KR101340998B1 - Liquid crystal display device and driving method thereof - Google Patents

Abstract

The present invention relates to a liquid crystal display device capable of adjusting a storage capacitor and a driving method thereof.

The liquid crystal display device includes a liquid crystal display panel including a liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, and a storage capacitor for maintaining a voltage of the liquid crystal cell; A common voltage supply unit supplying a common voltage to the common electrode; And a storage voltage supply unit supplying a storage voltage to the storage electrode of the storage capacitor, wherein the storage capacitor includes: the pixel electrode, the storage electrode facing the pixel electrode, and a semiconductor formed between the pixel electrode and the storage electrode. And storage layers formed to be separated at intersections with the common electrode, wherein the storage electrodes formed to be separated are connected to each other through auxiliary storage electrodes formed together with source and drain electrodes of the thin film transistor. It features.

Description

Liquid crystal display and its driving method {LIQUID CRYSTAL DISPLAY DEVICE AND DRIVING METHOD THEREOF}

1 is a view schematically showing a conventional liquid crystal display device.

2 is a view showing waveforms of data voltages in a conventional liquid crystal display.

3 is a diagram illustrating the size of a storage capacitor Cst according to a conventional storage voltage Vst.

4 is a diagram illustrating a liquid crystal display according to a first embodiment of the present invention.

5 is a plan view illustrating a portion of a thin film transistor array substrate in a liquid crystal display according to a first exemplary embodiment of the present invention.

FIG. 6 is a cross-sectional view taken along lines II ′ and II-II ′ of FIG. 5;

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

8 is a plan view illustrating a portion of a thin film transistor array substrate in a liquid crystal display according to a second exemplary embodiment of the present invention.

FIG. 9 is a cross-sectional view taken along line III-III ′ and IV-IV ′ of FIG. 8;

10 is a cross-sectional view illustrating a storage capacitor on which a semiconductor layer is formed.

11 is a view showing the size of the storage capacitor (Cst) according to the storage voltage (Vst) in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

50, 70: liquid crystal display panels 52, 72: data driving circuit

54, 74: gate driving circuit 56, 76: common voltage supply

58, 78: storage voltage supply unit 102, 202: gate line

104, 204: data lines 106, 206: TFT

108, 208: gate electrode 110, 210: drain electrode

112, 212: source electrodes 113, 213, 119, 219: contact holes

114, 214: pixel electrodes 116, 216: common electrode

118, 218, 226: storage electrode 120, 220: auxiliary storage electrode

122, 222, 228: storage capacitors

144 and 244 substrate 146 and 246 gate insulating film

148, 248: active layer 150, 250: ohmic contact layer

151: semiconductor layers 152, 252: protective film

The present invention relates to a liquid crystal display device capable of adjusting a storage capacitor and a driving method thereof.

Liquid crystal displays are widely used in display devices of office equipment, monitors of computers, and even large-screen televisions with the recent development of process and driving technologies. Such a liquid crystal display device displays an image by adjusting the light transmittance of the liquid crystal using an electric field.

1 is a view schematically showing a conventional liquid crystal display device.

Referring to FIG. 1, a conventional liquid crystal display includes a data line DL and a gate line GL that cross each other, and a liquid crystal cell formed by the intersection of the data line DL and the gate line GL. In the liquid crystal cell, a thin film transistor (TFT), a pixel electrode (Ep), a liquid crystal layer, a common electrode (Ec), a storage electrode (Est) is formed.

The gate electrode of the TFT is connected to the gate line GL, the drain electrode is connected to the data line DL, and the source electrode is connected to the pixel electrode Ep. The TFT supplies the liquid crystal voltage supplied through the data line DL to the pixel electrode Ep in response to the scan pulse of the gate line GL.

The common electrode Ec is formed to face the pixel electrode Ep, and a liquid crystal layer is disposed between the common electrode Ec and the pixel electrode Ep to form a liquid crystal capacitor Clc. The liquid crystal layer is driven through an electric field formed by the voltage difference between the common electrode Ec and the pixel electrode Ep to adjust the light transmittance.

The storage capacitor Cst is formed between the pixel electrode Ep and the storage electrode Est to maintain a constant data voltage charged in the liquid crystal cell.

The common electrode Ec and the storage capacitor Cst are supplied with the common voltage Vcom through a common voltage supply unit (not shown).

Parasitic capacitors Cgd and Cgs are generated between the gate electrode and the drain electrode of the TFT, and between the gate electrode and the source electrode.

The conventional liquid crystal display further includes a gate drive integrated circuit supplying a scan pulse to the gate line GL, and a data drive integrated circuit supplying a data voltage to the data line DL.

The liquid crystal display is driven in an inversion method to periodically invert the polarity of the data voltage as shown in FIG. 2 in order to reduce deterioration and afterimage of the liquid crystal.

Referring to FIG. 2, after a positive data voltage is supplied to a specific liquid crystal cell during a scan period (1 horizontal period) of an nth frame period Fn, a scan period of an n + 1th frame period Fn + 1 is performed. The negative data voltage is supplied to the same liquid crystal cell. During the nth frame period Fn, the liquid crystal cell is charged by the positive data voltage output from the data drive IC (D-IC), and then ΔVp by the parasitic capacitor of the TFT described above. The positive voltage maintains a low positive voltage (Vp (+)). On the other hand, during the n + 1 th frame period (Fn + 1), the voltage of the liquid crystal cell is charged by the negative data voltage output from the D-IC, and then the absolute voltage is increased by ΔVp by the parasitic capacitor of the TFT. Maintains high negative voltage Vp (-). Therefore, even when the data voltage of the same gray level is supplied to the liquid crystal cell, the luminance of the liquid crystal cell is higher at the negative data voltage than the positive data voltage.

The positive voltage Vp (+) of the liquid crystal cell is a difference voltage between the positive data voltage Vdata (+) and the common voltage Vcom, that is, Vp (+) = | Vdata (+)-Vcom |. The negative voltage Vp (−) of the liquid crystal cell is a difference voltage between the negative data voltage Vdata (−) and the common voltage Vcom, that is, Vp (−) = │Vdata (−) − Vcom│.

When the polarity of the data voltage is inverted every frame period even in the data of the same gray level, the brightness fluctuates in units of frame periods, and as a result, the observer feels flickering of the screen periodically. In addition, when the voltage charged in the liquid crystal cell is changed according to the polarity of the data voltage, afterimages appear on the screen due to the asymmetry of the data.

In order to set Vp (+) and Vp (-) equally, there is a method of adjusting the magnitude of the common voltage Vcom. However, in this case, since the liquid crystal capacitor Clc is different for each liquid crystal cell, ΔVp can be completely compensated. none.

Such ΔVp causes quality deterioration such as afterimages not only in the data of the same gradation but also in the data of other gradations. In particular, even gradations such as white and black have a greater adverse effect on image quality in large data.

The following equation calculates the magnitude of ΔVp, where ΔVg is the absolute value of the difference between the high and low voltages of the scan pulse.

Referring to Equation 1, it can be seen that ΔVp is inversely proportional to the storage capacitor Cst and the liquid crystal capacitor Clc. That is, the larger the size of the storage capacitor Cst or the liquid crystal capacitor Clc, the smaller the ΔVp, and the smaller the size of the storage capacitor Cst or the liquid crystal capacitor Clc, the larger the ΔVp.

In the conventional LCD, since the storage capacitor Cst and the liquid crystal capacitor Clc are supplied with the same common voltage Vcom as shown in FIG. 1, the liquid crystal capacitor Clc has the same size as the storage capacitor Cst. Becomes Therefore, since the storage capacitor Cst is small in the gray scale having a small liquid crystal capacitor Clc, and the storage capacitor Cst is large in the gray scale having a large liquid crystal capacitor Clc, a larger difference occurs in ΔVp when the gray scale is different.

FIG. 3 is a diagram illustrating the size of the storage capacitor Cst according to the storage voltage Vst in the liquid crystal display of the normally black mode. The storage voltage Vst means the common voltage Vcom. Point A is the point where the positive data voltage is supplied to the white gradation, point B is the point where the negative data voltage is supplied to the white gradation, and point C is the point where the positive data voltage is supplied to the black gradation. Denotes a point at which a negative data voltage for black gradation is supplied.

Referring to FIG. 3, it can be seen that a difference occurs in the storage capacitor Cst when the positive data voltage is supplied and the negative data voltage is supplied. In addition, the average storage capacitor Cst when the positive data voltage is supplied in the black gradation and the negative data voltage when the positive data voltage is supplied in the white gradation is supplied when the average storage capacitor Cst is supplied in the black gradation. Is smaller than the average storage capacitor (Cst). In the normally black mode, the liquid crystal capacitor Clc is larger in the white gray because the data voltage is larger in the white gray than in the black gray. That is, the sum of the average storage capacitor Cst and the liquid crystal capacitor Clc in the black gradation is smaller than the sum of the average storage capacitor Cst and the liquid crystal capacitor Clc in the white gradation, and thus a difference occurs in the magnitude of ΔVp. As described above, such difference in ΔVp size also causes deterioration in image quality in other grayscales.

Referring to Equation 1, even when the size of the liquid crystal capacitor Clc is different, when the size of the storage capacitor Cst is compensated by the difference of the liquid crystal capacitor Clc, it can be seen that the size of ΔVp is uniformly adjusted.

However, the liquid crystal display according to the related art has a problem in that the storage capacitor Cst cannot be adjusted differently from the liquid crystal capacitor Clc by receiving the same common voltage Vcom between the liquid crystal capacitor Clc and the storage capacitor Cst.

Accordingly, an object of the present invention is to provide a liquid crystal display and a driving method thereof capable of adjusting a storage capacitor.

In order to achieve the above object, a liquid crystal display according to a first embodiment of the present invention is a liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, and the voltage of the liquid crystal cell A liquid crystal display panel including a storage capacitor for maintaining a temperature; A common voltage supply unit supplying a common voltage to the common electrode; And a storage voltage supply unit supplying a storage voltage to the storage electrode of the storage capacitor, wherein the storage capacitor includes: the pixel electrode, the storage electrode facing the pixel electrode, and a semiconductor formed between the pixel electrode and the storage electrode. And storage layers formed to be separated at intersections with the common electrode, wherein the storage electrodes formed to be separated are connected to each other through auxiliary storage electrodes formed together with source and drain electrodes of the thin film transistor. It features.

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The thin film transistor includes a semiconductor layer including an active layer and an ohmic contact layer; The semiconductor layer of the storage capacitor includes only the active layer.

The liquid crystal display according to the second exemplary embodiment of the present invention is a liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, and connected to the common electrode to maintain a voltage of the liquid crystal cell. A liquid crystal display panel including a first storage capacitor to separate the common electrode, and a second storage capacitor separated from the common electrode to maintain a voltage of the liquid crystal cell; A common voltage supply unit supplying a common voltage to the common electrode and the first storage capacitor; And a storage voltage supply unit supplying a storage voltage to the second storage capacitor, wherein the first storage capacitor includes the pixel electrode and a first storage electrode facing the pixel electrode. Includes a pixel electrode, a second storage electrode facing the pixel electrode, and a semiconductor layer formed between the pixel electrode and the second storage electrode, wherein the second storage electrode is formed at an intersection with the common electrode. The second storage electrodes may be formed to be separated, and the second storage electrodes may be connected to each other through an auxiliary storage electrode formed together with the source and drain electrodes of the thin film transistor.

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The thin film transistor includes a semiconductor layer including an active layer and an ohmic contact layer; The semiconductor layer of the second storage capacitor includes only the active layer.

A driving method of a liquid crystal display device according to a first embodiment of the present invention is to maintain a voltage of a liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, and the liquid crystal cell. A method of driving a liquid crystal display including a storage capacitor, the method comprising: supplying a common voltage to the common electrode; And supplying a storage voltage to a storage electrode of the storage capacitor, wherein the common voltage and the storage voltage are different from each other, and the storage electrode is formed to be separated at an intersection with the common electrode and is formed to be separated. The storage electrodes are connected to each other through an auxiliary storage electrode formed together with the source and drain electrodes of the thin film transistor.

A driving method of a liquid crystal display according to a second exemplary embodiment of the present invention includes a liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, and a common electrode connected to the common electrode. A method of driving a liquid crystal display including a first storage capacitor for maintaining a voltage, the method comprising: a liquid crystal display panel including a second storage capacitor connected to the pixel electrode and separated from the common electrode to maintain a voltage of the liquid crystal cell; Forming a; Supplying a common voltage to the common electrode and the first storage capacitor; And supplying a storage voltage to the second storage capacitor; The common voltage and the storage voltage are different from each other, and the first storage capacitor includes the pixel electrode and a first storage electrode facing the pixel electrode, and the second storage capacitor includes the pixel electrode and the pixel. A second storage electrode facing the electrode, and a semiconductor layer formed between the pixel electrode and the second storage electrode, wherein the second storage electrode is formed to be separated at an intersection with the common electrode, The formed second storage electrodes are connected to each other through an auxiliary storage electrode formed together with the source and drain electrodes of the thin film transistor.

Other objects and advantages of the present invention in addition to the above object will become apparent from the description of the preferred embodiment of the present invention with reference to the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 4 to 11.

4 is a diagram illustrating a liquid crystal display according to a first embodiment of the present invention.

Referring to FIG. 4, in the liquid crystal display according to the first exemplary embodiment of the present invention, a plurality of data lines DL and a plurality of gate lines GL intersect each other, and liquid crystal cells provided due to the crossing are arranged in a matrix type. A liquid crystal display panel 50 having a thin film transistor TFT formed therein, a data driving circuit 52 supplying a data voltage to the data lines DL, and a gate supplying scan pulses to the gate lines GL. The driving circuit 54 includes a common voltage supply unit 56 for supplying a common voltage Vcom to the common electrode Ec, and a storage voltage supply unit 58 for supplying a storage voltage Vst to the storage electrode Est. .

The liquid crystal display panel 50 is formed by bonding a thin film transistor array substrate on which a thin film transistor array is formed and a color filter array substrate on which a color filter array is formed, with the liquid crystal layer interposed therebetween.

The data lines DL and the gate lines GL formed on the thin film transistor array substrate of the liquid crystal display panel 50 are perpendicular to each other. The TFT connected to the intersection of the data lines DL and the gate lines GL receives the data voltage supplied through the data line DL in response to the scan pulse of the gate line GL. Ep).

The liquid crystal display panel 50 has a horizontal electric field driving method such as IPS (In Plane Switching) mode, FFS (Fringe Field Switching) mode, and a vertical electric field driving method such as twisted nematic (TN) mode and vertical alignment (VA) mode. It is roughly classified into a liquid crystal display panel.

When the liquid crystal display panel 50 is a horizontal electric field driving method, the common electrode Ec is further formed on the thin film transistor array substrate, and a black matrix and a color filter are formed on the color filter array substrate. The liquid crystal capacitor Clc is formed in the liquid crystal layer between the pixel electrode Ep and the common electrode Ec, and the data voltage supplied to the pixel electrode Ep and the common voltage Vcom supplied to the common electrode Ec. The liquid crystal having dielectric anisotropy rotates through the horizontal electric field due to the potential difference of to adjust the light transmittance.

When the liquid crystal display panel 50 has a vertical electric field driving method, a black matrix, a color filter, a common electrode Ec, and the like are formed on the color filter array substrate. The liquid crystal capacitor Clc is formed in the liquid crystal layer between the pixel electrode Ep and the common electrode Ec, and is supplied to the data voltage supplied to the pixel electrode Ep and the common electrode Ec located on the color filter array substrate. The liquid crystal having dielectric anisotropy rotates through a vertical electric field due to a potential difference from the common voltage Vcom to adjust the light transmittance.

A polarizing plate having an orthogonal optical axis is attached to the thin film transistor array substrate and the color filter array substrate of the liquid crystal display panel 50, and an alignment layer for determining the pretilt angle of the liquid crystal is further formed on the inner surface in contact with the liquid crystal layer. In addition, a storage capacitor Cst is further formed on the thin film transistor array substrate of each liquid crystal cell. The storage capacitor Cst is formed between the pixel electrode Ep to which the data voltage is supplied and the storage electrode Est to which the storage voltage Vst is supplied from the storage voltage supply unit 58 to constant the data voltage charged in the liquid crystal cell. Keep it.

The data driving circuit 52 converts the input digital video data into an analog data voltage using a gamma voltage and supplies the analog data voltage to the data lines DL.

The gate driving circuit 54 sequentially supplies scan pulses to the gate lines GL to select a horizontal line of the liquid crystal cell to which a data voltage is supplied. In other words, the gate driving circuit 54 turns on or off the pixel switching element TFT connected to the gate lines GL by sequentially supplying scan pulses to the gate lines GL. The turned-on pixel switching element TFT conducts the data voltages to the pixel electrode Ep by conducting the data lines DL and the pixel electrode Ep.

The common voltage supply unit 56 generates a common voltage Vcom and supplies it to the common electrode Ec, and the storage voltage supply unit 58 generates a storage voltage Vst and supplies it to the storage electrode Est. That is, in the liquid crystal display according to the first exemplary embodiment of the present invention, the storage voltage supply unit 58 for supplying the storage voltage Vst to the storage electrode Est is separately formed, so that the storage voltage is independent of the common voltage Vcom. The voltage Vst can be adjusted. Therefore, the liquid crystal display according to the first exemplary embodiment of the present invention can adjust ΔVp by adjusting the storage capacitor Cst to a desired size. The storage voltage Vst may use a gate high voltage or a gate low voltage supplied from the source printed circuit board to the gate driving circuit 54 without forming a separate storage voltage supply unit 58.

FIG. 5 is a plan view illustrating a portion of a thin film transistor array substrate in a liquid crystal display according to a first exemplary embodiment of the present invention, and FIG. 6 is a cutaway line taken along lines II ′ and II-II ′ of FIG. 5. One cross section. 5 and 6 illustrate a thin film transistor array substrate having a horizontal electric field driving method, but the first embodiment of the present invention can be applied to a vertical electric field driving method.

5 and 6, the structure of the thin film transistor array substrate according to the first embodiment of the present invention will be described in detail.

5 and 6, the thin film transistor array substrate according to the first exemplary embodiment of the present invention may include a gate line 102 and a data line intersecting the gate insulating layer 146 on the lower substrate 144. 104, the TFT 106 formed at each intersection thereof, the pixel electrode 114 and the common electrode 116 formed so as to form a horizontal electric field in the liquid crystal cell provided in the intersection structure, and the pixel electrode 114 overlapping each other. The storage electrode 118 is formed in the portion to form the storage capacitor 122.

The thin film transistor 106 allows the data voltage of the data line 104 to be supplied to the pixel electrode 114 in response to the scan pulse of the gate line 102. To this end, the thin film transistor 106 includes a gate electrode 108 connected to the gate line 102, a drain electrode 110 connected to the data line 104, and a source electrode 112 connected to the pixel electrode 114. ). The thin film transistor 106 further includes a semiconductor layer overlapping the gate electrode 108 with the gate insulating layer 146 therebetween. The semiconductor layer includes an active layer 148 and an ohmic contact layer 150. The active layer 148 forms a channel between the drain electrode 110 and the source electrode 112 and is also overlapped with the data line 104. The ohmic contact layer 150 is formed on the active layer 148 to make ohmic contact with the data line 104, the drain electrode 110, and the source electrode 112.

The pixel electrode 114 is connected to the source electrode 112 of the thin film transistor 106 through the first contact hole 113 penetrating the passivation layer 152 and is formed in the liquid crystal cell.

The storage electrode 118 is formed simultaneously with the gate line 102, the gate electrode 108, and the common electrode 116, and has a portion of the pixel electrode 114 interposed with the gate insulating layer 146 and the passivation layer 152 therebetween. Overlaps. The storage electrode 118 forms a pixel electrode 114 and a storage capacitor 122. The storage capacitor 122 is supplied to the pixel electrode 114 so that the charged data voltage is stably maintained until the next data voltage is supplied.

Since the common electrode 116 and the storage electrode 118 are separately supplied with the common voltage and the storage voltage, the common electrode 116 and the storage electrode 118 are insulated without being connected to each other. Therefore, when the common electrode 116 and the storage electrode 118 cross, it has an insulated structure. At the intersection 124 of the common electrode 116 and the storage electrode 118, one of the common electrode 116 and the storage electrode 118 is formed separately. 5 and 6 illustrate a structure in which the storage electrode 118 is separated from each other. First, the storage electrode 118 is formed at the same time as the gate line 102, the gate electrode 108, and the common electrode 116, and is formed to be separated at the intersection 124 with the common electrode 116. . Thereafter, the auxiliary storage electrode 120 is formed along with the data line 104, the drain electrode 110, and the source electrode 112. The auxiliary storage electrode 120 is connected to the storage electrode 120 through the second contact holes 119 to conduct the separated storage electrode 118.

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

Referring to FIG. 7, in the liquid crystal display according to the second exemplary embodiment of the present invention, a plurality of data lines DL and a plurality of gate lines GL intersect each other, and the liquid crystal cells provided due to the crossing are arranged in a matrix type. A liquid crystal display panel 70 having a thin film transistor TFT formed therein, a data driving circuit 72 supplying a data voltage to the data lines DL, and a gate supplying scan pulses to the gate lines GL. The storage voltage Vst is supplied to the common circuit supply unit 76 and the second storage electrode Est2 that supply the common voltage Vcom to the driving circuit 74, the common electrode Ec, and the first storage electrode Cst1. The storage voltage supply unit 78 is provided.

The liquid crystal display panel 70 is formed by bonding a thin film transistor array substrate on which a thin film transistor array is formed and a color filter array substrate on which a color filter array is formed, with the liquid crystal layer interposed therebetween.

The data lines DL and the gate lines GL formed on the thin film transistor array substrate of the liquid crystal display panel 70 are perpendicular to each other. The TFT connected to the intersection of the data lines DL and the gate lines GL receives the data voltage supplied through the data line DL in response to the scan pulse of the gate line GL. Ep).

The liquid crystal display panel 70 is a horizontal field driving method such as IPS (In Plane Switching) mode, FFS (Fringe Field Switching) mode, and a vertical field driving method such as twisted nematic (TN) mode and vertical alignment (VA) mode. It is roughly classified into a liquid crystal display panel.

When the liquid crystal display panel 70 is a horizontal electric field driving method, the common electrode Ec is further formed on the thin film transistor array substrate, and a black matrix, a color filter, and the like are formed on the color filter array substrate. The liquid crystal capacitor Clc is formed in the liquid crystal layer between the pixel electrode Ep and the common electrode Ec, and the data voltage supplied to the pixel electrode Ep and the common voltage Vcom supplied to the common electrode Ec. The liquid crystal having dielectric anisotropy rotates through the horizontal electric field due to the potential difference of to adjust the light transmittance.

When the liquid crystal display panel 70 is a vertical electric field driving method, a black matrix, a color filter, a common electrode Ec, and the like are formed on the color filter array substrate. The liquid crystal capacitor Clc is formed in the liquid crystal layer between the pixel electrode Ep and the common electrode Ec, and is supplied to the data voltage supplied to the pixel electrode Ep and the common electrode Ec located on the color filter array substrate. The liquid crystal having dielectric anisotropy rotates through a vertical electric field due to a potential difference from the common voltage Vcom to adjust the light transmittance.

A polarizing plate having an orthogonal optical axis is attached to the thin film transistor array substrate and the color filter array substrate of the liquid crystal display panel 70, and an alignment layer for determining the pretilt angle of the liquid crystal is further formed on the inner surface of the liquid crystal display panel 70. In addition, first and second storage capacitors Cst1 and Cst2 are further formed on the thin film transistor array substrate of each liquid crystal cell. The first storage capacitor Cst1 is formed between the pixel electrode Ep supplied with the data voltage and the first storage electrode Est1 supplied with the common voltage Vcom, and the second storage capacitor Cst2 has a data voltage. The pixel electrode Ep is formed between the supplied pixel electrode Ep and the second storage electrode Est2 supplied with the storage voltage Vst from the storage voltage supply unit 78. The first and second storage capacitors Cst1 and Cst2 maintain a constant data voltage charged in the liquid crystal cell.

The data driving circuit 72 converts the input digital video data into an analog data voltage using a gamma voltage and supplies the analog data voltage to the data lines DL.

The gate driving circuit 74 sequentially supplies scan pulses to the gate lines GL to select a horizontal line of a liquid crystal cell to which a data voltage is supplied. In other words, the gate driving circuit 74 turns on or off the pixel switching element TFT connected to the gate lines GL by sequentially supplying scan pulses to the gate lines GL. The turned-on pixel switching element TFT conducts the data voltages to the pixel electrode Ep by conducting the data lines DL and the pixel electrode Ep.

The common voltage supply unit 76 generates a common voltage Vcom to supply the common electrode Ec and the first storage electrode Est1, and the storage voltage supply unit 78 generates a storage voltage Vst to generate second storage. It supplies to the electrode Est. That is, the liquid crystal display according to the first exemplary embodiment of the present invention forms two storage electrodes to increase the capacity of the storage capacitor so that the liquid crystal display can be stably driven. In addition, the storage voltage supply unit 78 that supplies the storage voltage Vst to the second storage electrode Est2 may be separately formed to adjust the storage voltage Vst regardless of the common voltage Vcom. Therefore, the liquid crystal display according to the second exemplary embodiment of the present invention can adjust ΔVp by adjusting the second storage capacitor Cst2 to a desired size. The storage voltage Vst may use a gate high voltage or a gate low voltage supplied from the source printed circuit board to the gate driving circuit 74 without forming a separate storage voltage supply unit 78.

FIG. 8 is a plan view illustrating a portion of a thin film transistor array substrate in a liquid crystal display according to a second exemplary embodiment of the present invention, and FIG. 9 is a cut-away view taken along lines III-III 'and IV-IV' of FIG. 8. It is a cross section. 8 and 9 illustrate a thin film transistor array substrate having a horizontal electric field driving method, but the second embodiment of the present invention can be applied to a vertical electric field driving method.

8 and 9, the structure of the thin film transistor array substrate according to the second embodiment of the present invention will be described in detail.

8 and 9, the thin film transistor array substrate according to the second exemplary embodiment of the present invention may include a gate line 202 and a data line intersecting a gate insulating layer 246 therebetween on a lower substrate 244. 204, the TFT 206 formed at each intersection thereof, the pixel electrode 214 and the common electrode 216 formed so as to form a horizontal electric field in the liquid crystal cell provided in the intersection structure, and the pixel electrode 214 overlapping each other. A second storage electrode 226 formed on the first storage electrode 226 to form a first storage capacitor 228 and an overlapping portion of the pixel electrode 214 to form a second storage capacitor 222. 218).

The thin film transistor 206 allows the data voltage of the data line 204 to be supplied to the pixel electrode 214 in response to the scan pulse of the gate line 202. To this end, the thin film transistor 206 includes a gate electrode 208 connected to the gate line 202, a drain electrode 210 connected to the data line 204, and a source electrode connected to the pixel electrode 214. 212). The thin film transistor 206 further includes a semiconductor layer overlapping the gate electrode 208 with the gate insulating layer 246 interposed therebetween. The semiconductor layer includes an active layer 248 and an ohmic contact layer 250. The active layer 248 forms a channel between the drain electrode 210 and the source electrode 212 and is also overlapped with the data line 204. The ohmic contact layer 250 is formed on the active layer 248 to make ohmic contact with the data line 204, the drain electrode 210, and the source electrode 212.

The pixel electrode 214 is connected to the source electrode 212 of the thin film transistor 206 through the first contact hole 213 penetrating the passivation layer 252 and is formed in the liquid crystal cell.

The first and second storage electrodes 226 and 218 are formed at the same time as the gate line 202, the gate electrode 208, and the common electrode 216, and a part of the pixel electrode 214, the gate insulating layer 246, and the passivation layer. Overlaid with 252 in between. The first and second storage electrodes 228 and 218 form the pixel electrode 214 and the first and second storage capacitors 228 and 222. The first and second storage capacitors 228 and 222 are supplied to the pixel electrode 214 so that the charged data voltage is stably maintained until the next data voltage is supplied.

The first storage electrode 226 is connected to the common electrode 216 to receive a common voltage, but the second storage electrode 218 is not connected to each other because the storage voltage is independently supplied to the common electrode 216. do. Therefore, when the second storage electrode 218 crosses the common electrode 216 or the first storage electrode 226, the second storage electrode 218 has an insulated structure. At the intersection 224 of the common electrode 216 and the second storage electrode 218, one of the common electrode 216 and the second storage electrode 218 is formed separately. 8 and 9 illustrate a structure in which the second storage electrodes 218 are separated from each other. First, the second storage electrode 218 is formed at the same time as the gate line 202, the gate electrode 208, the common electrode 216, and the first storage electrode 226, and intersects with the common electrode 216. In the part 224 is formed to be separated. Thereafter, the auxiliary storage electrode 220 is formed along with the data line 204, the drain electrode 210, and the source electrode 212. The auxiliary storage electrode 220 is connected to the second storage electrode 218 through the second contact holes 219 to conduct the second storage electrode 218 separated therefrom.

FIG. 10 is a cross-sectional view illustrating the storage capacitor 122 having the semiconductor layer 151 formed therebetween, and the semiconductor capacitor 151 between the storage capacitor 122 illustrated in FIG. 6, that is, the pixel electrode 114 and the storage electrode 118. ) Is shown. In FIG. 10, the passivation layer 152 has an opening in a region where the pixel electrode 114 and the storage electrode 118 overlap with each other. The gate insulating layer 146 also has the pixel electrode 114 and the storage electrode ( 118 may have an opening in an overlapping area. The semiconductor layer 151 includes an active layer formed of amorphous silicon and the like, and has a higher dielectric constant than the passivation layer 152 and the gate insulating layer 146, thereby increasing the capacity of the storage capacitor 122. 10 illustrates the liquid crystal display according to the first embodiment of the present invention as an example, the semiconductor layer 151 may be applied to the storage capacitor of the liquid crystal display according to the second embodiment of the present invention.

FIG. 11 is a diagram illustrating the size of the storage capacitor Cst according to the storage voltage Vst in the liquid crystal display of the normally black mode. The storage voltage Vst is set higher than that of the graph of FIG. 3. One case is shown. Point A 'is the point where the positive data voltage is supplied to the white tone, B' point is the point where the negative data voltage is supplied to the white tone, and C 'point is the positive data voltage for the black tone. The point to be supplied is shown, and the point D 'is a point at which a negative data voltage for black gradation is supplied.

Referring to FIG. 11, it can be seen that the size of the storage capacitor Cst is increased both in the positive gray and the negative polarity in the black gradation. In addition, when the positive data voltage is supplied in the black gradation and the average storage capacitor Cst when the negative data voltage is supplied, the positive data voltage is supplied in the white gradation and the negative data voltage is supplied. Is larger than the average storage capacitor (Cst). In the normally black mode, the liquid crystal capacitor Clc is larger in the white gray because the data voltage is larger in the white gray than in the black gray. That is, according to the present invention, since the size of the storage capacitor Cst can be adjusted, the size of the storage capacitor Cst is largely adjusted so that the size of the liquid crystal capacitor Clc is small in the black gradation, and thus the white gradation and the black gradation. Can be adjusted in the same manner. In addition, since the size of the storage capacitor Cst can be adjusted, the image quality can be improved by reducing the size of ΔVp.

As described above, the liquid crystal display and the driving method thereof according to an exemplary embodiment of the present invention include a storage voltage supply unit supplying a storage voltage to the storage electrode, and a common voltage supply unit supplying a common voltage to the common electrode, respectively. By supplying a voltage to the storage electrode and the common electrode, the storage capacitor can be adjusted.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the 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 (9)

A liquid crystal display panel including a liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, and a storage capacitor for maintaining a voltage of the liquid crystal cell; A common voltage supply unit supplying a common voltage to the common electrode; And A storage voltage supply unit supplying a storage voltage to the storage electrode of the storage capacitor, The storage capacitor, And a semiconductor layer formed between the pixel electrode, the storage electrode facing the pixel electrode, and the pixel electrode and the storage electrode. The storage electrode is formed to be separated from the intersection with the common electrode, And the storage electrodes separated from each other are connected to each other through an auxiliary storage electrode formed together with the source and drain electrodes of the thin film transistor. delete The method of claim 1, The thin film transistor includes a semiconductor layer including an active layer and an ohmic contact layer; And the semiconductor layer of the storage capacitor includes only the active layer. A liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, a first storage capacitor connected to the common electrode to maintain a voltage of the liquid crystal cell, and separated from the common electrode A liquid crystal display panel including a second storage capacitor to maintain a voltage of the liquid crystal cell; A common voltage supply unit supplying a common voltage to the common electrode and the first storage capacitor; And A storage voltage supply unit supplying a storage voltage to the second storage capacitor; The first storage capacitor, The pixel electrode and a first storage electrode facing the pixel electrode; The second storage capacitor, The pixel electrode, a second storage electrode facing the pixel electrode, and a semiconductor layer formed between the pixel electrode and the second storage electrode, The second storage electrode is formed to be separated from the intersection with the common electrode, And the second storage electrodes formed to be separated are connected to each other through an auxiliary storage electrode formed together with the source and drain electrodes of the thin film transistor. delete delete 5. The method of claim 4, The thin film transistor includes a semiconductor layer including an active layer and an ohmic contact layer; The semiconductor layer of the second storage capacitor includes only the active layer. A driving method of a liquid crystal display device comprising a liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, and a storage capacitor for maintaining a voltage of the liquid crystal cell. Supplying a common voltage to the common electrode; And Supplying a storage voltage to a storage electrode of the storage capacitor, The common voltage and the storage voltage are different from each other, The storage electrode is formed to be separated from the intersection with the common electrode, And the storage electrodes formed to be separated are connected to each other through an auxiliary storage electrode formed together with the source and drain electrodes of the thin film transistor. Driving a liquid crystal display device including a liquid crystal cell driven by an electric field between a pixel electrode and a common electrode, a thin film transistor connected to the pixel electrode, and a first storage capacitor connected to the common electrode to maintain a voltage of the liquid crystal cell. In the method, Forming a liquid crystal display panel connected to the pixel electrode and separated from the common electrode, the liquid crystal display panel including a second storage capacitor to maintain a voltage of the liquid crystal cell; Supplying a common voltage to the common electrode and the first storage capacitor; And Supplying a storage voltage to the second storage capacitor; The common voltage and the storage voltage are different from each other, The first storage capacitor, The pixel electrode and a first storage electrode facing the pixel electrode; The second storage capacitor, The pixel electrode, a second storage electrode facing the pixel electrode, and a semiconductor layer formed between the pixel electrode and the second storage electrode, The second storage electrode is formed to be separated from the intersection with the common electrode, And the second storage electrodes formed to be separated are connected to each other through an auxiliary storage electrode formed together with the source and drain electrodes of the thin film transistor.

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