KR20030037824A - Multi-domain liquid crystal display device - Google Patents

Abstract

The present invention relates to a multi-domain liquid crystal display device in which the shape of the light shielding layer is modified to improve contrast and afterimage. In particular, the multi-domain liquid crystal display device according to the present invention has at least two pixels defined by crossing gate and data lines. A first substrate divided into domains and having a thin film transistor and a pixel electrode formed on the pixel, a second substrate facing the first substrate, and a color filter layer formed thereon, a liquid crystal layer formed between the first and second substrates; The first and second alignment layers formed on the inner side surfaces of the first and second substrates, and the light shielding layer are provided at points where the electric field direction and the direction in which the liquid crystals stand in the outer portion of the pixel are opposite.

Description

Multi-domain Liquid Crystal Display Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device (LCD), and more particularly, to a multi-domain liquid crystal display device that compensates a viewing angle by dividing one pixel into several domains.

Recently, as the performance of the active matrix liquid crystal display is rapidly developed, the active matrix liquid crystal display is widely used in applications such as flat-panel TV systems or portable computers and high-information monitors.

In particular, the TN (TN) display mode of an active matrix liquid crystal display device is formed by forming electrodes on two substrates, arranging the liquid crystal directors to be twisted by 90 °, and then driving the liquid crystal director by applying a voltage to the electrodes. It is used a lot.

However, TN mode liquid crystal display devices have fundamental problems such as narrow viewing angle characteristics and late response characteristics, especially late response characteristics in gray scale operation.

In order to solve this problem, various new concepts of the liquid crystal display device have been proposed.

For example, a multi-domain mode that compensates for a viewing angle by dividing a pixel into several domains and changing a viewing angle of each domain, and an IPS that applies a transverse electric field by placing two electrodes on one plane. In-Plane Switching mode, negative liquid crystal with negative dielectric anisotropy, Vertical Alignment (VA) mode using a vertical alignment film, and film-compensated mode for compensating a viewing angle with a compensation film.

Hereinafter, a multi-domain liquid crystal display device and a manufacturing method thereof will be described with reference to the accompanying drawings.

1A to 1E are cross-sectional views illustrating a manufacturing process of a TDTN liquid crystal display device according to a first exemplary embodiment, FIG. 2 is a plan view showing a rubbing direction of a TDTN liquid crystal cell according to a first exemplary embodiment, and FIG. A sectional view of a TDTN liquid crystal display device according to the first embodiment of the present invention.

4 is a plan view of a liquid crystal display device showing a structure of a black matrix for preventing light leakage, and FIG. 5 is a plan view of a liquid crystal display device showing a structure of a storage wiring for preventing light leakage.

The multi-domain mode introduced to solve the narrow viewing angle problem in the TN mode is a method of mutually compensating a weak viewing angle direction by dividing one pixel into several sub-pixels, and splits one pixel into two domains (Two). Domain TN) and Four Domain TN (FDTN) for dividing one pixel into four domains.

In the method of dividing the domain of the TDTN, as shown in FIG. 1A, a polymer material is coated and cured on the substrate 10 having various patterns including the ITO electrode 11 to form an alignment layer 12 and a rubbing roll ( 13) by rubbing in the first direction, and as shown in FIGS. 1B to 1D, the photosensitive film 15 is coated on the entire surface of the alignment film 12 rubbed in the first direction and a photolithography process is performed. After the photoresist film 15 remains only in the region II, a rubbing process is performed on the exposed alignment layer 12 in the second direction. Subsequently, as illustrated in FIG. 1E, when the photosensitive film 15 of the second region is removed, two domains of first and second directions having different alignment directions are formed in one pixel.

At this time, the upper substrate of the liquid crystal display element is rubbed in the same direction as the solid line of FIG. 2, and the lower substrate is rubbed in the same direction as the dotted line of FIG. 2 to compensate for the field of view angle.

The alignment layer is a rubbing alignment layer, and a polymer material such as polyimide or polyamide is used.

Subsequently, as shown in FIG. 3, when the upper and lower substrates 10a and 10b in which the domains are divided by rubbing are bonded to each other and the liquid crystal layer 14 is formed therebetween, the alignment direction of the liquid crystal molecules differs for each domain. Is formed.

In this case, in addition to the common electrode 11a, which is an ITO electrode, a black matrix (not shown) for blocking light leakage and color filter layers (R, G, B) for color realization are further formed on the upper substrate 10a. In addition to the pixel electrode 11b serving as the ITO electrode, the lower substrate 10b has a scan line ("16" in FIG. 4) and a signal line ("17" in FIG. 4) and the two wirings which are intersected to define a plurality of pixels. Further, a thin film transistor (“18” of FIG. 4) is formed at an intersection of to selectively apply a voltage to the pixel electrode 11b.

In the TDTN liquid crystal display device formed as described above, a domain in one pixel is divided into I and II regions so that the viewing angle and the direction of the viewing angle based on the arrangement of the liquid crystal molecules of the region I and the viewing angle of the viewing angle based on the arrangement of the liquid crystal molecules of the region II are mutually different. Compensated to solve the conventional narrow viewing angle problem (see FIG. 2).

In this case, a disclination line, which is a discontinuity line of liquid crystal alignment, causes light leakage in the domain and the boundary region of the domain. In the NW mode, the foreground line is generated in the dark state, so the foreground line is generated. Is blocked by black matrix or storage wiring to block leakage light.

In detail, as illustrated in FIG. 4, the black matrix 19 of the upper substrate is formed to overlap the scan line 16, the signal line 17, and the thin film transistor 18 of the lower substrate, which are regions in which the liquid crystal array cannot be controlled. Of course, in order to block the leakage light at the domain boundary portion is formed extending to the boundary portion of the domain. The black matrix 19 is formed using metals, such as Cr and CrOx, which have high reflectance.

Alternatively, as shown in FIG. 5, the storage wiring 29 may be formed to block leakage light at the domain boundary without additional black matrix.

However, forming a multi-domain by only rubbing has a disadvantage in that the process is very complicated by the photolithography technique and the damage or contrast ratio of the alignment layer is reduced. Thus, TDTN (Two-Domain), which controls the pretilt angle by combining UV and rubbing, is used. TN) mode was introduced.

6A through 6D are cross-sectional views illustrating a manufacturing process of a TDTN mode liquid crystal display device according to a second embodiment, FIG. 7 is a cross-sectional view of a TDTN mode liquid crystal display device according to a second embodiment, and FIG. 8 is a slit. A cross-sectional view of a liquid crystal display device in which domains are divided by.

9 is a plan view of a TDTN mode liquid crystal display device according to the prior art, FIG. 10 is a photograph showing a light leakage of a liquid crystal display device for explaining a conventional problem, and FIG. 11 is a view of a conventional TDTN mode liquid crystal display device. It is a graph which shows sectional drawing and light leakage in the point.

In the domain-divided TDTN mode by combining rubbing and light irradiation, as shown in FIGS. 6A and 6B, an alignment layer 32 is formed on a substrate 30 having various patterns including the ITO electrode 31 and a rubbing roll. After rubbing in one direction using 33 to form a high pretilt angle, as shown in FIG. 6C, the mask 35 is covered so that only the second region of the alignment layer 32 is shielded, and ultraviolet (UV) ultra- Violet Ray) is irradiated to apply energy to the first region to create a low pretilt region. Thus, as shown in FIG. 6D, a high-tilt region and a low-tilt region are present in one pixel.

In this case, the alignment layer 32 uses a polymer material such as polyimide.

The mask used for light irradiation is characterized in that a region corresponding to half of one pixel is a light blocking portion and a region corresponding to the other half is a light transmitting portion.

In the TDTN mode liquid crystal display device formed as described above, the domain in one pixel is divided into two regions as shown in FIG. 7. In the first region, the liquid crystal molecules 32a are arranged by the high pretilt alignment layer of the upper substrate. It is arranged by the high pretilt alignment film of the lower substrate. This compensates for the viewing angles.

The liquid crystal display device formed through the above manufacturing process is made by one rubbing process and one UV irradiation, thereby simplifying the process and having the advantage of high brightness.

Since then, a method of providing the VA mode and the field distortion means as a method of not performing the rubbing process has been introduced.

First, although not shown, the VA mode liquid crystal display device uses a negative liquid crystal having a negative dielectric anisotropy and a vertical alignment layer. The VA mode liquid crystal display device initially arranges the long axes of the liquid crystal molecules perpendicular to the alignment layer plane, and then applies a voltage above a threshold voltage to the liquid crystal molecules. Light is selectively transmitted by causing the major axis of to move toward the alignment film plane in the vertical direction of the alignment film plane.

In this case, the negative type liquid crystal molecules have a property of tilting in the vertical direction with respect to the electric field, and the vertical alignment layer is an alignment layer that does not require a separate rubbing treatment, so that the liquid crystal molecules do not lie in disorder in various directions when moving toward the alignment layer plane.

The VA mode divides the alignment direction of the liquid crystal molecules into a plurality of directions and may implement a wide viewing angle more effectively when a compensation film is used.

On the other hand, by forming a structure or a slit (side-electrode, ribs, etc.) on the substrate may distort the electric field applied to the liquid crystal layer to position the director of the liquid crystal molecules in the desired direction.

8 is a cross-sectional view of a liquid crystal display device in which domains are divided by slits 49, which are electric field distortion means, and the slits 49 are formed by partially removing the pixel electrode 48. As shown in FIG.

Specifically, the liquid crystal display device including the electric field distortion means is a pixel electrode by depositing a transparent conductive material ITO on the first substrate 40 formed with the gate wiring and data wiring, and the thin film transistor formed at the intersection of the two wiring A 48 is formed, and a portion of the pixel electrode 48 is selectively removed to form a straight slit 49 parallel to the gate line. Thereafter, the second substrate 41 including the black matrix, the color filter layer (not shown), and the common electrode 44 is bonded to face the first substrate 40, and the first and second substrates are bonded to each other. The liquid crystal is sealed between the 40 and 41 to form the liquid crystal layer 42.

At this time, a structure such as a projection may be formed without forming the slit 49.

When a voltage equal to or greater than the threshold voltage is applied to the liquid crystal display, the electric field is distorted by the field distortion means such as the slit 49 or the projection, and the liquid crystal molecules 42a are inclined in different directions about the field distortion means. Lose.

As a result, the liquid crystal directors face each other and the viewing angle is compensated, thereby ensuring a wide viewing angle.

As described above, the black matrix or the storage wiring overlaps the domain boundary where the alignment direction of the liquid crystal is divided to prevent light leakage. This is because when the light is leaked at the domain boundary where the electric field is unstable and it is difficult to control the alignment of the liquid crystal, the contrast ratio is lowered and the image quality is deteriorated, such as interference of the image.

The viewing angle has been improved by introducing various modes as described above. Among them, the multi-domain liquid crystal display device divided into domains by combining rubbing and light irradiation will be described in detail as follows.

9 is an example of a multi-domain liquid crystal display device that is domain-divided by combining rubbing and one light irradiation as described above, and after the rubbing treatment in the "T" direction, the upper substrate irradiated with light to the first region, and " And a lower substrate irradiated with light to the second region after rubbing in the B " direction, and a liquid crystal layer formed between the upper and lower substrates.

That is, the upper substrate is composed of the region II which is the high pretilt region and the region I which is the low pretilt region, and the lower substrate is composed of the region I which is the high pretilt region and the region II which is the low pretilt region. The high pretilt region and the low pretilt region of the upper substrate correspond to the low pretilt region and the high pretilt region of the lower substrate, respectively.

At this time, the liquid crystal molecules are controlled and arranged by the high pretilt alignment films of the upper and lower substrates. The liquid crystal molecules in the region I are arranged by the alignment film of the lower substrate, and the liquid crystal molecules in the region II are arranged by the alignment film of the upper substrate. As a result, the liquid crystal directors face each other to compensate for the viewing angle, thereby securing a wide viewing angle.

For reference, reference numeral 54a of FIG. 9 denotes a liquid crystal molecule close to the lower substrate, and “54b” denotes a liquid crystal molecule close to the upper substrate.

In the TDTN liquid crystal display device, when an electric field is not applied between the upper and lower substrates, the liquid crystal molecules are initially oriented as shown in FIG. 9, and thus light is transmitted in any orientation, so that a white level is displayed and an electric field above a threshold is applied. In this case, the liquid crystal molecules are switched in the direction of the arrow so that incident light linearly polarized by the polarizer of the lower substrate does not pass through the polarizer of the upper substrate, thereby displaying a black level. In other words, it becomes a white background mode.

At this time, the polarizing plate of the upper substrate is attached so that the polarization axis direction is the "B" direction, and the polarizing plate of the lower substrate is attached so that the polarization axis direction is perpendicular to the polarization axis direction of the upper substrate.

The liquid crystal display device formed through the above manufacturing process has the advantage of simplifying the process because it is made of one rubbing process and one light irradiation.

However, in the multi-domain liquid crystal display device, in addition to light leakage at the domain boundary, light leakage also occurs at the pixel edge on the data line side as shown in FIG. 10. Fig. 10 shows the light leakage immediately after switching from the bright state to the dark state, whereby the brightness at that position is brightened for several seconds.

In particular, the light leakage on the side of the data wiring is different from the direction in which the side electric field is generated at the edge of the pixel electrode and the direction in which the liquid crystal is standing at that point, resulting in a foreground line ("L": disclination line), which is generated by the foreground line. (See Fig. 9)

The light absorbing metal layer is overlapped to prevent light leakage. As described above, the black matrix or the storage wiring is overlapped to prevent light leakage at the domain boundary where the alignment direction of the liquid crystal is divided.

FIG. 11 shows a data line 57 insulated from and interposed between a first pixel electrode 51a, a second pixel electrode 51b adjacent thereto, and the first and second pixel electrodes 51a and 51b. As a graph showing the cross-sectional view schematically and the light transmittance Tr according to the dimension R of each pattern, it can be seen that light leakage is strongly generated at the data line 57 side and the edge of the second pixel electrode 51b.

At this time, the light leakage on the upper portion of the data line 57 is blocked by the black matrix 55 of the upper substrate, but the light leaks at the foreground line point where there is no separate light blocking layer.

When light leaks in this way, the contrast ratio is lowered and the image quality is degraded, such as interference of the image.

That is, the conventional multi-domain liquid crystal display device as described above has the following problems.

When a voltage is applied to the pixel electrode, a lateral electric field is formed between the pixel electrode and the neighboring pixel electrode. If the lateral electric field is opposite to the direction in which the liquid crystal stands, the liquid crystal molecules cause reverse tilt, thereby forming a foreground line. do.

Through this part, light leakage occurs, which reduces the contrast ratio of the device, thereby degrading image quality.

The present invention has been made to solve the above problems, and an object thereof is to provide a multi-domain liquid crystal display device for improving contrast and afterimage.

1A to 1E are cross-sectional views illustrating a manufacturing process of a TDTN liquid crystal display device according to a first embodiment of the present invention.

2 is a plan view illustrating a rubbing direction of a TDTN liquid crystal cell according to a first embodiment of the present invention;

3 is a cross-sectional view of a TDTN liquid crystal display device according to a first embodiment of the prior art.

4 is a plan view of a liquid crystal display device showing a structure of a black matrix for preventing light leakage.

5 is a plan view of a liquid crystal display device showing a structure of a storage wiring to prevent light leakage;

6A to 6D are cross-sectional views illustrating a manufacturing process of a TDTN mode liquid crystal display device according to a second embodiment of the present invention.

Fig. 7 is a sectional view of a TDTN mode liquid crystal display device according to a second conventional embodiment.

8 is a cross-sectional view of a liquid crystal display device in which domains are divided by slits.

9 is a plan view of a TDTN mode liquid crystal display device according to the prior art.

10 is a photograph showing light leakage of a liquid crystal display device for explaining the conventional problem.

Fig. 11 is a graph showing a cross-sectional view of a conventional TDTN mode liquid crystal display device and light leakage at that point.

12 is a plan view of a DDTN mode liquid crystal display device according to a first embodiment of the present invention.

13 is a plan view of a DDTN mode liquid crystal display device according to a second embodiment of the present invention.

* Explanation of symbols on the main parts of the drawings

101: gate wiring 101a: gate electrode

102: data wiring 102a: source electrode

102b: drain electrode 103: semiconductor layer

109: black matrix 113: pixel electrode

119: Gate BM

According to an aspect of the present invention, there is provided a multi-domain liquid crystal display device including: a first substrate in which a pixel defined by crossing gate lines and data lines is divided into at least two domains, and a thin film transistor and a pixel electrode formed on the pixel; A second substrate facing the first substrate and having a color filter layer formed thereon, a liquid crystal layer formed between the first and second substrates, a first and second alignment layers formed on inner surfaces of the first and second substrates; The light shielding layer is provided at a point in which an electric field direction and a liquid crystal standing direction are opposite to each other in the outer portion of the pixel.

That is, the present invention is characterized in that in the mode of dividing the domain by combining rubbing and optical alignment, a light shielding layer is formed on the edge of the pixel on the data line side to improve contrast and afterimage of the multi-domain liquid crystal display device.

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

12 is a plan view of a DDTN mode liquid crystal display device according to a first embodiment of the present invention, and FIG. 13 is a plan view of a DDTN mode liquid crystal display device according to a second embodiment of the present invention.

As shown in FIG. 12, the multi-domain liquid crystal display device according to the present invention includes a gate wiring 101 and a data wiring 102 defining pixels by crossing vertically, a thin film transistor formed at an intersection of the two wirings, and the thin film. A lower substrate on which an ITO pixel electrode 113 connected to a transistor is disposed, a color filter layer (not shown) for implementing colors, and a common electrode (not shown) of ITO material corresponding to the pixel electrode 113 are disposed. An upper substrate facing the lower substrate and a liquid crystal layer formed between the upper and lower substrates.

The liquid crystal layer may be formed by dropping the liquid crystal on at least one substrate by using a dispensor before bonding the upper and lower substrates, in addition to the general injection method.

In this case, a chiral dopant may be added to the liquid crystal, and the thin film transistor may be formed on the entire surface including the gate electrode 101a branched from the gate wiring 101 and the gate electrode 101a. A gate insulating film (not shown), a semiconductor layer 103 formed on the gate insulating film on the gate electrode 101a, and a source extending from the data line 102 and formed at both ends of the semiconductor layer 103, respectively. It consists of drain electrodes 102a and 102b.

In addition, an alignment layer is further formed on inner surfaces of the upper and lower substrates on which the patterns are formed. The alignment layer is coated with a polymer material such as polyimide and cured, and then subjected to alignment by combining rubbing and light irradiation.

Thus, the upper substrate is composed of the region II which is the high pretilt region and the region I which is the low pretilt region, and the lower substrate is composed of the region I which is the high pretilt region and the region II which is the low pretilt region. The liquid crystal in the region I is controlled by the alignment film of the upper substrate having high pretilt, and the liquid crystal in the region II is controlled by the alignment film of the lower substrate.

A slit is further formed at the boundary of the first and second regions to stabilize the orientation at the domain boundary. The slit is formed by patterning the pixel electrode 113.

As the first and second alignment layers 115a and 115b, polyvinylcinnamate, polyazobenzene, polysiloxane-cinnamate, and the like, which are photoalignment films, may be used in addition to polyimide.

In addition, linearly polarized light, non-polarized light, partial polarized light, non-polarized light, deep UV, mid UV, or the like may be used as light used for light irradiation.

When the multi-domain liquid crystal display device is turned on, the liquid crystal is driven in a predetermined direction, but the liquid crystal is arranged in an undesired state due to instability of the electric field, and light leakage occurs at that point.

Therefore, before forming the color filter layer to block the light leakage as described above, the black matrix serving as the light blocking layer is formed at a position where it is difficult to control the direction of the liquid crystal.

Particularly, in the present invention, the black matrix 109 of the upper plate is removed as shown in FIG. To extend.

However, as the area of the black matrix increases, the luminance of the device decreases, so that the black matrix has a minimum area within the range of blocking light leakage.

At this time, although not shown, light leakage at the domain boundary portion overlaps any one of the black matrix, the storage wiring, and the gate BM to shield the light.

The storage line is formed at the same time as the gate line to be electrically connected to the common electrode at the pad part, and the gate BM is formed at the same time as the gate line but electrically floated.

Another embodiment of the present invention is characterized in that the gate BM is formed without forming a black matrix on the pixel edge on the data wiring side.

That is, as shown in FIG. 13, the gate BM 119 formed to shield light leakage at the domain boundary portion is formed to extend to the edge of the first region on the side of the neighboring data line 102.

The gate BM 119 may be formed to overlap the data line 102.

The gate BM 119 is formed at the same time to be parallel to the gate wiring 101 and is electrically floating. When electricity flows through the gate BM 119, another side electric field is formed in the extended portion, so that light leakage may occur, thereby electrically floating.

Therefore, although not shown, a liquid crystal display device that shields light leakage by using the gate BM should be further provided with a separate storage electrode.

The first and second embodiments may be applied to the TDTN mode in addition to the DDTN mode.

On the other hand, field distortion means such as slits and protrusions may be further formed at the domain boundary, and the slit becomes a boundary of the domain dividing one pixel, and when the alignment direction between the electric field generated by the slit and the liquid crystal coincides, The orientation at the boundary is stabilized. In addition, light leakage at the domain boundary does not occur.

The shape of the slit can be variously modified, such as +, U-shaped.

The multi-domain liquid crystal display device of the present invention as described above has the following effects.

By covering the light leakage at the edge of the pixel with a light blocking layer such as a black matrix or a gate BM, the contrast ratio can be improved and the dynamic afterimage that can occur when switching from the bright state to the dark state can be eliminated.

In addition, since a separate process for forming the light shielding layer is not added, it may be manufactured without an additional process.

Claims (11)

A first substrate in which a pixel defined by crossing gate and data lines is divided into at least two domains, the first substrate having a thin film transistor and a pixel electrode formed on the pixel, a second substrate facing the first substrate and having a color filter layer; The liquid crystal layer formed between the first and second substrates, the first and second alignment layers formed on the inner surfaces of the first and second substrates, and the direction in which an electric field and a liquid crystal stand among the outer portions of the pixel are opposite. A multi-domain liquid crystal display device characterized in that the light shielding layer is provided at the phosphorus point. The multi-domain liquid crystal display of claim 1, wherein the light blocking layer overlaps the data line. The multi-domain liquid crystal display of claim 1, further comprising a slit at the domain boundary. The multi-domain liquid crystal display of claim 1, wherein any one of a black matrix, a storage line, and a gate BM overlaps the domain boundary. The multi-domain liquid crystal display of claim 4, wherein the light blocking layer is formed integrally with the black matrix. 6. The multi-domain liquid crystal display device of claim 5, wherein the black matrix is formed to be wider by overlapping the data line. The multi-domain liquid crystal display of claim 4, wherein the light blocking layer is integrally formed with the gate BM. The multi-domain liquid crystal display of claim 7, wherein the gate BM is formed at the same time as the gate wiring. The multi-domain liquid crystal display of claim 1, wherein the first and second alignment layers are aligned by rubbing and light irradiation. The multi-domain liquid crystal display of claim 1, wherein the domain is divided into two domains. The multi-domain liquid crystal display of claim 10, wherein the liquid crystal molecules of the first region and the liquid crystal molecules of the second region of the domain are arranged in different directions.