KR20070002677A - Liquid crystal display device - Google Patents

Abstract

An LCD is provided to facilitate return of a polymer alignment layer to an initial state and prevent a defect such as disclination by forming a common electrode and a pixel electrode on one substrate and providing an auxiliary electrode on a facing substrate. A thin film transistor(TFT) and a pixel electrode(117) are formed in a unit pixel defined by a gate line and a data line intersecting each other on a first substrate. A facing electrode is formed on the first substrate and forms an electric field together with the pixel electrode. A second substrate faces and is bonded with the first substrate, and includes an auxiliary electrode(125). A liquid crystal layer(130) is formed between the first and second substrates. Polarizers(150) are formed outside the first and second substrates.

Description

Liquid Crystal Display Device

1 is a plan view of a conventional IPS mode liquid crystal display device.

2 is a diagram for explaining driving characteristics of FLCP.

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

4 is a view showing the arrangement of the polarizing plate and the initial alignment of the polymer alignment film according to the present invention.

5a and 5b is a view showing the alignment state of the polymer alignment film with or without voltage applied.

6 is a cross-sectional view of a liquid crystal display device according to a second embodiment of the present invention.

* Explanation of symbols on the main parts of the drawings

111 TFT array substrate 112 color filter array substrate

113: liquid crystal layer 117: pixel electrode

124: common electrode 125: auxiliary electrode

130: polymer alignment layer 150: polarizing plate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and in particular, to improve the response speed of a liquid crystal by using a polymer alignment film having liquid crystal properties. A liquid crystal display device to be effectively removed.

Recently, the liquid crystal display device, one of the flat panel display devices that are attracting attention, is an element that changes the optical anisotropy by applying an electric field to a liquid crystal that combines the liquidity and the optical properties of the crystal, which is applied to a conventional cathode ray tube. Compared with low power consumption, small volume, large size and high definition, it is widely used in flat screen TVs, portable computers and monitors.

Among the active matrix liquid crystal display devices, twisted nematic (TN) type liquid crystal display devices are mainly used. In the twisted nematic method, electrodes are installed on two substrates and the liquid crystal directors are arranged to be twisted by 90 °. It is a technique of driving a liquid crystal director by applying a voltage to an electrode.

Twisted nematic liquid crystal displays (TN LCDs) are in the spotlight for their ease of portability and reduced power consumption because they offer excellent contrast, color reproducibility, and thinness. However, there is a disadvantage in that the viewing angle is narrow and the response speed to the applied voltage is slow, making it difficult to reproduce the moving image.

In order to solve the viewing angle problem of the TN method, an IPS mode (In-Plane Switching Mode) for forming two electrodes on one substrate and controlling the director of the liquid crystal with a transverse electric field generated between the two electrodes has been introduced.

The IPS mode liquid crystal display device is generally composed of a color filter array substrate and a thin film transistor array substrate disposed opposite to each other and having a liquid crystal layer therebetween, wherein the color filter array substrate includes a black matrix for preventing light leakage; Color filter layers of R, G, and B are formed on the black matrix to form colors, and the thin film transistor array substrate has gate and data lines defining unit pixels and intersecting points of the gate and data lines. The formed thin film transistor and the common electrode and the pixel electrode which cross each other alternately and generate a transverse electric field are formed. In this case, an alignment layer for determining an initial alignment direction of the liquid crystal layer is further provided on the inner surfaces of the two substrates.

That is, as shown in FIG. 1, the common electrode 524 and the pixel electrode 517 are formed parallel to each other on the same substrate, and a horizontal electric field in a horizontal direction with respect to the substrate is applied by applying a voltage between the two electrodes. By generating, the liquid crystal molecules are rotated while being kept horizontal with respect to the substrate. In this case, a data voltage is applied to the pixel electrode 517, and a Vcom voltage, which may be a reference voltage with respect to the data voltage, is applied to the common electrode 524.

On the other hand, in order to further improve the response speed of the IPS mode liquid crystal display device, a polymer alignment film having liquid crystal properties is used as the alignment layer. For example, ferroelectric liquid crystal (FLC) is adopted. Ferroelectric liquid crystals have a very fast response time of several tens us to several tens of milliseconds due to inverted switching by spontaneous polarization, since the viewing angle characteristics are greatly improved because they are switched in plane with respect to the substrate.

In general, as shown in FIG. 2, when the voltage is not applied, the ferroelectric liquid crystal is uniformly inclined in the θ direction with respect to the normal line of the liquid crystal layer, and then a specific voltage is applied to the common electrode 524 and the pixel electrode 517. When is applied, the spontaneous polarization (Ps) direction of the ferroelectric liquid crystal molecules 525 is switched by the property of being directed in the direction of the electric field.

At this time, the ferroelectric liquid crystal molecules 525 rotate around the cone according to the size of the electric field, thereby switching light continuously. The gray is controlled by the angle at which the liquid crystal molecules rotate, and the opening angle may be adjusted by the intensity of the voltage applied between the reflective electrode and the common electrode.

When the electric field is not applied to the IPS mode liquid crystal display device, the long axis of the ferroelectric liquid crystal molecules 525 is initially oriented so as to have an angle of 45 degrees with respect to the pixel electrode 517, and when the electric field is applied to the applied data voltage. Rotates 45 degrees or -45 degrees, and when the polymer alignment layer is rearranged in a predetermined direction by a voltage applied thereto, the liquid crystal molecules of the liquid crystal layer are rearranged accordingly to determine the degree of light transmission.

That is, since the ferroelectric liquid crystal molecules 525 have spontaneous polarizations of + and-, the ferroelectric liquid crystal molecules 525 are rotated from ② to ③ during full white driving according to the applied voltage, and at ② when full black driving is performed. Rotate to ①.

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

That is, the IPS mode was introduced to improve the viewing angle of a general liquid crystal display device. However, it was difficult to play a video image due to a slow response speed. Thus, to improve the response speed, a liquid crystal quality was not used without using polyimide as an alignment layer. A polymer aligning film having was used.

However, when the ferroelectric aligning agent is used, there is no problem when driving the device by applying a voltage, but there is a problem in that the resilience of the liquid crystal molecules is weak when switching off the voltage, so that it is difficult to switch to the initial state. When the voltage is turned off, the liquid crystal molecules are restored to the initial alignment state at the anchoring energy of the liquid crystal molecules because the anchoring energy of the polymer alignment layer is generally weak.

Accordingly, the present invention has been made to solve the above problems, by forming a common electrode and a pixel electrode on one substrate and further comprising an auxiliary electrode on the opposite substrate to improve the restoring force of the polymer alignment layer to improve the display of the device. It is an object of the present invention to provide a liquid crystal display device which prevents defects such as clearance and implements a fast response speed.

According to an exemplary embodiment of the present invention, a liquid crystal display device includes a thin film transistor and a pixel electrode formed in a unit pixel defined by gate lines and data lines intersecting each other on a first substrate, and on the first substrate. A counter electrode formed to form an electric field together with the pixel electrode, a second substrate facing and bonded to the first substrate, and an auxiliary electrode formed thereon; a liquid crystal layer formed between the first and second substrates; It is characterized by including the first and second polarizing plates formed on the outside of the second substrate, respectively.

That is, the present invention is characterized by having three electrodes to drive the liquid crystal faster and more accurately to prevent defects such as disclination and to implement a fast response speed.

In detail, an in-plane switching mode (IPS mode) for forming a common electrode and a pixel electrode on one substrate and controlling a director of a liquid crystal by a transverse electric field generated between the two electrodes is provided on an opposite substrate facing the substrate. An auxiliary electrode is further provided.

Alternatively, in the FFS mode (Fringe Field Switching) in which the liquid crystal molecules are operated by a fringe field formed between the counter electrode and the pixel electrode by forming a narrow gap between the counter electrode and the pixel electrode on one substrate. An auxiliary electrode is further provided on the opposing opposing substrate.

In this case, a Vcom voltage applied to the common electrode and the counter electrode may be applied to the auxiliary electrode, a pixel voltage applied to the pixel electrode may be applied, and a voltage of another level may be applied.

On the other hand, the polymer alignment layer, for example, by providing a polymer alignment layer having a liquid crystal quality such as chiral smetic liquid crystal (Chiral Smetic Liquid Crystal Material), FLCP (Ferroelectric Liquid Crystal Polymer) to improve the viewing angle and response speed. In the case of FLCP, the characteristics of switching with respect to the substrate plane are used, and the liquid crystal layer between the FLCP alignment layer is switched with respect to the substrate plane by the FLCP film to improve the viewing angle, and the response speed of the liquid crystal layer is 1 ms high-speed response. It is intended to obtain excellent moving picture quality by having characteristics.

Hereinafter, a liquid crystal display device according to the present invention will be described with reference to the accompanying drawings.

First embodiment

3 is a cross-sectional view of a liquid crystal display device according to a first embodiment, and FIG. 4 is a view showing an arrangement of a polarizing plate and an initial alignment of a polymer alignment layer according to the present invention, and FIGS. 5A and 5B are polymer alignment layers according to whether voltage is applied. It is a figure which shows the orientation state of the.

The first embodiment further includes an auxiliary electrode for the conventional IPS mode, and as shown in FIG. 3, the color filter array substrate 112 having the liquid crystal layer 113 disposed therebetween and disposed opposite to each other. ) And a thin film transistor array substrate 111, wherein the color filter array substrate 112 includes an auxiliary electrode 125 on a front surface thereof, and the thin film transistor array substrate 111 includes a plurality of common electrodes 124 and a plurality of common electrodes 124. The pixel electrode 117 is formed to be alternated between the common electrode 124 and parallel to the common electrode 124.

In this case, the common electrode 124 receives a Vcom signal from an external driving circuit, and the pixel electrode 117 is connected to a drain electrode of the thin film transistor TFT to receive a pixel signal. This causes a lateral electric field.

The Vcom voltage applied to the common electrode may be applied to the auxiliary electrode 125, the pixel voltage applied to the pixel electrode may be applied, or another level voltage may be applied. To prevent.

The pixel electrode 117 and the auxiliary electrode 125 are formed by depositing and patterning a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO), and the common electrode 124 is the pixel. Formed with a transparent conductive material on the same layer as the electrode or on a layer different from the pixel electrode, copper (Cu), aluminum (Al), aluminum alloy (AlNd), tin (Sn), molybdenum (Mo), chromium (Cr) and titanium (Ti), tantalum (Ta), molybdenum-tungsten (MoW) and the like can be formed of an opaque metal layer.

In this case, the liquid crystal layer 113 may use a negative type or a positive type as a nematic liquid crystal and is driven by the transverse electric field.

For reference, although not shown, the color filter array substrate further includes a black matrix for preventing light leakage on the auxiliary electrode, and a color filter layer of R, G, and B for realizing color on the black matrix. The thin film transistor array substrate further includes a gate line and a data line defining unit pixels under the common electrode and the pixel electrode, and a thin film transistor at an intersection point of the gate line and the data line.

The TFT may include a gate electrode branched from the gate wiring, a gate insulating layer stacked on the gate electrode, and amorphous silicon (a-Si: H) deposited on the gate electrode. Ohmic contact layer formed by depositing a semiconductor layer formed in an island shape and n + a-Si implanted with impurity ions into amorphous silicon to improve contact contact between the semiconductor layer and the upper layer. And a source / drain electrode formed on the semiconductor layer by branching from the data line.

Meanwhile, the polarizer 150 is further provided on the outer surfaces of the color filter array substrate 112 and the TFT array substrate 111, and the polymer alignment layer 130 is further provided on the inner surfaces of the two substrates. It can be produced in a normally black mode by adjusting the transmission axis of the) and the angle of the director of the liquid crystal molecules.

That is, as illustrated in FIG. 4, the polymer alignment layer is initially oriented in the direction of the arrow, and the upper polarizer (upper POL) and the lower polarizer (lower POL) are disposed such that the polarization axes have an angle of 45 degrees from the electrodes 117 and 124. However, the polarization axes of the upper polarizer and the lower polarizer are perpendicular to each other. Subsequently, a constant voltage is applied to the polymer alignment layer in the initial alignment state to fix a predetermined gray level to a black state.

When no voltage is applied to the liquid crystal display, the liquid crystal molecules 225a of the polymer alignment layer are arranged in parallel with the polarization axis of the lower polarizer (lower POL), as shown in FIG. 5A. The black level is realized by not allowing light to pass through the polarization axis of the upper polarizing plate which is arranged side by side with the polarization axis of the vertical polarizer. When a voltage is applied, as shown in FIG. 5B, the liquid crystal molecules 225a of the alignment layer are arranged in the direction perpendicular to the electrodes by the transverse electric field. Accordingly, the liquid crystal layer is also arranged in the direction perpendicular to the electrodes to emit light. The white level is achieved by transmitting.

Thereafter, the polymer alignment layer arranged to be perpendicular to the electrode by the transverse electric field should be restored to an initial state. In order to compensate for the weak anchoring energy of the polymer alignment layer, an arbitrary voltage is applied to the auxiliary electrode to facilitate the polymer alignment layer to the initial state. To be restored. Accordingly, the problem that the restoring force of the polymer alignment layer is weak and not randomly arranged, may be randomly arranged to cause disclination.

 For reference, chiral smectic liquid crystal and FLCP (ferroelectric liquid crystal polymer) may be used as the polymer alignment layer 130, and the alignment direction of the liquid crystal layer is controlled by molecular movement of the polymer alignment layer.

For example, when a specific voltage is applied, the FLCP is switched by a property such that the direction of the spontaneous polarization is directed in the direction of the electric field. The voltage is applied to the liquid crystal display device to cross the common electrode 124 and the pixel electrode 117. When the electric field is formed, the molecules of the FLCP film are rearranged to move left and right along the outer surface of the cone due to the property that the direction of spontaneous polarization is directed in the direction of the electric field, and adjacent to the FLCP film by the molecular movement of the FLCP film. The directors of the liquid crystal molecules switch in parallel in the transverse electric field direction with respect to the substrate plane, and as a result, the entire liquid crystal molecules are switched in a batch.

As a result, switching of the liquid crystal is performed by the polymer alignment layer 130 such as the FLCP film, and the nematic liquid crystal layer 113 is responsible for the polarization efficiency related to the optical anisotropy Δn. In particular, when the FLCP film is used as the polymer alignment layer, a very fast response speed of about 1 ms is realized by inversion switching by spontaneous polarization, so that the response speed is fast and a wide viewing angle can be realized.

Second embodiment

6 is a cross-sectional view of the liquid crystal display device according to the second embodiment.

The second embodiment further includes an auxiliary electrode for the conventional FFS mode. As shown in FIG. 4, the color filter array substrate 212 is disposed to face each other and includes a liquid crystal layer 213 therebetween. ) And a thin film transistor array substrate 211, wherein the color filter array substrate 212 is provided with an auxiliary electrode 225 on the front surface, and the thin film transistor array substrate 211 has a plate formed with a tube inside the pixel. And a pixel electrode 217 having a plurality of slits 215 insulated from the counter electrode 224 and the counter electrode 224.

In this case, the counter electrode 224 receives a Vcom signal from an external driving circuit, and the pixel electrode 217 is connected to a drain electrode of the thin film transistor TFT to receive a pixel signal. The fringe field is generated between the slits.

The width of the slit 215 is approximately 2 to 6 μm, and the liquid crystal is driven by a fringe field formed between the pixel electrode 217 and the counter electrode 224. That is, the liquid crystals that were initially oriented by rubbing when no voltage is applied are rotated by the fringe field so that light is transmitted.

The auxiliary electrode 225 may be applied with a Vcom voltage applied to the common electrode, a pixel voltage applied to the pixel electrode, or a different level voltage may be applied. prevent.

The pixel electrode 217, the counter electrode 224, and the auxiliary electrode 225 are formed by depositing and patterning a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

In this case, the liquid crystal layer 213 may use a negative type or a positive type as a nematic liquid crystal and is driven by the electric field.

The polarizer 250 is further provided on the outer surfaces of the color filter array substrate 212 and the TFT array substrate 211, and the polymer alignment layer 230 is further provided on the inner surfaces of the two substrates. At this time, the transmission axis of the polarizing plate 250 and the angle of the director of the liquid crystal molecules may be adjusted to produce a normally black mode.

The arrangement of the polarizing plate and the initial orientation of the polymer alignment film are similar to and similar to those described in the first embodiment. The upper polarizer (upper POL) and the lower polarizer (lower POL) are arranged such that the polarization axes have an angle of 45 degrees from the electrodes, but are perpendicular to each other, and the polymer alignment layer has an arbitrary angle between the polarization axes of the upper polarizer and the lower polarizer. It gives a constant voltage and fixes a certain gray level to a black state.

When no voltage is applied to the liquid crystal display device, the liquid crystal molecules of the polymer alignment layer are arranged in parallel with the polarization axis of the lower polarizing plate (lower POL). Accordingly, the liquid crystal layer is also arranged in parallel with the polarization axis of the lower polarizing plate. The black level is realized by not transmitting light through the polarization axis. When the voltage is applied, the liquid crystal molecules of the alignment layer are arranged in the direction perpendicular to the electrodes by the transverse electric field. Accordingly, the liquid crystal layer is also arranged in the direction perpendicular to the electrodes to transmit white light.

Thereafter, the polymer alignment layer arranged to be perpendicular to the electrode by the transverse electric field should be restored to an initial state. In order to compensate for the weak anchoring energy of the polymer alignment layer, an arbitrary voltage is applied to the auxiliary electrode to facilitate the polymer alignment layer to the initial state. To be restored. Accordingly, the problem that the restoring force of the polymer alignment layer is weak and not randomly arranged, may be randomly arranged to cause disclination.

As the polymer alignment layer 230, chiral smectic liquid crystal and FLCP (ferroelectric Liquid Crystal Polymer) may be used, and the alignment direction of the liquid crystal layer is controlled by molecular movement of the polymer alignment layer.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

The liquid crystal display device according to the present invention as described above has the following effects.

First, a common electrode and a pixel electrode may be formed on one substrate, and an auxiliary electrode may be further provided on an opposing substrate so that the polymer alignment layer may be easily restored to an initial state, thereby preventing defects such as declining.

That is, in the case of the liquid crystal display device having the polymer alignment layer, it is possible to eliminate the declining phenomenon that occurs when no electric field is applied.

Second, since the FLCP can be used as the polymer alignment film formed on the inner surface of the substrate, the viewing angle of the device can be improved by switching the FLCP film with respect to the substrate plane, and the response speed of the device can be improved.

Therefore, the moving image quality of the liquid crystal display device is excellent.

Claims (9)

A thin film transistor and a pixel electrode formed in the unit pixel defined by the gate wiring and the data wiring crossing each other on the first substrate; An opposite electrode formed on the first substrate to form an electric field together with the pixel electrode; A second substrate opposed to the first substrate and having an auxiliary electrode formed thereon; A liquid crystal layer formed between the first and second substrates; And a polarizing plate formed on the outside of the first and second substrates, respectively. The method of claim 1, And a polymer alignment layer having liquid crystal properties inside the first and second substrates, respectively. The method of claim 2, The polymer alignment layer is a chiral smectic liquid crystal or a liquid crystal display device characterized in that the FLCP (ferroelectric Liquid Crystal Polymer). The method of claim 1, The liquid crystal layer is a liquid crystal display device, characterized in that the nematic liquid crystal. The method of claim 1, And the counter electrode is formed in parallel with the pixel electrode to generate a transverse electric field. The method of claim 1, And the counter electrode has a plurality of slits to form a fringe field together with the pixel electrode. The method of claim 1, The auxiliary electrode is a liquid crystal display device, characterized in that provided in the plate shape on the front of the second substrate. The method of claim 1, And a voltage of a Vcom voltage, a pixel voltage, or another level is applied to the auxiliary electrode. The method of claim 1, The auxiliary electrode is a liquid crystal display device, characterized in that the transparent conductive layer.

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