KR100257862B1 - In-plane switching mode liquid crystal display device - Google Patents

Abstract

PURPOSE: A liquid crystal display device in plane switching mode is to divide a pixel into a plurality of regions to vary the structure of a data electrode from that of a common electrode, thereby preventing a gray inversion and a color shift. CONSTITUTION: The first and second substrates are provided which include a plurality of pixels divided into a plurality of regions. A liquid crystal layer is formed between the first and second substrates. A gate line(101) and a data line(102), respectively are arranged longitudinally and horizontally on the first substrate. A TFT(thin film transistor) is formed on an intersecting point of the gate line and the data line. The first and second electrodes are formed on the first substrate. The first and second electrodes are formed in the pixels so as to switch a size of a liquid crystal molecule in each region of the liquid crystal layer differently from that of a liquid crystal molecule in neighboring region.

Description

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

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a transverse electric field type liquid crystal display device having improved viewing angle characteristics and improved driving characteristics according to a driving environment.

Recently, a large area has been strongly demanded in thin film transistor liquid crystal displays (TFT LCDs), which are widely used in portable televisions and notebook computers. However, the above-described TFT LCDs have a problem in that contrast ratio is changed depending on the viewing angle. In order to solve this problem, various liquid crystal display devices such as a twisted nematic liquid crystal display device equipped with an optical compensation plate and a multi-domain liquid crystal display device have been proposed. It is difficult to solve the problem that the contrast ratio decreases and the color changes depending on the viewing angle.

Another type of liquid crystal display device that is proposed to realize a wide viewing angle is a liquid crystal display device of the in plane switching mode (JAPAN DISPLAY 92 P547, Japanese Patent Laid-Open No. 7-36058, Japanese Patent Laid-Open No. 7-225538, It is proposed to ASIA DISPALY 95 P107.

1 is a view showing a conventional transverse electric field type liquid crystal display device. As shown in the drawing, a conventional transverse electric field type liquid crystal display device is arranged on a substrate in a pixel parallel with the gate wiring 1 and the data wiring 2 and the gate wiring 1 which define a pixel region. The common wiring 3, the thin film transistor arranged at the intersection of the gate wiring 1 and the data wiring 2, and the data electrode 8 arranged in the pixel substantially parallel to the data wiring 2. And a common electrode 9. The thin film transistor includes a gate electrode 5 connected to the gate wiring 1, a semiconductor layer 15 formed on the gate electrode 5, and a data wiring 2 formed on the semiconductor layer 15. It consists of a source electrode 6 and a drain electrode 7 respectively connected to the data electrode 8. The common electrode 9 in the pixel is connected to the common wiring 3 and the data electrode 8 is connected to the drain electrode 7 of the thin film transistor.

In the transverse electric field type liquid crystal display device configured as described above, when a voltage is applied from an external driving circuit, a transverse electric field parallel to the surface of the substrate is applied to the liquid crystal layer so that the liquid crystal molecules in the liquid crystal layer 30 have the transverse electric field described above. It rotates along, thereby controlling the amount of light passing through the liquid crystal layer 30.

However, even in the above-described transverse electric field type liquid crystal display device, since an electric field of the same magnitude is applied to the liquid crystal layer 30 when a voltage is applied, liquid crystal molecules are arranged in one direction. Therefore, not only gray inversion occurs in the viewing angle direction of the long axis direction of the liquid crystal but also color shift occurs. Since the color conversion in the long axis direction and the short axis direction of the liquid crystal occurs differently, a red shift and a blue shift occur in each direction.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and by dividing the pixel into a plurality of regions, the structure of the data electrode and the common electrode of each region is different, thereby preventing the gray inversion by changing the degree of rotation of the liquid crystal molecules in each region. It is an object of the present invention to provide a transverse electric field type liquid crystal display device in which color conversion is prevented.

Another object of the present invention is to provide a transverse electric field type liquid crystal display device in which the voltage region having the maximum transmittance is enlarged so that the driving characteristics are not degraded even when the driving environment is changed.

In order to achieve the above object, a transverse electric field type liquid crystal display device according to the present invention comprises a first substrate and a second substrate including a pixel divided into a plurality of regions, and a gate wiring vertically and horizontally arranged on the first substrate. And a thin film transistor disposed at an intersection point of the data wiring, the gate wiring and the data wiring, a common wiring formed in parallel with the gate wiring in the pixel region, and formed in the pixel region, and having a gap in each region. Data electrodes and common electrodes parallel to each other formed differently from the distance between adjacent regions, a first alignment film coated over the entire first substrate, and a second substrate formed near the gate wiring, data wiring, and common wiring. A light shielding layer for preventing light leakage, a color filter layer formed on the light shielding layer, a second alignment film formed on the color filter layer, the first substrate and the second substrate. It consists of the liquid crystal layer formed in between.

Since the spacing between the common electrode and the data wiring in each region of the pixel is different from the electrode spacing in the adjacent region, when an electric field of the same intensity is applied, the degree of response of the liquid crystal molecules to the above-mentioned electric field is different so that the electric field in each region is different. Degree of rotation is different from the degree of rotation in the adjacent area.

In addition, since the voltage region having the maximum transmittance becomes large, stable display characteristics can be ensured even when the viscosity and dielectric anisotropy of the liquid crystal change with temperature.

1 is a plan view of a conventional transverse electric field type liquid crystal display device.

2 is a plan view of a transverse electric field type liquid crystal display device according to the present invention;

3A is a cross-sectional view taken along the line AA ′ of FIG. 2.

FIG. 3B is a cross-sectional view taken along the line BB ′ of FIG. 2.

4 is a view showing driving of liquid crystal molecules in a transverse electric field type liquid crystal display device according to the present invention;

5 is a graph showing the transmittance of the transverse electric field type liquid crystal display device according to the present invention.

-Explanation of symbols for the main parts of the drawing-

101: gate wiring 102: data wiring

103: common wiring 105: gate electrode

106: source electrode 107: drain electrode

108: data electrode 109: common electrode

110: first substrate 111: second substrate

112: gate insulating film 115: active layer

116: n ⁺ layer 123: alignment layer

128: black mask 130: liquid crystal layer

135, 136: liquid crystal molecules

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

2 is a plan view of a transverse electric field type liquid crystal display device according to the present invention. As shown in the figure, the pixel region defined by the gate wiring 101 and the data wiring 102 is divided into an X region and a Y region. In the actual liquid crystal display device, n x m pixels exist by the n gate wirings 101 and the m data wirings 102, but only one pixel is shown in the drawing for convenience of description. A thin film transistor is formed at the intersection of the gate wiring 101 and the data wiring 102, and the common wiring 103 is arranged at the center of the pixel region. In the drawing, the X area and the Y area of the pixel are divided around the common wiring 103 described above. In the pixel region, the data electrodes 108 are arranged in parallel with the data wirings 102 so that the drain electrodes 107 of the thin film transistors are connected. The common electrodes 109 are arranged in parallel with the data electrodes 108 described above. And is connected to the common wiring 103. A feature of the present invention is that, as shown in the figure, the number of electrodes 108 and 109 in the X region and in the Y region is different. In the X region, two data electrodes 108 are arranged between the three common electrodes 109, and in the Y region, one data electrode 108 is arranged between the two common electrodes 109. Of course, the number of electrodes 108 and 109 as shown in the figure is for convenience of description. In a practical liquid crystal display device, there is no need to limit the number of electrodes 108 and 109 as described above, and in any case, the number of electrodes 108 and 109 in the X region and the Y region is different. In addition, although the pixel is divided into two regions, the electrode structure of each region may be formed differently from the electrode structure of other regions by dividing into three or more regions.

The difference in the number of electrodes in the X and Y regions means the difference in the distance between the data electrode 108 and the common electrode 109. In the figure, the spacing between the electrodes in the X region is smaller than the spacing between the electrodes in the Y region. Therefore, since the electric field is a distance function, when an electric field of the same magnitude is applied between the electrodes 108 and 109, the degree to which the liquid crystal molecules in the intermediate region between the electrodes 108 and 109 react to the electric field described above is different. You lose.

3 (a) and 3 (b) are cross-sectional views taken along line A-A 'and line B-B' of FIG. 2, respectively. That is, FIG. 3A is a cross-sectional view of the X area, and FIG. 3B is a cross-sectional view of the Y area. As shown in FIG. 3A, the thin film transistor includes a gate electrode 105 formed on the first substrate 110, a gate insulating film 112 stacked on the gate electrode 105, and the gate insulating film ( The active layer 115 formed on the 112 and the n ⁺ layer 116 formed on the active layer 115, the source electrode 106 and the drain electrode 107 formed on the n ⁺ layer 116. The gate electrode 105 is formed at the same time as the gate wiring 101 and the common wiring 103. The gate electrode 105 is formed by laminating and etching Mo, Al, Ta, and Al alloys by a sputtering method. An inorganic material, such as SiNx, is deposited on the entire first substrate 110 by CVD (chemical vapor deposition). The active layer 115 and the n ⁺ layer 116 are formed by etching amorphous silicon (a-Si) and n ⁺ a-Si stacked by the CVD method. The data wiring 102, the source electrode 106, the drain electrode 107, and the data electrode 108 are formed by etching a metal thin film of Cr, Ta, Al, Al alloy or the like deposited by the sputtering method.

The common electrode 109 formed in the pixel region is formed of the same material as the gate wiring 101 and the gate electrode 105 on the first substrate 110, and the data electrode 108 is formed of the gate insulating film 112. The source electrode 106, the drain electrode 107, and the data wiring 102 described above are simultaneously formed of the same material. The passivation layer 120 is formed by stacking SiNx, SiOx, or the like on the gate insulating layer 112, the data electrode 108, and the thin film transistor by a CVD method.

The first alignment layer 123a is coated on the common electrode 109 and the passivation layer 120. Although the alignment direction 123a made of polyimide is determined by mechanical rubbing, the alignment film 123a made of photoreactive material such as polyvinylcinnemate (PVCN) -based material or polysiloxane-based material is irradiated with light such as ultraviolet rays. The orientation direction is determined by. In the optical alignment process described above, the alignment direction is determined according to whether the irradiated light is polarized, the polarization direction, and the number of irradiation times. In general, in the case where the above-described polysiloxane-based material or PVCN-based material is used as the alignment film, the alignment direction is determined by irradiating the ultraviolet light once or twice. The method of irradiating light once includes a method of obliquely irradiating unpolarized light with respect to the alignment layer, a method of obliquely irradiating polarized (particularly linearly polarized) light, a method of obliquely irradiating partially polarized light, and the like. In the method of irradiating twice, the two degeneracy alignment directions are determined by inclining or vertically irradiating the polarized light with respect to the alignment layer once, and then irradiating the polarized light again to select a desired direction among the two alignment directions. .

The black substrate 128 and the color filter layer 129, which are light blocking layers, are formed on the second substrate 111. It is also possible to form an overcoat layer on the black mask 128 and the color filter layer 129 to improve surface stability and to improve flatness. The black mask 128 is to prevent light leakage near the gate wiring 101, near the data wiring 102, near the common wiring 103, and near the thin film transistor, and is formed of Cr / CrOx thin film or black resin. do. In the color filter layer 129, R, G, and B layers are repeatedly formed for each pixel. After the second alignment layer 123b made of polyimide or a photoreactive material is coated on the color filter layer 129, the orientation direction is determined by rubbing or irradiation of light. In addition, a liquid crystal is injected in a vacuum state between the first substrate 110 and the second substrate 111 to form the liquid crystal layer 130.

The electrodes 108 and 109 in the Y region shown in Fig. 3B are formed at the same time as the electrodes in the X region. As shown in the figure, the number of data electrodes 108 and common electrodes 109 in the region Y is smaller than the number of electrodes 108, 109 in region X in FIG. Due to the structural difference between the electrodes, when an electric field is applied between the electrodes 108 and 109, the degree to which the liquid crystal molecules respond to the electric field is different.

4 is a view showing driving of liquid crystal molecules in X and Y regions. When the halftone voltage is applied, the liquid crystal molecules 135 in the liquid crystal layer 130 arranged along the alignment direction of the alignment layers 123a and 123b by the transverse electric field generated between the electrodes 108 and 109 along the electric field. Rotate At this time, the intensity of the electric field is the same in the X region and the Y region. However, since the interval between the electrodes 108 and 109 in the X region is smaller than the interval in the Y region, the extent to which the liquid crystal molecules 135 in the intermediate region between the electrodes 108 and 109 react to the electric field described above is X region. Will become larger at. Therefore, as shown in the figure, the liquid crystal molecules in the X region rotate more than the liquid crystal molecules in the Y region in the electric field of the same intensity.

As a result, since the alignment of the liquid crystal molecules 136 in the X region and the alignment of the liquid crystal molecules 136 in the Y region after voltage application are different, the viewing angle characteristics in each region are compensated for each other and the color according to the viewing angle The conversion will also be compensated. In the figure, the solid line shows the liquid crystal molecules 135 when no voltage is applied, and the dotted line shows the liquid crystal molecules 136 when voltage is applied.

5 is a diagram illustrating the transmittance in the X region, the Y region, and the entire pixel region. In the figure, X represents the transmittance of the X region, Y represents the transmittance of the Y region, and (X + Y) / 2 represents the transmittance of the entire pixel. As shown in the figure, the region of the voltage showing the maximum transmittance Tmax in the entire pixel is the region from the maximum transmittance in the X region to the maximum transmittance in the Y region. In general, the liquid crystal changes in viscosity and dielectric anisotropy depending on the driving environment such as temperature. However, in the present invention, since the voltage region having the maximum transmittance (Tmax) is increased as described above, the liquid crystal display operates well.

According to the present invention, since one pixel is divided into a plurality of regions having different electrode structures, the degree of response of the liquid crystal molecules to the transverse electric field in each region is different so that gray inversion and color conversion occur. prevent. In addition, since the voltage region having the maximum transmittance becomes large, it has good driving characteristics even in the change of the driving environment.

Claims (4)

A first substrate and a second substrate including a plurality of pixels divided into a plurality of regions; A liquid crystal layer formed between the first substrate and the second substrate; Gate wiring and data wiring arranged vertically and horizontally on the first substrate; A thin film transistor formed at an intersection point of the gate line and the data line; And a first electrode and a second electrode formed on the first substrate and switching the liquid crystal molecules of each region in the liquid crystal layer to a different size from the liquid crystal molecules of the adjacent region. The transverse electric field liquid crystal display device according to claim 1, wherein the first electrode is a common electrode, and the second electrode is a data electrode. A first substrate and a second substrate including a plurality of pixels divided into a plurality of regions; A liquid crystal layer formed between the first substrate and the second substrate; Gate wiring and data wiring arranged vertically and horizontally on the first substrate; A thin film transistor formed at an intersection point of the gate line and the data line; And a first electrode and a second electrode formed on the first substrate, wherein the gaps in the respective areas are different from the gaps in the adjacent areas. A first substrate and a second substrate including a plurality of pixels divided into a plurality of regions; A liquid crystal layer formed between the first substrate and the second substrate; Gate wiring and data wiring arranged vertically and horizontally on the first substrate; A thin film transistor formed at an intersection point of the gate line and the data line; A transverse electric field liquid crystal display device which is arranged in the pixel and has a different number in each area than an adjacent area, and comprises a first electrode and a second electrode formed on the first substrate.

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