KR100827461B1 - Cross field switchhing mode liquid crystla display - Google Patents

Abstract

The present invention discloses a liquid crystal display device driven in a cross field, and the disclosed liquid crystal display device includes a transparent insulating substrate; A plurality of gate bus lines and data bus lines cross-arranged to define unit pixels on the substrate; A common bus line arranged in parallel and spaced apart from the gate bus line in the unit pixel; A thin film transistor disposed at an intersection of the gate bus line and the data bus line; A counter electrode disposed in the unit pixel and comprising a first plate electrode and a second branch electrode formed of a transparent conductive film; And a first branch electrode formed of a transparent conductive film disposed on an upper surface of the first plate electrode of the counter electrode under an insulating film, and a second plate formed of a transparent conductive film disposed under an insulating film under a second branch electrode of the counter electrode. And a pixel electrode configured as an electrode, wherein the first plate electrode and the second branch electrode of the counter electrode are electrically contacted with the common bus line, and the first branch electrode and the second plate electrode of the pixel electrode are connected to the thin film transistor. The first and second branch electrodes are electrically contacted, and each of the first and second branch electrodes includes a plurality of branches, and a branch disposed at an edge of the branches is inclined with respect to the vertical direction.

Description

CROSS FIELD SWITCHHING MODE LIQUID CRYSTLA DISPLAY}

1 is a plan view showing a conventional fringe field switching mode liquid crystal display device.

2 and 3 are plan and cross-sectional views of a cross-field switching mode liquid crystal display according to an exemplary embodiment of the present invention.

4 is a view for explaining the operation principle of the cross-field switching mode liquid crystal display according to an embodiment of the present invention.

5 is a view for explaining a cross-field switching mode liquid crystal display device according to another embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

11: glass substrate 12: gate bus line

13 common bus line 14 pixel electrode

14a: first branch electrode 14b: second plate electrode

15 gate insulating film 16 data bus line

17: protective film 18: counter electrode

18a: first plate electrode 18b: second branch electrode

20: liquid crystal TFT: thin film transistor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a cross field switching mode liquid crystal display device having improved response speed and light efficiency through formation of an inclined pixel electrode.

Liquid crystal display (Liquid Crystal Display) has been developed in place of the CRT (Cathod-ray tube). In particular, the thin film transistor liquid crystal display device has been in the spotlight in the information display of a portable terminal device, the screen display of a notebook PC, the monitor of a laptop computer, etc., and thus, the utilization of the thin film transistor as a display device that can replace the CRT has been very high. .

Such a liquid crystal display device, in particular, a thin film transistor liquid crystal display device, has typically adopted a TN (Twist Nematic) mode as its driving mode. However, the TN mode liquid crystal display device has a disadvantage in that the viewing angle is narrow, and thus the use of the TN mode liquid crystal display device is limited. Therefore, an in-plane switching (hereinafter referred to as IPS) mode is proposed to provide a liquid crystal having a wide viewing angle. Although the display device is implemented, this also shows limitations in terms of aperture ratio and transmittance.

Accordingly, a fringe field switching mode liquid crystal display (hereinafter referred to as FFS-LCD) capable of improving the aperture ratio and transmittance while maintaining the characteristics of the wide viewing angle of the IPS mode liquid crystal display has been proposed by the present applicant. And Korean Patent Application No. 98-9243.                         

In the FFS-LCD, a counter electrode and a pixel electrode are formed of a transparent metal such as ITO so that the gap between the electrodes is smaller than the cell gap, which is a structural difference from the IPS mode liquid crystal display device. By operating the fringe field generated between the liquid crystal molecules present on the electrodes, all the high opening ratio and high transmittance as well as high brightness and wide viewing angle.

FIG. 1 is a plan view showing an array substrate of a conventional FFS-LCD. As shown in FIG. 1, a gate bus line 2 and a data bus line 6 are alternately arranged so that a unit pixel is defined. Near the intersection between 2 and 6, a thin film transistor (TFT) is arranged as a switching element.

A counter electrode 4 having a plate shape and made of a transparent conductive film such as ITO is disposed in the unit pixel, and the common bus line 3 is located at a position in the unit pixel spaced apart from the gate bus line 2 as far as possible. It is arranged in parallel with the gate bus line (2). The common bus line 3 is formed to continuously supply a common signal to the counter electrode 4, and is formed at the same time as the gate bus line 2 and extends in parallel with the data bus line 6. And light blocking means disposed at both edges of the counter electrode 4.

A pixel electrode 8 having a slit shape and made of a transparent conductive film such as ITO is arranged to overlap the counter electrode 4 in the unit pixel with an insulating film (not shown) interposed therebetween, and a part of the thin film transistor It is in contact with (TFT).

Although not shown, the array substrate having the above-described structure is bonded to the color filter substrate having the black matrix and the color filter and interposed between the liquid crystal layer composed of negative liquid crystal molecules. In this case, the array substrate and the color filter substrate are bonded to have a larger gap than the gap between the counter electrode and the pixel electrode provided in the array substrate.

In the FFS-LCD, negative liquid crystal molecules are rotated by causing the pixel electrode 8 to cause a potential difference between the liquid crystal molecules on the counter electrode 4 that serves as storage and the common electrode Vcom. As a result, the light that has advanced through the polarizing plate proceeds toward the color filter substrate to display a predetermined image.

However, the FFS-LCD has a superior viewing angle compared to the IPS and TN mode liquid crystal display devices, but due to unwanted parasitic capacitance due to overlapping of the counter electrode and the pixel electrode, the residual image is long when the same image is implemented for a long time. There is a problem in terms of the screen quality, such as).

Accordingly, an object of the present invention is to provide a cross-field switching mode liquid crystal display device capable of suppressing the generation of afterimages in an FFS-LCD.

In addition, another object of the present invention is to provide a cross-field switching mode liquid crystal display device capable of improving transmittance as well as response speed and light efficiency.

Liquid crystal display device of the present invention for achieving the above object, a transparent insulating substrate; A plurality of gate bus lines and data bus lines cross-arranged to define unit pixels on the substrate; A common bus line arranged in parallel and spaced apart from the gate bus line in the unit pixel; A thin film transistor disposed at an intersection of the gate bus line and the data bus line; A counter electrode disposed in the unit pixel and comprising a first plate electrode and a second branch electrode formed of a transparent conductive film; And a first branch electrode formed of a transparent conductive film disposed on an upper surface of the first plate electrode of the counter electrode under an insulating film, and a second plate formed of a transparent conductive film disposed under an insulating film under a second branch electrode of the counter electrode. And a pixel electrode configured as an electrode, wherein the first plate electrode and the second branch electrode of the counter electrode are electrically contacted with the common bus line, and the first branch electrode and the second plate electrode of the pixel electrode are connected to the thin film transistor. The first and second branch electrodes are electrically contacted, and each of the first and second branch electrodes includes a plurality of branches, and a branch disposed at an edge of the branches is inclined with respect to the vertical direction.

According to the present invention, a cross field occurs in a unit pixel, and a part of the pixel electrode is formed to be inclined with respect to the vertical direction so that a horizontal field occurs, so that afterimage generation can be suppressed, as well as response speed and light efficiency. And the viewing angle and transmittance can be improved.

(Example)

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 and 3 are a plan view and a cross-sectional view of a cross-field switching mode liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the gate bus line 12 and the data bus line 16 are arranged in an intersecting manner so that unit pixels are limited, and the common bus line 13 is spaced apart from the gate bus line 12 as much as possible. It is arranged in parallel with the gate bus line 12 in the position. A thin film transistor TFT is disposed as a switching element near the intersection point between the lines 12 and 16. The counter electrode 18 and the pixel electrode 14 made of a transparent conductive film such as ITO are arranged to overlap each other under an insulating film (not shown) in the unit pixel.

In the above, the counter electrode 18 is an electrical contact to the common bus line 13, the first plate electrode 18a and a second branch electrode in which a predetermined number, for example, three branches are arranged in a unit group It consists of 18b. The pixel electrode 14 is electrically contacted to the thin film transistor TFT and includes a second plate electrode 14b alternately arranged with the first plate electrode 18a, and a predetermined number of branches, for example, three branches. And a first branch electrode 14a alternately arranged with the second branch electrode 18b in a unit group. The electrical contact with the thin film transistor TFT is preferably made with a source electrode of the thin film transistor TFT.

Referring to FIG. 3, a thin film transistor TFT is formed in a transparent insulating substrate, for example, a glass substrate 11, and a counter electrode 18 and a pixel electrode 14 are formed on a substrate region corresponding to a pixel region. The insulating film is formed to overlap with the gate insulating film 15 and the protective film 17 in more detail.

The first plate electrode 18a of the counter electrode 18 is disposed on the upper side of the common bus line 13 and is in direct contact with each other. The first plate electrode 18a is disposed above the common bus line 13 and the insulating layer. The second branch electrode 18b is in electrical contact with the common bus line 13 through a contact hole formed on the insulating layer, and the first branch electrode of the pixel electrode 14 disposed above the thin film transistor TFT. 14a) is electrically contacted with the thin film transistor TFT through a contact hole, and the second plate electrode 14b is also disposed under the thin film transistor TFT to be in electrical contact with the thin film transistor TFT. In addition, the first and second plate electrodes 18a and 14b are formed on the glass substrate 11, and the first branch electrode 14a is provided with an insulating film on the upper side of the first plate electrode 18a. The second branch electrode 18b is formed to be overlapped in the state, and the second branch electrode 18b is formed to overlap with the insulating film interposed on the second plate electrode 14b. In particular, the branches disposed on both sides of the first and second branch electrodes 14a and 18b may be formed to be inclined with respect to the vertical direction through selective etching of the insulating layer including the gate insulating layer 15 and the passivation layer 17. do.

In FIG. 3, reference numeral 16 denotes a data bus line, Vcom denotes a voltage applied from the common bus line 13, and Vsig denotes a voltage applied from the thin film transistor TFT.

In the liquid crystal display of the present invention having the structure as described above, the field between the counter electrode 18 and the pixel electrode 14, as well as the inclined first and second branch electrodes 14a, 18b facing each other. Since the field is generated between), the liquid crystal is driven by the cross field. Accordingly, in the liquid crystal display of the present invention, the liquid crystal is deflected in the opposite field directions between neighboring regions, thereby obtaining an improved viewing angle and transmittance than the conventional FFS-LCD.

4 is a view for explaining the principle of operation of the liquid crystal display device according to an embodiment of the present invention, wherein the same parts as in FIG. 3 are denoted by the same reference numerals.

As shown, a voltage of Vcom is applied to the first plate electrode 18a and the second branch electrode 18b of the counter electrode 18, and the second plate electrode 14b and the first branch electrode of the pixel electrode ( As a voltage of Vsig is applied to 14a), a field occurs between the first plate electrode 18a and the second branch electrode 18b and between the second plate electrode 14b and the first branch electrode 14a. At the same time, as voltages of different polarities are applied to the first branch electrodes 14a and the second branch electrodes 18b disposed above the first and second plate electrodes 18a and 14b with the insulating film interposed therebetween. Branches disposed at the edges of the branches of the first and second branch electrodes 14a and 18b are formed to be inclined with respect to the vertical direction so that a field occurs between the opposite branches.

As a result, in the pixel structure of the present invention, a cross field occurs, and in particular, one or more of the first and second branch electrodes 14a and 18b are formed in an inclined form. You have a domain.

Therefore, a cross field is formed between the adjacent electrodes, and the electric field applied to the liquid crystal 20 is made stronger by the inclined electrode, and a horizontal field having an inclined surface instead of the circular field is formed in the liquid crystal 20. By applying to, the response speed and the light efficiency can be improved, and the concentration of the field can be prevented, and the afterimage problem, which is a problem in the conventional FFS-LCD, is solved. In addition, the liquid crystals 20 are deflected in the field directions opposite to each other between neighboring regions, so that the viewing angle and transmittance are also improved.

5 is a diagram for describing a cross-field driving liquid crystal display according to another exemplary embodiment of the present invention. According to this embodiment, the first and second branch electrodes 14a, 18b are composed of two branches, compared to that of the previous embodiment.

In such a structure as well, a cross field is formed, and the field applied to the liquid crystal by the field between the inclined electrodes becomes stronger, so that the response speed and the light efficiency can be improved.

Meanwhile, in the embodiment of the present invention, although two plate electrodes and branch electrodes are provided and described, two or more plate electrodes and branch electrodes may be provided in the unit pixel as necessary. In addition, although two or three branches form a unit group of a branch electrode, it is also possible to comprise three or more branches of the branch electrode.

Therefore, this invention can be implemented in various changes in the range which does not deviate from the summary.

As described above, the present invention not only causes the cross field to occur between them by changing the design of the counter electrode and the pixel electrode, but also forms a portion of the branch electrode to be inclined so that a horizontal field occurs between the inclined electrodes. In addition, since the afterimage problem can be solved and the intensity of the field on the liquid crystal can be increased, the response speed and the light efficiency can be improved, and in addition, the viewing angle can be achieved by forming two or more domains in the unit pixel. And the transmittance can be improved, as a result, the screen quality of the liquid crystal display device can be improved.

Claims (3)

Transparent insulating substrates; A plurality of gate bus lines and data bus lines cross-arranged to define unit pixels on the substrate; A common bus line arranged in parallel and spaced apart from the gate bus line in the unit pixel; A thin film transistor disposed at an intersection of the gate bus line and the data bus line; A counter electrode disposed in the unit pixel and comprising a first plate electrode and a second branch electrode formed of a transparent conductive film; And A first branch electrode made of a transparent conductive film and disposed under an insulating film on the first plate electrode of the counter electrode, and a second plate electrode made of a transparent conductive film and disposed under an insulating film under a second branch electrode of the counter electrode Including a pixel electrode consisting of, The first plate electrode and the second branch electrode of the counter electrode are electrically contacted with the common bus line, the first branch electrode and the second plate electrode of the pixel electrode are electrically contacted with the thin film transistor, And each of the first branch electrode and the second branch electrode includes a plurality of branches, and a branch disposed at an edge of the branches is inclined with respect to a vertical direction. The cross-field switching mode liquid crystal display device according to claim 1, wherein the inclined branch is formed by removing the insulating film. The cross-field switching mode liquid crystal display of claim 1, wherein the first and second branch electrodes include two or three branches.

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