JP2002244145A - Liquid crystal display device of fringe field drive mode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device of a fringing field drive mode which can improve image quality characteristic by preventing alignment fault. SOLUTION: The liquid crystal display device of the fringing field drive mode contains an upper substrate and a lower substrate which are arranged at a prescribed distance and on which unit pixels are restricted, a liquid crystal layer which is arranged therebetween the contains a large number of liquid crystal molecules, a counter electrode 55 which is formed at the unit pixel on the lower substrate, a pixel electrode 59 which generates a fringing field together with the counter electrode and moves the liquid crystal molecules in the unit pixel, a horizontally aligned film which is arranged between the lower substrate and the liquid crystal layer and has a prescribed rubbing axis, a vertically aligned film which is interposed between the upper substrate and the liquid crystal layer, a polarizer which is arranged on an outside surface of the lower substrate and has a prescribed polarizing axis and a decomposer which is arranged on an outside surface of the upper substrate and has a prescribed absorbing axis. Further, the counter electrode 55 and the pixel electrode 59 form a first fringing field and a second fringing field of two directions being symmetrical to each other in the unit pixel, when a field is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fringe field driving mode liquid crystal display (Fringe Field).
Switching mode LCD: FF
More specifically, HAN (Hybrid) that can prevent poor alignment and improve image quality characteristics.
d Alignment Nematic) mode.

[0002]

2. Description of the Related Art Recently, FFS-LCDs have been replaced by conventional IPS.
(In-Plane Switching) mode LC
It has been proposed to improve the low aperture ratio and transmission of D. Such an FFS-LCD includes upper and lower substrates separated by a predetermined cell gap, a liquid crystal layer interposed between the upper and lower substrates, a counter electrode (ie, a relative electrode) formed on the inner surface of the lower substrate, and a pixel. Including electrodes. The counter electrode and the pixel electrode are formed of a transparent conductor, and the interval between the counter electrode and the pixel electrode is formed smaller than the cell gap. Accordingly, fringe fields are formed between the electrodes and on the electrodes, and the liquid crystal molecules located between the electrodes and on the electrodes are operated.

FIG. 1 is a plan view showing a lower substrate of a conventional FFS-LCD. Referring to FIG. 1, a gate bus line 3 and a data bus line 7 are connected to a lower substrate 1.
Are arranged in a crossover manner, and a unit pixel is limited. Near the intersection of the gate bus line 3 and the data bus line 7, a thin film transistor (TFT) is arranged.

The counter electrode 2 is formed of a transparent conductor, and is formed for each unit pixel. At this time, the counter electrode 2 may be formed in a square plate shape or a comb.
b) It can be formed in the form. Common signal line 30
Is arranged to contact the counter electrode 2 in order to continuously supply a common signal to the counter electrode 2.

At this time, the common signal line 30 is formed of a metal film having excellent signal transmission characteristics, and is generally formed of a gate bus line metal film. Such a common signal line 30 is parallel to the gate bus line 3 and contacts a predetermined portion of the counter electrode 2, and extends from the first portion 30 a in parallel with the data bus line 7, And a second portion 30b arranged between the counter electrode 2 and the data bus line 7.

The pixel electrode 9 is formed in a unit pixel so as to overlap the counter electrode 2. At this time, the pixel electrode 9 and the counter electrode 2 are electrically insulated. Pixel electrode 9
Includes a rectangular slit 9 a formed in a plate shape and exposing the counter electrode 2. At this time, a predetermined portion of the pixel electrode 9 contacts the thin film transistor TFT.

On the other hand, although not shown, the upper substrate is
It faces the lower substrate 1 with a width larger than the distance between the pixel electrode 9 and the counter electrode 2. A liquid crystal layer (not shown) including a large number of liquid crystal molecules is interposed between the upper and lower substrates. At this time, as the liquid crystal molecules, a substance having a positive or negative dielectric anisotropy is used. A horizontal alignment film (not shown) is formed on the inner surface of the lower substrate 1 and the inner surface of the upper substrate.

Each of the horizontal alignment films has a rubbing axis (r) that is not parallel to each other.
The rubbing axis forms a predetermined angle with the gate bus line 3 (for example, about 10 to 50 degrees when the dielectric anisotropy is negative).
On an outer surface of the lower substrate 1, a polarizer (not shown) having a polarization axis in a predetermined direction is arranged.
An analyzer (not shown) having an absorption axis orthogonal to the polarization axis is disposed on the outer surface of the upper substrate. At this time, the polarization axes are parallel to the rubbing axis.

A conventional FFS-L having such a configuration
The CD operates as follows. First, unless a voltage is applied between the counter electrode 2 and the pixel electrode 9, that is, an electric field is not formed, the liquid crystal molecules are arranged such that their long axes are parallel to the rubbing axis. Thus, the light that has passed through the polarizer does not change its traveling direction while passing through the liquid crystal layer, and cannot pass through a decomposer having an absorption axis perpendicular to the polarization axis. Therefore, the screen is dark
Present.

On the other hand, when a predetermined voltage is applied between the counter electrode 2 and the pixel electrode 9, a fringe field is formed between the counter electrode 2 and the pixel electrode 9 so that the projection line is parallel to the gate bus line. This fringe field
It reaches the whole area above the counter electrode 2 and the pixel electrode 9, and all the liquid crystal molecules above the electrodes 2 and 9 are operated. Therefore, a high aperture ratio and a high transmittance are realized.

However, the conventional FFS-LCD is
Although high aperture ratio and high transmittance can be realized, such FF
The S-LCD requires a process of rubbing the alignment films on the upper and lower substrates in a predetermined direction in order to specify the initial alignment direction of the liquid crystal molecules. As is well known, the rubbing process has a high failure rate and easily damages the alignment film surface.

In the dark state (ie, before a voltage is applied between the counter electrode and the pixel electrode), such misalignment causes misalignment of liquid crystal molecules and the like, and light leakage occurs. As a result, the image quality characteristics of the FFS-LCD deteriorate.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide an FFS-LCD capable of preventing poor alignment and improving image quality. LCD is to be provided.

[0014]

In order to achieve the above object, a fringe field drive mode liquid crystal display device according to the present invention comprises: an upper substrate and a lower substrate, each having a predetermined distance and having a limited number of unit pixels; A liquid crystal layer including a large number of liquid crystal molecules interposed between the upper and lower substrates, a counter electrode formed in a unit pixel of the lower substrate, and a fringe field are generated together with the counter electrode, and the liquid crystal molecules in the unit pixel are generated. A pixel electrode to be operated, a horizontal alignment film interposed between the lower substrate and the liquid crystal layer and having a predetermined rubbing axis, a vertical alignment film interposed between the upper substrate and the liquid crystal layer, and an outer surface of the lower substrate. In a fringe field drive mode liquid crystal display device including a polarizer disposed and having a predetermined polarization axis and a decomposer disposed on the outer surface of the upper substrate and having a predetermined absorption axis, And the pixel electrode, characterized in that it is arranged so during field application, the first fringe field and the second fringe field in two directions symmetrical with the unit pixel is formed.

It is preferable that a phase compensation film is further interposed between at least one of the lower substrate and the polarizer and between at least one of the upper substrate and the decomposer. In addition, the phase compensation film is composed of hardened disk type liquid crystal molecules,
The liquid crystal molecules of the phase compensation film are preferably arranged such that the refractive index anisotropy of the liquid crystal molecules in the liquid crystal layer is compensated.

[0016]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 2 is a perspective view schematically illustrating an FFS-LCD according to an embodiment of the present invention, and FIG. 3 is a plan view illustrating a lower substrate of the FFS-LCD according to the embodiment of the present invention. Referring to FIG. 2, the lower substrate 50 and the upper substrate 70 face each other at a predetermined distance d. A liquid crystal layer 80 having predetermined liquid crystal molecules 80a is interposed between the lower substrate 50 and the upper substrate 70. On this occasion,
As the liquid crystal molecules 80a, a material having a positive or negative dielectric anisotropy can be selectively used.

As shown in FIG. 3, a gate bus line 51 and a data bus line 53 are provided on the inner surface of the lower substrate 50.
Are arranged in a matrix form so as to constitute a unit pixel. Here, the gate bus line 51 extends in the x-axis direction in the figure, and the data bus line 53 extends in the y-axis direction perpendicular to the x-axis. At the intersection of the gate bus line 51 and the data bus line 53, a thin film transistor TFT as a switching element is arranged. At this time, a gate insulating film (not shown) is interposed between the gate bus line 51 and the data bus line 53 to insulate them.

In each of the unit pixels, a counter electrode 55 is arranged in a plate form. The counter electrode 55 is formed of a transparent conductor, for example, an ITO material. Common signal line 57 for transmitting a common signal to counter electrode 55
Are arranged to be in contact with the counter electrode 55. Such a common signal line 57 contacts a predetermined portion of the counter electrode 55 and extends in parallel with the gate bus line 51, and extends from the first portion 57a to contact the counter electrode 55. , A second portion 57b and a third portion 57c arranged between the counter electrode 55 and the data bus line 53. Here, the second portion 57b and the third portion 57c of the common signal line 57 serve to prevent light leakage between the counter electrode 55 and the data bus line 53.

The pixel electrode 59 is arranged to overlap the counter electrode 55 with a gate insulating film (not shown) interposed. In addition, the pixel electrode 59 is configured such that fringe fields in two directions can be simultaneously formed in one unit pixel. For example, the pixel electrode 59
Second portion 57b or third portion 5 of common signal line 57
A first branch 59a extending to overlap 7c;
The second branch 5 extending from the first branch 59a and extending parallel to the gate bus line 51 so as to divide the counter electrode 55 into a first region A1 and a second region A2.
9b, a plurality of third branches 59c extending obliquely from the first and second branches 59a, 59b toward the first region A1 of the counter electrode 55, and first and second branches 59a, A plurality of fourth branches 59d extending obliquely from 59b toward the second region A2 of the counter electrode 55.

The pixel electrode 59 is connected to the third branch 5.
A fifth branch 59e connecting one end of the first branch 9c and a sixth branch 59f connecting one end of the fourth branch 59d.
And further included. Fifth and sixth branches 59e, 59
f can extend in parallel with the gate bus line 51 and extend so as to overlap a predetermined portion of the counter electrode 55 or the common signal line 57. In addition, the pixel electrode 59 is electrically connected to the thin film transistor TFT, and in this embodiment, for example, the sixth branch 59f contacts a predetermined portion.

As shown in FIG. 4, the third branch 59c extends so as to form a predetermined angle θ with respect to the x-axis, and the fourth branch 59d forms a right angle with the third branch 59c. To be extended. Here, the angle θ formed by the third branch 59c and the x-axis is about 45 ° to 90 ° when a liquid crystal having a positive dielectric anisotropy is used for the liquid crystal layer (80 in FIG. 2).
When the liquid crystal having a negative dielectric anisotropy is used for the liquid crystal layer, the angle is preferably about 0 ° to 45 °.

Referring to FIG. 2, a horizontal alignment film 62 is disposed on the surface of the resultant lower substrate 50, and a vertical alignment film 72 is disposed on the inner surface of the upper substrate 70. The horizontal alignment film 62 has a rubbing axis (R in FIG. 4) directed in the x-axis direction in the drawing, whereas the vertical alignment film 72 has no rubbing axis. That is, the FFS-LCD of the present invention has a HAN (Hybrid Align).
ment Nematic) mode. on the other hand,
Since the vertical alignment film 72 does not have a rubbing axis, it is not necessary to perform a conventional rubbing process on the vertical alignment film 72.

A polarizer 65 having a predetermined polarization axis (P in FIG. 4) is disposed outside the lower substrate 50, and an absorption axis (FIG. 4) orthogonal to the polarization axis is disposed outside the upper substrate 70. (A) is disposed. The polarization axis P of the polarizer 65 is normally opaque (normally opaque).
In order to realize the black state, the absorption axis A
And coincides with the rubbing axis R. That is, the polarization axis P matches the x-axis, and the absorption axis A matches the y-axis.

On the other hand, between the lower substrate 50 and the polarizer 65,
The first for compensating the anisotropy of the refractive index of the liquid crystal molecules 80a
Is interposed. Further, a second phase compensation film 78 for compensating the refractive index anisotropy of the liquid crystal molecules 80a is interposed between the upper substrate 70 and the decomposer 75. As shown in FIG. 5, each of the phase compensation films 68 and 78 has a cured disk type liquid crystal molecule 68.
a, 78a. Phase compensation films 68, 78
Of the liquid crystal molecules 68a and 78a of the liquid crystal layer 80
0a is arranged to compensate for the refractive index anisotropy of
Complete darkness can be obtained before voltage application. Both the first and second phase compensation films 68 and 78 may be formed, or only one of them may be formed.

The FFS-LCD having the above configuration is
The operation is performed as follows (hereinafter, see FIGS. 2 to 5). First, unless a voltage is applied between the counter electrode 55 and the pixel electrode 59, that is, if an electric field is not formed, the liquid crystal molecules 80a are long on the rubbing axis R and the substrate surface due to the horizontal alignment film 62 on the lower substrate 50 side. The substrates are arranged so that their axes are parallel to each other, and the longer the substrate surface is, the longer the vertical axis is. Accordingly, the light passing through the polarizer 65 does not change its polarization direction while passing through the liquid crystal layer 80, and cannot pass through the decomposer 75 having the absorption axis A perpendicular to the polarization axis P. Therefore,
The screen presents darkness. At this time, the first and second phase compensation films 68 and 78 compensate for the refractive index anisotropy of the liquid crystal molecules 80a, and the screen becomes completely dark.

On the other hand, when a predetermined voltage is applied between the counter electrode 55 and the pixel electrode 59, the third and fourth branches 59c and 59d of the pixel electrode 59 and the third and fourth branches 59c and 59d Counter electrode 55 exposed by
, A symmetrical two-way fringe field is formed. Due to such fringe fields, the liquid crystal molecules 80a between and above the counter electrode 55 and the pixel electrode 59 are both twisted. Accordingly, the light that has passed through the polarizer 65 changes its polarization state while passing through the liquid crystal layer 80, and passes through the decomposer 75 having the absorption axis A orthogonal to the polarization axis P. Therefore,
The screen becomes white. At this time, most of the liquid crystal molecules 80a in the unit pixel are twisted, so that a high transmittance and a high aperture ratio can be realized.

Further, since the fringe field is formed in two directions when a voltage is applied due to the arrangement characteristics of the counter electrode 59, the liquid crystal molecules 80a are arranged while forming a double domain by the fringe field, and the viewing angle is large. Be improved. Also, the liquid crystal molecules 80a on the upper substrate 70 side
Are already vertically aligned, the liquid crystal molecules 80a
Driven with even faster response time. Further, since the vertical alignment film 72 on the upper substrate 70 does not require a separate rubbing step, alignment defects on the upper substrate 70 are eliminated, and when dark, misalignment of liquid crystal molecules can be prevented, and image quality defects can be reduced. Be improved. In particular, since a phase compensation film is interposed on each of the outer surfaces of the upper and lower substrates and a complete darkness can be realized, the contrast ratio is greatly improved.

The present invention is not limited to only the above-described embodiments. For example, in the above-described embodiment, the counter electrode and the pixel electrode are configured such that a symmetrical fringe field in two directions is formed in a unit pixel, but a symmetrical fringe field is formed for each unit pixel. Thus, a counter electrode and a pixel electrode may be configured.
The present invention can be implemented with various modifications without departing from the scope of the invention.

[0029]

As has been described in detail above, the present invention can prevent poor alignment and improve image quality.

[Brief description of the drawings]

FIG. 1 is a plan view showing a lower substrate of a fringe field driving mode liquid crystal display according to the related art.

FIG. 2 is a perspective view schematically illustrating a fringe field driving mode liquid crystal display device according to an embodiment of the present invention.

FIG. 3 is a plan view showing a lower substrate of the fringe field driving mode liquid crystal display device according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating a directional relationship among a polarization axis of a polarizer, an absorption axis of a decomposer, a rubbing axis of a horizontal alignment film, and a branch of a pixel electrode according to an embodiment of the present invention.

FIG. 5 is a diagram for explaining a phase compensation method using a phase compensation film according to an example of the present invention.

[Explanation of symbols]

 Reference Signs List 50 Lower substrate 51 Gate bus line 53 Data bus line 55 Counter electrode 57 Common signal line 59 Pixel electrode 62 Horizontal alignment film 65 Polarizer 68 First phase compensation film 70 Upper substrate 72 Vertical alignment film 75 Decomposer 78 Second phase Compensation film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kim Jin-man South Korea 465 Mido-ri, Ogyeong-myeon, Icheon-si, Gyeonggi-do 604-604 (72) Inventor Lee Sung-hee, South Korea 49-1 Modern apartment 102-1206 F-term (reference) 2H049 BA02 BA06 BA42 BB03 BC04 BC22 2H090 LA01 LA06 LA09 MA01 MA02 MA16 MB01 2H091 FA08X FA08Z FA11X FA11Z FB02 FD08 GA02 GA03 GA06 GA11 2H092 GA14 GA20 NA01 PA10 PA11

Claims (4)

[Claims] An upper and lower substrate having a predetermined distance and having a limited number of unit pixels; a liquid crystal layer including a plurality of liquid crystal molecules interposed between the upper and lower substrates; A counter electrode formed in the unit pixel, a pixel electrode for generating a fringe field together with the counter electrode to operate the liquid crystal molecules in the unit pixel, and interposed between the lower substrate and the liquid crystal layer; A horizontal alignment film having a rubbing axis, a vertical alignment film interposed between the upper substrate and the liquid crystal layer, a polarizer disposed on an outer surface of the lower substrate and having a predetermined polarization axis, and the upper substrate A fringe field drive mode liquid crystal display device including a decomposer having a predetermined absorption axis,
Wherein the counter electrode and the pixel electrode are arranged such that, when a field is applied, a symmetrical first fringe field and a second fringe field are formed in the unit pixel in two directions. Drive mode liquid crystal display device. 2. The fringe field according to claim 1, wherein a phase compensation film is further interposed between the lower substrate and the polarizer and between at least one of the upper substrate and the decomposer. Drive mode liquid crystal display device. 3. The phase compensation film is composed of hardened disk-type liquid crystal molecules, and the liquid crystal molecules of the phase compensation film compensate for the anisotropy of the refractive index of the liquid crystal molecules in the liquid crystal layer. The fringe field drive mode liquid crystal display device according to claim 2, wherein the fringe field drive mode liquid crystal display device is arranged. 4. The rubbing axis of the horizontal alignment film coincides with the polarization axis of the polarizer, and the polarization axis of the polarizer and the absorption axis of the decomposer are orthogonal to each other. 2. The fringe field drive mode liquid crystal display device according to 1.