KR20090056205A - Liquid crystal display device and driving method thereof - Google Patents

Abstract

A liquid crystal display and a driving method thereof are provided to drive a liquid crystal molecule by only using an electric force, thereby simplifying a process as improving power consumption and having memory property. First and second substrates(120,150) are separated from each other as facing together. Gate lines and data lines are formed in an upper part of the first substrate, and cross each other to define a pixel area. A thin film transistor is connected to the gate lines and the data lines. A first common electrode(140) is formed in the pixel region of the first substrate's upper part. Pixel electrodes(136) are formed in the pixel region of the first common electrode's upper part, and are connected to the thin film transistor. A second common electrode is formed in a lower part of the second substrate. A liquid crystal layer is formed between the pixel electrodes and the second common electrode.

Description

Liquid Crystal Display Device And Driving Method Thereof}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a simplified process and memory characteristics and a driving method thereof.

Cathode Ray Tubes (CRTs) have been mainly used in display devices such as televisions and monitors until recently. However, these cathode ray tubes have disadvantages of high weight and volume and high driving voltage.

Accordingly, there is a need for a flat panel display (FPD) having excellent characteristics such as light weight and low power consumption, and a liquid crystal display (LCD device) or an electroluminescent device (ELD) has been developed.

In general, a liquid crystal display device is a non-light emitting device that implements an image by using a refractive index difference using optical anisotropy of a liquid crystal layer interposed between an array and a color filter substrate. Here, the liquid crystal layer is driven by the electric field generated by applying the alignment force and the voltage of the alignment film.

1 is a cross-sectional view of a conventional liquid crystal display device.

As shown in FIG. 1, the liquid crystal display device 10 may be formed between the first and second substrates 20 and 50 and the first and second substrates 20 and 50 spaced apart from each other. ).

The pixel region P is defined in the first substrate 20 by gate lines (not shown) and data lines (not shown) that cross each other.

A gate electrode 22 is formed in each pixel region P on the inner surface of the first substrate 20, and a gate insulating film 24 is formed on the gate electrode 22. An active layer 26 is formed in a region corresponding to the gate electrode 22 on the gate insulating layer 24, and an ohmic contact layer 28 is formed on both ends of the active layer 26. The source electrode 30 and the drain electrode 32 spaced apart from each other are formed on the ohmic contact layer 28. The gate electrode 22, the active layer 26, the source electrode 30, and the drain electrode 32 form a thin film transistor T. The passivation layer 34 is formed on the source electrode 30 and the drain electrode 32, and the pixel electrode 36 connected to the drain electrode 32 is formed in each pixel region P on the passivation layer 34. Is formed. The first alignment layer 38 is formed on the pixel electrode 36.

The black matrix 52 is formed at the boundary of the pixel region P on the inner surface of the second substrate 50, and the color filter layer includes red, green, and blue color filters in each pixel region P under the black matrix 52. 54 is formed. The common electrode 56 is formed under the color filter layer 54, and the second alignment layer 58 is formed under the common electrode 56.

The liquid crystal layer 70 is formed between the first and second alignment layers 38 and 58. The first and second alignment layers 38 and 58 are formed through a rubbing process, and a strong surface alignment control force is formed between the liquid crystal molecules of the liquid crystal layer 70 and the first and second alignment layers 38 and 58 by the rubbing process. orientation restoring force is generated through surface anchoring energy.

The liquid crystal layer 70 is driven by the alignment restoring force of the first and second alignment layers 38 and 58 and the electric force between the pixel electrode 36 and the common electrode 56.

That is, when voltage is applied to the pixel electrode 36 and the common electrode 56, an electric field is generated, and the liquid crystal molecules of the liquid crystal layer 70 are rearranged by the electric force generated by the generated electric field.

If no voltage is applied to the pixel electrode 36 and the common electrode 56, the liquid crystal molecules of the rearranged liquid crystal layer 70 return to their original arrangement by the orientation restoring force.

Therefore, the liquid crystal layer 70 may have two states having different transmittances, and the liquid crystal display device 10 displays an image by using the same.

However, the first and second alignment layers 38 and 58 are formed by rubbing rubbing the polymer layer with fibers such as a rubbing cloth after forming the polymer layer with a polymer material such as polyimide. Therefore, the formation of the first and second alignment films 38 and 58 for the orientation restoring force requires a complicated process.

 In addition, static electricity may be generated by rubbing, and the static electricity may adversely affect devices such as the thin film transistor T formed on the substrate.

In the state where no electric field is generated between the pixel electrode 36 and the common electrode 56, the liquid crystal layer 70 returns to its original state due to the orientation restoring force, and thus the same image data is required even when the same image is to be displayed. To re-enter the liquid crystal layer 70 must be rearranged. For example, a liquid crystal display device driven at a refresh rate of 60 Hz to 120 Hz requires input of image data every 1/60 second to 1/120 second, thereby increasing power consumption.

SUMMARY OF THE INVENTION The present invention has been devised to solve the above problems, and an object thereof is to provide a liquid crystal display device and a method of driving the same, by simplifying a process, improving power consumption, and driving memory by driving liquid crystal molecules only with electric force.

The present invention, the first and second substrates facing each other and spaced apart to achieve the above object; A gate wiring and a data wiring formed on the first substrate and crossing each other to define a pixel area; A thin film transistor connected to the gate line and the data line; A first common electrode formed in the pixel area on the first substrate; A pixel electrode formed in the pixel region on the first common electrode and connected to the thin film transistor; A second common electrode formed under the second substrate; A liquid crystal display device including a liquid crystal layer formed between the pixel electrode and the second common electrode is provided.

The liquid crystal layer directly contacts the pixel electrode and the second common electrode without the alignment layer. The liquid crystal display may further include a first alignment suppression layer formed between the liquid crystal layer and the pixel electrode, and a second alignment suppression layer formed between the liquid crystal layer and the second common electrode. Surface energy of the first and second alignment suppression layers is lower than that of the pixel electrode and the first common electrode, respectively.

The first common electrode is formed on an entire surface of the pixel region, and the pixel electrode is connected to the thin film transistor and has a horizontal portion extending in parallel to the gate wiring, and a plurality of parallel portions extending from the horizontal portion in parallel with the data wiring. The second common electrode is formed on a lower front surface of the second substrate.

The liquid crystal display further comprises an interlayer insulating film covering the thin film transistor and a protective layer covering the first common electrode, wherein the first common electrode is formed on the interlayer insulating film, and the pixel electrode is on the protective layer. Can be formed on.

The liquid crystal display further includes an interlayer insulating layer covering the first common electrode and a protective layer covering the thin film transistor, wherein the first common electrode is formed on the first substrate, and the thin film transistor is disposed on the first substrate. The pixel electrode may be formed on the interlayer insulating layer, and the pixel electrode may be formed on the protective layer.

First and second common voltages are applied to the first and second common electrodes, respectively, and data voltages between the first and second common voltages are applied to the pixel electrodes.

The data voltage is displayed while changing between the equipotential voltage and the second common voltage such that the equipotential surfaces of the electric field generated by the first and second common voltages are the same as the pixel electrodes.

On the other hand, the present invention comprises the steps of forming a gate wiring and a data wiring on the first substrate to cross each other to define a pixel region; Forming a thin film transistor connected to the gate line and the data line; Forming a first common electrode in the pixel region; Forming a pixel electrode connected to the thin film transistor in the pixel area on the first common electrode; Forming a second common electrode on the second substrate; Bonding the first and second substrates to face the pixel electrode and the second common electrode; It provides a method of manufacturing a liquid crystal display device comprising the step of forming a liquid crystal layer between the pixel electrode and the second common electrode.

The method of manufacturing the liquid crystal display may further include forming a first alignment suppression layer on the pixel electrode, and forming a second alignment suppression layer on the common electrode. Surface energy of the bidirectional suppression layer is lower than that of the pixel electrode and the first common electrode, respectively.

On the other hand, the present invention comprises the steps of applying a first common voltage to the first common electrode on the first substrate; Applying a data voltage to the pixel electrode on the first common electrode; Applying a second common voltage to a second common electrode below the second substrate facing the first substrate and spaced apart from the second substrate; Arranging liquid crystal molecules of a liquid crystal layer formed between the pixel electrode and the second common electrode according to the electric field generated by the first common voltage, the data voltage, and the second common voltage. Provide a method.

The applying of the data voltage may include displaying grayscales while changing between the equipotential voltage and the second common voltage such that the equipotential surfaces of the electric field generated by the first and second common voltages are the same as the pixel electrodes. Steps.

The liquid crystal display displays a black image when the data voltage is the equipotential voltage, and the liquid crystal display displays a white image when the data voltage is the second common voltage.

The method of driving the liquid crystal display device may further include maintaining the arrangement of liquid crystal molecules of the liquid crystal layer by floating the first common electrode, the pixel electrode, and the second common electrode.

According to the present invention, since the alignment film is not formed, the rubbing process and the like can be omitted, thereby simplifying the manufacturing process of the liquid crystal display device and preventing the defect caused by the alignment film forming process.

In addition, since the liquid crystal molecules are driven only by the electric force, the liquid crystal display has memory characteristics and power consumption is reduced.

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

The present invention drives the liquid crystal molecules by the electric force of the vertical, horizontal electric field by the three electrodes instead of the orientation restoring force by the alignment film to achieve the above object.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, where only the same reference numerals are used for the same parts.

2 is a plan view of an array substrate of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 3 is a cross-sectional view of the liquid crystal display according to an exemplary embodiment of the present invention, and is cut along the cutting line III-III of FIG. Corresponds to.

As shown in FIGS. 2 and 3, the liquid crystal display device 110 is a liquid crystal formed between the first and second substrates 120 and 150 facing each other and the first and second substrates 120 and 150. Layer 170.

A gate wiring 142 and a gate electrode 122 extending from the gate wiring 142 are formed on an inner surface of the first substrate 120 called an array substrate, and a gate is formed on the gate wiring 142 and the gate electrode 122. The first insulating layer 124, which is an insulating film, is formed.

An active layer 126 made of pure silicon is formed on the first insulating layer 124 corresponding to the gate electrode 122, and an impurity-doped silicon is formed on the active layer 126. The ohmic contact layer 128 is formed.

A source electrode 130 and a drain electrode 132 spaced apart from each other are formed on the ohmic contact layer 128, and at the same time, the data line 144 defining the pixel region P by crossing the gate line 142 is formed. 1 is formed on the insulating layer 124. The source electrode 130 extends from the data line 144.

The gate electrode 122, the active layer 126, the source electrode 130, and the drain electrode 132 form a thin film transistor T connected to the gate wiring and the data wiring 142 and 144.

The second insulating layer 146, which is an interlayer insulating layer, is formed on the thin film transistor T, and the first common electrode 140 is formed on the entire pixel area P on the second insulating layer 146. The first common electrode may be horizontally connected to each other through the first common electrode of the adjacent pixel region P and the common electrode connector 140a. According to the exemplary embodiment of the present invention, the first common electrodes of the adjacent pixel regions in the horizontal direction are connected to each other and vertical to apply the same common voltage to the first common electrodes in the horizontal direction corresponding to the same gate wiring and scan the same. The first common electrodes of the adjacent pixel regions in the lateral direction are not connected to each other, but in another embodiment, the first common electrodes of the adjacent pixel regions in the horizontal / vertical direction are all connected or the first common electrodes of the adjacent pixel regions in the vertical direction are connected. The first common electrodes of the connected and horizontally adjacent pixel regions may not be connected to each other.

In addition, in the present exemplary embodiment, the first common electrode 140 is formed on the thin film transistor T, but in another embodiment, the first common electrode may be integrally formed on the entire surface of the first substrate 120 under the thin film transistor. In this case, the second insulating layer may be formed between the first common electrode and the thin film transistor, that is, between the first common electrode and the gate electrode, and the third insulating layer may be formed to cover the thin film transistor.

A third insulating layer 148, which is a protective layer, is formed on the first common electrode 140, and a drain contact hole CNT exposing the drain electrode 132 is formed in the second and third insulating layers 146 and 148. Is formed.

The pixel electrode 136 connected to the drain electrode 132 of the thin film transistor T is formed in the pixel region P on the third insulating layer 148 through the drain contact hole CNT.

The pixel electrode 136 is connected to the drain electrode 132 and extends in parallel with the gate line 142. A plurality of vertical lines extend in parallel with the data line 144 from the horizontal part 136a. Section 136b.

In the present embodiment, the plurality of vertical portions 136b have bar shapes spaced parallel to each other. In another embodiment, the plurality of vertical parts 136b may have a bar shape having a zigzag shape having at least one bent portion to secure wide viewing angle characteristics. It may be formed concentrically or helically.

A black matrix 152 is formed on the inner surface of the second substrate 150 called the color filter substrate so as to correspond to the gate wiring 142, the data wiring 144, and the thin film transistor T of the first substrate 120. do.

A color filter layer 154 including red, green, and blue color filters is formed in the opening of the black matrix 152 corresponding to the pixel region P, and a second common electrode 156 is formed under the color filter layer 154. The second substrate 150 is integrally formed on the front surface.

The liquid crystal layer 170 is formed between the pixel electrode 136 of the first substrate 120 and the second common electrode 156 of the second substrate 150.

Here, an alignment layer is not formed between the pixel electrode 136 and the liquid crystal layer 170, and between the second common electrode 156 and the liquid crystal layer 170, and the liquid crystal layer 170 includes the pixel electrode 136 and the first electrode. The two common electrodes 156 are in direct contact with each other.

Therefore, the formation of the alignment layer such as the formation of the polymer material layer and rubbing can be omitted, thereby simplifying the manufacturing process of the liquid crystal display 110 and preventing the defect caused by the alignment layer forming process.

By the way, in the liquid crystal display device according to another embodiment of the present invention, not only the alignment layer is formed so that the liquid crystal layer is not aligned, but also the alignment suppression layer may be formed so that the liquid crystal layer is not aligned by any other factor. This will be described in detail with reference to the drawings.

4 is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention, in which the same parts as in FIG. 3 are assigned the same reference numerals and description thereof will be omitted.

As shown in FIG. 4, a first alignment suppression layer 160 is formed on the pixel electrode 136 of the liquid crystal display 110 according to another exemplary embodiment, and a lower portion of the second common electrode 156 is disposed below the pixel electrode 136. The second alignment suppression layer 162 is formed.

Therefore, the liquid crystal layer 170 is formed between the first and second alignment suppression layers 160 and 162, instead of directly contacting the pixel electrode 136 and the second common electrode 156.

Even when the alignment film does not exist, the liquid crystal may be formed according to the liquid crystal flow conditions at the time of liquid crystal injection for forming the liquid crystal layer 170, the electrode formation conditions such as the pixel electrode or the second common electrode, or the insulating film formation conditions below. The layer 170 may be oriented. If the liquid crystal layer 170 is oriented, the liquid crystal display is driven by electric force and alignment restoring force and thus does not have memory characteristics.

Therefore, in the liquid crystal display according to another exemplary embodiment of the present invention, in order to prevent an undesired alignment of the liquid crystal layer, between the pixel electrode 136 and the liquid crystal layer 170 and the second common electrode 156 and the liquid crystal layer ( First and second alignment suppression layers 160 and 162 are formed between the two sides 170, respectively.

The first and second alignment suppression layers 160 and 162 may be made of a material that does not interact with each other because the surface energy is sufficiently low in relation to the liquid crystal molecules of the liquid crystal layer 170. The bidirectional suppression layers 160 and 162 may be formed to have lower surface energy than the pixel electrode 136 or the second common electrode 156.

By forming the first and second alignment suppression layers 160 and 162, the liquid crystal layer 170 is not aligned, and as a result, generation of alignment restoring force of the liquid crystal layer 170 is prevented.

Meanwhile, the liquid crystal display according to the exemplary embodiment of the present invention generates a vertical or horizontal electric field by applying a voltage to the pixel electrode and the first and second common electrodes, and controls the arrangement of the liquid crystal molecules by the electric force generated by the generated electric field. This will be described in detail with reference to the drawings.

5A to 5D are diagrams illustrating an operating state of the liquid crystal display according to the exemplary embodiment of the present invention, and show a ready state, a first operating state, a second operating state, and a memory state, respectively. For convenience, only the first common electrode 140, the pixel electrode 136, and the second common electrode 156 to which the voltage is applied and the liquid crystal layer 170 of the pixel region P are schematically illustrated.

4A to 4C illustrating driving states of liquid crystal molecules by applying voltage, first and second common voltages Vcom1 and Vcom2 are applied to the first and second common electrodes 140 and 156 of the liquid crystal display 110. Is applied and a data voltage Vdata is applied to the pixel electrode 136 while the first and second common electrodes 140 and 156 are shown in FIG. 4D, which shows a state in which an arrangement of liquid crystal molecules is maintained without applying a voltage. And the pixel electrode 136 are floating.

Specifically, in FIG. 4A, in which the liquid crystal display device 110 is ready, a first common voltage Vcom1, for example, 0 V is applied to the first common electrode 140, and the first data is applied to the pixel electrode 136. A voltage Vdata1, for example, 0V is applied, and a second common voltage Vcom2, for example, 10V, is applied to the second common electrode 156.

In this state, the first and second substrates 120 and 150 are respectively formed by the first common electrode 140 and the second common electrode 156 and by the pixel electrode 136 and the second common electrode 156. The vertical electric field E in the vertical direction is generated, and the liquid crystal molecules 170a of the liquid crystal layer 170 are arranged by the generated vertical electric field, so that the liquid crystal display 110 displays a black image. .

However, at this time, since the first common electrode 140 and the pixel electrode 136 have the same potential, the vertical electric field and the pixel electrode 136 and the first by the first common electrode 140 and the second common electrode 156 are formed. The vertical electric field by the two common electrodes 156 forms different equipotential surfaces around the pixel electrode 136, so that the vertical electric field is partially distorted around the pixel electrode 136. Therefore, light leakage exists in the black image of the liquid crystal display 110. Here, the equipotential surface refers to a surface perpendicular to the direction of the electric field and having the same electric potential, and in the case of the vertical electric field perpendicular to the first and second substrates 120 and 150, Multiple equipotential surfaces are formed in parallel.

In FIG. 4B, the first operating state of the liquid crystal display device 110, a first common voltage Vcom1, for example, 0 V is applied to the first common electrode 140, and a second data voltage is applied to the pixel electrode 136. (Vdata2), for example, 2V to 3V, and a second common voltage Vcom2, for example, 10V, is applied to the second common electrode 156.

In this state, a vertical electric field E is generated by the first common electrode 140 and the second common electrode 156 and also by the pixel electrode 136 and the second common electrode 156, respectively. The liquid crystal molecules 170a of the liquid crystal layer 170 are arranged along the electric field, and the liquid crystal display 110 displays a black image.

In addition, different first common voltages Vcom1 and second data voltages Vdata2 are applied to the first common electrode 140 and the pixel electrode 136 to have different potentials from each other. The second data voltage Vdata2 may be determined such that the equipotential surfaces of the vertical electric field generated by the second common electrode 156 and the pixel electrode 136 form the same plane, and the second data voltage Vdata2 satisfying such a condition. ) Is called the equipotential voltage.

Here, the distance between the first common electrode 140 and the pixel electrode 136 and the dielectric constant of the medium, the distance between the pixel electrode 136 and the second common electrode 156 and the dielectric constant of the medium are appropriate second data voltages ( Vdata2 is an element for determining an equipotential voltage. A second insulating layer 146 exists between the first common electrode 140 and the pixel electrode 136, and the pixel electrode 136 and the second common electrode ( Since the liquid crystal layer 170 is present between 156, the second data voltage Vdata2 is appropriately determined by the dielectric constant and thickness of the second insulating layer 146 and the dielectric constant and thickness of the liquid crystal layer 170 (that is, the cell gap). : Equipotential voltage) is determined.

Accordingly, when the second data voltage Vdata2 (equal potential voltage) that satisfies this condition is applied to the pixel electrode 136, the vertical electric field generated by the first common electrode 140 and the second common electrode 156 is generated. The vertical electric field generated by the pixel electrode 136 and the second common electrode 156 is completely coincident with each other. As a result, the liquid crystal molecules 170a of the liquid crystal layer 170 are not distorted and are arranged by a perfect vertical electric field so that the liquid crystals The display device 110 displays a perfect black image.

In FIG. 4C, which is a second operation state of the liquid crystal display device 110, a first common voltage Vcom1, for example, 0 V is applied to the first common electrode 140, and a third data voltage is applied to the pixel electrode 136. Vdata3, for example, 10V is applied, and a second common voltage Vcom2, for example, 10V, is applied to the second common electrode 156.

In this state, a vertical electric field is generated by the first common electrode 140 and the second common electrode 156, and a horizontal electric field is generated by the pixel electrode 136 and the first common electrode 140. In more detail, the pixel electrode 136 and the first common electrode 140 are vertically upward from the pixel electrode 136, and are horizontally bent between the pixel electrodes 136 and then the lower first common electrode 140. A U-shaped electric field E directed to) is generated. However, since the horizontal component between the pixel electrodes 136 is used to drive the liquid crystal molecules 170a of the liquid crystal layer 170, the horizontal of the electric field generated by the pixel electrode 136 and the first common electrode 140 is horizontal. It can be understood that the component arranges the liquid crystal molecules 170a, which may be described as generating a horizontal electric field by the pixel electrode 136 and the first common electrode 140.

Meanwhile, since the pixel electrode 136 and the second common electrode 156 have the same potential, no electric field is generated by the pixel electrode 136 and the second common electrode 156. In addition, since the distance between the first common electrode 140 and the second common electrode 156 is very large compared to the distance between the first common electrode 140 and the pixel electrode 136, the first common electrode 140 ) And the size of the vertical electric field by the second common electrode 156 may be negligible compared to the size of the horizontal electric field by the first common electrode 140 and the pixel electrode 136.

Therefore, in the second operation state of the liquid crystal display device 110, the liquid crystal molecules 170a of the liquid crystal layer 170 are arranged along the horizontal electric field by the first common electrode 140 and the pixel electrode 136, and the liquid crystal The display device 110 displays a white image.

In FIG. 4D, the memory state of the liquid crystal display device 110, the first common electrode 140, the pixel electrode 136, and the second common electrode 156 are floated.

Therefore, there is no electric field generated by the first common electrode 140, the pixel electrode 136, and the second common electrode 156, so that the liquid crystal molecules 170a of the liquid crystal layer 170 are not rearranged. Keep the previous arrangement.

In the conventional liquid crystal display device, when the electrodes on both sides of the liquid crystal layer are floated, the liquid crystal molecules of the liquid crystal layer return to the original arrangement state due to the orientation restoring force between the liquid crystal layer and the alignment layer, but do not maintain the previous arrangement state. In the case of the liquid crystal display device 110 according to the embodiment, since the alignment layer is not formed, the alignment restoring force does not act on the liquid crystal molecules 170a of the liquid crystal layer 170.

Therefore, when the first common electrode 140, the pixel electrode 136, and the second common electrode 156 are suspended, the generation of the electric field stops, and the liquid crystal molecules 170a of the liquid crystal layer 170 are in an initial arrangement state. It is not returned to maintaining the previous arrangement, that is, the arrangement along the electric field immediately before floating.

Since this state is maintained until the generation of a new electric field, the liquid crystal display 110 may display an image without re-entering the periodic image data, thereby improving power consumption. In particular, in the case of an image in which there is no change in the image data or a change in only a portion, such as a still image, it is possible to display the image by selectively applying a voltage only to the changed portion, in which case the refresh rate can be minimized. Therefore, low power consumption can be driven.

In the present embodiment, the first common electrode 140, the pixel electrode 136, and the second common electrode 156 are floated for the memory state. In another embodiment, the first common electrode 140 is grounded and the pixel is grounded. The memory state may be secured by only floating the electrode 136 and the second common electrode 156.

6A to 6C are diagrams illustrating an electric field and an equipotential surface of a liquid crystal display according to an exemplary embodiment of the present invention, and show a ready state, a first operating state, and a second operating state, respectively. 6A to 6C, dotted lines represent electric field lines of electric fields (ie, directions of electric fields), and solid lines represent equipotential surfaces (or equipotential lines) of electric fields.

As shown in FIG. 6A, in the ready state of the liquid crystal display, the first common voltage Vcom1 and the first data voltage are respectively applied to the first common electrode 140, the pixel electrode 136, and the second common electrode 156. Vdata1 and the second common voltage Vcom2 may be applied. For example, about 0V, about 0V, and about 10V may be applied, respectively.

An electric field is generated by applying a voltage to the first common electrode 140, the pixel electrode 136, and the second common electrode 156. The electric field lines of the electric field are perpendicular to the pixel electrode 136. ) Is distorted between the pixel electrodes 136 and toward the center between the pixel electrodes 136.

The equipotential surface perpendicular to the electric field lines is horizontally formed above the pixel electrode 136, but has a shape that sags between the pixel electrodes 136 as a lower first common electrode 140, which is the first common electrode 140. ) And the same voltage are applied to the pixel electrode 136.

In this case, the liquid crystal display 110 displays a black image. The liquid crystal display 110 may display an image by using the ready state, but may not be directly used to display an image because light leakage exists.

As shown in FIG. 6B, in the first operation state of the liquid crystal display, the first common voltage Vcom1 and the second common electrode 140, the pixel electrode 136, and the second common electrode 156 are respectively applied. The data voltage Vdata2 and the second common voltage Vcom2 may be applied, for example, about 0V, about 2V to 3V, and about 10V, respectively.

An electric field is generated by applying a voltage to the first common electrode 140, the pixel electrode 136, and the second common electrode 156. An electric field line of the electric field is formed between the pixel electrode 136 and the second common electrode 156. It is uniformly and vertically generated in all regions, and an equipotential surface is generated in parallel with the first and second substrates in all regions between the pixel electrode 136 and the second common electrode 156.

This is possible by applying a second data voltage Vdata2 to the pixel electrode 136 such that the pixel electrode 136 is an equipotential surface of the electric field generated by the first and second common electrodes 140, 156. The same electric field may be generated when the pixel electrode 136 does not exist between the first and second common electrodes 140 and 156.

In addition, the liquid crystal molecules 170a of the liquid crystal layer 170 are arranged along the vertical electric fields generated by the first and second common electrodes 140 and 156 so that the liquid crystal display displays a perfect black image.

As illustrated in FIG. 6C, in the second operation state of the liquid crystal display, the first common voltage Vcom1 and the first common electrode 140, the pixel electrode 136, and the second common electrode 156 are respectively applied. The third data voltage Vdata3 and the second common voltage Vcom2 may be applied. For example, about 0V, about 10V, and about 10V may be applied, respectively.

An electric field is generated by applying a voltage to the first common electrode 140, the pixel electrode 136, and the second common electrode 156. The electric field lines of the electric field are perpendicular to the pixel electrode 136. Are formed horizontally between the pixel electrodes 136.

In addition, an equipotential surface perpendicular to the electric line of force is generated in a concentric shape around the pixel electrode 136.

In this case, the liquid crystal molecules 170a of the liquid crystal layer 170 are arranged along the horizontal electric field generated between the pixel electrode 136 by the first common electrode 140 and the pixel electrode 136. ) Displays a white image.

By driving the liquid crystal display 110 between the first and second operating states, a gray image having a luminance between black and white can be displayed, which will be described in detail with reference to the accompanying drawings.

7 is a transmittance-voltage curve (TV curve) of the liquid crystal display according to the exemplary embodiment of the present invention.

FIG. 7 illustrates first and second common voltages Vcom1 and Vcom2 applied to the first and second common electrodes 140 and 156, respectively, and a voltage applied to the pixel electrode 136 at the first data voltage Vdata1. It is a result of simulating the transmittance of the liquid crystal display device which appears when the third data voltage Vdata3 is changed through the second data voltage Vdata2.

For example, the change in transmittance of the liquid crystal display is described by changing the data voltage from about 0V to about 10V while the first and second common electrodes 140 and 156 are respectively applied with about 0V and about 10V.

As shown in FIG. 7, when the data voltage applied to the pixel electrode 136 is about 0.4 V, the transmittance of the liquid crystal display is not 0% but has a larger value. The presence of light leakage in the ready state of 5a.

The transmittance is maintained at about 0% until the data voltage reaches about 5V, and then gradually increases at about 5.5V. Thereafter, at a data voltage of about 9.5V, the transmittance becomes a maximum value and then decreases again.

Accordingly, the liquid crystal display may display images of various gray levels by changing the data voltage applied to the pixel electrode between about 5.5V and about 9.5V.

As described above, in the liquid crystal display according to the exemplary embodiment of the present invention, the liquid crystal molecules are driven by the vertical electric field and the horizontal electric field by applying voltage to three electrodes of the first and second common electrodes and the pixel electrode without forming the alignment layer. .

This simplifies the manufacturing process of the liquid crystal display device and prevents defects caused by the alignment film forming process.

In addition, since the liquid crystal molecules are driven by electric force instead of orientation restoring force, the liquid crystal display may have memory characteristics, thereby minimizing the input of periodic data voltages, thereby improving power consumption.

1 is a cross-sectional view of a conventional liquid crystal display device

2 is a plan view of an array substrate of a liquid crystal display according to an exemplary embodiment of the present invention.

3 is a cross-sectional view of a liquid crystal display according to an exemplary embodiment of the present invention.

4A to 4D are diagrams showing operating states of the liquid crystal display according to the exemplary embodiment of the present invention.

5A to 5C are diagrams illustrating electric fields and equipotential surfaces of a liquid crystal display according to an exemplary embodiment of the present invention.

6 is a transmittance-voltage curve of a liquid crystal display according to an exemplary embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

110: liquid crystal display device 120: first substrate

150: second substrate 136: pixel electrode

140: first common electrode 156: second common electrode

Claims (14)

First and second substrates facing each other and spaced apart from each other; A gate wiring and a data wiring formed on the first substrate and crossing each other to define a pixel area; A thin film transistor connected to the gate line and the data line; A first common electrode formed in the pixel area on the first substrate; A pixel electrode formed in the pixel region on the first common electrode and connected to the thin film transistor; A second common electrode formed under the second substrate; Liquid crystal layer formed between the pixel electrode and the second common electrode Liquid crystal display comprising a. The method of claim 1, The liquid crystal layer is in direct contact with the pixel electrode and the second common electrode. The method of claim 1, And a first alignment suppression layer formed between the liquid crystal layer and the pixel electrode, and a second alignment suppression layer formed between the liquid crystal layer and the second common electrode. The surface energy of the liquid crystal display device is lower than the surface energy of the pixel electrode and the first common electrode, respectively. The method of claim 1, The first common electrode is formed on an entire surface of the pixel region, and the pixel electrode is connected to the thin film transistor and has a horizontal portion extending in parallel to the gate wiring, and a plurality of parallel portions extending from the horizontal portion in parallel with the data wiring. And a second common electrode formed on a front surface of the lower side of the second substrate. The method of claim 1, A liquid crystal display further comprising an interlayer insulating layer covering the thin film transistor and a protective layer covering the first common electrode, wherein the first common electrode is formed on the interlayer insulating layer, and the pixel electrode is formed on the protective layer. Device. The method of claim 1, An interlayer insulating film covering the first common electrode and a protective layer covering the thin film transistor, wherein the first common electrode is formed on the first substrate, and the thin film transistor is formed on the interlayer insulating film. The pixel electrode is formed on the passivation layer. The method of claim 1, And first and second common voltages are respectively applied to the first and second common electrodes, and a data voltage between the first and second common voltages is applied to the pixel electrodes. The method of claim 7, wherein And the data voltage is displayed while changing between the equipotential voltage and the second common voltage such that the equipotential surfaces of the electric field generated by the first and second common voltages are the same as the pixel electrodes. Forming a gate line and a data line on the first substrate to cross each other to define a pixel area; Forming a thin film transistor connected to the gate line and the data line; Forming a first common electrode in the pixel region; Forming a pixel electrode connected to the thin film transistor in the pixel area on the first common electrode; Forming a second common electrode on the second substrate; Bonding the first and second substrates to face the pixel electrode and the second common electrode; Forming a liquid crystal layer between the pixel electrode and the second common electrode Method of manufacturing a liquid crystal display device comprising a. The method of claim 9, Forming a first alignment suppression layer on the pixel electrode, and forming a second alignment suppression layer on the common electrode, wherein the surface energy of the first and second alignment suppression layers is respectively A method of manufacturing a liquid crystal display device having lower surface energy than the pixel electrode and the first common electrode. Applying a first common voltage to the first common electrode on the first substrate; Applying a data voltage to the pixel electrode on the first common electrode; Applying a second common voltage to a second common electrode below the second substrate facing the first substrate and spaced apart from the second substrate; Arranging liquid crystal molecules of a liquid crystal layer formed between the pixel electrode and the second common electrode along an electric field generated by the first common voltage, the data voltage, and the second common voltage; Method of driving a liquid crystal display device comprising a. The method of claim 11, The applying of the data voltage may include displaying grayscales while changing between the equipotential voltage and the second common voltage such that the equipotential surfaces of the electric field generated by the first and second common voltages are the same as the pixel electrodes. A driving method of a liquid crystal display device comprising the step. The method of claim 12, And the liquid crystal display displays a black image when the data voltage is the equipotential voltage, and the liquid crystal display displays a white image when the data voltage is the second common voltage. The method of claim 11, And floating the first common electrode, the pixel electrode, and the second common electrode to maintain an arrangement of liquid crystal molecules of the liquid crystal layer.

Images