KR20040022937A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: A liquid crystal display is provided to improve the texture of the liquid crystal display. CONSTITUTION: A liquid crystal display includes liquid crystal cells(R,G,B) for expressing red, green and blue, and storage capacitors. At least one of the polarities of the liquid crystal cells is different from the other polarities. The capacitance values of the storage capacitors are decided on the basis of the polarities of the liquid crystal cells. The polarity of the liquid crystal cell that expresses green is opposite to the polarity of the liquid crystal cells that represent red and blue. The capacitance value of the storage capacitor of the liquid crystal that expresses green is smaller than the capacitance values of the storage capacitors of the liquid crystal cells that represent red and blue. The storage capacitors are composed of a storage line and a pixel electrode(38) that is superposed on the storage line, having an insulating layer formed between the storage line and the pixel electrode.

Description

Liquid crystal display device {LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that can improve the image quality.

Conventional liquid crystal display devices display an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display device includes a liquid crystal panel in which liquid crystal cells are arranged in a matrix and a driving circuit for driving the liquid crystal panel.

In fact, the liquid crystal display device has an electrode arrangement structure of a thin film transistor substrate which determines the shape of a liquid crystal cell in a liquid crystal panel in which gate lines GL1, GL2,..., And data lines DL1, DL2,. In detail, as shown in FIGS. 1 and 2. The pixel electrode 8 is provided in the cell region between the gate lines GL1, GL2,..., And the data lines DL1, DL2,. The pixel electrode 8 is connected to any one of the data lines DL1, DL2, ... via the source and drain electrodes 4, 6 of the thin film transistor 12 (hereinafter, referred to as TFT) which is a switch element. Will be connected to one. The gate electrode 2 of the TFT 12 is connected to any one of the gate lines GL1, GL2, ..., which causes the pixel voltage signal to be applied to the pixel electrodes 8 for each line. The TFT 12 causes the pixel voltage supplied to the data lines DL1, DL2, ... to be charged in the pixel electrode 8 in response to the gate high voltage Vgh supplied to the gate lines GL1, GL2,... do. The liquid crystal cells are driven by an electric field applied to the liquid crystal between the pixel electrode 8 and the common electrode (not shown) according to the pixel voltage supplied to the corresponding pixel electrode 8 to adjust the light transmittance. Will be displayed. In this case, the liquid crystal cells are corresponding pixels from the data lines DL1, DL2, ... when the TFT 12 is turned on by the gate high voltage Vgh which is sequentially supplied to the gate lines GL1, GL2, .... The charging voltage is maintained to maintain the charging voltage until the TFT 12 is turned on again.

As shown in FIG. 1, the pixel voltage charged in the liquid crystal cell of the n-th gate line is formed by the storage capacitor Cst formed by overlapping the pixel electrode 8 and the previous gate line GLn-1. As shown in FIG. 2, the pixel electrode 8 is held by the storage capacitor Cst formed by overlapping the corresponding pixel electrode 8 with the storage line SL corresponding thereto.

For each frame, the gate high voltage Vgh is applied only to the gate lines GL1, GL2, ... for each frame only during one horizontal period 1H, in which the pixel voltage is applied to the pixel electrode 8. Is supplied and the gate low voltage Vgl is supplied in the remaining period. The storage capacitor Cst maintains the voltage charged at the current pixel electrode 8 by the gate low voltage Vgl supplied to the previous gate line GL1 or is applied to the storage voltage supplied to the storage line SL. As a result, the voltage charged in the pixel electrode 8 at the present stage is maintained.

In the liquid crystal display device, three driving methods such as a frame inversion method, a line inversion method, and a dot inversion method are mainly used to drive the liquid crystal cells. have.

The frame inversion driving method inverts the polarity of the pixel voltage signal supplied to the liquid crystal cells whenever the frame is changed. In the line inversion driving method, polarities of pixel voltage signals supplied to liquid crystal cells are reversed according to a line on the liquid crystal panel, that is, a gate line. In addition, the dot inversion method enables the pixel voltage signals having opposite polarities to be supplied to adjacent liquid crystal cells, and the polarities of the pixel voltage signals supplied to the liquid crystal cells are inverted for each frame.

In the dot inversion driving method, positive and negative pixel voltages are repeatedly applied to the liquid crystal cell in the gate line direction of the liquid crystal panel, and the colors are B (black), W (white), B, W .. ... or W, B, W, B .... is displayed repeatedly. In this case, a poor image quality such as Greenish occurs in a dot pattern such as a Windows Shutdown pattern.

This will be described in detail with reference to FIGS. 3 to 5 as follows.

In the liquid crystal display having the front gate-type storage capacitor shown in FIG. 1, the pixel voltage is gated through the storage capacitor Cst and the first parasitic capacitor Cgd formed between the gate line GL and the data line DL. A liquid crystal display device having a common storage capacitor introduced into the line GL and having a common storage capacitor shown in FIG. 2 includes a storage capacitor Cst and a second parasitic capacitor Csd formed between the data line DL and the storage line SL. The data voltage flows into the storage line SL. The storage voltage becomes unstable due to the pixel voltage flowing into the storage line SL and the gate line GL. Due to the unstable storage voltage, the average value of the pixel voltage actually charged in the liquid crystal cell also becomes unstable.

For example, when the storage voltage level is moved downward, the positive and negative pixel voltages charged in the liquid crystal cell are also moved downward by ΔV as shown in FIG. 3. At this time, the pixel voltage charged in the liquid crystal cell is changed in proportion to the amount of change in the storage voltage level.

Accordingly, the positive and negative pixel voltages symmetrical with respect to the conventional common voltage are asymmetrically formed with respect to the common voltage. That is, the voltage difference between the unstable negative pixel voltage -Vp 'and the common voltage Vcom is much larger than the voltage difference between the unstable positive pixel voltage + Vp' and the common voltage Vcom. Accordingly, the liquid crystal cell to which the unstable positive pixel voltage (+ VP ') is applied is relatively dark as shown in FIG. 4 while the liquid crystal cell to which the negative pixel voltage (-Vp') is applied is relatively bright. It becomes visible.

As a result, the luminance of the liquid crystal cells R and B for implementing red and blue colors in the dot pattern of the entire screen is reduced, while the luminance of the liquid crystal cell G for implementing green with different polarities is increased. Accordingly, as shown in FIG. 5, a greenish phenomenon occurs in which the entire screen is close to green. This greenish phenomenon occurs in proportion to the capacity value of the storage capacitor Cst.

In order to eliminate the greenish phenomenon, when the capacity value of the storage capacitor is reduced, flicker may occur on the screen, thereby degrading image quality.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of improving image quality.

1 is a plan view showing a liquid crystal display device having a conventional shear gate type storage capacitor.

2 is a plan view illustrating a liquid crystal display device having a conventional common storage capacitor.

3 is a waveform diagram illustrating pixel voltages unstable by the storage capacitors illustrated in FIGS. 1 and 2.

4 is a diagram illustrating a luminance difference between liquid crystal cells due to the pixel voltage shown in FIG.

5 is a view showing a greenish phenomenon appearing in a conventional specific pattern.

6 is a plan view illustrating a liquid crystal display device having a front gate type storage capacitor according to a first embodiment of the present invention.

7A to 7C are cross-sectional views illustrating storage capacitors of the liquid crystal cells illustrated in FIG. 6.

8 is a plan view illustrating a liquid crystal display device having a common storage capacitor according to a second embodiment of the present invention.

9A and 9B are cross-sectional views illustrating storage capacitors of the liquid crystal cells illustrated in FIG. 8.

<Explanation of symbols for the main parts of the drawings>

2,32 gate electrode 4,34 source electrode

6,36 drain electrode 8,38 pixel electrode

10,40r, 40g, 40b: storage electrode 12,42: thin film transistor

31 substrate 50 gate insulating film

52: protective film

In order to achieve the above objects, the liquid crystal display device according to the present invention is a liquid crystal cell that implements red, green, and blue with at least one polarity differently formed, and a storage capacitor whose capacitance is determined corresponding to the polarity of the liquid crystal cell. Characterized in having a.

The polarity of the liquid crystal cell implementing green is opposite to that of the liquid crystal cell implementing red and blue, and the polarity of the liquid crystal cell is inverted in units of two data lines of the liquid crystal cell.

The capacitance value of the storage capacitor of the liquid crystal cell embodying the green color may be smaller than that of the liquid crystal cell embodying the red color and the blue color.

The storage capacitors of the liquid crystal cells are formed of a storage electrode and a pixel electrode overlapping the storage line with an insulating layer interposed therebetween.

The area of the storage line overlapping the pixel electrode of the liquid crystal cell implementing green is relatively smaller than that of the liquid crystal cell implementing red and blue.

The thickness of the insulating layer formed between the pixel electrode and the storage line of the liquid crystal cell implementing green is relatively thicker than that of the liquid crystal cell implementing red and blue.

The storage capacitor of the liquid crystal cells may be formed of a pixel electrode overlapping the gate line with a gate line and an insulating layer therebetween.

The area of the gate line overlapping with the pixel electrode of the liquid crystal cell implementing green is relatively smaller than that of the liquid crystal cell implementing red and blue.

The thickness of the insulating layer formed between the pixel electrode and the gate line of the liquid crystal cell implementing green is relatively thicker than that of the liquid crystal cell implementing red and blue.

The storage capacitors of the liquid crystal cells are formed of a storage electrode overlapping the gate line with a gate line and an insulating layer therebetween.

The area of the gate line overlapping the storage electrode of the liquid crystal cell implementing green is relatively smaller than that of the liquid crystal cell implementing red and blue.

The area of the storage electrode overlapping the gate line of the liquid crystal cell implementing green is relatively smaller than that of the liquid crystal cell implementing red and blue.

The thickness of the insulating layer formed between the gate line and the storage electrode of the liquid crystal cell implementing green is relatively thicker than that of the liquid crystal cell implementing red and blue.

The storage capacitor whose capacitance varies according to the polarity of the liquid crystal cell is characterized in that it is applied to a specific pattern, such as a Windows Shutdown pattern.

Other objects and features of the present invention in addition to the above object will become apparent from the description of the accompanying examples.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 6 to 9B.

Referring to FIG. 6, the liquid crystal display according to the first exemplary embodiment of the present invention includes a liquid crystal cell implementing red, green, and blue having different capacitance values of at least one storage capacitor. In particular, the capacitance GCst of the storage capacitor of the liquid crystal cell implementing green (G) is smaller than that of the liquid crystal cells implementing red (R) and blue (B).

In the liquid crystal display shown in FIG. 6, a pixel electrode 38 is provided in a cell region between the gate lines GL1, GL2,..., And the data lines DL1, DL2,. The pixel electrode 38 is connected to any one of the data lines DL1, DL2,... Through the source and drain electrodes 34 and 36 of the thin film transistor (hereinafter, referred to as TFT) 42 as a switch element. Will be connected to one. The gate electrode 32 of the TFT 42 is connected to any one of the gate lines GL1, GL2, ..., which causes the pixel voltage signal to be applied to the pixel electrodes 38 for one line. The TFT 42 causes the pixel voltage supplied to the data lines DL1, DL2, ... to be charged in the pixel electrode 38 in response to the gate high voltage Vgh supplied to the gate lines GL1, GL2, .... do. The liquid crystal cells are driven by an electric field applied to the liquid crystal between the pixel electrode 38 and the common electrode (not shown) according to the pixel voltage supplied to the corresponding pixel electrode 38 to adjust the light transmittance. Will be displayed. In this case, the liquid crystal cells are the corresponding pixels from the data lines DL1, DL2, ... when the TFT 42 is turned on by the gate high voltage Vgh which is sequentially supplied to the gate lines GL1, GL2, .... The charging voltage is maintained to maintain the charging voltage until the TFT 42 is turned on again.

The pixel voltage charged in the liquid crystal cell of any n-th gate line is maintained by the storage capacitor Cst formed by overlapping the storage electrode 40 with the previous gate line GLn-1.

The gate high voltage Vgh is generally applied to each of the gate lines GL1, GL2, ... for each frame only during the time when the corresponding gate line is driven, that is, during one horizontal period 1H in which the pixel voltage is applied to the pixel electrode 38. Is supplied and the gate low voltage Vgl is supplied in the remaining period. The storage capacitor Cst maintains the voltage charged in the current pixel electrode 38 by the gate low voltage Vgl supplied to the previous gate line.

In such a liquid crystal display, in order to drive the liquid crystal cells, the pixel voltage signals having opposite polarities are supplied to adjacent liquid crystal cells and the polarity of the pixel voltage signals supplied to the liquid crystal cells in each frame is inverted. Driven in a manner. In particular, the liquid crystal display device has two dots in which the polarities of the pixel voltage signals are inverted in units of two data lines, and the polarities of the pixel voltages of the data lines DL1, DL2, ... are inverted in units of horizontal periods. It is driven in an inversion manner.

That is, the liquid crystal cell implementing green (G) is charged with a pixel voltage having a different polarity than the liquid crystal cell implementing red (R) and blue (B). That is, a liquid crystal cell implementing green (G) charges a negative pixel voltage, while a liquid crystal cell implementing red (R) and blue (B) charges a positive pixel voltage. Alternatively, a liquid crystal cell implementing green (G) charges a positive pixel voltage, while a liquid crystal cell implementing red (R) and blue (B) charges a negative pixel voltage.

The capacitance GCst of the storage capacitor of the liquid crystal cell implementing green (G) with different polarities is a liquid crystal cell implementing red (R) and blue (B) in a dot pattern such as a Windows Shutdown pattern. It is formed relatively smaller than that of (RCst, BCst).

To this end, in the liquid crystal cell implementing green (G), the overlapping area between the previous gate line GL1 and the storage electrode 40 which is proportional to the capacitance value of the storage capacitor is formed to be relatively small. That is, the area of the storage electrode 40g of the liquid crystal cell implementing green G is relatively small as shown in FIG. 7A, or the line width of the previous gate line GL1 is shown in FIG. 7B. It is formed relatively small.

Alternatively, the distance between the previous gate line GL1 and the storage electrode 40 which is inversely proportional to the capacitance value of the storage capacitor in the liquid crystal cell implementing green G is relatively far as shown in FIG. 7C. To this end, the thickness of the insulating film 50 formed between the previous gate line GL1 and the storage electrode 40g of the liquid crystal cell implementing green (G) is a liquid crystal cell implementing red (R) and blue (B). Is formed relatively thicker than that of 50.

As such, the capacitance GCst of the storage capacitor of the liquid crystal cell implementing green (G) is made relatively small, so that the variation range of the storage voltage level is smaller than that of the liquid crystal cell implementing red (R) and blue (B). Relatively small As the variation in the storage voltage level that implements such green becomes smaller, the variation in the green luminance decreases. Accordingly, the greenish phenomenon is reduced.

In addition, the front gate type storage capacitor may be formed by overlapping the pixel electrode 38 and the previous gate line GL1. By using the front gate type storage capacitor, the capacitance GCst of the storage capacitor of the liquid crystal cell implementing green G is relatively small. That is, the overlapping area between the gate line GL1 and the pixel electrode 38 of the liquid crystal cell of green color is reduced or the distance between the gate line GL1 and the pixel electrode 38 is relatively far. .

8 is a diagram illustrating a liquid crystal display device according to a second embodiment of the present invention.

Referring to FIG. 8, the liquid crystal display according to the second exemplary embodiment of the present invention has the same components except that the storage capacitor is formed of the storage line and the pixel electrode as compared to the liquid crystal display of FIG. 6. do.

The pixel voltage charged in the liquid crystal cell of any n-th gate line shown in FIG. 8 is maintained by the storage capacitor Cst formed by overlapping the storage line SL1 and the pixel electrode 38.

The gate high voltage Vgh is generally applied to each of the gate lines GL1, GL2, ... for each frame only during the time when the corresponding gate line is driven, that is, during one horizontal period 1H in which the pixel voltage is applied to the pixel electrode 38. Is supplied and the gate low voltage Vgl is supplied in the remaining period. The storage capacitor 40 maintains the voltage charged in the pixel electrode at the present time by the storage voltage supplied to the storage line SL.

In such a liquid crystal display, in order to drive the liquid crystal cells, the pixel voltage signals having opposite polarities are supplied to adjacent liquid crystal cells and the polarity of the pixel voltage signals supplied to the liquid crystal cells in each frame is inverted. Driven in a manner. In particular, the liquid crystal display device has two dots in which the polarities of the pixel voltage signals are inverted in units of two data lines, and the polarities of the pixel voltages of the data lines DL1, DL2, ... are inverted in units of horizontal periods. It is driven in an inversion manner.

That is, the liquid crystal cell implementing green (G) charges pixel voltages of different polarities from the liquid crystal cells implementing red (R) and blue (B). That is, a liquid crystal cell implementing green (G) charges a negative pixel voltage, while a liquid crystal cell implementing red (R) and blue (B) charges a positive pixel voltage. Alternatively, a liquid crystal cell implementing green (G) charges a positive pixel voltage, while a liquid crystal cell implementing red (R) and blue (B) charges a negative pixel voltage.

The capacitance GCst of the storage capacitor of the liquid crystal cell implementing green (G) with different polarities is a liquid crystal cell implementing red (R) and blue (B) in a dot pattern such as a Windows Shutdown pattern. It is formed smaller than that of (RCst, BCst).

To this end, the overlap area between the corresponding storage line SL2 and the pixel electrode 38 which is proportional to the capacitance value of the storage capacitor is formed in the liquid crystal cell implementing green (G). That is, the line width of the corresponding storage line SL2 of the liquid crystal cell implementing green G is relatively small as shown in FIG. 8A.

Alternatively, the distance between the corresponding storage line SL2 and the pixel electrode 38 which is inversely proportional to the capacitance value of the storage capacitor in the liquid crystal cell implementing green G may be relatively far as shown in FIG. 8B. To this end, a gate insulating film 50 and a protective layer 52 are formed between the corresponding storage line SL2 and the pixel electrode 38 of the liquid crystal cell implementing green (G), while red (R) and blue ( Only the gate insulating layer 50 is formed between the storage line SL2 and the pixel electrode 38 of the liquid crystal cell implementing B).

As described above, since the capacitance value of the storage capacitor of the liquid crystal cell implementing green (G) is made relatively small, the variation range of the storage voltage level is relatively smaller than that of the liquid crystal cell implementing red (R) and blue (B). . Since the variation in the storage voltage level that implements the green (G) is small, the variation in the green luminance is reduced. Accordingly, the greenish phenomenon can be reduced.

In addition, the storage capacitor of the liquid crystal cell implementing red (R), green (G) and blue (B) may be formed differently.

As described above, the liquid crystal display according to the present invention forms a capacitance value of the storage capacitor of the liquid crystal cell different in polarity from the adjacent liquid crystal cell in a specific pattern different from that of the adjacent liquid crystal cell. That is, the capacitance value of the storage capacitors of liquid crystal cells having different polarities can be formed to be relatively small, thereby reducing the change in luminance of the liquid crystal cells. Accordingly, it is possible to prevent the entire screen from being seen in the color of the liquid crystal cell having different polarities.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (14)

Liquid crystal cells that implement red, green, and blue colors in which at least one polarity is formed differently; And a storage capacitor whose capacitance is determined corresponding to the polarity of the liquid crystal cell. The method of claim 1, The polarity of the liquid crystal cell embodying the green is opposite to the polarity of the liquid crystal cell embodying the red and blue colors, And the polarity of the liquid crystal cell is inverted in units of two data lines of the liquid crystal cell. The method of claim 2, And a capacitance value of the storage capacitor of the liquid crystal cell implementing the green color is smaller than that of the liquid crystal cell implementing the red and blue colors. The method of claim 1, And the storage capacitor of the liquid crystal cells is formed of a storage electrode and a pixel electrode overlapping the storage line with an insulating layer therebetween. The method of claim 4, wherein And an area of the storage line overlapping the pixel electrode of the liquid crystal cell implementing the green color is smaller than that of the liquid crystal cell implementing the red and blue colors. The method of claim 4, wherein The thickness of the insulating layer formed between the pixel electrode and the storage line of the liquid crystal cell for implementing the green is relatively thicker than that of the liquid crystal cell for implementing the red and blue. The method of claim 1, And the storage capacitor of the liquid crystal cells is formed of a gate electrode and a pixel electrode overlapping the gate line with an insulating layer therebetween. The method of claim 7, wherein And an area of the gate line overlapping the pixel electrode of the liquid crystal cell embodying the green color is smaller than that of the liquid crystal cell embodying the red and blue colors. The method of claim 7, wherein The thickness of the insulating layer formed between the pixel electrode and the gate line of the liquid crystal cell for implementing the green is relatively thicker than that of the liquid crystal cell for implementing the red and blue. The method of claim 1, And the storage capacitor of the liquid crystal cells is formed of a gate electrode and a storage electrode overlapping the gate line with an insulating layer therebetween. The method of claim 10, The area of the gate line overlapping the storage electrode of the liquid crystal cell implementing the green is relatively smaller than that of the liquid crystal cell implementing the red and blue. The method of claim 10, The area of the storage electrode overlapping the gate line of the liquid crystal cell for implementing the green is relatively smaller than that of the liquid crystal cell for implementing the red and blue. The method of claim 10, The thickness of the insulating layer formed between the gate line and the storage electrode of the liquid crystal cell for implementing the green is relatively thicker than that of the liquid crystal cell for implementing the red and blue. The method of claim 1, The storage capacitor of which the capacitance varies according to the polarity of the liquid crystal cell is applied to a Windows Shutdown pattern.