KR20020002055A - Fringe field switching mode lcd - Google Patents

Abstract

PURPOSE: An FFS-LCD(Fringe Field Switching-Liquid Crystal Display) is provided to compensate anisotropy in refractive index of LC molecules by arranging a fringe field of a selected unit pixel area symmetrically with a fringe field of a near pixel area to a data bus line and symmetrically with an electric field between upper and lower pixel areas to a gate bus line, and to improve the characteristics of definition by preventing color shift. CONSTITUTION: A counter electrode(15) is formed in each unit pixel area(P1,P2,P3,P4). The counter electrodes are arranged with specific distances to keep insulation between a gate bus line(11) and a data bus line(13). Pixel electrodes(17) are overlapped over the counter electrodes. Each pixel electrode includes a frame type body unit(17a) overlapped with the edge of a counter electrode, and plural diagonal branches(17b) arranged regularly to divide the body unit into several areas. The diagonal branches of the pixel electrode are symmetric with other diagonal branches(17b) of a near unit pixel. If voltage is fed to the counter electrode and the pixel electrode, a fringe field is formed between the exposed counter electrode of each pixel and the diagonal branches of the pixel electrode. The diagonal branches of the pixel electrode are arranged symmetrically in each unit pixel area. The fringe field is symmetric with another fringe field of a near pixel to the gate bus line and the data bus line respectively.

Description

Fringe field drive mode liquid crystal display device {FRINGE FIELD SWITCHING MODE LCD}

The present invention relates to a fringe field drive mode liquid crystal display device, and more particularly, to a fringe field drive mode liquid crystal display device capable of improving image quality characteristics.

In general, a fringe field switching mode LCD (FFS-LCD) is proposed to improve the low aperture ratio and transmittance of a general in-plane switching (IPS) LCD. Filed in US Pat. No. 98-9243.

The FFS-LCD includes a top and bottom substrate spaced apart from each other with a predetermined cell gap, a liquid crystal interposed between the top and bottom substrates, and a counter electrode and a pixel electrode formed on the inner side of the bottom substrate. The counter electrode and the pixel electrode are formed of a transparent conductor, and the distance between the counter electrode and the pixel electrode is smaller than the cell gap. Accordingly, a fringe field is formed between the electrodes and over the electrodes.

1 is a plan view showing a lower substrate structure of an FFS-LCD.

Referring to the same figure, the gate bus line 2 and the data bus line 4 are arranged on the lower substrate 1 so as to define a unit pixel, and the gate bus line 2 and the data bus line 4 are separated from each other. The thin film transistor TFT is disposed near the intersection point.

The counter electrode 5 is a transparent conductor and is formed for each unit pixel. The counter electrode 5 includes a plurality of branches 5a arranged at equal intervals and a body portion 5b connecting one end of the branch 5a to the counter electrode 5 of adjacent pixels. At this time, the counter electrode 5 receives a common signal continuously.

The pixel electrode 7 is formed in each unit pixel space so as to overlap with the counter electrode 5. The pixel electrode 7 contacts the drain electrode of the thin film transistor TFT while connecting the comb portion 7a respectively inserted in the branch 5a and the one end of the comb portion 7a while being parallel to the data bus line 4. And a bar 7b. The pixel electrode 7 is also formed of a transparent conductor. The counter electrode 5 and the pixel electrode 7 are insulated with the gate insulating film interposed therebetween.

On the other hand, although not shown in the drawing, the upper substrate (not shown) facing the lower substrate 1 is less than the distance between the comb portion 7a of the pixel electrode 7 and the branch 5a of the counter electrode 5. They are opposed to each other over a large distance. In addition, a liquid crystal layer having a plurality of liquid crystal molecules is interposed between the lower substrate 1 and the upper substrate.

The FFS-LCD having such a configuration operates as follows.

When a voltage is applied between the counter electrode 5 and the pixel electrode 7, the distance between the upper and lower substrates is greater than the distance between the counter electrode 5 and the pixel electrode 7, so that a vertical component is included between the two electrodes. Fringe field E is formed. This fringe field extends over the counter electrode 5 and the pixel electrode 7 so that all of the liquid crystal molecules on the electrode are operated. Thereby, a high opening rate and a high transmittance can be realized.

In the conventional FFS-LCD described above, most of the liquid crystal molecules in the pixel space are all operated to obtain a high opening ratio and a high transmittance. However, when an electric field is formed between the counter electrode and the pixel electrode, liquid crystal molecules having refractive index anisotropy operate simultaneously in the same direction, so that the polar angle is near 0 ° and the azimuth is near 0 °, 90 °, 180 °, and 270 °. In spite of the condition, a certain color appears. This phenomenon is called color shift, and the color shift is described in more detail by the following equation (1).

T ≒ T ₀ sin2 (2χ) · sin2 (π · Δnd / λ) .............. (Equation 1)

T: transmittance

T ₀ : Transmittance for reference light

χ: angle formed between the optical axis of the liquid crystal molecules and the polarization axis of the polarizer

Δn: refractive index anisotropy

d: distance or gap between the upper and lower substrates (thickness of the liquid crystal layer)

λ: incident light wavelength

According to Equation 1, in order to obtain the maximum transmittance T, χ should be π / 4 or Δnd / λ should be π / 2. At this time, when Δnd is changed (because the refractive index anisotropy value of the liquid crystal molecules changes depending on the viewing direction), the λ value is changed to satisfy π / 2. Accordingly, the color corresponding to the changed light wavelength [lambda] is displayed on the screen.

Therefore, in the direction α looking toward the shortening of the liquid crystal molecules 9, as Δn is relatively decreased, the wavelength of incident light for reaching the maximum transmittance is relatively shortened. Accordingly, the user sees blue having a wavelength shorter than that of white.

On the other hand, in the direction (beta) facing the long axis of the liquid crystal molecules 9, the wavelength of the incident light becomes relatively long as Δn is relatively increased. Accordingly, the user sees yellow with a wavelength longer than that of white. For this reason, image quality characteristics fall.

Accordingly, an object of the present invention is to solve the above-mentioned conventional problems, and to provide an FFS-LCD capable of improving color shift.

1 is a plan view of a typical fringe field driving mode liquid crystal display.

2 is a fringe field driving mode liquid crystal display according to an exemplary embodiment of the present invention.

3 is a fringe field driving mode liquid crystal display according to another exemplary embodiment of the present invention.

(Explanation of symbols for the main parts of the drawing)

11-Gate Bus Line 13-Data Bus Line

15,150-counter electrode 17-pixel electrode

17a-body portion of the pixel electrode 17b-oblique branch of the pixel electrode

In order to achieve the above object of the present invention, according to an embodiment of the present invention, the upper and lower substrate spaced at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A gate bus line and a data bus line arranged in a matrix on the lower substrate to define a unit pixel; Thin film transistors formed around intersection points of the gate bus lines and the data bus lines, respectively; Transparent counter electrodes each formed in the unit pixel and having a rectangular plate shape; And a transparent pixel electrode overlapping the counter electrode and electrically contacting the thin film transistor and generating a fringe field together with the counter electrode, wherein the pixel electrode includes a frame-shaped body portion disposed at an edge of the counter electrode. And a plurality of diagonal branches disposed at equal intervals so as to partition the body part into a predetermined space and having a predetermined angle with a gate bus line or a data bus line, wherein the diagonal branches of the pixel electrode are formed in other adjacent pixels. It is characterized by symmetrical up, down, left and right with the diagonal branch of the pixel electrode.

In addition, according to another embodiment of the present invention, the upper and lower substrate spaced apart a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A gate bus line and a data bus line arranged in a matrix on the lower substrate to define a unit pixel; Thin film transistors formed around intersection points of the gate bus lines and the data bus lines, respectively; Transparent counter electrodes formed in the unit pixels, respectively; And a transparent pixel electrode overlapping the counter electrode and electrically contacting the thin film transistor and generating a fringe field together with the counter electrode, wherein the counter electrode comprises a frame-shaped body portion and the body portion in a predetermined space. A diagonal branch which is disposed at equal intervals so as to be partitioned and forms a predetermined angle with the gate bus line or the data bus line, wherein the pixel electrode includes a frame-shaped body portion overlapping the frame-shaped body portion of the counter electrode; The body portion is divided into predetermined spaces and includes a plurality of diagonal branches respectively disposed between the diagonal branches of the counter electrode, wherein the diagonal branches of the counter electrode and the pixel electrode are formed of the pixel electrodes formed in other adjacent pixels. It is characterized by the symmetry of the linear branch up, down, left and right.

(Example)

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

2 is a plan view of an FFS-LCD according to an embodiment of the present invention, and FIG. 3 is a plan view of an FFS-LCD according to another embodiment of the present invention.

First, referring to FIG. 2, the lower electrode 10 is spaced apart from the upper substrate (not shown) at a predetermined distance. A liquid crystal layer (not shown) containing several liquid crystal molecules is interposed between the upper and lower substrates. A plurality of gate bus lines 11 are arranged in the x-axis direction on the lower substrate 10, and a plurality of data bus lines 13 are arranged in the y-axis direction substantially perpendicular to the x-axis direction, so that each matrix The unit pixel spaces p1, p2, p3, and p4 of the form are defined. A gate insulating film (not shown) is interposed between the gate bus line 11 and the data bus line 13 to insulate these two lines. In addition, the gate bus line 11 and the data bus line 13 are formed of an opaque metal film having excellent conductivity, for example, one metal film selected from MoW, Al, Ta, and Ti.

A thin film transistor (TFT) serving as a switching role is provided near the intersection point of the gate bus line 11 and the data bus line 13.

Counter electrodes 15 are formed in the unit pixel spaces p1, p2, p3, and p4. At this time, the counter electrode 15 is formed of a transparent conductor, for example, an ITO layer, and is formed in a rectangular plate shape. At this time, the counter electrodes 15 arranged in one row are all in contact with a common electrode line (not shown) made of an opaque metal film. In addition, the counter electrode 15 is spaced apart from the gate bus line 11 and the data bus line 13 by a predetermined distance to maintain insulation.

The pixel electrode 17 is formed to overlap the upper portion of the counter electrode 15. The pixel electrode 17 has a frame-shaped body portion 17a disposed to overlap the edge portion of the counter electrode 15 and the body portion 17 at a predetermined angle with the gate bus line 11 or the data bus line. It includes a plurality of diagonal branches 17b arranged at equal intervals so as to partition the into several spaces. In this case, the diagonal branch 17b of the pixel electrode 17 is symmetrical with the diagonal branch 17b of the unit pixel adjacent to the top, bottom, left and right of the corresponding unit pixel.

At this time, the fringe field may be formed between the diagonal branch 17b of the pixel electrode and the counter electrode 15 exposed by the diagonal branch 17b so that the fringe field may be formed between the pixel electrode 17 and the counter electrode 15. The distance, that is, the thickness of the gate insulating film is smaller than the distance between the upper and lower substrates, and the width of the diagonal branch 17a and the exposed counter electrode 15 is such that all of the liquid crystal molecules present thereon can be operated when the field is applied. .

When a voltage is applied to the counter electrode 15 and the pixel electrode 17 of the liquid crystal display having such a configuration, between the exposed counter electrode 15 of each pixel and the diagonal branch 17b of the pixel electrode 17. Fringe field E is formed. At this time, since the diagonal branches 17b of the pixel electrodes forming the field are arranged symmetrically in the unit pixel spaces p1, p2, p3, and p4, the fringe field E is also vertically adjacent The fringe field E formed in another pixel is symmetrical with respect to the gate bus line or the data bus line, respectively.

Accordingly, the liquid crystal molecules 20 are also arranged parallel to each other in the same pixel space as shown in FIG. 4, but with respect to the data bus line or the gate bus line with respect to the liquid crystal molecules disposed in the pixel spaces adjacent to each other up, down, left and right. They are arranged symmetrically.

Therefore, although one domain is viewed from the side of the unit pixel, from the side of the plurality of unit pixels, the plurality of domains are formed because they are arranged to be symmetrical with adjacent pixels, respectively. Accordingly, both the short axis and the long axis of the liquid crystal molecules are seen in any direction of the screen. Therefore, the refractive index anisotropy of the liquid crystal molecules is compensated, and color shift phenomenon is prevented.

3 is a plan view of an FFS-LCD for explaining another embodiment of the present invention.

The embodiment has the same form as the above-described embodiment, the gate bus line, the data bus line, the thin film transistor, and the pixel electrode, and only the structure of the counter electrode is different. Therefore, in the present embodiment, the description of the same parts will be omitted, and only the structure of the counter electrode will be described.

Similar to the pixel electrode 17, the counter electrode 150 according to the present exemplary embodiment may have a plurality of body portions 150a formed at a predetermined angle with the frame-shaped body portion 150a and the gate bus line 11 or the data bus line. It includes a plurality of diagonal branches 150b that divide into spaces. In this case, the diagonal branches 150b of the counter electrode 150 are disposed at predetermined distances between the diagonal branches 17b of the pixel electrodes 17, and the diagonal branches 150b of the pixel electrodes 17 are disposed. Arranged in parallel. In addition, the body portion 150a of the counter electrode 150 and the body portion 17a of the pixel electrode 17 overlap each other. Thus, even when the counter electrode 150 is formed in the form of a diagonal branch, the same effects as in the above-described embodiment are obtained.

As described above in detail, according to the present invention, in the FFS-LCD, the fringe fields formed in the selected unit pixel space are symmetrical with respect to the fringe fields formed in the left and right pixel spaces of the corresponding pixel with respect to the data bus line. They are symmetrical with respect to the electric field and gate bus lines formed in the upper and lower pixel spaces. Accordingly, an electric field symmetrical for each unit pixel is formed, and multiple domains are formed in the FFS-LCD. Therefore, the refractive index anisotropy of the liquid crystal molecules is compensated, and color shift is prevented, thereby improving image quality characteristics.

In addition, this invention can be implemented in various changes within the range which does not deviate from the summary.

Claims (4)

Upper and lower substrates spaced apart by a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A gate bus line and a data bus line arranged in a matrix on the lower substrate to define a unit pixel; Thin film transistors formed around intersection points of the gate bus lines and the data bus lines, respectively; Transparent counter electrodes each formed in the unit pixel and having a rectangular plate shape; And A transparent pixel electrode overlapping the counter electrode and electrically contacting the thin film transistor, the transparent pixel electrode generating a fringe field together with the counter electrode; The pixel electrodes may be arranged at regular intervals so as to divide the body portion into predetermined spaces and form a plurality of diagonal branches formed at predetermined angles with a gate bus line or a data bus line. Including, And an oblique branch of the pixel electrode is symmetrical with the oblique branch of the pixel electrode formed in another adjacent pixel. The method of claim 1, wherein a distance between the pixel electrode and the counter electrode is smaller than a distance between the upper and lower substrates. The width of the counter electrode exposed by the oblique branch and the oblique branch of the pixel electrode is FFS-LCD, characterized in that the liquid crystal molecules present thereon can be operated when the field is applied. Upper and lower substrates spaced apart by a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A gate bus line and a data bus line arranged in a matrix on the lower substrate to define a unit pixel; Thin film transistors formed around intersection points of the gate bus lines and the data bus lines, respectively; Transparent counter electrodes formed in the unit pixels, respectively; And A transparent pixel electrode overlapping the counter electrode and electrically contacting the thin film transistor, the transparent pixel electrode generating a fringe field together with the counter electrode; The counter electrode may include a frame-shaped body portion and an oblique branch disposed at equal intervals so as to partition the body portion into a predetermined space and having an angle with a gate bus line or a data bus line. The pixel electrode may include a frame-shaped body portion overlapping the frame-shaped body portion of the counter electrode, and a plurality of diagonal branches respectively disposed between the diagonal branches of the counter electrode and partitioning the body portion into a predetermined space. Including, And an oblique branch of the counter electrode and the pixel electrode is symmetrical with the oblique branch of the pixel electrode formed in another adjacent pixel. The method of claim 3, wherein a distance between the diagonal branch of the pixel electrode and the diagonal branch of the counter electrode is smaller than the distance between the upper and lower substrates. The diagonal branch of the pixel electrode and the width of the diagonal branch of the counter electrode are FFS-LCD, characterized in that the liquid crystal molecules present thereon can be operated when the field is applied.