KR100956149B1 - LCD with improved viewing angle and response speed - Google Patents

Abstract

An object of the present invention is to provide a liquid crystal display device having an improved viewing angle and response speed. In particular, the liquid crystal display device relates to a liquid crystal display device that divides a domain by a surrounding electric field, and to represent gray. By setting the lowest voltage to a value higher than the threshold voltage value, and inducing the tilt direction of the liquid crystal molecules in advance before the liquid crystal molecules are arranged by the electric field, the response speed and viewing angle characteristics in the entire domain are improved. It has the advantage of being able to.

Description

Liquid crystal display device having improved viewing angle and response time             

1A and 1B are views of a TN mode liquid crystal display device having a general mono domain structure, and FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the cutting line I-I 'of FIG. 1A.

2A to 2C are views of a liquid crystal display having a domain division structure using a conventional peripheral electric field. FIG. 2A is a plan view of one pixel portion of an array substrate, and FIG. 2B is a plan view of one pixel portion of a color filter substrate. 2C is a cross-sectional view taken along the line II-II ′ of FIGS. 2A and 2B.

3 is a graph showing a voltage application characteristic of a conventional liquid crystal display.

4A and 4B are diagrams showing simulation results showing an arrangement and luminance characteristics of liquid crystals at an arbitrary time in the liquid crystal display having the voltage application characteristic of FIG.

5A and 5B illustrate a liquid crystal display according to a first embodiment of the present invention. FIG. 5A is a cross-sectional view of one pixel portion of the liquid crystal display according to the present embodiment, and FIG. 5B illustrates a liquid crystal display according to the present embodiment. Graph showing voltage application characteristics of a liquid crystal display device.                 

6A and 6B are diagrams showing simulation results of liquid crystal array and luminance characteristics in the liquid crystal display having the voltage application characteristic according to FIG. 5;

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having an improved viewing angle and response speed.

In general, a liquid crystal display device is formed by arranging two substrates on which electric field generating electrodes are formed so that the surfaces on which the two electrodes are formed face each other, injecting a liquid crystal material between the two substrates, and then applying a voltage to the two electrodes. By moving the liquid crystal molecules by an electric field, the device expresses an image by the transmittance of light that varies accordingly.

A liquid crystal display device may be formed in various forms. Currently, an active matrix LCD (AM-LCD) having a thin film transistor and pixel electrodes connected to the thin film transistor in a matrix manner has excellent resolution and video performance. It is the most noticeable.

The liquid crystal display device has a structure in which a pixel electrode is formed on a lower substrate and a common electrode is formed on an upper substrate, and the liquid crystal molecules are driven by an electric field in a direction perpendicular to the substrate between the two electrodes.                         

Such a liquid crystal display has a 90 ° twisted structure when no voltage is applied, and has a liquid crystal array characteristic that is constant for each subpixel defined as a twisted nematic (TN) mode that is arranged perpendicular to the substrate when voltage is applied and a minimum unit that implements a screen. Mono domain structure is mainstream.

1A and 1B are views of a TN mode liquid crystal display device having a general mono domain structure. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the cutting line II ′ of FIG. 1A.

In FIG. 1A, the gate wiring 12 and the data wiring 14 are formed in directions crossing each other, and the thin film transistor T is formed at the intersection of the gate wiring 12 and the data wiring 14. An area where the gate line 12 and the data line 14 cross each other is defined as a pixel area P, and the pixel electrode 16 is formed in the above-described pixel area P connected to the thin film transistor T. have.

Arrows in the pixel region P indicate the rubbing process directions of the upper and lower alignment layers, which are not shown, and are rubbed in directions perpendicular to each other in the pixel region P without domain division. .

In FIG. 1B, the first and second substrates 10 and 30 are disposed to face each other, and a thin film transistor T, which is a switching element, is formed on an inner surface of the first substrate 10, and the thin film transistor T is formed. The pixel electrode 16 is formed to be connected to the first electrode, and the first alignment layer 18 is formed in an area covering the thin film transistor T and the pixel electrode 16.

On the inner surface of the second substrate 30, a black matrix 32 is formed at a position corresponding to the thin film transistor T, and a color filter 34 is formed below the black matrix 32. The common electrode 36 is formed on the lower surface of the color filter 34, and the second alignment layer 38 is formed on the lower surface of the common electrode 36.

The liquid crystal layer 50 is interposed between the first and second alignment layers 18 and 38, and as described above with reference to FIG. 1A, the first and second alignment layers 18 and 38 are rubbed in directions perpendicular to each other. It is. For example, the liquid crystal layer 50 has a 90 ° twisted structure when no voltage is applied, and corresponds to a TN mode liquid crystal layer arranged in a vertical direction with respect to the substrate when voltage is applied, and the liquid crystal layer shown in the drawing is in a voltage applied state. The arrangement structure of.

As shown in the figure, when voltage is applied, the liquid crystal molecules 52 are arranged perpendicular to the substrate surface to serve as a shutter for a kind of light source, which is controlled by the long axis of the liquid crystal molecules 52 according to the viewing angle variation. Since the brightness of the screen is unevenly felt by the user due to the difference between the intensity of L1 and the intensity of light L2 controlled by the shortening of the liquid crystal molecules 52, there is a disadvantage of having a narrow viewing angle due to such a phenomenon.

In order to improve this disadvantage, a multi-domain structure for dividing the arrangement of the liquid crystal into sub-pixel units or pixel units into a symmetric structure has been proposed.

In general, the multi-domain structure of the TN mode liquid crystal display device is configured by adjusting the rubbing direction of the liquid crystal alignment layer or by electric field distortion. According to the latter method, a peripheral field is formed by electric field distortion. In order to stabilize the arrangement of the liquid crystal in the multi-domain structure has been the most attention in recent years.                         

2A to 2C are views of a liquid crystal display having a domain division structure using a conventional peripheral electric field. FIG. 2A is a plan view of one pixel portion of an array substrate, and FIG. 2B is a plan view of one pixel portion of a color filter substrate. 2C is a cross-sectional view taken along the cutting line II-II ′ of FIGS. 2A and 2B, and illustrates a two-domain structure as an example, and a description of the overlapping portions of FIGS. 1A and 1B will be omitted.

In the pixel region P of FIG. 2A, a peripheral electrode 62 is formed at a position overlapping with an edge of the pixel electrode 66 in an insulated state from the pixel electrode 66. The projection pattern 86 is formed in the center part (position which transversely crosses on a figure) of P).

Hereinafter, the stacking structure of FIGS. 2A and 2B will be described in detail with reference to FIG. 2C. The first and second substrates 60 and 80 are disposed to face each other, and the left and right sides of the first substrate 60 are disposed on the inner surface. The peripheral electrode 62 is positioned in the insulating layer 64, and the insulating layer 64 is formed at a position covering the peripheral electrode 62, and a pixel electrode overlapping with both sides of the peripheral electrode 62 at a center portion on the insulating layer 64. 66 is formed, and the first alignment layer 68 is formed in the region covering the pixel electrode 66. The black matrix 81, the color filter 82, and the common electrode 84 are sequentially formed on the inner surface of the second substrate 80, and overlap the center of the pixel electrode 66 under the common electrode 84. The projection pattern 86 is formed in the position, and the second alignment layer 88 is formed in the region covering the projection pattern 86.

The liquid crystal layer 90 is interposed between the first and second alignment films 68 and 88.

Here, an electric field that distorts the arrangement of the liquid crystal layer 90 is generated in the section between the peripheral electrode 62 and the pixel electrode 66 and the protrusion pattern 86 part. These electric fields are defined as the peripheral electric field 94. .

In forming the peripheral electric field, a structure in which the peripheral electrode 62 and the pixel electrode 66 are spaced apart from each other by a predetermined interval may be possible.

On the other hand, when the alignment direction of the first alignment layer 68 is from left to right as shown by the arrow in the drawing, the first domain (iii a) on the left side and the second domain (iii) on the right side of the projection pattern 86. b), since the liquid crystal molecules 92 positioned in the second domain iii b are arranged in the same direction as the alignment direction, there is no problem in the arrangement of the liquid crystal molecules 92 even when the electric field is formed. In the case of the liquid crystal molecules 92 positioned at (iii a), the alignment of the liquid crystal molecules 92 is difficult to control in a short time because the liquid crystal molecules 92 must be arranged in the opposite direction to the alignment direction for domain division.

In particular, the alignment direction of the first liquid crystal molecule groups iv a adjacent to the first and second alignment layers 68 and 88 is determined by the alignment layer, but the second liquid crystal molecule groups iv b positioned in the center layer are applied. As described above, in the case of the second liquid crystal molecule group iv b located in the domain opposite to the alignment direction, the response speed is slower than that of the other liquid crystal molecules. Therefore, the viewing angle characteristic is lowered.

In order to solve this problem, when the peripheral electric field is increased, the area of formation of the peripheral electrode and the projection pattern must be increased, and the aperture ratio is reduced. When the peripheral electric field is reduced in consideration of the aperture ratio, the domain effect is reduced by the peripheral electric field. There was a problem that the stability is lowered and the response speed of the liquid crystal becomes smaller.

3 is a graph illustrating voltage application characteristics of a conventional liquid crystal display device. The x-axis is a response time and the y-axis is a voltage size. When the white mode is normally used, gray ( gray) the minimum voltage for the representation is the white voltage (V _W), and to define the maximum voltage for implementing the black brightness in the black voltage (V _B), the original is typically white voltage (V _W) value of the threshold voltage Designed to be lower than (V _th ).

4A and 4B illustrate simulation results showing an arrangement and luminance characteristics of liquid crystals at an arbitrary time in the liquid crystal display having the voltage application characteristic of FIG. 3, wherein the liquid crystal display is applied to an electric field. The present invention relates to a liquid crystal display having a structure in which domains are divided, and is illustrated by using a normally white mode as an example.

4A illustrates the arrangement and luminance characteristics of liquid crystals after 50 ms of application of a black voltage. In the case of liquid crystal molecules positioned in a pixel region when voltage is applied, full black luminance may be achieved in the vertical direction. In the case of the located liquid crystal molecule group (region a), the arrangement of the middle layer liquid crystal molecules is scattered, and thus, it is possible to realize that light leakage is not achieved without realizing black luminance.

FIG. 4B shows the light leakage phenomenon in a specific area (area c) when the on-time response time for implementing black luminance is within 50 ms and the transmittance characteristic at 10 ms (60 ms on the graph) is shown. As a result, the black luminance characteristic was not good (27.42%).

As described above, according to the voltage application method applied to the structure of dividing the domain by the electric field, the light leakage phenomenon occurs severely in the specific region (the liquid crystal molecular group region to be arranged by the electric field in the opposite direction to the alignment direction). And there was a problem that the viewing angle characteristic is lowered.

In order to solve the above problems, an object of the present invention is to provide a liquid crystal display device having an improved viewing angle and response speed. In particular, the liquid crystal display device corresponds to a liquid crystal display device that divides a domain by a surrounding electric field. In the present invention, the lowest voltage for expressing gray is set to a value higher than a threshold voltage value, Before the liquid crystal molecules are aligned, the tilt direction of the liquid crystal molecules is induced in advance to improve response speed and viewing angle characteristics in the entire domain.

In order to achieve the above object, a first aspect of the present invention provides a liquid crystal display device in which a domain is divided by a peripheral electric field that distorts an arrangement direction of liquid crystal molecules, the liquid crystal display device comprising: first and second substrates disposed to face each other; First and second transparent electrodes formed on inner surfaces of the first and second substrates, respectively; First and second alignment layers formed on inner surfaces of the first and second transparent electrodes, respectively; A liquid crystal layer interposed between the first and second alignment layers; First and second peripheral electrodes formed on the first substrate to overlap each end of the first transparent electrode with an insulating layer beneath the first transparent electrode; An electric field distortion pattern formed in the shape of a protrusion corresponding to a central portion of the first transparent electrode below the second transparent electrode of the second substrate, and forming a tilt in a direction in which the liquid crystal layer is arranged by an electric field The liquid crystal display device is characterized in that the magnitude of the lowest voltage indicating white or black has a value larger than a threshold voltage.

A thin film transistor is formed on each of the pixel regions that are the smallest units for implementing the screen on the first substrate and is connected to the first transparent electrode. A color filter is disposed between the second substrate and the second transparent electrode. It is characterized in that it is further formed.

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According to a second aspect of the present invention, there is provided a semiconductor device comprising: first and second substrates disposed to face each other; First and second transparent electrodes formed on inner surfaces of the first and second substrates, respectively; First and second alignment layers formed on inner surfaces of the first and second transparent electrodes, respectively; A liquid crystal layer interposed between the first and second alignment layers; First and second peripheral electrodes formed on the first substrate to overlap each end of the first transparent electrode with an insulating layer beneath the first transparent electrode; A method of dividing a domain by a peripheral electric field including an electric field distortion pattern formed in a protrusion shape corresponding to a central portion of the first transparent electrode under the second transparent electrode of the second substrate and distorting the arrangement direction of liquid crystal molecules; A method of driving a liquid crystal display device, comprising: applying a first voltage having a voltage magnitude capable of tilting liquid crystal molecules in a direction of forming an electric field in a predetermined direction, the first voltage representing a gray; Applying a threshold voltage which is a voltage for inducing an initial arrangement by an electric field of the liquid crystal molecules; And implementing a black screen or a white screen by applying a second voltage, which is the highest voltage representing the gray, wherein the first voltage has a value greater than a threshold voltage. To provide.

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

First Embodiment

5A and 5B illustrate a liquid crystal display according to a first embodiment of the present invention. FIG. 5A is a cross-sectional view of one pixel portion of the liquid crystal display according to the present embodiment, and FIG. 5B illustrates a liquid crystal display according to the present embodiment. It is a graph which shows the voltage application characteristic of a liquid crystal display device.

In FIG. 5A, the first and second substrates 110 and 130 are disposed to face each other, and the first field distortion patterns 112 are formed on the left and right sides of the inner surface of the first substrate 110, respectively. An insulating layer 114 is formed in a region covering the first field distortion pattern 112, and the first transparent electrode 116 is positioned at an overlapping side of the first field distortion pattern 112 with an upper portion of the insulating layer 114. ) Is formed, and a first alignment layer 118 is formed at a position covering the first transparent electrode 116.

The black matrix 131, the color filter 132, and the second transparent electrode 134 are sequentially formed on the inner surface of the second substrate 130, and the first transparent electrode 116 is disposed below the second transparent electrode 134. The second field distortion pattern 136 is formed at a position overlapping with the center portion of the center), and a second alignment layer 138 is formed at a position covering the second field distortion pattern 136, and the first and second alignment layers The liquid crystal layer 150 is interposed between 118 and 138.

The liquid crystal molecules 152 positioned in the liquid crystal layer 150 may be disposed between the first field distortion pattern 112 and the pixel electrode 116 and the peripheral electric field 154 generated at the formation of the second field distortion pattern 136. Has a two domain structure arranged in different directions.

The black matrix 131 described above is formed at a position overlapping with the first and second field distortion patterns 112 and 136, and may be omitted in some cases.

The liquid crystal layer 150 may include a second liquid crystal molecule group (Ia) positioned between a first liquid crystal molecule group (I a) adjacent to the first and second alignment layers 118 and 138 and a first liquid crystal molecule group (I a). I b), and in particular, the second liquid crystal molecule group I b is tilted in the direction of forming the electric field before the electric field is formed, and specifically, the second liquid crystal molecule group I b is tilted. The driving method will be described with reference to the following drawings.

On the other hand, the first field distortion pattern 112 and the first transparent electrode 116 may form a peripheral electric field in a state spaced apart from each other.

In FIG. 5B, when the normally white mode is taken as an example, the white voltage V _{W ′} , which is the lowest voltage for expressing gray, has a higher value than the threshold voltage V _th , and the black voltage that is the highest voltage. (V _{B '} ) can apply the same value as the black voltage in the same mode.

In the liquid crystal display having a structure in which a domain is divided by an electric field, a response voltage is generated such that light leakage occurs in a specific region by setting a minimum voltage lower than a threshold voltage to express gray regardless of a monodomain structure. And there was a problem that the viewing angle characteristic is lowered. However, in the present invention, the above-described minimum voltage value is set to a value higher than the threshold voltage so as to induce the alignment direction of the liquid crystal according to the tilt direction for each domain before the electric field is formed, thereby improving the black luminance characteristic in the entire domain. Can improve response speed and viewing angle characteristics.

6A and 6B are diagrams showing simulation results of liquid crystal array and luminance characteristics in the liquid crystal display having the voltage application characteristic according to FIG. 5.

The region A of FIG. 6A is for the same mode condition region as that of the region a of FIG. 4A. In the past, light leakage phenomena were found due to scattering of the arrangement of liquid crystal molecules in this region. Also, it can be seen that the light leakage phenomenon is much reduced as in the region B because it is arranged relatively normally. Moreover, the light leakage phenomenon appearing in the region B can be blocked by the field distortion pattern of the upper substrate.

FIG. 6B illustrates the transmittance characteristic after 10ms of on-time response time (60ms on the graph) under the same condition as that of FIG. 4B. The light leakage phenomenon (region C) in a specific region (region D) is also significantly reduced compared to the conventional art. It can be seen that the luminance characteristic is also improved (27.42%-> 26.09%).                     

However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

As described above, according to the liquid crystal display device in which the domain is divided by the peripheral electric field according to the present invention, the size of the minimum voltage for expressing gray is set to a value larger than the threshold voltage, so that the size of the peripheral electric field is small. Since the electric field is already formed in the tilted direction in each domain tilt direction, it is possible to quickly induce the arrangement of the liquid crystal in all domains, thereby improving the viewing angle and response speed.

Claims (8)

In a liquid crystal display device of a method of dividing a domain by a peripheral electric field that distorts the alignment direction of liquid crystal molecules, First and second substrates disposed to face each other; First and second transparent electrodes formed on inner surfaces of the first and second substrates, respectively; First and second alignment layers formed on inner surfaces of the first and second transparent electrodes, respectively; A liquid crystal layer interposed between the first and second alignment layers; First and second peripheral electrodes formed on the first substrate to overlap each end of the first transparent electrode with an insulating layer beneath the first transparent electrode; An electric field distortion pattern formed in a projection shape corresponding to a central portion of the first transparent electrode under the second transparent electrode of the second substrate. It includes, wherein the liquid crystal layer to form a tilt (tilt) in the direction arranged by the electric field, the magnitude of the lowest voltage indicating white or black has a value greater than the threshold voltage (threshold voltage) LCD display device. The method of claim 1, And a thin film transistor formed on each of the pixel areas, the smallest unit for implementing a screen, on the first substrate and connected to the first transparent electrode. delete The method of claim 1, And a color filter further formed between the second substrate and the second transparent electrode. delete delete First and second substrates disposed to face each other; First and second transparent electrodes formed on inner surfaces of the first and second substrates, respectively; First and second alignment layers formed on inner surfaces of the first and second transparent electrodes, respectively; A liquid crystal layer interposed between the first and second alignment layers; First and second peripheral electrodes formed on the first substrate to overlap each end of the first transparent electrode with an insulating layer beneath the first transparent electrode; A method of dividing a domain by a peripheral electric field including an electric field distortion pattern formed in a protrusion shape corresponding to a central portion of the first transparent electrode under the second transparent electrode of the second substrate and distorting the arrangement direction of liquid crystal molecules; In the driving method of the liquid crystal display device, Applying a first voltage having a voltage magnitude capable of tilting the liquid crystal molecules in a predetermined direction in the electric field formation direction, the minimum voltage representing gray; Applying a threshold voltage which is a voltage for inducing an initial arrangement by an electric field of the liquid crystal molecules; Implementing a black screen or a white screen by applying a second voltage which is the highest voltage representing the gray Wherein the first voltage has a value greater than a threshold voltage. delete

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