KR20070023248A - Fringe-field switching liquid crystal display - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display (LCD) using Prince-Field Switching (FFS) mode. In the FFS mode, two layers of transparent electrode structures have a plane shape. When the other structure has a closed "day" shaped slit or finger type electrode structure, reverse twist occurs at the corner of the electrode, which results in a disclination line in which light is not transmitted. This results in a decrease in transmittance and an increase in driving voltage. In the present invention, the slit electrode structure adopts an open form of the “d” -shaped structure, thereby reducing the incidence of the conventional disclination line by half, thereby increasing the transmittance and decreasing the driving voltage. .

LCD display, fringe-field switching, transmittance, reverse twist

Description

Prince-field switching liquid crystal display

1 is a pixel structure and a disclination generation area of a transmissive LCD using a conventional FFS mode.

2 is an LCD side view (A-A 'and B-B') of the conventional FFS mode.

3 is an FFS pixel structure and disclination generation region according to the present invention.

4 is an LCD side view (C-C 'and D-D') of the FFS mode according to the present invention.

5 is a dual domain FFS pixel structure in accordance with the present invention.

6 is an FFS pixel structure in which both layers of the transparent electrode according to the present invention have an inclined " d "

The present invention relates to a high-definition FFS mode LCD pixel structure, and more specifically, to change the conventional closed trapezoidal electrode structure to the open "d" shape structure of the LCD that can increase the transmittance and lower the driving voltage than the conventional structure It is about.

In general, various liquid crystal modes exist in the liquid crystal display. TN (Twisted nematic) liquid crystal mode has good light efficiency but has a disadvantage in that the viewing angle is narrow because liquid crystal molecules occur to one side when voltage is applied. To overcome this, in-plane switching (IPS) mode has been developed. In this mode, since the liquid crystal molecules rotate in one direction parallel to the substrate, the viewing angle is superior to that of TN, but the light efficiency is lowered at the upper portion of the electrode, the driving voltage is high, and color gaze problems exist depending on the viewing angle. The high-opening IPS structure was adopted to improve the transmittance, and the electrode structure was wedge-shaped to improve the color problem. FFS mode has been proposed to remedy various problems with IPS.

In the FFS mode, since the common electrode and the pixel electrode are transparent electrodes, there is a disadvantage that the mask surface increases by one compared with the conventional TN. However, because the liquid crystal molecules are rotated almost parallel to the substrate by the strong fringe electric field in the entire region on the electrode, the wide viewing angle, high transmittance, and low driving voltage can be simultaneously achieved.

Looking at the electrode structure in one FFS pixel in more detail, as shown in Fig. 1, the common electrode is generally patterned in the form of a plane (1), the insulating film is coated (2), and then the pixel electrode (3) is tilted. "In the form of a ruler. In the electrode structure, it can be seen that the electric field direction 4 of the center portion of the pixel is different from the electric field direction 5 of the electrode corner. In the FFS mode, the liquid crystals are initially uniformly arranged in the horizontal direction. In the center of the pixel, the liquid crystals are twisted clockwise by an electric field, while in the corner region of the electrode, the liquid crystals are twisted counterclockwise. This occurs and disclination lines that do not transmit light occur in many corner areas. These disclination lines not only reduce the transmittance of the LCD but also delay the response speed and increase the driving voltage. In addition, the liquid crystal molecules are rotated in one direction when adopting a “day” electrode structure that is inclined in one direction, which causes color fading according to the angle. Improved image quality by rotating in both directions. However, even in such an electrode structure, diclination lines occur in each electrode corner, resulting in deterioration of image quality.

An object of the present invention is to improve the image quality by minimizing the generation area of the disclination line, that is, the problem in the conventional FFS liquid crystal display as described above, the electrode for optimizing the electrode structure to minimize the generation of electric field to generate the disclination line It's about structure.

In order to achieve the object as described above, the present invention proposes a "d" shaped structure in which the slit electrode structure is opened to minimize the generation area of the disclination line and improve image quality. It was.

Example 1

Example 1 is a transmissive LCD using an FFS mode including an inclined " d " electrode structure of two layers of transparent electrodes. On the transparent glass substrate or the plastic substrate, the transparent electrode 1 of the first layer is patterned in a plane shape, and the gate electrode 9 and the insulating film and semiconductor layer 2, the signal line 11 and the source / drain layer 10, and the insulating film A layer, an inclined " d " shaped transparent electrode 12 is formed as shown in FIG. The top plate uses a substrate formed on a glass or plastic substrate with a filter capable of producing red, blue, and green colors to achieve full color. Both substrates are coated with a horizontal liquid crystal alignment film of several thousand micrometers or less and then rubbed in opposite directions. Next, the cell gap is placed between 2 and 6 μm on the upper and lower plates, and the liquid crystal enters the bonded substrate through a dropping method or a vacuum injection method. In this case, when a liquid crystal having a negative dielectric anisotropy is used, the rubbing direction becomes a vertical direction, that is, a signal line electrode direction, and when a liquid crystal having a positive dielectric anisotropy is used, the scanning line electrode direction is a horizontal direction. At this time, the phase delay value of the liquid crystal layer is to have a value of 0.2 ~ 0.5 ㎛ yarn. The polarizing plate having the transmission axis crossed on the upper and lower plates is used, and one of the two axes is aligned with the liquid crystal optical axis.

Such a liquid crystal cell shows a black state before voltage is applied and light begins to be transmitted as voltage is applied. The difference from the conventional structure is that the reverse twist of the liquid crystal occurs in the corner of the electrode when adopting the electrode structure proposed in the present invention, the area where the disclination line (6) occurs to 1/2 of the conventional, resulting in an increase in transmittance. In addition, since collision between molecules is reduced, this leads to an improvement in response speed of the driving voltage drop effect compared with the prior art.

Comparing FIG. 2, which is an electrode side of the related art, to FIG. 4, which is an invention of the invented " d " electrode structure, as shown in FIG. It can be seen that does not match.

In addition, in the present invention, the width 8 of each electrode in the " d " structure shows an optimal transmittance at a value of 12 mu m or less between the electrode and the electrode within 8 mu m.

Further, in the present invention, the thickness of the transparent electrodes is 1500 Å or less, the insulating film between the electrodes is characterized in that the 1000 Å or more.

 Further, in the present invention, the inclination 13 of the "d" shaped structure electrode is characterized by being 1 degree or more and 46 degrees or less.

Example 2

Unlike the first embodiment, the second embodiment of the present invention has an FFS mode in which two layers of transparent electrodes are arranged in a mirror symmetrical arrangement of a "d" ruled electrode structure inclined about the center of the pixel horizontal direction in which the upper layers are inclined. It is a transmissive LCD using.

5 is a cross-sectional view of a pixel structure of an FFS transmissive LCD according to a second embodiment of the present invention. As shown, the transparent electrode 1 of the first layer on the transparent glass substrate or the plastic substrate is patterned in the form of a plane, the gate electrode 9 and the insulating film and semiconductor layer 2, the signal line 11 and the source / drain layer. (10), the transparent electrode 14 of the inclined " d " structure is arranged in a mirror symmetrical form with respect to the center of the pixel horizontal direction as shown in FIG.

Example 3

Example 3 has a structure in which the transparent electrodes of both layers are arranged in an inclined " d " It is a transmissive LCD using FFS mode.

6 is a cross-sectional view of a pixel structure of an FFS transmissive LCD according to a third embodiment of the present invention. As shown in the figure, the upper transparent electrode is arranged as the inclined " d " shaped transparent electrode 12, and the lower transparent electrode is also arranged as the transparent electrode 15 having the same structure. In the same manner as in Example 1, the insulating film and the semiconductor layer 2 exist between the electrodes, and the gate electrode 9, the signal line 11, and the source / drain layer 10 are disposed.

Transmissive or semi-transmissive LCD using the FFS mode electrode structure according to the present invention has the effect that the transmittance is improved, the driving voltage is lowered and the response speed is faster than the conventional FFS mode LCD. This is a technique that allows more precise control of the liquid crystal director while using the conventional process, and will greatly contribute to image quality improvement while maintaining the cost as it is.

Claims (3)

Using FFS mode In the transparent electrode structure of the two layers of the thin film transistor, Patterning the transparent electrode of the first layer in a plane form on the transparent glass substrate or the plastic substrate; The transparent electrode of the second layer was formed in the form of an inclined " Coating a horizontal liquid crystal alignment film on the two substrates at several thousand micrometers or less and then rubbing in opposite directions; The cell gap between the upper and lower plates is between 2 and 6 μm and the liquid crystal enters the bonded substrate through a dropping method or a vacuum injection method; At this time, the phase delay value of the liquid crystal layer is to have a value between 0.2 ~ 0.5 ㎛; Fringe-field switching liquid crystal display device using a polarizing plate whose transmission axis is crossed on the upper and lower sides, and one of the two axes coincides with the liquid crystal optical axis. The method according to claim 1, wherein the width of each electrode in the letter structure is within 8 μm and the distance between the electrode and the electrode has a value of 12 μm or less; The thickness of the transparent electrodes is 2000 Å or less, and the insulating film between the electrodes has a value of 1000 Å or more; Fringe-field switching liquid crystal display device characterized in that the inclination of the "d" structure electrode is 1 degree or more and 46 degrees or less.       The method of claim 1, wherein the first layer is patterned in the shape of an inclined " d " Fringe-field switching liquid crystal display device in which the transparent electrode of the second layer is also patterned in the shape of an inclined “d” electrode with an insulating film interposed therebetween.

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