KR20070082756A - Liquid crystal display - Google Patents

Abstract

An LCD(Liquid Crystal Display) is provided to improve a light transmission rate of the entire LCD by enhancing a horizontal electric field component of a fringe field by including an inclination layer. A thin film transistor display panel(100) includes a common electrode(26) on an insulating substrate, a pixel electrode including a plurality of main electric-field generators(80a) and insulated from the common electrode, and an inclination layer(75) formed between the main electric-field generators. A facing display panel(200) faces the thin film transistor display panel, and is separated from the thin film transistor display panel. A liquid crystal layer(300) is formed between the thin film transistor display panel and the facing display panel. The liquid crystal layer is formed of liquid crystals having positive dielectric anisotropy.

Description

Liquid crystal display

1 is a cross-sectional view of a liquid crystal display according to an exemplary embodiment of the present invention.

2 is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention.

3A to 5C are diagrams showing light transmittances according to simulation results of the experimental and comparative examples.

<Description of the symbols for the main parts of the drawings>

11, 21: alignment film 25: common electrode line

26: common electrode 75: pretilt film

80: pixel electrode 80a: main electric field generating unit

80b: connector 100: thin film transistor array panel

200: opposing display panel 300: liquid crystal layer

311: liquid crystal

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device including a common electrode and a pixel electrode in one display panel.

The liquid crystal display is one of the most widely used flat panel display devices. The liquid crystal display is composed of two substrates on which electrodes are formed and a liquid crystal layer interposed therebetween. It is a display device that controls the amount of light transmitted by arranging.

Liquid crystal displays have the advantages of easy thinning, relatively low power consumption, and almost no harmful electromagnetic waves. However, the liquid crystal display has various disadvantages in that it is inferior to the front visibility. Liquid crystal array and driving methods are being developed.

In order to realize a wide viewing angle, the common electrode and the pixel electrode are positioned on one display panel, and the gaps thereof are formed to be narrower than the gap between the upper and lower display panels, so that a fringe field is formed on the common electrode and the pixel electrode. PLS (Plane to Line Switching) mode to attract attention is attracting attention.

In the liquid crystal display of the PLS mode, a region where the vertical field component is dominant and a region where the horizontal field component is dominant has different luminance. This may eventually be a factor to lower the light transmittance of the liquid crystal display.

An object of the present invention is to provide a liquid crystal display device having improved light transmittance.

Technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

According to an exemplary embodiment of the present invention, a liquid crystal display device includes a common electrode on an insulating substrate, a pixel electrode insulated from the common electrode and including a plurality of main field generators, and the main field generator. The thin film transistor array panel includes a thin film transistor array panel including a formed pretilt film, an opposing display panel facing the thin film transistor array panel and spaced apart from the thin film transistor array panel, and a liquid crystal layer formed between the thin film transistor array panel and the opposing display panel.

Specific details of other embodiments are included in the detailed description and the drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity.

When an element or layer is referred to as "on" another element or layer, it is expressly exempt from intervening other elements specifically in the middle, such as "directly on" or "immediately above." Unless otherwise specified, all layers including other layers or other elements directly above or in between are included. Like reference numerals refer to like elements throughout. "And / or" includes each and all combinations of one or more of the items mentioned.

First, a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to FIG. 1. 1 is a cross-sectional view of a liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 1, the liquid crystal display according to the exemplary embodiment of the present invention is formed on the thin film transistor array panel 100 on the lower side and the opposing display panel 200 on the upper side facing the thin film transistor array panel 100, and the positive dielectric constant is formed between them. It consists of a liquid crystal layer 300 made of a liquid crystal having anisotropy. Alignment layers 11 and 21 are formed on the display panels 100 and 200, and upper and lower polarizers 12 and 22 are attached to outer surfaces of the upper panel 200 and the lower panel 100, respectively. . At this time, each of the alignment layers 11 and 21 is subjected to a rubbing process, for example, to form an angle of about 10 ° or less with respect to the main electric field generator 80a of the pixel electrode 80 described later.

In the thin film transistor array panel 100 made of a transparent insulating material such as glass, a unit pixel is defined by crossing gate lines (not shown) and data lines (not shown), and thin film transistors, which are switching elements, are disposed at each intersection. . The common electrode 26 made of a transparent conductive material is disposed in the unit element, and the pixel electrode 80 is disposed in the unit pixel so as to overlap the common electrode 26. The pixel electrode 80 is also made of a transparent conductive material and is electrically insulated from the common electrode 26. The pixel electrode 80 includes a plurality of main electric field generators 80a that are parallel to the data lines and spaced at equal intervals, and a connection part 80b that connects them, and is electrically connected to the drain electrode 66 of the thin film transistor. have.

Also including an insulating substrate 210 of a transparent insulating material such as glass, the opposite display panel 200 facing the thin film transistor array panel 100 and the black matrix 220 for preventing light leakage generated at the edge of the unit pixel and The red, green, and blue color filters 230 and the black matrix 220 and the overcoat layer 240 to planarize the step generated by the color filter 230 is included.

Hereinafter, the thin film transistor array panel 100 will be described in more detail.

For example, chromium (Cr), molybdenum (Mo), titanium (Ti), tantalum (Ta), aluminum (Al), silver (Ag), or an alloy thereof on the first insulating substrate 10 made of transparent glass or the like. A gate wiring made of a single film or a multilayer film is formed. The gate line may include a gate line (not shown) that transmits a gate signal, a gate pad (not shown) formed at one end of the gate line to receive a signal from the outside, and a gate electrode 24 of the thin film transistor protruding from the gate line. Include.

The common electrode line 25 transmits a common voltage to the common electrode 26, and is formed in a horizontal direction adjacent to the gate line in parallel with the gate line. The common electrode line 25 may be formed on the same layer as the gate line. The common electrode line 25 may be formed of the same material as the material forming the gate wiring for convenience of processing.

The common electrode 26 is connected to the common electrode line 25 to receive a common voltage from the common electrode line 25. The common electrode 26 is a substantially rectangular planar electrode arranged in a matrix form and substantially fills the space defined by the gate line and the data line (the space corresponding to the unit pixel). The common electrode 26 is made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). The common electrode 26 may be formed on the same layer as the common electrode line 25. In this case, the common electrode 26 may include a connection branch for electrically connecting the common electrode line 25. In addition, the common electrode 26 may be electrically connected to the common electrode line 25 by partially overlapping and contacting the common electrode line 25.

On the gate line, the gate electrode 24, the common electrode line 25, and the common electrode 26, a gate insulating film 30 made of an inorganic insulator such as silicon nitride covers them.

A semiconductor layer 40 made of hydrogenated amorphous silicon or the like is formed on the gate insulating film 30. The semiconductor layer 40 may be formed in an island shape, and may have a linear shape or another shape depending on a manufacturing method. The semiconductor layer 40 forms a thin film transistor together with the lower gate electrode 24, the source electrode 65 and the drain electrode 66 disposed thereon, and forms a channel.

The ohmic contacts 55 and 56 are formed on the semiconductor layer 40. The ohmic contacts 55 and 56 are made of, for example, n + hydrogenated amorphous silicon doped with n-type impurities at a high concentration. The ohmic contacts 55 and 56 may be collectively patterned together with, for example, the semiconductor layer 40 to have substantially the same outer shape, such as an island shape or a linear shape, but in this case, the central parts may have separate structures. The point may be different from the shape of the semiconductor layer 40. That is, the ohmic contacts 55 and 56 are physically separated from each other, and their separated shapes may be substantially the same as the separated shapes of the source electrode 65 and the drain electrode 66 thereon.

On the gate insulating layer 30 and the ohmic contacts 55 and 56, chromium (Cr), molybdenum (Mo), titanium (Ti), tantalum (Ta), aluminum (Al), silver (Ag), alloys thereof, and the like A data wiring made of a single film or a multilayer film is formed. The data line includes a data line (not shown) that intersects the gate line formed in the vertical direction, and a source electrode 65, a source electrode 65, and a gate branched from the data line (not shown) in the direction of the gate electrode 24. The drain electrode 66 is separated from the electrode 24. The data line may be made of the same material as the gate line, but may be made of another material, and may be appropriately selected in consideration of adhesion to a lower structure, specific resistance, unit price, and the like.

A passivation layer 70 is formed on the data line, the source electrode 65, the drain electrode 66, and the exposed semiconductor layer 40 to cover these and the gate insulating layer 30. The passivation layer 70 may be made of an inorganic layer such as silicon nitride or silicon oxide. In the passivation layer 70, a contact hole 77 exposing the drain electrode 66, a contact hole exposing the data pad (not shown), and a contact hole exposing the gate pad are formed. Among them, the contact hole exposing the gate pad penetrates to the gate insulating film 30 under the protective film 70.

A pretilt film 75 formed of a tapered structure and having an inclined surface and made of an insulating material is formed on the passivation layer 70. Preferably, the pretilt film 75 may be formed in the shape of a mountain having a gradually thin thickness from both the center to both directions.

The pretilt film 75 may be formed by forming an organic film on the protective film 70 and selectively exposing the mask using a mask including a semi-transmissive region through which light partially passes. In this case, the interval between the lowest points of the pretilt film 75 is adjusted so that the main electric field generating unit 80a of the pixel electrode 80 may be positioned to overlap the lowest point of the mountain pretilt film 75.

The pretilt film 75 allows the initial orientation of the liquid crystal having a positive dielectric anisotropy constituting the liquid crystal layer 300 to have a pretilt angle of a predetermined angle according to the inclination of the pretilt film 75. When a fringe field is formed between the common electrode 26 and the pixel electrode 80 by applying a voltage to the liquid crystal display, the liquid crystal is arranged in parallel with the fringe field within a rapid time. In other words, the response speed of the liquid crystal is increased.

In addition, the pretilt film 75 affects the horizontal electric field component of the fringe field formed between the common electrode 26 and the pixel electrode 80. That is, when the pretilt film 75 is absent, the main electric field indicates that the vertical electric field component of the fringe field is dominant in the center of the main electric field generator 80a of the pixel electrode 80 or between the main electric field generator 80a. By exposing the pretilt film 75 having a predetermined slope between the generators 80a, the horizontal electric field component in the region can be strengthened. That is, the liquid crystal due to the electric field of the vertical component of the fringe field may have a greater movement in the azimuthal direction due to the horizontal electric field component than the movement in the polar direction to improve the light transmittance.

The pretilt film 75 may be made of, for example, an organic material having a dielectric constant of about 3 to about 5 F / m. In addition, although the height and width of the pretilt film 75 may be variously modified, for example, when the pretilt film 75 has a mountain shape, the pretilt film 75 has a height of about 0.2 to 2 μm at the highest point, and between the lowest points. The spacing can be about 4 to 4.52 mu m.

Although not shown in the drawing, the pretilt film 75 may be formed on the upper portion of the contact hole 77. In this case, the pretilt film 75 may also be formed by extending the contact hole 77 of the protective film 70. There may be.

A pixel electrode 80, an auxiliary gate pad (not shown), and an auxiliary data pad (not shown) are formed on the passivation layer 70 and the pretilt layer 75.

The pixel electrode 80 receives a data voltage from the drain electrode 66 and rotates the liquid crystal by generating an electric field together with the lower common electrode 26. The pixel electrode 80 is made of a transparent conductive material such as ITO or IZO, and includes, for example, a plurality of main field generators 80a having a comb-tooth shape and a connection unit 80b connecting the main field generators 80a. do. The main electric field generator 80a occupies most of the pixel electrode 80 and generally extends vertically in parallel with the data line. The main electric field generator 80a is formed on the pretilt film 75 to expose the highest point of the pretilt film 75 between the main electric field generator 80a. The connecting portion 80b serves to connect the main electric field generating portion 80a at the periphery of the pixel electrode 80 and is positioned adjacent to a gator line (not shown) to form an outer side of the pixel electrode 80. . The shape of the contact surface of the pixel electrode 80 with the pretilt film 76 has the same shape as that of the pretilt film 76, that is, the inclined shape.

The auxiliary gate pads and the auxiliary data pads are connected to the gate pads through the contact holes, and the auxiliary data pads are connected to the data pads through the contact holes to compensate for the adhesion between the auxiliary gate pads and the auxiliary data pads and the external device. It protects them. The auxiliary gate pad and the auxiliary data pad may be made of the same material as the pixel electrode 80, for example, ITO or IZO.

When the thin film transistor array panel 100 as described above is aligned with the opposing display panel 200, the liquid crystal layer 300 is formed therebetween, and the horizontal alignment is performed, the basic structure of the liquid crystal display device according to the exemplary embodiment of the present invention is provided. do.

Next, a liquid crystal display according to another exemplary embodiment of the present invention will be described with reference to FIG. 2. 2 is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention.

The liquid crystal display according to another exemplary embodiment of the present invention is substantially the same as the liquid crystal display according to the exemplary embodiment of the present invention except for the stacking order of the pretilt film and the pixel electrode formed on the thin film transistor array panel. The difference from the liquid crystal display according to the exemplary embodiment will be described.

As shown in FIG. 2, the liquid crystal display according to the exemplary embodiment of the present invention includes a thin film transistor array panel 100 on the lower side, an upper display panel 200 facing the opposite side, and a positive dielectric constant formed therebetween. It consists of a liquid crystal layer 300 made of a liquid crystal having anisotropy. In this case, alignment layers 11 and 21 are formed on each of the display panels 100 and 200, and upper and lower polarizing plates 12. 22 are formed on outer surfaces of the upper display panel 200 and the lower display panel 100, respectively. Attached. In this case, the opposing display panel 200, the liquid crystal layer 300, the alignment layers 11 and 21, and the polarizing plates 12 and 22 are the same as the liquid crystal display according to the exemplary embodiment of the present invention.

Hereinafter, the thin film transistor array panel 100 will be described in more detail.

From the gate wiring on the first insulating substrate 10 to the passivation layer 70 in which the contact hole 77 is formed, the same as in the liquid crystal display according to the exemplary embodiment of the present invention, overlapping description thereof will be omitted. .

The pixel electrode 80 including a plurality of comb-shaped main electric field generators 80a made of a transparent conductive material such as ITO or IZO and a connection unit 80b connecting the main electric field generator 80a to the upper portion of the passivation layer 70. ) And an auxiliary gate pad and an auxiliary data pad.

Between the main field generator 80a of the pixel electrode 80 formed on the passivation layer 70, a pretilt film 75 having an inclined surface and having an inclined surface is formed. Preferably, the pretilt film 75 may be formed in the shape of a mountain having a gradually thin thickness from both the center to both directions.

The pretilt film 75 may be formed by forming an organic film on the passivation film 70 on which the pixel electrode 80 is formed, and selectively exposing using a mask including a translucent region. Although not shown, the cell gap retaining member may be formed together by the same photographic process for forming the pretilt film 75.

As described above, in the liquid crystal display according to the exemplary embodiment of the present invention, the pretilt film 75 may have a pretilt angle of a predetermined angle according to the inclination of the pretilt film 75, thereby providing a voltage to the liquid crystal display device. When applied, the response speed of the liquid crystal may be increased.

In addition, the pretilt film 75 affects the horizontal field component of the fringe field formed between the common electrode 26 and the pixel electrode 80 as in the liquid crystal display according to the exemplary embodiment of the present invention. In other words, the pretilt film 75 strengthens the horizontal field component of the fringe field in the center of the main field generator 80a of the pixel electrode 80 or between the main field generator 80a, and in this region. The light transmittance can be improved by increasing the movement of the liquid crystal in the azimuth direction.

Since the dielectric constant, the height of the highest point, the distance between the lowest points, and the like of the pretilt film 75 are the same as in the liquid crystal display according to the exemplary embodiment of the present invention, redundant descriptions thereof will be omitted.

When the thin film transistor array panel 100 as described above is aligned with the opposing display panel 200, the liquid crystal layer 300 is formed therebetween, and the horizontal alignment is performed, a basic structure of the liquid crystal display device according to another exemplary embodiment of the present invention is provided. do.

Hereinafter, the present invention will be described in more detail with reference to experimental and comparative examples. However, it should be understood that the following experimental examples are intended to illustrate the present invention and the present invention is not limited by the following experimental examples.

Experimental Example  One

Simulation using 2D MOS is performed on the liquid crystal display according to the exemplary embodiment of the present invention, and the results are shown in FIGS. 3A to 3C.

At this time, the liquid crystal layer 300 was composed of MAT-05-152 (positive dielectric anisotropic liquid crystal for TN), and the incident wavelength λ was 550 nm. The electrode width of the main electric field generator 80a of the pixel electrode was about 4 m, and the interval between the electrodes of the main electric field generator 80a was about 4 m. The dielectric constant? Of the pretilt film 75 was about 3 F / m, and the thickness at the highest point of the pretilt film 75 was about 5000 GPa. The rubbing angle of the alignment film was about 7.5 degrees. In addition, the common voltage V _com of the liquid crystal display device was driven at about 8V.

Experimental Example  2

Simulation using 2D MOS is performed on the liquid crystal display according to another exemplary embodiment of the present invention, and the results are shown in FIGS. 4A to 4B.

In this case, the simulation was performed under the same conditions as in Experimental Example 1 except that the common voltage V _com of the liquid crystal display is driven at about 7V.

Comparative example  One

A simulation using 2D MOS was performed on the liquid crystal display of the PLS mode without the pretilt film, and the results are shown in FIGS. 5A to 5C.

At this time, the liquid crystal layer 310 was composed of MAT-05-152 (positive dielectric anisotropy liquid crystal for TN), and the incident wavelength λ was 550 nm. The electrode width of the main electric field generator 80c of the pixel electrode was about 4 m, and the interval between the electrodes of the main electric field generator 80c was about 4 m. In addition, the common voltage V _com of the liquid crystal display device was driven at about 6V. Reference numerals 27, 71, 310, and 311 in FIGS. 5A to 5C correspond to a common electrode, a protective film, a liquid crystal layer, and a liquid crystal, respectively.

First, referring to the simulation result of Comparative Example 1, as shown in FIG. 5A, the average light transmittance of the liquid crystal display of Comparative Example 1 is about 42.18%. In this case, it can be seen that the light transmittance between the center of the main electric field generating unit 80c and the main electric field generating unit 80c of the pixel electrode has a light transmittance lower than that of the other regions.

This will be described in more detail with reference to FIGS. 5B and 5C. As illustrated in FIGS. 5B and 5C, the fringe field may be formed between the main electric field generator 80c and in an area corresponding to the center of the main electric field generator 80c. The vertical electric field component is dominant, whereby the movement in the polar angle direction of the liquid crystal 311 is predominant in the region, so that the light transmittance is relatively low.

In contrast, in the liquid crystal display devices of Examples 1 and 2, as shown in FIGS. 3A and 4A, the average light transmittances of the liquid crystal display devices are about 44.65% and 43.37%, respectively. As compared with the case of Comparative Example 1, it can be seen that the light transmittances of the liquid crystal display devices of Examples 1 and 2 are increased by about 2.47% and 2.29%, respectively.

3B, 3C, and 4B, the liquid crystal display devices of Experimental Examples 1 and 2 are disposed between the main electric field generators 80a, as shown in FIGS. 3B, 3C, and 4B. By including the formed pretilt film 75, the horizontal electric field component of the fringe field in the region corresponding to the center between the main electric field generating unit 80a and the main electric field generating unit 80a is increased, and the liquid crystal 301 The light transmittance at the center between the main electric field generator 80a or the center of the main electric field generator 80a can be improved by increasing the movement in the azimuth direction. As a result, the light transmittance of the entire liquid crystal display device is improved.

Compared with Comparative Example 1, the liquid crystal display in the case of Experimental Example 1 and Experimental Example 2 includes a pretilt film, the magnitude of the common voltage applied to the liquid crystal display is relatively large, but it has a positive dielectric anisotropy In the case of using a liquid crystal, the driving margin is larger than that of a liquid crystal having negative dielectric anisotropy, so it is not a problem.

Experimental Example  3

Simulation using 2D MOS was performed on the liquid crystal display according to the exemplary embodiment of the present invention. At this time, the simulation was performed under the same conditions as in Experiment 1 except that the width of the main field generator of the pixel electrode was about 4.5 μm, and the interval between the main field generators was about 4.5 μm. At this time, the average light transmittance was about 43.38%.

Comparative example  2

Simulation using 2D MOS was performed on the liquid crystal display of the PLS mode that did not include the pretilt film. At this time, the simulation was performed under the same conditions as in Experiment 1 except that the width of the main field generator of the pixel electrode was about 4.5 μm, and the interval between the main field generators was about 4.5 μm. At this time, the average light transmittance was about 40.86%.

Comparing the light transmittances of Comparative Example 2 and Experimental Example 3, the light transmittance of the liquid crystal display of Experimental Example 3 was about 2.52%, which is about 40.86% and 43.38%, respectively. It can be seen that this has a better light transmittance as compared with the case of Experimental Example 1 and Experimental Example 2. Accordingly, it can be seen from the above result that the light transmittance is improved as the width of the main field generating unit of the pixel electrode and the gap therebetween are wider.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above embodiments but may be manufactured in various forms, and having ordinary skill in the art to which the present invention pertains. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

As described above, the liquid crystal display according to the exemplary embodiments of the present invention may further improve the light transmittance of the entire liquid crystal display by further strengthening the horizontal electric field component of the fringe field including the pretilt film.

Claims (9)

A thin film transistor array panel including a common electrode on an insulating substrate, a pixel electrode insulated from the common electrode, the pixel electrode including a plurality of main field generators, and a pretilt layer formed between the main field generators; An opposing display panel facing the thin film transistor array panel and spaced apart from the thin film transistor array panel; And And a liquid crystal layer formed between the thin film transistor array panel and the opposing display panel. The method of claim 1, The liquid crystal display device comprising a liquid crystal having a positive dielectric anisotropy. The method of claim 2, The pretilt film has an acid structure in which the thickness becomes thinner from the center to both sides. The method of claim 3, wherein And the main electric field generating unit overlaps with the pretilt film at the lowest point of the pretilt film of the acid structure. The method of claim 4, wherein The height of the highest point of the said pretilt film of the said acid structure is 0.2-2 micrometers. The method of claim 4, wherein And a gap between the lowest points of the pretilt film having the acid structure is 4 to 4.5 µm. The method of claim 2, A liquid crystal display device having a dielectric constant of the pretilt film is 3 to 5 F / m. The method of claim 1, And an alignment layer on each of the opposing surfaces of the thin film transistor array panel and the opposing display panel. The method of claim 8, And a rubbing angle of the alignment layer forms an angle of 10 ° or less with the main field generator of the pixel electrode.

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