KR20050003267A - Vertical alignment liquid crystal display device for improving luminance - Google Patents

Abstract

PURPOSE: A vertical alignment LCD having improved luminance device is provided to control alignment of liquid crystal molecules positioned at the domain boundary by improving a structure of an electric field distortion unit such as a slit. CONSTITUTION: A vertical alignment LCD includes first and second substrates, a thin film transistor formed on the first substrate, a first transparent conductive film(118). The first transparent conductive film is formed on the first substrate, and has at least one slit(140) divided into a first opening and a second opening. A color filter is formed on the second substrate. A second transparent conductive film(128) is formed on the substrate in which the color filter is formed. A liquid crystal layer is formed between the first and second substrates. The liquid crystal layer is be formed of liquid crystal molecules(135) having negative dielectric anisotropy.

Description

Vertical alignment liquid crystal display with improved brightness {VERTICAL ALIGNMENT LIQUID CRYSTAL DISPLAY DEVICE FOR IMPROVING LUMINANCE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical alignment liquid crystal display, and more particularly, to a high brightness vertical alignment (VA) liquid crystal display (LCD) having improved field distortion means.

A liquid crystal display is an apparatus that expresses an image by using optical anisotropy of a liquid crystal. A flat panel display (FPD) that can replace a cathode ray tube (CRT) with advantages of thinness, small size, low power consumption, and high quality. ) As the main product.

The display operation mode of a general liquid crystal display device is a normally white mode using twisted nematic (TN) liquid crystals.

1 is an exploded perspective view schematically illustrating a typical twisted nematic liquid crystal display.

As shown in the figure, the twisted nematic liquid crystal display device is largely arranged between the array substrate 10 and the color filter substrate 20 and between the array substrate 10 and the color filter substrate 20. The liquid crystal layer 30 is formed.

Although not shown in the drawings, a pixel electrode and a common electrode, which are transparent conductive films for forming an electric field in the liquid crystal layer 30, are formed on the array substrate 10 and the color filter substrate 20. On the top, a horizontal alignment film is formed. The pair of horizontal alignment films are subjected to an alignment process by rubbing or the like in a direction orthogonal to each other.

In addition, polarization plates 15 and 25 are arranged on outer surfaces of the array substrate 10 and the color filter substrate 20 to adjust polarization axes parallel to the rubbing direction of each alignment layer.

The liquid crystal layer 30 is formed by injecting a nematic liquid crystal having positive dielectric anisotropy between the array substrate 10 and the color filter substrate 20 of the liquid crystal display device configured as described above. At this time, the liquid crystal molecules in contact with the pair of alignment layers are orthogonal to each other along the rubbing direction so that the liquid crystal molecules are sequentially rotated in the horizontal plane and are arranged at a 90 ° twist between the substrates 10 and 20. The nematic phase refers to a liquid crystal phase in which elongated molecules of the liquid crystal are irregular in position with each other but their major axes are all directed in a constant direction.

When light is incident on one substrate surface of the twisted nematic liquid crystal display device, the unpolarized incident light is linearly polarized while passing through the polarizing plate formed on the outer surface of the substrate, and the polarization direction is changed as the liquid crystal molecules are twisted while passing through the liquid crystal layer. It is rotated 90 ° and exits through the polarizer on the other substrate surface. That is, in the standard white mode, the bright state display is obtained when no voltage is applied.

On the other hand, when a voltage is applied to a pair of opposing electrodes, the torsion is eliminated because the nematic liquid crystal molecules having the positive dielectric anisotropy are oriented perpendicular to the substrate surface. In addition, the liquid crystal molecules do not exhibit birefringence (refractive anisotropy) with respect to linearly polarized light incident on the liquid crystal layer in the above state. Therefore, since the incident light does not change in the polarization direction, the light cannot pass through the other polarizing plate, thereby obtaining a dark display.

Since the twisted nematic liquid crystal display does not completely block the light in the off state, the contrast ratio is not good, and the contrast ratio changes with the angle, and the brightness of the halftone is reversed as the angle changes. There is a disadvantage that is difficult to obtain. In particular, there is a viewing angle problem such as that image quality is not symmetrical with respect to the front face.

In order to solve the narrow viewing angle problem of the conventional LCD, a film-compensation mode for compensating the viewing angle using a compensation film, dividing the pixel into multiple domains, and changing the field of view angle for each domain There is a technique such as a multi-domain mode for compensating a viewing angle and an in-plane switching mode for generating an electric field in a horizontal direction by placing two electrodes on the same substrate.

On the other hand, the vertical alignment mode uses a negative liquid crystal having a negative dielectric anisotropy and a vertical alignment layer, and has a higher contrast ratio than the twisted nematic method, and when the alignment direction of the liquid crystal molecules is divided into a plurality of directions, the viewing angle is effectively It will be possible to improve.

FIG. 2 is a cross-sectional view illustrating a general vertically aligned liquid crystal display device, in which an alignment state of liquid crystal molecules when a voltage is applied.

As shown in the figure, the vertical alignment liquid crystal display device is largely composed of an array substrate 10 and a color filter substrate 20 and a liquid crystal layer 30 formed between the array substrate 10 and the color filter substrate 20. It is.

On the array substrate 10 and the color filter substrate 20, a first transparent conductive film 18 and a second transparent conductive film 28 for forming an electric field in the liquid crystal layer 30 are formed. Vertical alignment films (not shown) are formed on the transparent conductive films 18 and 28.

At this time, the electric field distortion means 40 is formed on the common electrode 28 which is a 2nd transparent conductive film.

The electric field distortion means 40 serves to control the orientation of the liquid crystal molecules 35 by distorting the electric field formed between the pair of electrodes 18 and 28. That is, when the electric field distorted by the electric field distortion means 40 is used, the orientation of the director of the liquid crystal molecules 35 can be controlled.

Such a vertically aligned liquid crystal display device is superior in various aspects, such as contrast ratio and response speed, compared to the twisted nematic method. In addition, when the orientation direction of the liquid crystal molecules are divided into a plurality of directions and a compensation film is used, the viewing angle can be effectively improved.

Meanwhile, dielectric protrusions or slit structures formed on an array substrate or a color filter substrate to distort an electric field divide liquid crystal molecules into a plurality of domain regions, and unwanted images are displayed on the boundary surface of the divided domains. That is, since the liquid crystal molecules are oriented in the vertical direction with respect to the substrate at the interface of the domain, all light passing through them is blocked at the color filter substrate and is always displayed in black regardless of the display gray scale. As a result, there is a problem that the brightness of the liquid crystal display is reduced and the image quality is lowered.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a vertical alignment liquid crystal display device having increased luminance by improving the structure of the slit, which is an electric field distortion means, to control the alignment of liquid crystal molecules located at the domain boundary.

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

1 is an exploded perspective view schematically showing a typical twisted nematic liquid crystal display.

2 is a cross-sectional view showing a general vertical alignment liquid crystal display.

3 is a plan view illustrating a portion of a vertical alignment liquid crystal display according to an exemplary embodiment of the present invention.

4A and 4B are enlarged views of the slit portion according to the present invention.

** Explanation of symbols for main parts of drawings **

18,118: 1st transparent conductive film 28,128: 2nd transparent conductive film

35,135: liquid crystal molecules 40,140: field distortion means

140a, 240a: first opening 140b, 240b: second opening

In order to achieve the above object, the vertical alignment liquid crystal display of the present invention is a first substrate and a second substrate, a thin film transistor formed on the first substrate, formed on the first substrate and divided into a first opening and a second opening A first transparent conductive film including at least one slit, a color filter formed on the second substrate, a second transparent conductive film formed on the substrate on which the color filter is formed, and a liquid crystal layer formed between the first substrate and the second substrate It is configured to include.

In addition, the vertical alignment liquid crystal display of the present invention includes a first substrate, a second substrate, a thin film transistor formed on the first substrate, a first transparent conductive film formed on the substrate on which the thin film transistor is formed, and a color filter formed on the second substrate. And a second transparent conductive film formed on the second substrate and including at least one slit divided into a first opening and a second opening, and a liquid crystal layer formed between the first and second substrates.

The liquid crystal layer may be formed of liquid crystal molecules having negative dielectric anisotropy.

The first opening and the second opening may be configured to have different widths, and the first opening may be configured to have a smaller width than the second opening.

In addition, the second opening may be configured in the form of a polygon, or may be configured in the form of a circle.

In addition, the vertical alignment liquid crystal display device of the present invention is formed between the first substrate and the second substrate, the thin film transistor formed on the first substrate, the color filter formed on the second substrate, the liquid crystal formed between the first substrate and the second substrate A liquid crystal layer made of molecules, a first transparent conductive film formed on the first substrate to form a first directional electric field in the liquid crystal molecules, a second transparent conductive film formed on the second substrate, and formed on the transparent conductive film, And at least one first slit for forming a second directional electric field and at least one second slit for forming a third directional electric field in the liquid crystal molecules.

The first direction electric field may be formed in a direction perpendicular to the first substrate or the second substrate, and the second direction electric field may be formed in a direction perpendicular to the first substrate or the second substrate and perpendicular to the first slit. have.

In addition, the third direction electric field may be formed in a direction parallel to the first substrate or the second substrate and parallel to the first slit.

The second slit may be formed on both sides of the narrow width of the first slit.

Hereinafter, a preferred embodiment of a vertical alignment liquid crystal display of the present invention will be described with reference to the accompanying drawings.

3 is a plan view illustrating a part of a vertically aligned liquid crystal display according to an exemplary embodiment of the present invention, in which an alignment state of liquid crystal molecules is particularly shown when a voltage is applied.

As shown in the figure, a first transparent conductive film 118 and a second transparent conductive film 128 for forming an electric field in the liquid crystal layer are formed on the array substrate and the color filter substrate, respectively, and the pair of transparent conductive Vertical alignment films (not shown) are formed on the films 118 and 128. The alignment layer may be formed of a material such as polyimide, polyamide, or polysiloxane-cinnamate, cellulose-cinnamate, which are photoalignment layers.

Although not shown in the drawings, a polarizing plate is formed on the outer surface of the array substrate and the color filter substrate. In addition, a phase difference film may be attached to at least one of the array substrate and the color filter substrate. The retardation film is a negative uniaxial film having one axis and is used to compensate the viewing angle.

In this case, the common electrode 128, which is the second transparent conductive film, includes the slit 140 to distort the electric field.

The slit 140 serves to control the orientation of the liquid crystal molecules 35 as a means for distorting the electric field formed between the pair of electrodes 118 and 128. That is, when the electric field distorted by the slit 140 is used, the orientation of the director of the liquid crystal molecules 35 may be controlled.

In this embodiment, although the slit 140, which is an electric field distortion means, is formed only on the second transparent conductive film 128, it may be formed on the first transparent conductive film 118, and the first transparent conductive film 118 and the second transparent material may be formed. It may be formed on all of the conductive films 128.

In addition, a structure such as a protrusion or an auxiliary electrode may be formed at a predetermined portion on the first transparent conductive film 118 or the second transparent conductive film 128 together with the slit 140.

In this case, the slit 140 is used for orientation control by dividing the liquid crystal molecules 135 in the pixel region into domains having a plurality of alignment orientations.

Such an orientation division divides one pixel into two or more regions, in one region the liquid crystal rises or falls in a certain direction, and in the other region the liquid crystal rises in the opposite direction. Allow polling. That is, by forming regions having different viewing angle characteristics within one pixel, the viewing angle characteristics can be averaged to ensure a wide viewing angle when viewed as a whole.

In the vertically aligned liquid crystal display, the long axis of the liquid crystal molecules 135 having negative dielectric anisotropy is oriented in the vertical direction with respect to the surface of the vertical alignment layer. Accordingly, the liquid crystal molecules 135 on the substrate surface are oriented perpendicular to the substrate surface, and the liquid crystal molecules 135 near the slit 140 are oriented inclined with respect to the substrate surface.

At this time, when light is incident on one of the substrate surfaces without applying a voltage, the light passes along one polarizing plate and moves along the long axis direction of the linearly polarized and vertically aligned liquid crystal molecules. Since birefringence does not occur in the long axis direction of the liquid crystal molecules, incident light proceeds without changing the polarization direction and is absorbed by the other polarizing plate having a polarizing axis orthogonal to one polarizing plate. Therefore, when no voltage is applied, the display of the dark state is obtained (standard black mode).

Subsequently, when a voltage is applied to a pair of opposing transparent conductive films, the orientation orientation of the liquid crystal molecules is controlled by the orientation orientation of the liquid crystal molecules inclined in advance by the slit while the long axis of the liquid crystal molecules is parallel to the substrate surface. The molecule is tilted and oriented. That is, since the negative liquid crystal molecules used in the vertically aligned liquid crystal display have a property of tilting in the vertical direction with respect to the electric field, when the voltage above the threshold is applied, the long axis of the liquid crystal molecules is inclined in the horizontal direction. The electric field is distorted by the in slit so that the liquid crystal molecules are inclined and aligned in different directions with respect to the slit.

The liquid crystal molecules exhibit birefringence with respect to the linearly polarized light incident on the liquid crystal layer in the above state, and the polarization state of the incident light is changed according to the inclination of the liquid crystal molecules. Since the liquid crystal has anisotropy in the refractive index, linearly polarized light incident on the liquid crystal layer is elliptically polarized by birefringence and is transmitted through the second polarizing plate. The intensity of the transmitted light depends on the voltage applied to the liquid crystal layer. In addition, when the inclination of the liquid crystal molecules is controlled by changing the applied voltage, the transmittance of light transmitted through another polarizing plate is adjusted to enable gray scale display.

In this case, the slit 140 includes a region 140b which is partially wide. As a result, the liquid crystal molecules 135 at the domain interface are not oriented in the direction perpendicular to the substrate. That is, the electric field formed between the array substrate and the color filter substrate is distorted by the slit 140, and in particular, the domain is located in the slit 140 by the wide area 140b of the slit 140. The liquid crystal molecules 135 positioned at the interface are inclined and oriented in the slit direction.

The wide region 140b generates an electric field in the slit direction of the E2 direction at the domain boundary surface so as to control the orientation orientation of the liquid crystal molecules 135 positioned at the domain boundary surface.

That is, when a voltage is applied to the pair of transparent conductive films 118 and 128, the liquid crystal molecules 135 positioned at the domain boundary surface by the electric field in the E2 direction may cover the wide area 140b of the slit 140. Will be inclined toward In addition, the liquid crystal molecules 135 around the wide area 140b of the slit 140 are inclined and aligned with respect to the area 140b. Therefore, light is also transmitted through the domain boundary, so that the overall luminance can be increased and a desired image can be displayed.

Detailed description of the improved slit structure providing the above effect is as follows.

4A and 4B are enlarged views of the slit portion according to the present invention.

First, as shown in FIG. 4A, the slits 140 formed in the transparent conductive film may be divided into a first opening 140a and a second opening 140b having different widths.

That is, the first opening 140a is formed to have a constant width and the second opening 140b is formed to have a wider width than the first opening 140a, instead of having the same width as the conventional slit. Can be.

By the fringe electric field generated around the second opening 140b, the alignment direction of the liquid crystal molecules 135 positioned on the domain boundary surface may be controlled.

Although the illustrated second opening 140b has a rhombus shape, the second opening 140b may be formed in any other shape as long as it generates an electric field in the E2 direction. An example thereof is illustrated in FIG. 4B.

As shown in the figure, the slit 240 as the field distortion means is composed of a first opening 140a and a second opening 140b having different widths.

The first opening portion 240a of the slit 240 has the same shape as that of the first opening portion of the slit shown in FIG. 4A, but the second opening portion 240b has a circular shape.

The shapes of the second openings 140a and 140b of the slits 140 and 240 illustrated in FIGS. 4A and 4B may be variously modified, and may be formed to be narrower than the first openings 140a and 240a. In this case, the slits 140a and 140b including the second openings 140a and 140b may be formed in another shape such that the electric field component in the E2 direction is not zero.

Many details are set forth in the foregoing description but should be construed as illustrative of preferred embodiments rather than to limit the scope of the invention. Therefore, the invention should not be defined by the described embodiments, but should be defined by the claims and their equivalents.

As described above, the vertically aligned liquid crystal display according to the present invention improves the shape of the slit, which is an electric field distortion means, thereby controlling the orientation of the liquid crystal molecules at the domain boundary, thereby increasing the luminance of the liquid crystal display panel.

Claims (15)

A first substrate and a second substrate; A thin film transistor formed on the first substrate; A first transparent conductive film formed on the first substrate and including at least one slit divided into a first opening and a second opening; A color filter formed on the second substrate; A second transparent conductive film formed on the substrate on which the color filter is formed; And And a liquid crystal layer formed between the first substrate and the second substrate. A first substrate and a second substrate; A thin film transistor formed on the first substrate; A first transparent conductive film formed on the substrate on which the thin film transistor is formed; A color filter formed on the second substrate; A second transparent conductive film formed on the second substrate and including at least one slit divided into a first opening and a second opening; And And a liquid crystal layer formed between the first substrate and the second substrate. The vertically aligned liquid crystal display device according to claim 1 or 2, wherein the liquid crystal layer is made of liquid crystal molecules having negative dielectric anisotropy. According to claim 1 or claim 2, further comprising a first polarizing plate formed to have a polarization axis in a predetermined direction on the outer surface of the first substrate and a second polarizing plate perpendicular to the polarization axis and formed on the outer surface of the second substrate A vertical alignment liquid crystal display device. The vertical alignment liquid crystal display of claim 1 or 2, further comprising a first alignment layer formed on the product of the first substrate and a second alignment film formed on the product of the second substrate. 6. The vertical alignment liquid crystal display of claim 5, wherein the first alignment layer and the second alignment layer are vertical alignment layers. The vertical alignment liquid crystal display of claim 1 or 2, wherein the first opening and the second opening have different widths. The vertical alignment liquid crystal display of claim 7, wherein the second opening is formed in a polygonal shape. 8. The vertical liquid crystal display of claim 7, wherein the second opening is formed in a circular shape. 8. The vertical liquid crystal display of claim 7, wherein the first opening is narrower than the second opening. A first substrate and a second substrate; A thin film transistor formed on the first substrate; A color filter formed on the second substrate; A liquid crystal layer formed between the first substrate and the second substrate and composed of liquid crystal molecules; A first transparent conductive film formed on the first substrate and a second transparent conductive film formed on a second substrate to form a first direction electric field in the liquid crystal molecules; At least one first slit formed on the transparent conductive film and forming a second direction electric field on the liquid crystal molecules; And And at least one second slit formed in the first slit and forming a third direction electric field in the liquid crystal molecules. 12. The liquid crystal display of claim 11, wherein the first direction electric field is formed in a direction perpendicular to the first substrate or the second substrate. 12. The liquid crystal display of claim 11, wherein the second direction electric field is formed in a direction parallel to the first substrate or the second substrate and perpendicular to the first slit. 12. The vertical liquid crystal display of claim 11, wherein the third direction electric field is formed in a direction parallel to the first substrate or the second substrate and parallel to the first slit. 12. The vertical alignment liquid crystal display of claim 11, wherein the second slit is formed on both sides of a narrow width of the first slit.