KR100759966B1 - liquid crystal display - Google Patents

Abstract

The first insulating substrate, the second insulating substrate and the third insulating substrate are arranged side by side, the thin film transistor and the first pixel electrode are formed on the upper surface of the second substrate, and the second pixel electrode is formed on the lower surface of the second substrate. have. The first pixel electrode and the second pixel electrode are connected to each other through a hole formed in the second substrate. A first common electrode is formed on the first substrate, and a color filter, a black matrix, and a second common electrode are formed under the third substrate. Horizontal alignment films are formed on the first substrate and below the third substrate, respectively, and vertical alignment films are formed on the top and the bottom of the second substrate, respectively, so that the liquid crystal layers injected between the substrates exhibit hybrid alignment. It may be twisted by 90 °. Here, the two liquid crystal layers having the hybrid alignment are similar to those of the OCB type liquid crystal display, can be driven without applying a high voltage, and the high speed response effect of the hybrid alignment type liquid crystal display can be obtained. In addition, the two liquid crystal layers are twisted by 90 °, so that the liquid crystal molecules are mutually compensated in three dimensions to obtain a wide viewing angle, and when a uniaxial film is formed which is perpendicular to the liquid crystal molecules near the substrate. The white luminance in the vertical direction of the substrate is increased to ensure a wide wide viewing angle.

Alignment film, hybrid orientation, wide viewing angle, response speed, uniaxial film

Description

Liquid crystal display

1 is a cross-sectional view schematically showing a liquid crystal display device according to a first embodiment of the present invention;

2 is a schematic cross-sectional view of a liquid crystal display according to a second exemplary embodiment of the present invention.

3 is a cross-sectional view schematically illustrating a liquid crystal display device according to a third embodiment of the present invention;

4 is a cross-sectional view schematically illustrating a liquid crystal display device according to a fourth embodiment of the present invention;

FIG. 5 is a diagram illustrating an alignment of liquid crystals when voltage is applied in the liquid crystal display according to the fourth exemplary embodiment of the present invention.

FIG. 6 is a diagram illustrating the alignment of liquid crystals in the VI direction in FIG. 5.

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a high speed response speed and capable of low voltage driving.                         

The liquid crystal display is one of the most widely used flat panel display devices. The liquid crystal display includes two glass substrates having electrodes formed thereon, a liquid crystal layer interposed therebetween, and a polarizing plate attached to the outside of the two substrates. It is a device for displaying an image by changing the arrangement of the liquid crystal molecules of the liquid crystal layer by applying a voltage to the electrode and thereby controlling the amount of light transmitted.

In the liquid crystal display device of the twisted nematic type, the injected liquid crystal layer is twisted by 90 °, and the polarization direction of the light passing through the incident polarizer is rotated in the direction in which the liquid crystal rotates. When it is not applied, the light passes through the liquid crystal layer and becomes polarized light perpendicular to the polarization direction of the incident light, and the light passes through the rear polarizer placed so that the incident polarizer and the polarization axis are perpendicular to each other. When the electric field is applied, the liquid crystal molecules are arranged in the direction of the electric field so that the optical axis of the liquid crystal is placed in the direction of light propagation so that polarization cannot be changed. Thus, light is blocked by the rear polarizer. In this way, the state that light passes when no electric field is applied is called normally white, and if the rear polarizer is arranged in the same direction as the incident polarizer, light does not pass when no voltage is applied. It is called normally black. On the other hand, such a twisted nematic liquid crystal display has a problem that the viewing angle is narrow and the response speed is slow. To solve this problem, liquid crystal displays of vertical alignment, optically compensated birefrigence (OCB), or in plane switching (IPS) methods have been developed, but none of them satisfy the conditions of wide viewing angle, fast response, and low voltage driving. have.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a liquid crystal display device having a wide viewing angle and a high response speed and driving a low voltage.

In order to achieve the above object, in the present invention, two liquid crystal layers having a hybrid orientation are injected between three substrates.

According to the present invention, the first insulating substrate, the second insulating substrate and the third insulating substrate are arranged in parallel with each other and sequentially from below, the first thin film transistor is formed on the first substrate, and is connected to the first thin film transistor. The first pixel electrode is formed. A second thin film transistor is formed on the second substrate, and a second pixel electrode connected to the second thin film transistor is formed. First and second transparent electrodes are formed under the second and third substrates, respectively. The horizontal alignment layer is formed on the first pixel electrode and the second transparent electrode, respectively, and the vertical alignment layer is formed on the second pixel electrode and the first transparent electrode, respectively. The first liquid crystal layer is hybridly aligned between the first substrate and the second substrate, and the second liquid crystal layer is hybridly aligned between the second substrate and the third substrate.

Here, each of the first and second liquid crystal layers may be twisted 90 ° clockwise, and the uniaxial film is preferably attached to the outside of the third substrate, and the uniaxial film is also attached to the outside of the first substrate. Can be.

According to another embodiment of the present invention, the first insulating substrate, the second insulating substrate and the third insulating substrate are arranged in parallel with each other and sequentially from below, and the first thin film transistor is formed on the second substrate, A first pixel electrode connected to the thin film transistor is formed. A first transparent electrode is formed on the first substrate, a second transparent electrode connected to the first pixel electrode is formed under the second substrate, and is formed under the third substrate. 3 transparent electrodes are formed. Horizontal alignment layers are formed on the first transparent electrode and below the third transparent electrode, respectively, and vertical alignment layers are formed on the first pixel electrode and the second transparent electrode, respectively. The first liquid crystal layer is hybridly aligned between the first substrate and the second substrate, and the second liquid crystal layer is hybridly aligned between the second substrate and the third substrate.

In this case, each of the first and second liquid crystal layers may be twisted in a clockwise direction by 90 °, and the uniaxial film may be attached to the outside of the third substrate, and the uniaxial film may also be attached to the outside of the first substrate. Can be.

In the present invention, two liquid crystal layers each having a hybrid orientation are injected between three substrates, which is similar to an OCB type liquid crystal display device, and can be driven without applying a high voltage, thereby obtaining a fast response speed. In addition, the two liquid crystal layers are twisted by 90 °, so that the liquid crystal molecules are mutually compensated in three dimensions to obtain a wide viewing angle, and when a uniaxial film is formed which is perpendicular to the liquid crystal molecules near the substrate. In the vertical direction of the substrate can also transmit light.

Next, a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention.

First, the structure of the liquid crystal display according to the first exemplary embodiment of the present invention will be described in detail with reference to FIG. 1.

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

As shown in FIG. 1, the first insulating substrate 10, the second insulating substrate 20, and the third insulating substrate 30 are aligned. The first thin film transistor 11 is formed on each of the pixel regions on the first substrate 10, and the first pixel electrode 12 connected to the first thin film transistor 11 and made of a transparent conductive material such as ITO is formed. It is. An alignment layer 15 is formed on the first pixel electrode 12. The second thin film transistor 21 is formed on the second substrate 20 at the same position as the first thin film transistor 11 of the first substrate 10, and is connected to the second thin film transistor 21 and connected to ITO. The second pixel electrode 22 made of the same transparent conductive material is formed. The lower surface of the second substrate 20 is formed with a transparent electrode 24 made of a transparent conductive material such as ITO. An alignment layer 25 is formed on the second pixel electrode 22, and an alignment layer 26 is formed under the transparent electrode 24. A common electrode 33 made of a transparent conductive material such as ITO is formed on the entire surface of the lower surface of the third substrate 30 facing the second substrate 20, and an alignment layer 35 is formed under the common electrode 33. It is. Although not shown here, red, green, and blue color filters and a black matrix are formed on the third substrate 30.

Liquid crystals 100 and 200 are injected between the first substrate 10 and the second substrate 20 and between the second substrate 20 and the third substrate 30, respectively.

Here, the alignment layers 15 and 35 respectively formed on the upper surface of the first substrate 10 and the lower surface of the third substrate 30 are horizontal alignment films, and the alignment films formed on the upper and lower surfaces of the second substrate 20, respectively. 25 and 26 are vertical alignment layers, and each of the liquid crystal layers 100 and 200 injected between the three substrates 10, 20, and 30 by the alignment layers 15, 35, 25, and 26 exhibits hybrid alignment. . That is, the liquid crystal molecules 100 between the first substrate 10 and the second substrate 20 are oriented horizontally with respect to the first substrate 10 near the first substrate 10, but the second liquid crystal molecules 100 are horizontally aligned with the second substrate 20. Increasingly, the left end of the liquid crystal molecules 100 rises and is oriented perpendicular to the second substrate 20 near the second substrate 20, and between the second substrate 20 and the third substrate 30. Although the 200 is oriented horizontally to the third substrate 30 near the third substrate 30, the left end of the liquid crystal molecules 200 rises toward the second substrate 20 and near the second substrate 20. Is orthogonal to the second substrate 20.

In this way, a structure in which the liquid crystal molecules are continuously arranged vertically with respect to one of the two substrates and parallel with respect to the other substrate surface is called a hybrid alignment. The hybrid alignment liquid crystal display device does not need to apply a high voltage as compared to an OCB type liquid crystal display device that applies a high voltage for the initial liquid crystal alignment, and thus, low voltage driving is possible and the response speed is high. In addition, the sharpness of the color, the color unevenness is extremely small, there is an advantage that the separation of the color is easy.

However, since the directions of the liquid crystal molecules are different, the transmittance varies greatly depending on the viewing angle, thereby causing a narrow viewing angle. To this end, a wide viewing angle can be secured by attaching a compensation plate used in an OCB type liquid crystal display device, and the aperture ratio is not used because patterning a pixel electrode or a common electrode or forming a protrusion pattern on a substrate is not used to obtain the wide viewing angle. This can be prevented from decreasing. Transmittance can be freely adjusted by adjusting each cell gap. In the OCB type liquid crystal display device, the change in Δnd value is small due to voltage on / off, whereas the Δnd value can be adjusted widely by adjusting the cell gap.

In the first embodiment of the present invention, when the alignment layers 25 and 26 of the second substrate 20 are formed, both sides of the substrate are immersed in a solution containing a single molecule and then taken out to apply the monomolecular film to both sides of the substrate 20. An alignment film coating method can be used.

After manufacturing the three substrates 10, 20, and 30, the thin film transistor 11 may be formed on the first pixel electrode 12 of the first substrate 10 and the second pixel electrode 22 of the second substrate 20 during driving. , A signal for driving 21, and a common signal are applied to the transparent electrode 24 of the second substrate 20 and the common electrode 33 of the third substrate 30.

Meanwhile, in the first embodiment of the present invention, since the thin film transistors 11 and 21 must be formed on the two substrates 10 and 20, the number of processes increases. A method for solving this will be described with reference to FIG. 2 as a second embodiment of the present invention.

First, a structure of a liquid crystal display according to a second exemplary embodiment of the present invention will be described with reference to FIG. 2.

2 is a schematic cross-sectional view of a liquid crystal display according to a second exemplary embodiment of the present invention.

As shown in FIG. 2, the liquid crystal display according to the second embodiment of the present invention has a structure substantially the same as that of the first embodiment, but the structure of the first substrate 10 and the second substrate 20 is different.

The thin film transistor is not formed on the first substrate 10, and the first common electrode 12 made of a transparent conductive material such as ITO is formed on the entire surface, and the alignment layer 15 is formed thereon. The second substrate 20 has a hole 28 formed in the middle of the pixel area, and the thin film transistor 21 is formed in the pixel area on the second substrate 20, and is connected to the second substrate 20. The first pixel electrode 22 made of a conductive material is formed. A second pixel electrode 24 formed of a transparent conductive material such as ITO is formed on the bottom surface of the second substrate 20 through the hole 28 and connected to the first pixel electrode 22.

Although not illustrated here, the first pixel electrode 22 may be formed in the same position as the hole 28 formed in the second substrate 20 in the insulating film that may be formed between the two pixel electrodes 22 and 24. And the second pixel electrode 24 may be connected. An alignment layer 25 is formed on the first pixel electrode 22, and an alignment layer 26 is formed under the second pixel electrode 24 of the second substrate 20. The second common electrode 33 is formed on the entire surface of the lower surface of the third substrate 30, and the alignment layer 35 is formed under the second common electrode 33.

Here, the alignment layers 15 and 35 formed on the first substrate 10 and the third substrate 30 are horizontal alignment layers, and the alignment layers 25 and 26 formed on the top and bottom surfaces of the second substrate 20. Is a vertical alignment film, in which the alignment of the liquid crystal molecules 100 and 200 exhibits the same hybrid alignment as in the first embodiment.

The hole 28 of the second substrate 20 may be formed using a laser, or when the second substrate 20 is made of plastic, it may be formed by a photolithography process.

At this time, when the second substrate 20 is manufactured, a hole 28 is formed in the substrate 20, and then a second pixel electrode 24 is first formed on the bottom surface of the substrate 20. (24) The protective layer (not shown) which can protect is apply | coated. Next, after the thin film transistor 21 and the first pixel electrode 22 are formed on the upper surface of the substrate 20, the protective layer is removed and the alignment layers 25 and 26 are formed on the upper and lower surfaces of the substrate 20. .

After manufacturing the three substrates 10, 20, and 30, a signal for driving the thin film transistor 21 is applied to the first and second pixel electrodes 22 and 24 of the second substrate 20 during driving. The common signal is applied to the first common electrode 12 of the first substrate 10 and the second common electrode 33 of the third substrate 30.

As described above, in the second embodiment of the present invention, both the liquid crystal layers 100 and 200 may be driven even if the thin film transistor 21 is formed on only one substrate. Therefore, the number of manufacturing processes is greatly reduced as compared with the first embodiment.

Meanwhile, in the first and second embodiments of the present invention, since the driving is similar to that of the OCB type liquid crystal display, a plurality of compensation plates must be attached to the outer side of the first substrate 10 and the third substrate 30.

Next, a liquid crystal display device capable of securing a wide viewing angle without using a plurality of compensation plates will be described with reference to FIGS. 3 and 4 as the third and fourth embodiments of the present invention.

First, a structure of a liquid crystal display according to a third exemplary embodiment of the present invention will be described with reference to FIG. 3.

As shown in FIG. 3, the structure of the liquid crystal display according to the third exemplary embodiment has the same structure as that of the first exemplary embodiment except for the alignment of the liquid crystals 100 and 200.

That is, although the alignment of the liquid crystals 100 and 200 is in a hybrid alignment, the liquid crystal molecules 100 are horizontally aligned and twisted in a clockwise direction near the first substrate 10 when viewed from the third substrate 30. One end of the liquid crystal molecules 100 occurs, and the liquid crystal molecules 100 are in a 90 ° twisted orientation that is perpendicular to the second substrate 20 near the second substrate 20. In addition, the liquid crystal molecules 200 near the third substrate 30 are horizontally oriented and twisted in a clockwise direction so that one end of the liquid crystal molecules 200 occurs and the liquid crystal molecules 200 near the second substrate 20. ) Has a 90 ° twist orientation that is oriented perpendicular to the second substrate 20. Therefore, when the two liquid crystal layers 100 and 200 are viewed macroscopically, they are continuously twisted 180 degrees. In order to obtain such a twisted hybrid orientation, a chiral dopant is added, and the alignment layers 15 and 35 on the top surface of the first substrate 10 and the bottom surface of the third substrate 30 are formed as horizontal alignment layers. The alignment layers 25 and 26 on the upper and lower surfaces of the two substrates 20 are formed as vertical alignment layers.

After manufacturing the three substrates 10, 20, and 30, the thin film transistor 11 may be formed on the first pixel electrode 12 of the first substrate 10 and the second pixel electrode 22 of the second substrate 20 during driving. , A signal for driving 21, and a common signal are applied to the transparent electrode 24 of the second substrate 20 and the common electrode 33 of the third substrate 30.

In the liquid crystal molecules having such a twisted hybrid orientation, the rotation of the liquid crystal molecules when the voltage is applied causes the upper liquid crystal layer 200 and the lower liquid crystal layer 100 to rotate in opposite directions so that the liquid crystal molecules compensate each other in three dimensions. Done. Therefore, a wide viewing angle can be obtained without using a compensation plate.

On the other hand, the liquid crystal display device having the same structure as the second embodiment of the present invention can also have a twisted hybrid orientation as in the third embodiment.

This will be described as a fourth embodiment of the present invention with reference to FIG.

4 is a schematic cross-sectional view of a liquid crystal display according to a fourth exemplary embodiment of the present invention.

As shown in FIG. 4, the liquid crystal display according to the fourth exemplary embodiment has the same structure as the second exemplary embodiment except for the alignment of liquid crystals. The alignment of the liquid crystal is carried out in the same manner as in the third embodiment of the present invention, and the chiral dopant is added, and the alignment layers 15 and 35 on the upper surface of the first substrate 10 and the lower surface of the third substrate 30 are horizontal alignment layers. The alignment layers 25 and 26 on the upper and lower surfaces of the second substrate 20 are formed as vertical alignment layers.

After manufacturing the three substrates 10, 20, and 30, a signal for driving the thin film transistor 21 is applied to the first and second pixel electrodes 22 and 24 of the second substrate 20 during driving. The common signal is applied to the first common electrode 12 of the first substrate 10 and the second common electrode 33 of the third substrate 30.                     

Next, with reference to FIGS. 5 and 6, the principle of obtaining the wide viewing angle in the intermediate gray scales in the third and fourth embodiments of the present invention will be described.

FIG. 5 is a diagram illustrating the alignment of liquid crystals when the twist is slightly loosened by applying a voltage in the liquid crystal display according to the fourth exemplary embodiment of the present invention. FIG. 6 is a diagram illustrating the alignment of liquid crystals in the VI direction in FIG. 5. One drawing.

In FIG. 5, only three substrates 10, 20, 30, alignment layers 15, 25, 26, 35, and liquid crystal molecules 100, 200 are illustrated, and other components are omitted from the drawings for convenience of description.

The liquid crystal molecules 100 between the first substrate 10 and the second substrate 20 exhibit an azimuth angle of 45 ° on average, and the liquid crystal molecules 200 between the second substrate 20 and the third substrate 30 On average, the azimuth angle is 135 °. Although light is transmitted by the liquid crystal molecules when viewed from the side as in the A and B directions in FIG. 5, the light is not transmitted in the direction perpendicular to the substrate. Accordingly, the uniaxial film having the axis 301 perpendicular to the liquid crystal molecules oriented horizontally with the third substrate 30 near the third substrate 30 to transmit light in a direction perpendicular to the substrate is third Attached to the outside of the substrate 30.

In this case, the uniaxial film may be attached only to the outer side of the third substrate 30, or may be attached to the outer side of the first substrate 10 and the third substrate 30, respectively.

As described above, in the present invention, two liquid crystal layers are hybridly aligned between three substrates, which is similar to an OCB type liquid crystal display device, and can be driven without applying a high voltage, thereby obtaining a high response speed. In addition, the two liquid crystal layers are twisted by 90 °, so that the liquid crystal molecules are mutually compensated in three dimensions to obtain a wide viewing angle, and when a uniaxial film is formed which is perpendicular to the liquid crystal molecules near the substrate. Even in the vertical direction of the substrate, light transmittance is increased.

Claims (8)

A first insulating substrate, a second insulating substrate and a third insulating substrate which are parallel to each other and are arranged in order from below, A first thin film transistor formed on the first substrate, A first pixel electrode connected to the first thin film transistor, A second thin film transistor formed on the second substrate, A second pixel electrode connected to the second thin film transistor, First and second transparent electrodes respectively formed under the second and third substrates, A horizontal alignment layer formed on the first pixel electrode and under the second transparent electrode, A vertical alignment layer formed on the second pixel electrode and below the first transparent electrode, A first liquid crystal layer in hybrid orientation between the first substrate and the second substrate, A second liquid crystal layer in hybrid orientation between the second substrate and the third substrate Liquid crystal display comprising a. In claim 1, And the first and second liquid crystal layers are twisted by 90 ° in a clockwise direction, respectively. In claim 1, And a uniaxial film attached to an outer side of the third substrate. In claim 3, And a uniaxial film attached to an outer side of the first substrate. A first insulating substrate, a second insulating substrate and a third insulating substrate which are parallel to each other and are arranged in order from below, A first thin film transistor formed on the second substrate, A first pixel electrode connected to the first thin film transistor, A first transparent electrode formed on the first substrate, A second transparent electrode formed under the second substrate and connected to each of the first pixel electrodes through a hole formed in the second substrate; A third transparent electrode formed under the third substrate, A horizontal alignment layer formed on the first transparent electrode and below the third transparent electrode, A vertical alignment layer formed on the first pixel electrode and under the second transparent electrode, A first liquid crystal layer in hybrid orientation between the first substrate and the second substrate, A second liquid crystal layer in hybrid orientation between the second substrate and the third substrate Liquid crystal display comprising a. In claim 5, And the first and second liquid crystal layers are twisted by 90 ° in a clockwise direction, respectively. In claim 5, And a uniaxial film attached to an outer side of the third substrate. In claim 7, And a uniaxial film attached to an outer side of the first substrate.

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