KR20110078897A - Liquid crystal display device having low pre-tilt angle and manufacturing method of the same - Google Patents

Abstract

PURPOSE: A liquid crystal display device having a low pre-tilt angle is provided to solve the asymmetry of viewing angle contrast ratio. CONSTITUTION: A liquid crystal display device comprises a substrate in which alignment layers(101,301) with an alignment rubbing pattern is formed, a liquid crystal layer(200) which is touched with the alignment layer, and photoresist monomer which is hardened between liquid crystal layers. The photoresist monomer maintains the liquid crystal layer in horizontal state about the substrate.

Description

Liquid crystal display having low vertical pretilt angle and manufacturing method thereof {LIQUID CRYSTAL DISPLAY DEVICE HAVING LOW PRE-TILT ANGLE AND MANUFACTURING METHOD OF THE SAME}

The present invention relates to a liquid crystal display device having a liquid crystal layer arranged at a low pretilt angle and a manufacturing method thereof. In particular, the present invention relates to a liquid crystal display device and a method for manufacturing the same, in which the vertical pretilt angles of the liquid crystal layer initially oriented by the alignment layer are removed on the vertical plane in the liquid crystal display device by the horizontal electric field.

An active matrix liquid crystal display device displays an image using a thin film transistor (TFT) as a switching element. The liquid crystal display device can be miniaturized compared to a cathode ray tube (CRT), which is applied to a display device in a portable information device, an office device, a computer, and a television, and is rapidly replacing a cathode ray tube.

1 is a plan view illustrating a conventional horizontal field type liquid crystal display panel. FIG. 2 is a cross-sectional view illustrating a structure of a liquid crystal display panel taken along the line II ′ in FIG. 1.

1 and 2, the liquid crystal display panel includes a thin film transistor array substrate 10 having a thin film transistor TFT, a color filter substrate 30 having a color filter CF and a black matrix BM, It includes the liquid crystal layer 20 interposed therebetween. The thin film transistor array substrate of the horizontal field type liquid crystal display panel includes a gate line GL and a data line DL intersected on the lower transparent substrate SUBL, a thin film transistor TFT formed at each intersection thereof, and a cross structure thereof. The pixel electrode PXL and the common electrode COM formed to form a horizontal electric field in the pixel area provided as a second region, and the common line CL connected to the common electrode COM are provided.

The thin film transistor TFT may include a gate electrode G branched from the gate line GL, a semiconductor layer A formed to overlap the gate electrode G on the gate insulating layer GI covering the gate electrode G, A source electrode S branched from the data line DL and in contact with one end of the semiconductor layer A, and a drain electrode D facing the source electrode S and in contact with the other end of the semiconductor layer A. do. A passivation layer PASSI is formed on the thin film transistor TFT to protect the thin film transistor TFT. The pixel electrode PXL is formed on the passivation layer PASSI.

The gate line GL supplies a gate signal to the gate electrode G of the thin film transistor TFT. The data line DL supplies a pixel signal to the pixel electrode PXL through the drain electrode D of the thin film transistor TFT. The gate line GL and the data line DL are formed in an intersecting structure to define a pixel area. The common line CL is formed to be parallel to the gate line GL with the pixel region therebetween, and supplies a reference voltage for driving the liquid crystal to the common electrode PXL.

The thin film transistor TFT allows the pixel signal of the data line DL to be charged and held in the pixel electrode PXL in response to the gate signal of the gate line GL. The pixel electrode PXL is connected to the drain electrode D of the thin film transistor TFT and is formed in the pixel area. The common electrode COM is connected to the common line CL and is formed in the pixel area. In particular, the pixel electrode PXL and the common electrode COM are arranged to be parallel to each other in the pixel area. To this end, the common electrode COM has a plurality of bar shapes arranged at regular intervals in the vertical direction in the pixel area, and the pixel electrode PXL has a plurality of bar shapes disposed between the common electrodes COM. Equipped.

Accordingly, a horizontal electric field is formed between the pixel electrode PXL supplied with the pixel signal through the thin film transistor TFT and the common electrode COM supplied with the reference voltage through the common line CL. In particular, a horizontal electric field is formed between the rod-shaped pixel electrodes PXL and the common electrode COM arranged in the vertical direction.

By this horizontal electric field, the liquid crystal molecules arranged in the horizontal direction of the liquid crystal layer 20 interposed between the thin film transistor array substrate 10 and the color filter substrate 30 are rotated by dielectric anisotropy. As the light transmittance passing through the pixel region is changed, an image is realized. The liquid crystal layer 20 changes the light transmittance passing through the pixel region according to the degree of rotation of the liquid crystal molecules between a state arranged in a first direction and a state arranged in a second direction on a horizontal plane of the liquid crystal display device plane. Implement the image.

For this purpose, in the initial state, the liquid crystal molecules of the liquid crystal layer 20 should be aligned in a predetermined direction. Since simply injecting a liquid crystal material between the substrates does not provide a uniform arrangement of liquid crystal molecules, an alignment layer for setting the alignment direction of the liquid crystal molecules must be formed in the liquid crystal display device. In the manufacturing process of the liquid crystal display device, in the manufacturing process of the alignment film, after coating an organic film such as polyimide, the surface of the alignment film is rubbed with a rubbing cloth to form an alignment film having a pattern (for example, linear groove) in a predetermined direction. Then, the liquid crystal molecules of the liquid crystal layer 20 closest to the alignment layer maintain the alignment state in a uniform direction along a pattern of a predetermined direction formed on the alignment layer. The liquid crystals in the intermediate layer are affected by the alignment state of the liquid crystal molecules closest to the alignment layer to maintain the same alignment state.

3A and 3B are views illustrating a state in which an alignment film is processed by using a rubbing cloth on an alignment film coated on a surface of a thin film transistor substrate or a color filter substrate according to the prior art. When the pattern is formed on the alignment layers 11 and 31 using the rubbing cloth 50, the liquid crystal molecules LCM are arranged in a predetermined direction along the pattern. In a horizontal electric field type liquid crystal display, liquid crystal molecules (LCMs) are designed to align in a predetermined direction on a horizontal plane. However, since the pattern formed on the alignment layers 11 and 31 has a predetermined depth and a concave shape in the thickness direction of the alignment layers 11 and 31, the vertical pretilt angles of the liquid crystal molecules LMC inclined with respect to the horizontal state on the vertical plane are inclined. Has a pre-tilt angle α. Also, depending on the rubbing direction, the vertical pretilt angle may be inclined to the right as in FIG. 3A or may be inclined to the left as in FIG. 3B.

In addition, when the thin film transistor substrate 10 and the color filter substrate 30 including the alignment layers 11 and 31 are bonded to each other with the liquid crystal layer 20 interposed therebetween, they have a vertical pretilt angle in the left or right direction. Combining each case can result in all four cases. 4A through 4D are cross-sectional views illustrating the number of cases of the vertical pretilt angle that the liquid crystal layers interposed between the thin film transistor substrate and the color filter substrate may have. 4A illustrates that liquid crystal molecules close to the alignment layer 11 of the thin film transistor substrate 10 have a vertical pretilt angle in the right direction, and liquid crystal molecules close to the alignment layer 31 of the color filter substrate 30 have a vertical free direction in the left direction. The case of having a tilt angle is shown. FIG. 4B illustrates a case in which both liquid crystal molecules close to the alignment layer 11 of the thin film transistor substrate 10 and liquid crystal molecules close to the alignment layer 31 of the color filter substrate 30 have vertical pretilt angles in the right direction. FIG. 4C illustrates a case in which both liquid crystal molecules close to the alignment layer 11 of the thin film transistor substrate 10 and liquid crystal molecules close to the alignment layer 31 of the color filter substrate 30 have vertical pretilt angles in the left direction. 4A illustrates that liquid crystal molecules close to the alignment layer 11 of the thin film transistor substrate 10 have a vertical pretilt angle in the left direction, and liquid crystal molecules close to the alignment layer 31 of the color filter substrate 30 have a vertical free direction in the right direction. The case of having a tilt angle is shown.

Due to the vertical pretilt angle having different directions between the thin film transistor substrate 10 and the color filter substrate 30 bonded in this way, the contrast ratio is asymmetrically formed along the viewing angle direction on the front surface of the liquid crystal display. For example, in the case of FIGS. 4A and 4D, when viewed from the front of the LCD, contrast ratio asymmetry occurs in the up, down, left, and right directions. In the case of Fig. 4B, the contrast ratio asymmetry in the left and right directions on the upper side, and in the case of Fig. 4C, the contrast ratio asymmetry in the left and right directions on the lower side.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device and a method of manufacturing the same, which are designed to improve the problems caused by the prior art and improve the viewing angle contrast ratio asymmetry due to a vertical pretilt angle formed through a rubbing process for liquid crystal alignment. have. Another object of the present invention is to provide a liquid crystal display device and a manufacturing method thereof, wherein the liquid crystal molecules do not have a vertical pretilt angle by a rubbing groove formed in a rubbing process for liquid crystal alignment.

In order to achieve the above object, the liquid crystal display device according to the present invention, a substrate having an alignment film; A liquid crystal layer in contact with the alignment layer; And a photosensitive monomer that is photocured between the alignment layer and the liquid crystal layer to maintain the liquid crystal layer in a horizontal state with respect to the plane of the substrate.

The substrate having the alignment layer includes a thin film transistor substrate having a first alignment layer; And a color filter substrate having a second alignment layer.

The liquid crystal layer is in contact with the first alignment layer and the second alignment layer and interposed between the thin film transistor substrate and the color filter substrate; The photosensitive monomer may be photocured between the first alignment layer and the liquid crystal layer and between the second alignment layer and the liquid crystal layer.

The thin film transistor substrate may include a gate line and a data line perpendicular to each other; A pixel region having a matrix array formed by the gate line and the data line; A thin film transistor formed in the pixel region; A pixel electrode connected to the thin film transistor and formed in the pixel area; And a common electrode arranged in parallel with the pixel electrode in the pixel area to form a horizontal electric field.

The photocured photosensitive monomer is characterized in that one end is connected to the alignment pattern of the alignment layer, the other end is coupled to one side of the liquid crystal molecules of the liquid crystal layer.

The vertical pretilt angle with respect to the plane of the substrate of the liquid crystal layer is maintained in a horizontal state having a value of 0.3 degrees or less.

In addition, the liquid crystal display device manufacturing method according to the present invention, forming a thin film transistor substrate having a first alignment layer; Forming a color filter substrate having a second alignment layer; Forming a liquid crystal display panel by bonding the thin film transistor substrate and the color filter substrate so that a mixture of a main liquid crystal material and a photosensitive monomer is interposed between the first alignment layer and the second alignment layer; And irradiating ultraviolet rays to the liquid crystal display panel to cure the photosensitive monomer.

The forming of the thin film transistor substrate may include forming a gate line and a gate electrode branching from the gate line on the transparent substrate; Forming a gate insulating film on the gate line and the gate electrode; Forming a semiconductor layer on the gate insulating layer to overlap the gate electrode; Forming a data line orthogonal to the gate line on the gate insulating layer, a source electrode branching from the data line to contact one end of the semiconductor layer, and a drain electrode facing the source electrode and contacting the other end of the semiconductor layer; step; Forming a passivation layer covering the data line, the source electrode, and the drain electrode; Forming a pixel electrode on the passivation layer, the pixel electrode being connected to the drain electrode; And forming the first alignment layer covering the pixel electrode.

The forming of the gate line and the gate electrode may further include forming a common wiring which is flat with the gate line, and a common electrode which is branched from the common wiring and arranged in parallel with the pixel electrode.

The forming of the pixel electrode may further include forming a common line parallel to the gate line and a common electrode on the passivation layer and branched from the common line and arranged in parallel with the pixel electrode.

The forming of the color filter substrate may include forming a black matrix defining a pixel region having a matrix array on the transparent substrate; forming a color filter in the pixel region between the black matrices; The method may further include forming the first alignment layer on the color filter.

The forming of the liquid crystal display panel may include mixing such that the content ratio of the main liquid crystal material and the photosensitive monomer has any one of 99.0: 1.0 to 99.9: 0.1.

Curing the photosensitive monomer, characterized in that for irradiating ultraviolet light having a wavelength of 365nm with energy of 45mW / cm ² .

In the liquid crystal display according to the present invention, the liquid crystal molecules are aligned in parallel to the horizontal plane state without the vertical pretilt angle by the rubbing grooves formed through the rubbing process. Accordingly, in the liquid crystal display according to the present invention, contrast ratio asymmetry does not occur even at various viewing angles viewed from the front of the liquid crystal display. As a result, a good quality liquid crystal display device having improved contrast ratio at various viewing angles can be obtained.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. 5A through 5C are cross-sectional views illustrating a process of manufacturing a liquid crystal display according to an exemplary embodiment of the present invention.

The alignment films 101 and 301 are applied to the thin film transistor substrate 100 and the color filter substrate 300, respectively, and the surfaces of the alignment films 101 and 301 are rubbed with the rubbing cloth 500. Then, a pattern having a predetermined direction is formed on the surfaces of the alignment films 101 and 300. (FIG. 5A)

The thin film transistor substrate 100 and the color filter substrate 300 having the alignment layers 101 and 301 treated as the alignment layers are bonded to each other via the liquid crystal layer 200. At this time, the liquid crystal layer 200 includes a small amount of the photosensitive monomer 220 as a main component of the main liquid crystal material 210 satisfying the optical properties of the designed liquid crystal display device. For example, the main liquid crystal material 210 is a nematic liquid crystal, the content ratio of about 99.0 to 99.9%, and the photosensitive monomer 220 is formed in the liquid crystal layer 200 such that the content ratio of about 0.1 to 1.0%. do. The photosensitive monomer 220 is a material similar to liquid crystal and has a property of curing in response to light. The liquid crystal layer 200 maintains a state in which the liquid crystal layer 200 is uniformly oriented in a predetermined direction on a horizontal plane due to the rubbing pattern formed in the alignment process of the alignment layers 101 and 301. At the same time, the depth of the rubbing pattern is arranged in the inclined state with a vertical pretilt angle of about 1 to 3 degrees when viewed from the vertical plane. (FIG. 5B)

Ultraviolet rays are irradiated to the completed liquid crystal display panel to cure the photosensitive monomer 220. Then, the photosensitive monomers 220 are cured. In this case, the photosensitive monomers 220 are mainly cured while being attached to the surfaces of the alignment layers 101 and 301. It also has a tendency to bond with the liquid crystal molecules closest to the alignment films 101 and 301. That is, while the photosensitive monomer 220 is cured into a long ring shape, one end of the photosensitive monomer 220 is cured while being attached to the rubbing pattern of the alignment-oriented films 101 and 301. And the other end is combined with the downed portion of the nematic liquid crystal molecules having a pretilt angle. For this reason, the liquid crystal molecules closest to the alignment films 101 and 301 have a horizontal state in which the vertical pretilt angle is close to zero. Even the largest vertical pretilt angle has a value of 0.3 degrees or less. As for the conditions of the process of hardening the photosensitive monomer 220, it is preferable to irradiate the ultraviolet-ray whose wavelength band which has a maximum light quantity is 365 nm with the energy of 45 mW / cm <^2> . (FIG. 5C)

Table 1 below shows the measured values of the vertical pretilt angles of the liquid crystal molecules closest to the alignment layer in the liquid crystal display according to the related art, and the liquid crystal molecules closest to the alignment layer in the liquid crystal display according to the present invention. It is the result of comparing the measured value of the vertical pretilt angle. In Table 1, the samples according to the prior art and the samples according to the present invention were compared five by five. In Table 1, ultraviolet rays were irradiated under the same conditions as the present invention in the liquid crystal display according to the prior art. This was to determine whether the vertical pretilt angle was removed by a cause other than the photosensitive monomer. In the liquid crystal display device according to the present invention, both the vertical pretilt values before irradiation with ultraviolet rays and after irradiation with ultraviolet rays were measured.

division Panel sample number Vertical pretilt angle before exposure Post Exposure Vertical Pretilt Angle

Prior art

Sample C1 1.528 1.428 Sample C2 1.529 1.543 Sample C3 1.610 1.729 Sample C4 1.574 1.492 Sample C5 1.679 1.695

The present invention

Sample P1 1.477 0.033 Sample P2 1.611 0.004 Sample P3 1.505 0.035 Sample P4 1.471 -0.008 Sample P5 1.629 -0.046

As can be seen from the above results, after the photosensitive monomer 220 is cured, the liquid crystal molecules closest to the alignment layers 101 and 301 are changed to a horizontal state in which the vertical pretilt angle is close to 0 degrees. In the state of simply including the photosensitive monomer 220 has a vertical pretilt angle substantially the same as the prior art. However, it can be seen that after the photosensitive monomer 220 is cured, the vertical pretilt angle is removed. In the liquid crystal display according to the prior art, almost no difference occurs before or after irradiating ultraviolet rays. That is, as the photosensitive monomer 220 is cured between the alignment layers 101 and 301 and the liquid crystal molecules, it can be seen that the liquid crystal molecules inclined at the vertical pretilt angle are returned to the horizontal state. The negative angle value indicates that the inclination angle in the left (right) direction is changed to the inclination angle in the right (left) direction.

6 is a graph showing the results of measuring the left and right viewing angle contrast ratios of the liquid crystal display according to the related art and the present invention. The liquid crystal display according to the prior art has shown a graph result having a high value in the center. This means that the difference between the left and right contrast ratios is large. On the other hand, the liquid crystal display according to the present invention shows a graph result having a low center portion and a gentle curve. This means that the difference between the left and right contrast ratios did not appear much.

In the embodiments of the present invention described above, the method focuses on the method of manufacturing the liquid crystal display device after forming the alignment layer. The present invention relates to a horizontal electric field type liquid crystal display device in which a liquid crystal layer is driven horizontally on a plane of a display panel. Therefore, it is obvious to those skilled in the art to apply the spirit of the present invention to a liquid crystal display device and a method of manufacturing the horizontal electric field method so far known, so a detailed description thereof is omitted.

For example, in order to form a horizontal electric field, a pixel electrode connected to the thin film transistor and a common electrode applying a common voltage are formed in parallel with each other. To this end, the common wiring for supplying the common voltage and the common electrode branching from the common wiring may be formed together when forming the gate wiring. In this case, the pixel electrode and the common electrode form a horizontal electric field, but are formed on different planes in cross section.

Alternatively, the pixel electrodes may be formed in parallel with each other on the same plane as the pixel electrodes. To this end, after the common wiring and the common electrode are formed on the passivation layer covering the thin film transistor, a pixel electrode connected to the thin film transistor on the passivation layer may be formed in parallel with the common electrode.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

1 is a plan view showing a conventional horizontal field type liquid crystal display panel.

FIG. 2 is a cross-sectional view illustrating a structure of a liquid crystal display panel taken along the line II ′ in FIG. 1.

3A and 3B are views showing a state in which an alignment film is treated by using a rubbing cloth on an alignment film coated on a surface of a thin film transistor substrate or a color filter substrate according to the prior art;

4A to 4D are cross-sectional views showing the number of cases of the vertical pretilt angle that the liquid crystal layers interposed between the thin film transistor substrate and the color filter substrate may have.

5A to 5C are cross-sectional views illustrating a process of manufacturing a liquid crystal display device according to an exemplary embodiment of the present invention.

Figure 6 is a graph showing the results of measuring the left and right viewing angle contrast ratio for the liquid crystal display according to the prior art and the present invention.

<Explanation of symbols for the main parts of the drawings>

SUBL: lower transparent substrate SUBU: upper transparent substrate

TFT: thin film transistor

BM: Black Matrix CF: Color Filter

SUB: transparent substrate GL: gate wiring

DL: data wiring CL: common wiring

G: gate electrode COM: common electrode

GI: gate insulating film A: semiconductor layer

S: source electrode D: drain electrode

PASSI: Protective film PXL: Pixel electrode

10, 100: thin film transistor substrate 30, 300: color filter substrate

11, 101: first alignment film 31, 301: second alignment film

20, 200: liquid crystal layer 210: main liquid crystal material

220: photosensitive monomer 50, 500: rubbing cloth

Claims (13)

A substrate on which an alignment film having an alignment rubbing pattern is formed; A liquid crystal layer in contact with the alignment layer; And And a photosensitive monomer which is photocured between the alignment layer and the liquid crystal layer to keep the liquid crystal layer horizontal to the plane of the substrate. The method of claim 1, The substrate having the alignment film, A thin film transistor substrate having a first alignment layer; And a color filter substrate having a second alignment layer. The method of claim 2, The liquid crystal layer is in contact with the first alignment layer and the second alignment layer and interposed between the thin film transistor substrate and the color filter substrate; And the photosensitive monomer is photocured between the first alignment layer and the liquid crystal layer and between the second alignment layer and the liquid crystal layer. The method of claim 2, The thin film transistor substrate, A gate line and a data line perpendicular to each other; A pixel region having a matrix array formed by the gate line and the data line; A thin film transistor formed in the pixel region; A pixel electrode connected to the thin film transistor and formed in the pixel area; And And a common electrode arranged in parallel with the pixel electrode in the pixel area to form a horizontal electric field. The method of claim 1, The photocured photosensitive monomer is one end is connected to the alignment pattern of the alignment layer, the other end is a liquid crystal display, characterized in that coupled to one side of the liquid crystal molecules of the liquid crystal layer. The method of claim 1, And a horizontal state in which the vertical pretilt angle with respect to the plane of the substrate of the liquid crystal layer has a value of 0.3 degrees or less. Forming a thin film transistor substrate having a first alignment layer; Forming a color filter substrate having a second alignment layer; Forming a liquid crystal display panel by bonding the thin film transistor substrate and the color filter substrate so that a mixture of a main liquid crystal material and a photosensitive monomer is interposed between the first alignment layer and the second alignment layer; And And irradiating ultraviolet rays to the liquid crystal display panel to cure the photosensitive monomer. The method of claim 7, wherein Forming the thin film transistor substrate, Forming a gate line and a gate electrode branching from the gate line on the transparent substrate; Forming a gate insulating film on the gate line and the gate electrode; Forming a semiconductor layer on the gate insulating layer to overlap the gate electrode; Forming a data line orthogonal to the gate line on the gate insulating layer, a source electrode branching from the data line to contact one end of the semiconductor layer, and a drain electrode facing the source electrode and contacting the other end of the semiconductor layer; step; Forming a passivation layer covering the data line, the source electrode, and the drain electrode; Forming a pixel electrode on the passivation layer, the pixel electrode being connected to the drain electrode; And And forming the first alignment layer covering the pixel electrode. The method of claim 8, Forming the gate line and the gate electrode, And a common wiring which is flat with the gate line, and a common electrode which branches from the common wiring and is arranged in parallel with the pixel electrode. The method of claim 8, Forming the pixel electrode, And forming a common wiring parallel to the gate wiring and a common electrode on the protective layer and branched from the common wiring and arranged in parallel with the pixel electrode. The method of claim 7, wherein Forming the color filter substrate, Forming a black matrix defining a pixel region having a matrix array on the transparent substrate Forming a color filter in the pixel region between the black matrices; And forming the first alignment layer on the color filter. The method of claim 7, wherein Forming the liquid crystal display panel, And a content ratio of the main liquid crystal material and the photosensitive monomer to have any one of values of 99.0: 1.0 to 99.9: 0.1. The method of claim 7, wherein Curing the photosensitive monomer, A method of manufacturing a liquid crystal display device comprising irradiating ultraviolet rays having a wavelength of 365 nm with energy of 45 mW / cm ² .

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