KR100279258B1 - LCD Display - Google Patents

Abstract

The present invention discloses a liquid crystal display device for preventing color fading.

The disclosed liquid crystal display device includes an upper and lower substrates facing each other with a liquid crystal layer interposed therebetween, and gate bus lines and data that are vertically cross-exposed in a matrix form on the lower substrate to define R, G, and B unit pixel spaces. A bus line, a counter electrode formed on the lower substrate in the unit pixel space, a pixel electrode formed on the lower substrate and forming an electric field together with the counter electrode, and horizontally formed on opposite surfaces of the upper and lower substrates A liquid crystal display device including an alignment layer, wherein the alignment directions are different for each unit pixel space, and the alignment directions of the liquid crystals are different when the electric field is formed.

Description

Liquid crystal display

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device for preventing color shift in a liquid crystal display device in in plane switching (hereinafter referred to as IPS) mode. It is about.

The liquid crystal display of the IPS mode is a transverse electric field driving liquid crystal display developed by Hitachi, Japan, in order to compensate for the viewing angle characteristic of the twisted nematic liquid crystal display (TN). (Principle and characteristic of electro-optical behaviour with in-plane switching mode, Asia display 95, p577 ~ 580)

In the IPS liquid crystal display, as shown in FIG. 1, all of the electrodes 2a and 2b for driving the liquid crystal molecules 3a are provided on the lower substrate 1 so that an electric field parallel to the surface of the lower substrate 1 is provided. To be formed.

However, the IPS liquid crystal display as described above has the following problems.

In the IPS liquid crystal display as described above, before the electric field is formed between the electrodes 2a and 2b, the liquid crystal molecules 3a are arranged along the alignment direction A of the alignment layer (not shown) formed on the lower substrate. do. Then, when an electric field is formed between the electrodes 2a and 2b, the liquid crystal molecules 3b are rotated to be parallel (or perpendicular) to the shape of the electric field E. At this time, the liquid crystal molecules 3b are rod-shaped, and since the lengths of the long axis and the short axis are different, a difference in optical anisotropy occurs, and a color change occurs in a predetermined direction.

More specifically, when the screen is viewed in the X direction in the figure, the liquid crystal molecules 2 are shortened so that the screen has a blue color with a shorter wavelength than white.

On the other hand, when the screen is viewed in the Y direction in the figure, the long axis of the liquid crystal molecules 2 is seen, and the yellow color has a longer wavelength than white. For this reason, the image quality of a liquid crystal screen falls. The technique is described in detail in SID'97, pages 929-932.

Accordingly, an object of the present invention is to solve the above-mentioned conventional problems, and to provide a liquid crystal display device for preventing color fading, which is capable of preventing the color shift of a liquid crystal screen and improving image quality deterioration in an IPS liquid crystal display device. do.

1 is a view for explaining a driving principle of a conventional IPS liquid crystal display.

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

3 is a view schematically showing an alignment direction of an alignment layer for each unit pixel according to the present invention.

(Explanation of symbols for the main parts of the drawing)

10: lower substrate 11: gate bus line

12a, 12b, 12c: data bus line 13: counter electrode

14 pixel electrode 20a, 20b, 20c: liquid crystal molecule

In order to achieve the above object of the present invention, the present invention, the upper and lower substrates facing each other with a liquid crystal layer interposed, vertically cross-exposed in a matrix form on the lower substrate, to define the R, G, B unit pixel space A gate bus line and a data bus line, a counter electrode formed on the lower substrate in the unit pixel space, a pixel electrode formed on the lower substrate and forming an electric field together with the counter electrode, and the upper and lower substrates. A liquid crystal display device comprising a horizontal alignment film formed on an opposing surface, wherein the alignment directions of the alignment film are different for each unit pixel space.

In addition, the present invention, the upper and lower substrates facing each other with the liquid crystal layer interposed therebetween, the gate bus line and the data bus line vertically cross-exposed in a matrix form on the lower substrate to define the R, G, B unit pixel space, A counter electrode formed on the lower substrate in the unit pixel space, a pixel electrode formed on the lower substrate and forming an electric field together with the counter electrode, and a horizontal alignment layer formed on opposite surfaces of the upper and lower substrates. A liquid crystal display device, wherein the alignment layer of the R unit pixel space is aligned to have an angle difference of 40 to 50 ° based on an electric field formed between the counter electrode and the pixel electrode, and the alignment layer of the G unit pixel space is a counter electrode and a pixel. It is aligned to have an angle difference of 220 to 230 degrees based on the electric field formed between the electrodes, the alignment layer of the B unit pixel space and the counter electrode It is characterized by being oriented so as to have an angle difference of 130 to 140 ° based on the electric field formed between the pixel electrode.

According to the present invention, in the main pixel consisting of three unit pixels, the direction of orientation of each unit pixel is formed to be different from each other so that the direction in which the liquid crystal molecules are parallel to the electric field when the electric field is applied are different. Accordingly, since the liquid crystal molecules are arranged in a structure in which short axis and long axis are compensated for each other without taking the same direction in a line, optical anisotropy of the liquid crystal molecules is compensated.

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

2 is a plan view of the liquid crystal display according to the present invention.

Referring to FIG. 2, the plurality of gate bus lines 11 and the plurality of data bus lines 12a, 12b, and 12c are cross-exposed in a matrix form on the lower insulating substrate 10 to form unit pixel spaces C1 and C2. , C3). In this case, in order to describe one main pixel as an example, one gate bus line and three data bus lines will be described as an example. The unit pixel space C1 is referred to as an R (red) pixel region, the unit pixel space C2 is referred to as a G (green) pixel region, and the unit pixel space C3 is referred to as a B (blue) pixel region. At this time, as known, the main pixel is a combination of red, green, and blue unit pixels. A gate insulating film (not shown) is interposed between the gate bus line 11 and the data bus lines 12a, 12b, 12c to insulate these two lines. In addition, the gate bus line 11 and the data bus lines 12a, 12b, and 12c are formed of an opaque metal film having excellent conduction characteristics.

A thin film transistor TFT is provided at each intersection of the gate bus line 11 and the data bus lines 12a, 12b, and 12c. The thin film transistor TFT includes a gate bus line 11a, a channel layer (not shown) stacked thereon, an etch stopper E, and a source electrode S overlapping both sides of the etch stopper E. And a drain electrode D. In this case, the drain electrode D is an electrode line extending from the data bus lines 12a, 12b, and 12c, and the source electrode S is an electrode line extending from the pixel electrode to be described later.

The counter electrode 13 is disposed in each of the unit pixel spaces C1, C2, and C3. The counter electrode 13 has a rectangular frame shape and has at least one bar 13a parallel to the data bus lines 12a, 12b, and 12c and which divides the inside of the counter electrode 13 in the longitudinal direction. It includes. Here, the bar 13a extends in parallel with the data bus lines 13a and 13b, and one bar 13a is formed in this embodiment. In the counter electrode 13, any one of the portions 13 parallel to the gate bus line 11, preferably the portion 13b further away from the corresponding gate bus line 11 may be adjacent to the unit pixel ( It is electrically connected to the counter electrode 13b of C1, C2, C3. In addition, the counter electrode 13 is formed of the same material as the gate bus line 11 and is formed on the lower substrate 10 surface together with the gate bus line 11.

The pixel electrode 14 for driving the molecules in the liquid crystal together with the counter electrode 13 is disposed in each of the unit pixel spaces C1, C2, and C3. Here, the pixel electrode 14 is overlapped with a portion 13b parallel to the gate bus line 11 in the counter electrode 13 with a gate insulating film (not shown) interposed therebetween. 14b) and at least one third region 14c connecting the first and second regions 14a and 14b. Since the third region 14c is parallel to the data bus lines 12a, 12b and 12c and is formed to be one more than the number of the bars 13a, the third region 14c in the present embodiment is divided into two. Dog. In addition, the first region 14a and the second region 14b are disposed in parallel with each other, and the third region 14c is disposed on both sides of the bar 13a.

In addition, the storage capacitors are formed in the first and second regions 14a and 14b of the pixel electrode 14 overlapping the counter electrode 13.

On the other hand, the pixel electrode region adjacent to the gate bus line 11 that selects the unit pixel, that is, the second region 14b, is partially drawn toward the thin film transistor TFT to form the source electrode S. FIG.

A lower alignment layer (not shown) for determining an initial state of the liquid crystal molecules, that is, a state before forming an electric field, is formed on the resultant of the lower substrate 10, and although not illustrated in the drawing, the upper alignment layer is also formed on the upper substrate. Is formed. Here, the alignment layer is initially a horizontal alignment layer for allowing the liquid crystal molecules to lie in parallel with the substrate, but the alignment directions are different for each unit pixel C1, C2, and C3.

That is, as illustrated in FIG. 3, the alignment direction r1 of the lower alignment layer of the R pixel region C1 refers to the electric field direction when the horizontal electric field E formed between the counter electrode and the pixel electrode is referred to as 0 °. A predetermined angle θ1 with respect to (E), preferably 40 to 50 degrees, more preferably, is made to be 45 degrees difference. That is, the liquid crystal molecules 20a present in the R pixel region C1 lie parallel to the substrate 10, and the long axes of the liquid crystal molecules 20a are arranged in parallel with the alignment direction r1. In addition, the liquid crystal molecules 20a are lifted up by a predetermined angle toward the 45 ° direction of the electric field.

The orientation direction r2 of the lower alignment film of the G pixel region C2 is such that the angle θ2 is preferably 220 to 230 ° more preferably 225 ° to the electric field direction E. That is, the liquid crystal molecules 20b present in the G pixel region C2 lie parallel to the substrate 10, and the long axes of the liquid crystal molecules 20b are arranged parallel to the alignment direction r2. In addition, the liquid crystal molecules 20b are lifted up by a predetermined angle toward the 225 ° direction of the electric field. Therefore, the liquid crystal molecules 20a and 20b in the R pixel region C1 and the G pixel region C2 are in the same direction, but the direction in which the liquid crystal molecules are lifted up is reversed.

The alignment direction r3 of the lower alignment layer of the B pixel region C3 is formed such that the angle θ3 is different with respect to the electric field direction E, preferably 130 to 140 °, and more preferably 135 °. That is, the liquid crystal molecules 20c present in the B pixel region C3 lie parallel to the substrate 10, and the long axes of the liquid crystal molecules 20c are arranged in parallel with the alignment direction r3. In addition, the liquid crystal molecule 20c is lifted upward by a predetermined angle toward the 135 ° direction with respect to the electric field E. FIG. Therefore, the liquid crystal molecules 20a and 20b present in the R pixel region C1 and the G pixel region C2 are ± 90 °.

As described above, as a method for aligning the unit pixels C1, C2, and C3 in different directions, a known light alignment technique is used. In addition, an upper alignment layer (not shown) of the upper substrate is aligned to have a 180 ° angle difference with the lower alignment layer.

Polarizing plates (not shown) are provided on the rear surfaces of the opposite surfaces of the upper and lower substrates. The polarization axis of the lower substrate side polarizer is parallel to the alignment direction r1 of the R pixel region C1, and the polarization axis of the upper substrate side polarizer crosses the polarization axis of the lower substrate side polarizer.

When a voltage is applied to the counter electrode 13 and the pixel electrode 14 of the liquid crystal display device having such a configuration and the electric field E is formed, the liquid crystal molecules 20a, 20b, and 20c arranged in the above-described alignment state are examples. For example, they are arranged parallel to the electric field. In this case, since the alignment directions r1, r2, and r3 are different for each unit pixel, the directions in which the liquid crystal molecules 20a, 20b, and 20c are twisted in the electric field direction are different.

That is, as shown in the drawing, the liquid crystal molecules 20a of the R pixel region C1 are arranged in parallel with the electric field E since the upwardly lifted portion is twisted in the clockwise direction.

As shown in the figure, the liquid crystal molecules 20b of the G pixel region C2 are also arranged in parallel with the electric field E so that the portion lifted up is twisted in the clockwise direction. At this time, the liquid crystal molecules 20a and 20b of the R pixel region C1 and the G pixel region C2 are arranged to be symmetrical with each other. That is, in the liquid crystal molecules 20a and 20b, the lifted portions are arranged to face each other.

As shown in the figure, the liquid crystal molecules 20c of the B pixel region C3 are arranged in parallel with the electric field E so that the portion lifted up is twisted in the counterclockwise direction.

As a result, since the direction in which the unit pixels are twisted when the electric field is applied is different, optical anisotropy of the liquid crystal molecules is compensated for in the middle layer of the liquid crystal layer. That is, when viewed from the side of the main pixel where three unit pixels are gathered, the liquid crystal molecules of the unit pixel are distorted in different directions, for example, even if the shortening of the liquid crystal molecules is seen in the R pixel region C1, G Alternatively, in the B pixel areas C2 and C3, the long axis of the liquid crystal molecules may be viewed to compensate for this, thereby solving the above-described anisotropy problem. Furthermore, even when the liquid crystal molecules are lifted up in the electric field direction, the portions lifted up are not oriented in the same direction but are arranged symmetrically with each other, thereby improving optical anisotropy of the liquid crystal molecules generated by the structure of the rod-shaped liquid crystal molecules.

The present invention is not limited to the above embodiment.

For example, in the present embodiment, the counter electrode is described as a frame shape including a bar 13a, and the pixel electrode 14 is formed to have the third region 14c on both sides of the bar 13a. Irrespective of the present invention, any of the pixel electrodes and the counter electrodes, which are the basic principles of the IPS structure, are formed in the lower substrate so as to form an electric field parallel to the substrate.

As described above in detail, according to the present invention, in the main pixel consisting of three unit pixels, the alignment directions of the respective unit pixels are aligned so that the alignment directions of the respective unit pixels are different, and when the electric field is applied, the liquid crystal molecules are twisted in parallel to the electric field. The directions are different. Accordingly, since the liquid crystal molecules are arranged symmetrically with each other without taking the same direction in a line, optical anisotropy of the liquid crystal molecules is compensated. Accordingly, color phenomena of the IPS liquid crystal display are prevented.

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

Claims (8)

Upper and lower substrates facing each other with the liquid crystal layer interposed therebetween; A gate bus line and a data bus line vertically cross-exposed in a matrix form on the lower substrate to define R, G, and B unit pixel spaces; A counter electrode formed on the lower substrate in the unit pixel space; A pixel electrode formed on the lower substrate and forming an electric field together with a counter electrode; And a horizontal alignment layer formed on opposite surfaces of the upper and lower substrates. The liquid crystal display of claim 1, wherein the alignment direction is different for each unit pixel space. The lower alignment layer of claim 1, wherein the lower alignment layer of the R unit pixel space is aligned to have an angle difference of 40 to 50 ° based on an electric field formed between the counter electrode and the pixel electrode, and the lower alignment layer of the G unit pixel space is countered. It is oriented so as to have an angle difference of 220 to 230 ° based on the electric field formed between the electrode and the pixel electrode, the lower alignment layer of the B unit pixel space is 130 to 140 ° angle based on the electric field formed between the counter electrode and the pixel electrode The liquid crystal display device which is oriented so as to have a difference. 3. The lower alignment layer of claim 2, wherein the lower alignment layer of the R unit pixel space is aligned to have a 45 ° angle difference based on an electric field formed between the counter electrode and the pixel electrode, and the lower alignment layer of the G unit pixel space is formed of a counter electrode. Orientated to have a 225 ° angle difference with respect to an electric field formed between the pixel electrodes, and the lower alignment layer of the B unit pixel space is aligned to have a 135 ° angle difference based on an electric field formed between the counter electrode and the pixel electrode. A liquid crystal display device characterized by the above-mentioned. The liquid crystal display of claim 3, wherein the direction of the lower alignment layer and the direction of the upper alignment layer have a 180 ° angle difference from each other. The liquid crystal display device of claim 1, wherein the counter electrode is formed for each unit pixel space, and includes at least one bar that divides a rectangular frame and divides the inside of the frame in a longitudinal direction. The display device of claim 5, wherein the pixel electrode is formed for each unit pixel, and connects the first and second regions overlapped with a portion parallel to a gate bus line in the counter electrode, and connects the first and second regions. And at least one third region disposed between the bar and a portion parallel to the data bus line in the counter electrode. Upper and lower substrates facing each other with the liquid crystal layer interposed therebetween; A gate bus line and a data bus line vertically cross-exposed in a matrix form on the lower substrate to define R, G, and B unit pixel spaces; A counter electrode formed on the lower substrate in the unit pixel space; A pixel electrode formed on the lower substrate and forming an electric field together with a counter electrode; A horizontal alignment layer formed on opposite surfaces of the upper and lower substrates; The alignment layer of the R unit pixel space is aligned to have an angle difference of 40 to 50 degrees based on an electric field formed between the counter electrode and the pixel electrode. The alignment layer of the G unit pixel space is aligned to have an angle difference of 220 to 230 ° based on an electric field formed between the counter electrode and the pixel electrode. And the alignment layer of the B unit pixel space is aligned to have an angle difference of 130 to 140 ° based on an electric field formed between the counter electrode and the pixel electrode. The alignment layer of claim 7, wherein the alignment layer of the R unit pixel space is aligned to have a 45 ° angle difference based on an electric field formed between the counter electrode and the pixel electrode, and the alignment layer of the G unit pixel space is a counter electrode and a pixel electrode. And an 225 ° angle difference based on an electric field formed therebetween, and the alignment layer of the B unit pixel space is aligned to have a 135 ° angle difference based on an electric field formed between the counter electrode and the pixel electrode. Liquid crystal display.

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