KR20070002224A - In-plane switching mode liquid crystal display device - Google Patents

Abstract

An in-plane switching mode liquid crystal display device is provided to block disclination areas between connection parts of common electrodes and pixel electrodes by common lines, thereby improving a valid aperture rate and improving luminance. An in-plane switching mode liquid crystal display device includes a plurality of gate and data lines(12,15) perpendicularly intersecting each other on a first substrate to define pixel areas. TFTs(Thin Film Transistors) are formed on the intersections between the gate and data lines. Common lines(25) are formed in parallel to the gate lines. A plurality of common electrodes(24) contact the common lines, wherein an end of each is connected to an upper end of a unit pixel integrally, and the other one overlaps the common line at a lower end of the unit pixel. A plurality of pixel electrodes(17) contact drain electrodes(15b) and are parallel to each other between the common electrodes, wherein an end of each is connected to the lower end of the unit pixel integrally and the other one overlaps the common line at the upper end of the unit pixel. A liquid crystal layer is formed between the substrates.

Description

Transverse electric field liquid crystal display device {IN-PLANE SWITCHING MODE LIQUID CRYSTAL DISPLAY DEVICE}

1 is a plan view of a unit pixel of a transverse electric field type liquid crystal display device according to the related art.

FIG. 2 is a detailed plan view in I of FIG. 1; FIG.

3 is a photograph showing a problem of a transverse electric field type liquid crystal display device according to the prior art.

4 is a plan view of a unit pixel of a transverse electric field type liquid crystal display device according to a first exemplary embodiment of the present invention.

5 is a plan view of a unit pixel of a transverse electric field type liquid crystal display device according to a second embodiment of the present invention;

6 is a cross-sectional view taken along line II-II ′ of FIG. 5.

* Explanation of symbols on the main parts of the drawings

11 TFT Array Substrate 12 Gate Wiring

12a: gate electrode 15: data wiring

15a: source electrode 15b: drain electrode

17 pixel electrode 18 first contact hole

19: second contact hole 24: common electrode

25: common wiring

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device (LCD), and more particularly, to a transverse electric field type liquid crystal display device which improves luminance by minimizing a discrepancy generation area at upper and lower ends of a unit pixel.

Recently, the liquid crystal display device, one of the flat panel display devices that are attracting attention, is an element that changes the optical anisotropy by applying an electric field to a liquid crystal that combines the liquidity and the optical properties of the crystal, which is applied to a conventional cathode ray tube. Compared with its low power consumption, small volume, large size, and high definition, it is widely used.

The liquid crystal display device has a variety of modes depending on the nature of the liquid crystal and the structure of the pattern.

Specifically, the TN mode (Twisted Nematic Mode) for arranging the liquid crystal directors to be twisted by 90 ° and then applying a voltage to the liquid crystal directors, and dividing one pixel into several domains to change the viewing angle of each domain to change the wide viewing angle. Multi-domain mode to implement, OCB mode (Optically Compensated Birefringence Mode) to compensate the phase change of light according to the direction of light by attaching the compensation film to the outer peripheral surface of the substrate, and two on one substrate In-Plane Switching Mode, in which the directors of the liquid crystal are twisted in parallel planes of the alignment layer, and the long axis of the liquid crystal molecules are vertically aligned with the alignment layer plane by using a negative liquid crystal and a vertical alignment layer. VA mode (Vertical Alignment).

Among them, the transverse electric field type liquid crystal display device is usually composed of a color filter array substrate and a thin film transistor array substrate disposed opposite to each other and having a liquid crystal layer therebetween.

That is, a black matrix for preventing light leakage and a color filter layer of R, G, and B for implementing color on the black matrix are formed on the color filter array substrate.

The thin film transistor array substrate includes gate wirings and data wirings defining unit pixels, switching elements formed at intersections of the gate wirings and data wirings, and a common electrode and a pixel electrode alternately crossing each other to generate a transverse electric field. Is formed. The switching element is a thin film transistor.

Hereinafter, a transverse electric field type liquid crystal display device according to the related art will be described with reference to the accompanying drawings.

1 is a plan view of a unit pixel of a transverse electric field liquid crystal display device according to the prior art, FIG. 2 is a detailed plan view of I of FIG. 1, and FIG. 3 is a photograph showing a problem of the transverse electric field liquid crystal display device according to the prior art. It is also.

Specifically, as shown in FIG. 1, the thin film transistor array substrate of the transverse electric field type liquid crystal display device includes a plurality of gate lines 112 arranged in a line and a plurality of data lines 115 perpendicularly intersecting with each other. A pixel is defined, and the unit pixel is formed to alternate between a thin film transistor (TFT) serving as a switching role, a plurality of common electrodes 124 parallel to the data line 115, and the common electrode 124. The pixel electrode 117 is parallel to the common electrode 124.

In this case, the common electrode 124 is connected to the common wiring 125 by the second contact hole 119 to receive a Vcom signal from an external driving circuit, and the common wiring 125 is parallel to the gate wiring 112. It is formed so as to overlap the lower portion of the common electrode 124 of the pixel edge is used as the capacitor lower electrode. The common electrode overlapping the common wiring is used as a capacitor upper electrode.

One end of the pixel electrode 117 is integrally connected to the pixel electrode 117 and connected to the drain electrode 115b of the thin film transistor TFT through the first contact hole 118 to receive the pixel signal. A predetermined region of the portion is used as the capacitor upper electrode.

Here, the common wiring 125 and the gate wiring 112 are formed on the same layer on the substrate as a low resistance metal material, and are formed on the data wiring with a gate insulating film interposed therebetween, and a protective film interposed therebetween. The pixel electrode 117 and the upper common electrode 124 are formed on the same layer of a transparent conductive material such as ITO. As such, the structure in which both the pixel electrode and the common electrode are made of a transparent conductive material such as ITO is called an ITO-ITO electrode structure.

However, in the case of the transverse electric field type liquid crystal display device having the ITO-ITO structure, there is a problem in that the field distortion occurs in the upper and lower ends of the unit pixels (common electrode connection part and pixel electrode connection part), thereby causing disclination.

Looking at the electric field distortion at the pixel electrode connection in detail, as shown in Figure 2, by applying 0V to the common electrode 124 and 5V to the pixel electrode 117, the horizontal electric field is a horizontal electric field between the two electrodes In this case, liquid crystal molecules (not shown), which are initially arranged in the rubbing direction, are rearranged in the direction of the electric field of the transverse electric field to control the transmission of light.

However, since the direction of rotation of the liquid crystal molecules in the region A and the direction of rotation of the liquid crystal molecules in the region C are opposite to each other, it is impossible to define which direction the liquid crystal molecules rotate in the region B. This is twisted. For this reason, a phenomenon in which polarization is hardly transmitted in the B region occurs, which causes a decrease in transmittance of the cell.

That is, as shown in FIG. 3, field distortion occurs at the upper and lower ends of the unit pixels (common electrode connection part and pixel electrode connection part “D”), thereby causing disclination in this area. Decreases the luminance.

The present invention has been made to solve the above problems, in the transverse electric field type liquid crystal display device of the ITO-ITO electrode structure, the end of the pixel electrode at the upper and lower ends of the unit pixel (connecting portion of the common electrode and connecting portion of the pixel electrode) Another object of the present invention is to provide a transverse electric field type liquid crystal display device which improves brightness and improves contrast ratio by overlapping the ends of the common electrode on the common wiring to prevent the disclination phenomenon.

The transverse electric field liquid crystal display device of the present invention for achieving the above object is a plurality of gate wiring and data wiring to define a unit pixel vertically crossing on the first substrate, and at the intersection of the gate wiring and data wiring A formed thin film transistor, a common wiring parallel to the gate wiring, a plurality of common electrodes contacting the common wiring, one end of which is integrally connected at the top of the unit pixel, and the other end of which overlaps the common wiring of the bottom of the unit pixel; A plurality of pixel electrodes contacted with the drain electrode and formed in parallel between the common electrodes, one end of which is integrally connected at the lower end of the unit pixel, and the other end of which overlaps the common wiring of the upper end of the unit pixel; And a liquid crystal layer formed between the second substrate and the second substrate.

That is, in the ITO-ITO electrode structure in which the common electrode and the pixel electrode are provided on the same layer, the screening area generated at the upper and lower ends of the unit pixel (connecting portion of the common electrode and pixel electrode) is shielded by common wiring. It is characterized in that the effective opening ratio is further secured and the luminance of the device is improved.

To this end, in order to overlap the ends of the pixel electrode on the common wiring on the upper end of the unit pixel and to prevent the overlapped ends of the pixel electrode and the common electrode connecting portion from being shorted with each other, a recess is formed in the common electrode connecting portion. A concave portion is formed in the pixel electrode connection portion in order to overlap the ends of the common electrode on the common wiring at the bottom of the unit pixel, and to prevent the overlapped end of the common electrode and the pixel electrode connection portion from shorting to each other.

Therefore, unlike the related art, only a transverse electric field is formed above and below the unit pixel, so that the control of the liquid crystal molecules is performed in a larger area, thereby contributing to the improvement of the contrast ratio of the device.

Such a transverse electric field type liquid crystal display device is particularly useful for a device in which the pixel electrode and the common electrode are formed on the same layer and thus the common electrode cannot be extended to the pixel electrode connection portion. This is because when the pixel electrode and the common electrode are formed on different layers, the common electrode may be formed to extend to the connection portion of the pixel electrode and overlap to remove the disclination region.

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

4 is a plan view of a unit pixel of a transverse electric field liquid crystal display device according to a first embodiment of the present invention, and FIG. 5 is a plan view of a unit pixel of a transverse electric field liquid crystal display device according to a second embodiment of the present invention. 6 is a cross-sectional view taken along line II-II 'of FIG. 5.

In the thin film transistor array substrate of the transverse electric field type liquid crystal display device according to the present invention, as shown in FIG. 4, a plurality of gate lines 12 arranged in a line and a plurality of data lines 15 perpendicularly intersecting therewith are provided. A unit pixel is defined, and the unit pixel includes a thin film transistor (TFT) that performs a switching role, a common electrode 25 that is parallel to the gate line, and transmits a Vcom voltage, and the second contact hole 119. A plurality of common electrodes 24 and a first contact hole 118 are contacted to the wiring and the Vcom voltage flows, one end is integrally connected at the top of the unit pixel, and the other end is overlapped with the common wiring at the bottom of the unit pixel. A pixel voltage flows by contacting the drain electrode 15b of the thin film transistor, one end of which is integrally connected at the bottom of the unit pixel, and the other end of the thin film transistor is connected to the common wiring at the top of the unit pixel. A plurality of pixel electrodes 17 are formed to be wrapped.

In this case, the thin film transistor TFT may include a gate electrode 12a, which is a predetermined region of the gate line 12, a gate insulating film (not shown) formed on the entire surface including the gate electrode 12a, and the gate electrode ( 12a) a semiconductor layer (not shown) formed on the gate insulating film on the upper portion, and a source electrode 15a and a drain electrode 15b branched from the data line 15 and formed on the semiconductor layer. A protective film (not shown), which is an insulating film, is further formed on the entire surface including the transistor, and the common electrode 24 and the pixel electrode 17 are provided on the protective film. The common electrode and the pixel electrode are formed to be parallel to each other in a unit pixel to generate a transverse electric field to control the driving of liquid crystal molecules.

Here, the common wiring 25 is formed parallel to the gate wiring, and is integrally connected at the edge of the unit pixel. That is, the common wiring is formed to be parallel to the gate wiring at the top of the unit pixel, and is formed to be parallel to the gate wiring at the bottom of the unit pixel, and the common wiring at the top of the unit pixel and the common wiring at the bottom of the unit pixel are adjacent to the data wiring. Connect at the pixel edge.

The common wiring is formed simultaneously with the gate wiring, and includes copper (Cu), aluminum (Al), aluminum alloy (AlNd: Aluminum Neodymium), molybdenum (Mo), chromium (Cr), titanium (Ti), and tantalum (Ta). And an opaque conductive material such as molybdenum-tungsten (MoW) to shield light from the top and bottom of the disclination region.

The common electrode 24 and the pixel electrode 17 are provided on the same layer, and are commonly formed using a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

In the ITO-ITO electrode structure, since the common electrode and the pixel electrode are formed on the same layer, in order to overlap one end of the common electrode and the pixel electrode on the upper part of the common wiring, the concave portion for securing the overlap margin of the connection part of the common electrode and the pixel electrode It must be formed at the joint. That is, at one end of the unit pixel, one end of the pixel electrode is inserted and overlapped on the common electrode, and at the bottom of the unit pixel, one end of the common electrode is inserted and overlapped on the common wiring. At this time, the recess of the pixel electrode and one end of the common electrode are not shorted, and the recess of the common electrode and one end of the pixel electrode are not shorted.

As a result, the user may shield the disclination region formed between the connecting portion of the pixel electrode and the end of the common electrode and the disclination region formed between the connecting portion of the common electrode and the end of the pixel electrode by the common wiring. It is not to be detected by the naked eye. In this case, the opening ratio is reduced by increasing the common wiring width because the end of the common electrode and the end of the pixel electrode are overlapped on the common wiring so as not to increase the width of the common wiring but to shield the disclination region by the common wiring. none.

The common electrode 24 and the pixel electrode 17 may be formed in a straight line shape or may be formed in a zigzag shape as shown in the drawing.

On the other hand, a pixel electrode overlaps the upper portion of the common line formed at the bottom of the unit pixel to form a storage capacitance (Cst). The common line at the bottom of the unit pixel serves as a capacitor lower electrode, and the pixel electrode overlapped thereon is a capacitor. It serves as an upper electrode, and a laminated film of a gate insulating film and a protective film provided between two layers serves as an insulating layer between the capacitor electrodes. Here, the storage capacitance is also formed by the common electrode overlapping the common wiring of the pixel edge.

However, a recess is formed in the pixel electrode connection portion so that one end of the common wiring may overlap the upper portion of the common wiring. As a result, an area of the capacitor upper electrode is reduced, resulting in a decrease in storage capacitance.

In order to solve this drawback, as shown in FIGS. 5 and 6, the drain electrode 15b may be extended to compensate for the reduced storage capacitance.

In general, the capacitance becomes larger as the capacitor electrode becomes larger, and becomes larger as the thickness of the insulating layer becomes thinner. To compensate for the reduced storage capacitance, the drain electrode 15b is extended to form the connection portion of the pixel electrode 17 and the common wiring 24. In addition to the capacitance Cst2 formed therebetween, the capacitance Cst1 formed between the extension portion of the drain electrode 15b and the common wiring 24 is additionally formed. Therefore, the disclination region can be removed with the storage capacitance secured. Reference numeral “11” denotes a TFT array substrate.

Lastly, although not shown, the color filter array substrate on which the black matrix, the color filter layer, and the overcoat layer are formed is opposed to the thin film transistor array substrate, and a liquid crystal layer is formed between the two substrates.

As described above, first and second polarizing plates are attached to the outer peripheral surfaces of the opposingly bonded thin film transistor array substrate and the color filter array substrate, respectively, so that their transmission axes are perpendicular to each other. At this time, the initial alignment direction of the liquid crystal is parallel to the transmission axis of any one of the polarizing plates to be in a normally black mode.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

The transverse electric field type liquid crystal display device of the present invention as described above has the following effects.

First, in the ITO-ITO electrode structure having the common electrode and the pixel electrode on the same layer, the end of the pixel electrode overlaps on the common wiring of the upper end of the unit pixel and the end of the common electrode on the common wiring of the lower end of the unit pixel. As a result, by shielding the disclination region generated at the connecting portion of the common electrode and the connecting portion of the pixel electrode by the common wiring, the effective aperture ratio is further secured, thereby improving the luminance of the device. The luminance of the device is improved.

Second, unlike in the related art, only a transverse electric field is formed on and below the unit pixel, so that the liquid crystal molecules are controlled in more regions, thereby improving the contrast ratio of the device.

Third, since the width of the common wiring is not extended to shield the disclination region, the opening area remains the same.

Claims (9)

A plurality of gate lines and data lines defining unit pixels at vertical crossings on the first substrate; A thin film transistor formed at an intersection point of the gate line and the data line; A common wiring parallel to the gate wiring; A plurality of common electrodes contacted with the common wiring, one end of which is integrally connected at the top of the unit pixel, and the other end of which overlaps the common wiring of the bottom of the unit pixel; A plurality of pixel electrodes formed to be in contact with the drain electrode and parallel between the common electrodes, one end of which is integrally connected at the bottom of the unit pixel, and the other end of which overlaps the common wiring of the top of the unit pixel; And a liquid crystal layer formed between the first substrate and the second substrate facing the first substrate. The method of claim 1, The common wiring is a horizontal field type liquid crystal display device, characterized in that provided on the same layer as the gate wiring. The method of claim 1, And the common wiring is formed of an opaque conductive layer. The method of claim 1, And the common electrode and the pixel electrode are provided on the same layer. The method of claim 1, And the common electrode and the pixel electrode are formed of a transparent conductive layer. The method of claim 1, And the pixel electrode and the transparent electrode are formed of indium tin oxide (ITO). The method of claim 1, And a pixel electrode in a portion where the end of the common electrode overlaps the common wiring has a concave portion. The method of claim 1, And the common wiring is integrally disposed at an edge of a unit pixel. The method of claim 1, And a common electrode at a portion where the end of the pixel electrode overlaps the common wiring has a concave portion.

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