KR101411678B1 - Liquid Crystal Display Device - Google Patents

Abstract

The present invention provides a horizontal electric field application type thin film transistor substrate having a high aperture ratio and a manufacturing method thereof. In addition, the present invention provides a horizontal field-applied thin film transistor substrate and a method of manufacturing the same, which can appropriately maintain the capacity of a storage capacitor.

The horizontal electric field application type thin film transistor substrate includes a gate line formed on a substrate; A data line crossing the gate line and the gate insulating film to define a pixel region; A thin film transistor connected to the gate line and the data line; A pixel electrode plate connected to the thin film transistor for each pixel region; A protective film formed on the gate insulating film to cover the data line, the thin film transistor, and the pixel electrode plate; And a common electrode formed over the entire surface of the array region where the thin film transistor array is formed and formed in a mesh shape on the protective film.

Description

[0001] The present invention relates to a liquid crystal display device,

1 is a plan view showing a thin film transistor substrate of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the thin film transistor substrate shown in FIG. 1 taken along the line I-I '; FIG.

3 is a plan view showing a color filter substrate of a liquid crystal display device according to an embodiment of the present invention.

4 is a cross-sectional view of the color filter substrate shown in FIG. 3 taken along line II - II '.

Figs. 5A to 5C are cross-sectional views after attaching the upper and lower substrates, injecting liquid crystals, and attaching the polarizer. Fig.

6 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention.

7 is a flow chart of data processing of the timing controller.

8 is a view for explaining an electric field direction and a posture of a liquid crystal in a white / gray state or a black state;

9 is a luminance versus time graph for white state (A) and black state (B).

10 is a simulation result showing an electric field direction and a liquid crystal orientation in the state A in Fig.

11 is a simulation result showing an electric field direction and a liquid crystal orientation in the state B in Fig.

Description of the Related Art

2: gate line 4-1: first data line

4-2: second data line 6: gate electrode

8-1: first source electrode 8-2: second source electrode

10-1: first drain electrode 10-2: second drain electrode

12-1: first contact hole 12-2: second contact hole

14: common electrode pattern 18: pixel electrode

20: lower substrate 22: gate insulating film

24-1: first active layer 24-2: second active layer

25-1: first semiconductor pattern 25-2: second semiconductor pattern

26-1: first ohmic contact layer 26-2: second ohmic contact layer

32: black matrix 34: color filter pattern

38: common electrode 50: liquid crystal display panel

52: Data driving circuit 54: Gate driving circuit

56: timing controller 58: common voltage generator

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 capable of reducing light leakage and a polling time in a black state in which a darkest gray scale is displayed in a horizontal electric field application type liquid crystal display device.

The liquid crystal display device displays an image by adjusting the light transmittance of the liquid crystal using an electric field. Such a liquid crystal display device is classified into a vertical electric field application type and a horizontal electric field application type depending on the direction of an electric field for driving the liquid crystal.

The vertical electric field application type liquid crystal display device drives the TN (Twisted Nematic) mode liquid crystal by the vertical electric field formed between the pixel electrodes and the common electrode arranged opposite to the upper and lower substrates. The vertical field-applied liquid crystal display device has a disadvantage in that the aperture ratio is large, but the viewing angle is as narrow as 90 degrees.

The horizontal field-applied liquid crystal display device drives the in-plane switching (IPS) mode liquid crystal by the horizontal electric field between the pixel electrode and the common electrode arranged in parallel to the lower substrate. Such an IPS mode liquid crystal display device has a wide viewing angle of about 160 degrees, but has a disadvantage of low aperture ratio and low transmittance. Specifically, in the IPS mode liquid crystal display device, in order to form an in-plane field, the interval between the common electrode and the pixel electrode for driving the liquid crystal is set wider than the interval between the upper and lower substrates, The common electrode and the pixel electrode are formed to have a wide width. An electric field substantially parallel to the substrate is formed between the pixel electrode and the common electrode formed in this manner, but the influence of the electric field is not exerted on the liquid crystal over the pixel electrode and the common electrode having a wide width, The upper liquid crystal is not driven and maintains the initial state. As a result, the liquid crystal that maintains the initial state can not transmit the light, which causes the aperture ratio and the transmittance to decrease.

A fringe field switching (FFS) type liquid crystal display device operated by a fringe field has been proposed in order to solve the disadvantage of the IPS mode liquid crystal display device. The FFS-type liquid crystal display device has a common electrode plate and pixel electrodes sandwiching an insulating film in each pixel region, and the interval between the common electrode plate and the pixel electrode is narrower than the interval between the upper and lower substrates, To form a parabolic fringe field. The liquid crystal molecules filled between the upper and lower substrates are operated by the fringe field, thereby improving the aperture ratio and the transmittance.

The horizontal electric field application type liquid crystal display device such as the IPS mode or the FFS mode has a characteristic of being vulnerable to light leakage in the black state as compared with the vertical field application type liquid crystal display device. That is, the horizontal electric field application type liquid crystal display device is realized by rubbing the liquid crystal so that the black state displaying the darkest gray level is parallel (or orthogonal) to one absorption (or transmission) axis of the orthogonal polarizer. However, in a horizontal electric field-applied liquid crystal display device, light leakage may be generated due to rubbing unevenness caused by various causes during the lower substrate step or rubbing process in the black state implementation. Such light leakage due to the liquid crystal alignment irregularity occurs more in a horizontal electric field applied liquid crystal display device than in a vertical electric field applied liquid crystal display device. This is because the initial front retardation is larger than that of the vertical electric field-applied liquid crystal display device.

Further, in a horizontal electric field application type liquid crystal display device, when a data voltage changes in a black state due to a slow response speed when a moving image is implemented, a display luminance corresponding to the data voltage does not reach a desired luminance, . That is, the liquid crystal in the horizontal electric field application type liquid crystal display device displays a gray level by being rised in the electric field forming direction from the initial orientation state when the data voltage is applied, and when the electric field is applied, So that the black state is displayed. At this time, the speed at which the liquid crystal is returned or polled is generally slow, not by the electric field force but by the elastic force of the liquid crystal, the rotational viscosity, and the anchoring energy between the alignment film and the liquid crystal. The slow response speed of such a horizontal electric field applied liquid crystal display device is more affected by the polling time than the rising time. As a result, the horizontal field-applied liquid crystal display device exhibits a motion blurring phenomenon in a moving image, and the display quality is lowered due to a decrease in the contrast ratio.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a liquid crystal display device capable of reducing the light leakage and the polling time in a black state in which the darkest gradation is displayed in a horizontal electric field application type liquid crystal display device.

In order to achieve the above object, a liquid crystal display according to an embodiment of the present invention includes a pixel electrode, a first common electrode that forms a horizontal electric field with the pixel electrode, and a second common electrode that forms a vertical electric field with the pixel electrode A liquid crystal cell; A first data line for supplying a first data voltage to the pixel electrode; A second data line supplying a second data voltage to the first common electrode; A common voltage supply line for supplying a common voltage to the second common electrode; And generating the second data voltage at substantially the same value as the first data voltage when the first data voltage is black gradation and generating the second data voltage at the same value as the common voltage except for the black gradation And a data voltage generating circuit.

The first common electrode is formed on the same substrate as the pixel electrode.

The first common electrode is formed in an independent pattern for each liquid crystal cell.

The second common electrode is formed on a substrate facing the substrate on which the pixel electrode is formed with a liquid crystal layer interposed therebetween.

Wherein the liquid crystal cell comprises: a first thin film transistor for switching supply of the first data voltage to the pixel electrode; And a second thin film transistor for switching supply of the second data voltage to the first common electrode.

Wherein the data voltage generating circuit includes: a timing controller for generating second digital video data differently corresponding to the second data voltage according to a gray level of the first digital video data corresponding to the first data voltage; And a data driving circuit for converting the first and second digital video data into the first and second data voltages, respectively.

Wherein the timing controller generates second digital video data substantially identical to the first digital video data through copying if the first digital video data is a black gradation, And inserts the data to generate it as second digital video data.

The digital black data is data that causes the second data voltage to be selected as the lowest level analog gamma voltage substantially equal to the common voltage.

The liquid crystal display device according to the embodiment of the present invention further includes a common voltage generator for supplying a common voltage to the second common electrode.

In order to achieve the above object, a liquid crystal display according to an embodiment of the present invention includes a liquid crystal layer, a first electrode pair for applying a horizontal electric field to the liquid crystal layer, and one of the first electrode pairs, A liquid crystal cell having a second electrode pair for applying a vertical electric field to the liquid crystal layer; And generating a potential difference between the first electrode pair and the second electrode pair to display a first gray level on the liquid crystal layer to form an equal potential on the first electrode pair, And a data voltage generating circuit for generating a second gray level on the liquid crystal layer.

According to an aspect of the present invention, there is provided a liquid crystal display comprising: a liquid crystal cell having first, second and third electrodes for driving liquid crystal molecules; And an electric field is formed between two electrodes formed on the same substrate among the electrodes in the first gray level to drive the liquid crystal molecules on the basis of a substantially same horizontal plane as the substrate surface, And a liquid crystal driving circuit for driving the liquid crystal molecules based on a plane substantially perpendicular to the substrate surface.

Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments 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. 1 to 11. FIG.

FIG. 1 is a plan view showing a thin film transistor substrate of a liquid crystal display according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line I-I 'of the thin film transistor substrate shown in FIG.

The thin film transistor substrate shown in FIGS. 1 and 2 includes a gate line 2 and a first data line 4-1 formed on the lower substrate 20 so as to cross each other with a gate insulating film 22 therebetween, And a first thin film transistor TFT1 formed for each pixel. The thin film transistor substrate includes a gate line 2 and a second data line 4-2 formed on the lower substrate 20 so as to cross each other with the gate insulating film 22 interposed therebetween and a second thin film transistor TFT2 . The thin film transistor substrate defines pixel regions in an intersection structure of the gate line 2 and the two data lines 4-1 and 4-2. A common electrode pattern 14 and a pixel electrode 18 are formed in the pixel region so as to form a fringe field F with a gate insulating film 22 and a protective film 28 interposed therebetween. Here, the gate insulating film 22 and the protective film 28 are formed of an inorganic insulating material such as Sin _x and are formed to have a thickness of 2000 ANGSTROM.

The first thin film transistor TFT1 causes the pixel electrode 18 to be charged with the first data voltage from the first data line 4-1 in response to the scan pulse from the gate line 2. [ To this end, the first thin film transistor TFT1 includes a gate electrode 6 connected to the gate line 2, a first source electrode 8-1 connected to the first data line 4-1, The first source electrode 8-1 and the first drain electrode 10-1 overlap each other with the gate electrode 6 and the gate insulating film 22 interposed therebetween, For the ohmic contact between the first active layer 24-1, the first source electrode 8-1 and the first drain electrode 10-1 and the first active layer 24-1, And a first semiconductor pattern 25-1 including a first ohmic contact layer 26-1.

The second thin film transistor TFT2 causes the second data voltage from the second data line 4-2 to be charged in the common electrode pattern 14 in response to the scan pulse from the gate line 2. [ To this end, the second thin film transistor TFT2 includes a gate electrode 6 connected to the gate line 2, a second source electrode 8-2 connected to the second data line 4-2, A second source electrode 8-2 and a second drain electrode 10-2 overlapping the gate electrode 6 and the gate insulating film 22 while being sandwiched between the first drain electrode 10-2 and the second drain electrode 10-2, The second active layer 24-2, the second source electrode 8-2, and the second drain electrode 10-2, which form a channel between the first active layer 24-2 and the second active layer 24-2, And a second semiconductor pattern 25-2 including a second ohmic contact layer 26-2 for the second ohmic contact layer 26-2.

The pixel electrode 18 is formed of a transparent metal layer and is formed for each pixel region. The pixel electrode 18 is connected to the first drain electrode 10-1 of the first thin film transistor TFT1 through the first contact hole 12-1 passing through the protective film 28, 14). The pixel electrode 18 forms a horizontal electric field together with the common electrode pattern 14 in the white and gray implementations to horizontally rotate liquid crystal molecules horizontally aligned between the thin film transistor substrate and the color filter substrate. The horizontal electric field formed between the common electrode pattern 14 and the pixel electrode 18 includes a fringe field F in the form of a parabola having a linear electric field and a curvature. The liquid crystal molecules at the upper edge of the pixel electrode slit 18 can be operated under the influence of the fringe field F since the start or end point of the fringe field F is near the upper edge of the pixel electrode 18. [ In addition, the pixel electrode 18 forms a vertical electric field together with a common electrode formed on the color filter substrate to realize liquid crystal molecules horizontally aligned between the thin film transistor substrate and the color filter substrate Tilt Up. The transmittance of light passing through the pixel region is changed according to the degree of rotation of the liquid crystal molecules, thereby realizing white and gray, and a black state is realized by tilting up the liquid crystal molecules.

The common electrode pattern 14 is formed of a transparent metal layer and is formed for each pixel region. The common electrode pattern 14 is connected to the second drain electrode 10-2 of the second thin film transistor TFT2 through the protective film 28 and the second contact hole 12-2 passing through the gate insulating film 22 And is formed to overlap the pixel electrode 18 under the pixel electrode 18. As shown in FIG. The common electrode pattern 14 is supplied with the second data voltage through liquid crystal driving through the second data line 4-2 connected thereto. The second data voltage has substantially the same value as the common voltage supplied to the common electrode formed on the color filter substrate in the white and gray implementation and has substantially the same value as the first data voltage in the black implementation showing the darkest gray scale .

The gate line 2 supplies a scan pulse to the gate electrodes 6 of the first and second thin film transistors TFT1 and TFT2 and is connected to a gate drive circuit (not shown) through a gate pad (not shown).

The first data line 4-1 supplies the first data voltage to the pixel electrode 18 through the first drain electrode 10-1 of the first thin film transistor TFT1. The second data line 4-2 supplies the second data voltage to the common electrode pattern 14 through the second drain electrode 10-2 of the second thin film transistor TFT2. These data lines 4-1 and 4-2 are connected to a data driving circuit (not shown) through a data pad (not shown).

A storage capacitor Cst for stably maintaining the first data voltage supplied to the pixel electrode 18 is formed on the overlapping portion of the common electrode pattern 14 and the pixel electrode 18. [

The liquid crystal display device according to the embodiment of the present invention having such a structure is characterized in that an electric field signal is applied between the common electrode pattern 14 of the thin film transistor substrate and the pixel electrode 18 or between the common electrode of the color filter substrate and the pixel electrode 18 And a normal black mode in which the screen display state is black before being applied.

FIG. 3 is a plan view showing a color filter substrate of a liquid crystal display device according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view taken along line II-II 'of FIG.

3 and 4, a color filter substrate of a liquid crystal display according to an embodiment of the present invention includes a black matrix 32, a color filter pattern 34, and an overcoat layer 34 sequentially stacked on an upper substrate 30, (36), and a common electrode (38).

The black matrix 32 is formed of a metal such as chrome oxide (CrOx) or chromium (Cr) having an optical density of 3.5 or more and a carbon-based organic material. The black matrix 32 includes a region where the first and second thin film transistors TFT1 and TFT2 of the thin film transistor substrate are formed and a region where the gate line 2 and the first and second data lines 4-1 and 4-2 ) And the peripheral region thereof.

The color filter pattern 34 includes a red layer formed on the R pixel region, a green layer formed on the G pixel region, and a blue layer formed on the B pixel region.

An overcoat layer 36 is formed on the entire surface of the black matrix 32 and the color filter pattern 34. The overcoat layer 36 serves to planarize the step of the inner surface due to the formation of the black matrix 32 and the color filter pattern 34.

A common electrode 38 is formed on the entire surface of the overcoat layer 36. The common electrode 38 is formed of a transparent conductive metal having excellent light transmittance such as indium tin-oxide (ITO) or indium zinc-oxide (IZO). The common voltage supplied to the common electrode 38 forms a vertical electric field with the first data voltage supplied to the pixel electrode 18 of the thin film transistor substrate in the case of a black display showing the darkest gradation, And tilt-up liquid crystal molecules horizontally aligned between the substrates. The common voltage is supplied to the common electrode 38 through a common voltage supply line (not shown).

Figs. 5A to 5C show cross-sectional views after attaching the upper and lower substrates 20 and 30, injecting liquid crystal, and attaching the polarizer. FIG. 5A is a cross-sectional view showing the posture of the liquid crystal in the off-black state, FIG. 5B is a cross-sectional view showing the posture of the liquid crystal in the on-black state, / Gray) state of the liquid crystal.

As shown in the figure, the upper and lower substrates 20 and 30 are bonded to each other by a sealant printed on the edge of the substrate and serving as an adhesive. A liquid crystal layer 131 is dropped or injected between the substrates 20 and 30 . The first and second polarizers 41 and 42 are attached to the outer circumferential surfaces of both the substrates 20 and 30 such that the transmission axes are orthogonal to each other. The rubbing direction of the alignment layer formed on the lower substrate 20 is aligned with the transmission axis of any polarizer, thereby implementing a normally black mode.

As shown in Fig. 5A, in the power-off state, the liquid crystal molecules 50 maintain the initial alignment state. Since the initial alignment state of the liquid crystal molecules 50 is parallel to the transmission axis of a polarizing plate, the transmittance of the pixel is close to 0% and becomes black.

5B, when a black data voltage is applied to the pixel electrode 18 through the first data line 4-1 in the power-on state, the liquid crystal molecules 50 horizontally aligned are tilt- Up. When the first data voltage indicating the black state is applied to the pixel electrode 18 through the first data line 4-1, the data voltage is applied to the lower substrate 20 through the second data line 4-2. The second data voltage applied to the common electrode pattern 14 of the second data electrode 14 is substantially the same as the first data voltage. An equal potential is generated between the pixel electrode 18 and the common electrode pattern 14 of the lower substrate 20 while a constant potential difference is generated between the pixel electrode 18 and the common electrode 38 of the upper substrate 30. [ . The liquid crystal molecules 50 horizontally aligned due to the vertical electric field tilt up and stand vertically between the two substrates 20 and 30. The black state is realized by the vertically aligned liquid crystal molecules 50. As described above, in the embodiment of the present invention, when the black state is realized by the black data voltage, the liquid crystal molecules 50 are driven through the vertical electric field to reduce the initial retardation in the black state, thereby reducing the light leakage. Conventionally, in order to realize a black state, the liquid crystal molecules 50 are returned (polled) to the initial alignment state only by the elastic force of the liquid crystal, the rotational viscosity, and the anchoring energy between the alignment film and the liquid crystal, The black state is realized by using the vertical electric field generated between the pixel electrode 18 and the common electrode 38 of the upper substrate 30 so that the polling time is significantly .

As shown in FIG. 5C, when the white / gray data voltage is applied to the pixel electrode 18 through the first data line 4-1 in the power-on state, the liquid crystal molecules 50 horizontally aligned in the horizontal direction . When a first data voltage indicating a white or gray state through the first data line 4-1 is applied to the pixel electrode 18, The second data voltage applied to the common electrode pattern 14 of the second substrate 20 has substantially the same magnitude as the common voltage applied to the common electrode of the upper substrate 30. The potential difference between the pixel electrode 18 and the common electrode pattern 14 of the lower substrate 20 which is relatively larger than the potential difference between the pixel electrode 18 and the common electrode 38 of the upper substrate 30 The liquid crystal molecules 50 are affected by the horizontal electric field. The liquid crystal molecules 50 horizontally aligned due to the influence of the horizontal electric field rotate in the horizontal direction to control the light transmittance to display white or gray.

FIG. 6 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention, and FIG. 7 is a data processing flowchart of a timing controller.

6, a liquid crystal display according to an exemplary embodiment of the present invention includes a plurality of first and second data lines D1A to DmA and D1B to DmB and a plurality of gate lines G1 to Gn, A liquid crystal display panel 50 in which a plurality of first and second thin film transistors TFT1 and TFT2 are formed for driving a liquid crystal cell in the liquid crystal display panel 50 and the first data lines D1A to DmA of the liquid crystal display panel 50, A data driving circuit 52 for supplying a first data voltage to the liquid crystal display panel 50 and supplying a second data voltage to the second data lines D1B to DmB of the liquid crystal display panel 50, A gate drive circuit 54 for supplying a scan pulse to the lines G1 to Gn and a second drive circuit 54 for driving the first data lines D1A to DmA in accordance with the gray level of the first digital video data R1G1B1 to be supplied to the first data lines D1A to DmA, The second digital video data R2G2B2 to be supplied to the lines D1B to DmB are differently generated and the driving circuits 52 and 54 And a timing controller 56, and a common voltage generating unit 58 for supplying a common voltage (Vcom) to the LCD panel 50 for controlling the driving timing.

Liquid crystal molecules are injected or dropped between two substrates of the liquid crystal display panel 50 and the first and second data lines D1A to DmA and D1B to DmB and the gate lines G1 to Gn Are mutually orthogonal. The first thin film transistor TFT1 formed at the intersection of the first data lines D1A to DmA and the gate lines G1 to Gn is connected to the first thin film transistor TFT1 on the first data lines D1A to DmA in response to the scan pulse. And supplies the data voltage to the pixel electrode 18 of the liquid crystal cell. The second thin film transistor TFT2 formed at the intersection of the second data lines D1B to DmB and the gate lines G1 to Gn is connected to the second thin film transistor TFT2 on the second data lines D1B to DmB in response to the scan pulse. And supplies the data voltage to the common electrode pattern 14 of the liquid crystal cell. Although not shown, a common voltage is supplied to the common electrode formed on the upper substrate. The liquid crystal cell changes the arrangement of the liquid crystal molecules by the horizontal electric field formed by the potential difference between the first data voltage supplied to the pixel electrode 18 and the second data voltage supplied to the common electrode pattern 14, To display white / gray. The liquid crystal cell tilts up the liquid crystal molecules by a vertical electric field formed by a potential difference between a first data voltage supplied to the pixel electrode 18 and a common voltage Vcom supplied to the common electrode of the upper substrate, Black is displayed by blocking. A storage capacitor for holding the charge voltage of the liquid crystal cell is formed between the common electrode pattern 14 and the pixel electrode 18. [

The timing controller 56 rearranges the first digital video data R1G1B1 supplied from the digital video card according to the resolution of the liquid crystal display panel 50 as shown in FIG. 7 (S10) The gradation of the data R1G1B1 is analyzed. The timing controller 56 outputs the gradation analysis result of the first digital video data R1G1B1 to be supplied to the second data lines D1B to DmB based on the result of the grayscale analysis of the first digital video data R1G1B1 to be supplied to the first data lines D1A to DmA. The timing controller 56 determines whether the gradation of the first digital video data R1G1B1 is a black gradation having the lowest gradation value. , The timing controller 56 generates the second digital video data R1G2B2 which is the same as the first digital video data R1G1B1 through the copying. (S30) If the black gradation is not obtained, The digital black data is generated by inserting the digital black data and generating it as the second digital video data R2G2B2. (S40) In the digital black data, the lowest level analog gamma voltage substantially equal to the common voltage Vcom is selected A data lock.

In addition, the timing controller 56 controls the driving timing of the driving circuits 52 and 54. To this end, the timing controller 56 generates a gate control signal GDC for controlling the gate drive circuit 54 by using the dot clock signal CLK and the horizontal / vertical synchronization signals H and Vsync input thereto And generates a data control signal (DDC) for controlling the data driving circuit (52). The gate control signal GDC includes a gate shift clock GSC, a gate output signal GOE, a gate start pulse GSP, and the like. The data control signal DDC includes a source start pulse SSP, a source shift clock SSC, a source output signal SOE, a polarity signal POL, and the like.

The data driving circuit 52 outputs the analog gamma voltage corresponding to the first digital video data R1G1B1 from the timing controller 56 in response to the data control signal DDC supplied from the timing controller 56, . In response to the data control signal DDC supplied from the timing controller 56, the data driving circuit 52 supplies the analog gamma voltage corresponding to the second digital video data R2G2B2 from the timing controller 56 to the second Select as the data voltage. The selected first data voltage is supplied to the first data lines D1A to DmA and the selected second data voltage is supplied to the second data lines D1B to DmB.

The gate drive circuit 54 responds to the gate control signal GDC supplied from the timing controller 56 and supplies a gate high pulse for turning on the thin film transistors TFT1 and TFT2 and the scan pulse thin film transistors TFT1 and TFT2 And a level shifter for shifting the voltage of the scan pulse to a level suitable for driving the liquid crystal cell. The shift register includes a shift register for sequentially generating scan pulses swinging between gate-low pulses for turning off the scan lines. In response to this scan pulse, the first and second thin film transistors TFT1 and TFT2 are turned on. When the first thin film transistor TFT1 is turned on, the first data voltage on the first data line is supplied to the pixel electrode 18 of the liquid crystal cell, and when the second thin film transistor TFT2 is turned on, 2 data voltage is supplied to the common electrode pattern 14 of the liquid crystal cell.

8 is a view for explaining the electric field direction and the posture of the liquid crystal in the white / gray state or the black state. In Fig. 8, Vd1 represents the first data voltage, Vd2 represents the second data voltage, and Vcom represents the common voltage.

Referring to FIG. 8, when a first data voltage Vd1 indicating a white or gray state is applied to the pixel electrode through the first data line, the first data voltage Vd1 applied to the common electrode pattern of the lower substrate through the second data line 2 data voltage Vd2 has substantially the same magnitude as the common voltage Vcom applied to the common electrode of the upper substrate. The liquid crystal molecules are rotated in the horizontal direction by a horizontal electric field between the pixel electrode and the common electrode pattern having a relatively large potential difference relative to the vertical electric field, thereby controlling the light transmittance to display white or gray.

On the other hand, when the first data voltage Vd1 indicating the black state is applied to the pixel electrode through the first data line, the second data voltage Vd2 applied to the common electrode pattern of the lower substrate through the second data line, Has substantially the same magnitude as the first data voltage Vd1. Therefore, the liquid crystal molecules are affected by the vertical electric field generated between the pixel electrode and the common electrode of the upper substrate, not by the horizontal electric field generated at the equal potential between the common electrode pattern of the pixel electrode and the lower substrate. The liquid crystal molecules horizontally aligned due to the vertical electric field tilt up and stand vertically between the upper and lower substrates. The black state is realized by the vertically aligned liquid crystal molecules.

9 is a graph of luminance versus time for the white state (A) and the black state (B), Fig. 10 is a simulation result showing the electric field direction and the liquid crystal orientation in the state A in Fig. 9, B < / RTI >

9 to 11, in the white state (A), the liquid crystal molecules are rotated in the horizontal direction by the horizontal electric field between the pixel electrode and the common electrode pattern to control the light transmittance to display white.

In the black state (B), the liquid crystal molecules are vertically generated by the vertical electric field between the common electrode of the pixel electrode and the upper substrate, thereby blocking light transmission and displaying black. When the black state (B) is implemented by applying a vertical electric field to the liquid crystal molecules, the initial retardation in the black state is reduced, and the light leakage is greatly reduced. Further, by applying a vertical electric field to realize a black state, the liquid crystal molecules 50 are returned (polled) to the initial alignment state only by the elastic force of the liquid crystal, the rotational viscosity, and the anchoring energy between the alignment film and the liquid crystal, The polling time is significantly reduced to less than 1 ms as compared to the conventional method.

As described above, in the liquid crystal display according to the present invention, when a common electrode is added to the upper substrate of the horizontal electric field applying type liquid crystal display device and a white / gray state is realized, the horizontal electric field between the common electrode pattern of the lower substrate and the pixel electrode The black state is displayed by using the vertical electric field between the common electrode and the pixel electrode of the upper substrate in the case of implementing the black state in which the darkest gray level is displayed.

The liquid crystal display according to the present invention can significantly reduce the light leakage and the polling time in the black state by using the vertical electric field to display the black state.

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 (29)

A liquid crystal cell having a pixel electrode, a first common electrode forming a horizontal electric field with the pixel electrode, and a second common electrode forming a vertical electric field with the pixel electrode; A first data line for supplying a first data voltage to the pixel electrode; A second data line supplying a second data voltage to the first common electrode; A common voltage supply line for supplying a common voltage to the second common electrode; And Generating the second data voltage at substantially the same value as the first data voltage when the first data voltage is black gradation and generating the second data voltage at the same value as the common voltage except for the black gradation And a data voltage generating circuit, In the liquid crystal cell, A first thin film transistor for switching supply of the first data voltage to the pixel electrode; And And a second thin film transistor for switching supply of the second data voltage to the first common electrode. The method according to claim 1, Wherein the first common electrode is formed on the same substrate as the pixel electrode. 3. The method of claim 2, And the first common electrode is formed in an independent pattern for each of the liquid crystal cells. The method according to claim 1, Wherein the second common electrode is formed on a substrate facing the substrate on which the pixel electrode is formed with a liquid crystal layer interposed therebetween. delete The method according to claim 1, Wherein the data voltage generating circuit comprises: A timing controller for differently generating second digital video data corresponding to the second data voltage according to a gray level of the first digital video data corresponding to the first data voltage; And And a data driving circuit for converting the first and second digital video data into the first and second data voltages, respectively. The method according to claim 6, The timing controller includes: If it is determined that the first digital video data is a black gradation, generating second digital video data substantially the same as the first digital video data through copying if the first gradation is black gradation, And the second digital video data is generated as second digital video data. 8. The method of claim 7, Wherein the digital black data is data for causing the second data voltage to be selected as the lowest level analog gamma voltage substantially equal to the common voltage. The method according to claim 1, And a common voltage generating unit for supplying a common voltage to the second common electrode. A liquid crystal cell having a liquid crystal layer, a first electrode pair for applying a horizontal electric field to the liquid crystal layer, and a second electrode pair for applying a vertical electric field to the liquid crystal layer, including any one of the first electrode pairs; And A first potential is generated in the first electrode pair and an equal potential is formed in the second electrode pair to display a first gray level in the liquid crystal layer, an equal potential is formed in the first electrode pair, and a potential difference is generated in the second electrode pair And a data voltage generating circuit for displaying a second gradation on the liquid crystal layer, Wherein the first electrode pair is a pixel electrode and a first common electrode formed on the same substrate, Wherein the liquid crystal cell comprises: a first thin film transistor for switching supply of a first data voltage to the pixel electrode; And a second thin film transistor for switching supply of a second data voltage to the first common electrode. delete 11. The method of claim 10, And the first common electrode is formed in an independent pattern for each of the liquid crystal cells. 11. The method of claim 10, And the second electrode pairs are pixel electrodes and second common electrodes formed on different substrates, respectively. delete 14. The method of claim 13, Wherein the data voltage generating circuit comprises: A timing controller for differently generating second digital video data corresponding to a second data voltage of the first common electrode according to a gray level of the first digital video data corresponding to the first data voltage of the pixel electrode; And And a data driving circuit for converting the first and second digital video data into the first and second data voltages, respectively. 16. The method of claim 15, The timing controller includes: And generating second digital video data substantially the same as the first digital video data through copying if the second grayscale is not the second grayscale, And generates the second digital video data as the second digital video data. 17. The method of claim 16, Wherein the digital black data is digital data for selecting a lowest level analog gamma voltage such that the second data voltage is substantially equal to a common voltage of the second common electrode. 17. The method according to claim 10 or 16, Wherein the first gradation is a gradation other than a black gradation, and the second gradation is a black gradation. 14. The method of claim 13, And a common voltage generating unit for supplying a common voltage to the second common electrode. A liquid crystal cell having first, second and third electrodes for driving liquid crystal molecules; And An electric field is formed between two electrodes formed on the same substrate among the electrodes at the first gray level so that the liquid crystal molecules are driven on the basis of a substantially same horizontal plane as the substrate surface, And a liquid crystal driving circuit which forms an electric field between each of the two electrodes so as to drive the liquid crystal molecules based on a plane substantially perpendicular to the substrate surface, Wherein the first and second electrodes are pixel electrodes and first common electrodes respectively formed on the same substrate and the third electrodes are formed on a substrate different from the first and second electrodes with the liquid crystal molecules interposed therebetween A second common electrode, In the liquid crystal cell, A first thin film transistor for switching supply of a first data voltage to the pixel electrode; And And a second thin film transistor for switching supply of a second data voltage to the first common electrode. 21. The method of claim 20, Wherein the first and second electrodes are pixel electrodes and first common electrodes respectively formed on the same substrate and the third electrodes are formed on a substrate different from the first and second electrodes with the liquid crystal molecules interposed therebetween And the first common electrode is a second common electrode. 21. The method of claim 20, And the first common electrode is formed in an independent pattern for each of the liquid crystal cells. delete delete 21. The method of claim 20, In the liquid crystal driving circuit, A timing controller for differently generating second digital video data corresponding to a second data voltage of the first common electrode according to a gray level of the first digital video data corresponding to the first data voltage of the pixel electrode; And And a data driving circuit for converting the first and second digital video data into the first and second data voltages, respectively. 26. The method of claim 25, The timing controller includes: And generating second digital video data substantially the same as the first digital video data through copying if the second grayscale is not the second grayscale, And generates the second digital video data as the second digital video data. 27. The method of claim 26, Wherein the digital black data is digital data for selecting a lowest level analog gamma voltage such that the second data voltage is substantially equal to a common voltage of the second common electrode. 27. The method of claim 20 or 26, Wherein the first gradation is a gradation other than a black gradation, and the second gradation is a black gradation. 21. The method of claim 20, And a common voltage generating unit for supplying a common voltage to the second common electrode.

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