KR20010003751A - LCD having high aperture ratio and high transmittance ratio - Google Patents

Abstract

PURPOSE: An LCD(liquid crystal display) of high aperture rate and transmittance is provided to improve color shift while not reducing aperture rate. CONSTITUTION: By applying voltage to counter/pixel electrodes(15,17), a fringe field is formed between the electrodes. Herein, teeth of comb unit(17a) of pixel electrode is symmetrically arranged by pixel unit(p1,p2,p3,p4). Thus, fringe fields are symmetrical with other fringe fields in adjacent pixels by gate/data bus lines. Liquid crystal molecules are symmetrical with other liquid crystal molecules in adjacent pixels by gate/data bus lines. Thus, plural domains are formed from a plural unit pixel point of view. Therefore, short/long axes of the liquid crystal molecule are seen regardless of viewpoint.

Description

High aperture ratio and high transmittance liquid crystal display {LCD having high aperture ratio and high transmittance ratio}

The present invention relates to a high aperture ratio and a high transmittance liquid crystal display device, and more particularly, to a high aperture ratio and a high transmittance liquid crystal display device capable of improving image quality characteristics.

In general, a high aperture ratio and a high transmittance liquid crystal display have been proposed to improve the low aperture ratio and transmittance of a general IPS mode liquid crystal display, and have been filed in Korean Patent Application No. 98-9243.

Such a high aperture ratio and high transmittance liquid crystal display device forms a counter electrode and a pixel electrode with a transparent conductor, and forms a gap between the counter electrode and the pixel electrode to be smaller than a gap between the upper and lower substrates, thereby forming a fringe field on the counter electrode and the pixel electrode. (fringe filed) is formed.

Such a high aperture and high transmittance liquid crystal display is shown in FIG. 1.

Referring to the drawings, the gate bus line 2 and the data bus line 4 are arranged on the lower substrate 1 to define unit pixels, and the intersection point of the gate bus line 2 and the data bus line 4 is defined. In the vicinity, a thin film transistor TFT is disposed.

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 inserted into the branch 5a, respectively, in parallel with the data bus line 4, and one end of the comb portion 7a. 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 9a 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 high aperture ratio and high transmittance liquid crystal display device 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 above-described high aperture ratio and high transmittance liquid crystal display, most of the liquid crystal molecules in the pixel space are all operated to achieve high aperture ratio and 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, the image quality characteristic of IPS-LCD falls.

In order to prevent such color shift, another conventional method is to bend the branch 5a of the counter electrode and the comb portion 7a of the pixel electrode 7 into a " " shape as shown in FIG. A method has been proposed. Then, electric fields in two directions symmetrically are formed in one unit pixel, thereby compensating for refractive index anisotropy of the liquid crystal molecules.

However, this technique is such that the branch 5a and the comb portion 7a are bent in a " " shape, whereby an area X where no electric field is formed, that is, the distance between the branch 5a of the counter electrode and the data bus line 4 is formed. Is increased. Accordingly, in this portion, the liquid crystal molecules are not operated so that the aperture ratio is reduced. As a result, the inherent purpose of achieving high opening rate and high transmittance cannot be achieved.

Accordingly, it is an object of the present invention to provide a high aperture ratio and high transmittance liquid crystal display device capable of improving color shift in a range that does not reduce the aperture ratio.

1 is a plan view of a typical high opening ratio and high transmittance liquid crystal display;

2 is a plan view of a high aperture ratio and high transmittance liquid crystal display for improving a conventional color shift.

3 is a plan view of a high aperture ratio and high transmittance liquid crystal display according to the present invention;

4 is a view schematically showing an electric field formed in the liquid crystal display device of the present invention and the arrangement of the liquid crystal molecules according thereto.

Explanation of symbols on main parts of drawing

11-Gate Bus Line 13-Data Bus Line

15-counter electrode 15a-common electrode wire

17a-comb 17b-bar

In order to achieve the above object of the present invention, the present invention, the upper and lower substrate facing each other at a predetermined distance; A liquid crystal layer comprising several liquid crystal molecules interposed between the upper and lower substrates; 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; A transparent counter electrode having a rectangular plate shape formed in each of the unit pixels; And a transparent pixel electrode formed to overlap the counter electrode, the plurality of comb teeth being parallel and arranged at equal intervals, and electrically connected to the thin film transistor while connecting one end of the comb teeth. The comb portion of one unit pixel to be selected forms a predetermined angle with respect to the data bus line direction, and the comb portion of the unit pixel adjacent to the selected unit pixel in a left and right direction is referenced to the comb portion of the selected pixel and the data bus line. The counter electrode of the unit pixel which is symmetrical with respect to the selected unit pixel in the up-down direction of the selected unit pixel is symmetrical with respect to the comb portion of the selected pixel and the gate bus line, and is exposed by the comb portion and the comb portion The interval of is smaller than the distance between the upper and lower substrates, Width of the counter electrode that is exposed by the comb tooth portion and the comb-section has, and that the two electric field by the electrode characterized in that the width to the extent that the electrode may have all of the parts.

At this time, the angle formed by the comb teeth and the data bus line direction is about 5 to 15 degrees.

According to the present invention, in the high aperture ratio and high transmittance liquid crystal display device, the electric fields formed in the selected unit pixel spaces are symmetrical with respect to the electric fields formed in the left and right pixel spaces of the pixel and the data bus lines, They are symmetrical with respect to the electric field and gate bus lines formed in the pixel space. Accordingly, symmetrical electric fields are formed for each unit pixel, and multiple domains are formed in the liquid crystal display. Therefore, the refractive index anisotropy of the liquid crystal molecules is compensated, and color shift is prevented, thereby improving image quality characteristics.

(Example)

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

3 is a plan view of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 is a diagram schematically showing an electric field formed in the liquid crystal display of the present invention and an arrangement of liquid crystal molecules according thereto.

First, referring to FIG. 3, a plurality of gate bus lines 11 are arranged in the x-axis direction on the lower substrate 10, and the plurality of data bus lines 13 are y-axis substantially perpendicular to the x-axis direction. Arranged in the direction, each unit pixel space p1, p2, p3, p4 is 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 among 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. In this case, the counter electrode 15 is formed of a transparent conductor and is formed in a square plate shape. At this time, the counter electrode 15 is in contact with the common electrode line 15a made of an opaque metal film, and is electrically connected to another adjacent counter electrode 15. The counter electrode 15 is spaced apart from the data bus line 13 by a predetermined distance.

The pixel electrode 17 is formed to overlap the upper portion of the counter electrode 15. The pixel electrode 17 is connected to a plurality of comb portions 17a arranged parallel to each other at equal intervals and one bar 17b electrically connected to the thin film transistor TFT while connecting one end of the comb portions 17a. Include. At this time, the comb portion 17a of the pixel electrode 17 forms an angle with the direction of the data bus line 15, that is, the y-axis direction, preferably about 5 to 15 degrees. In addition, the comb portion 17a of the selected unit pixel (for example, p3) and the comb portion 17a of the unit pixel p4 adjacent to the pixel (left and right in the x-axis direction) are connected to the data bus line ( 13) symmetrical with respect to On the other hand, the comb portion 17a of the selected unit pixel p3 and the comb portion 17a of the pixel p1 which are vertically adjacent to the pixel (adjacent in the y-axis direction) are connected to the gate bus line 11. It is symmetrical. In addition, the comb portion 17a of the pixel electrode is formed to overlap with the counter electrode 15 and is formed so as not to protrude outside the counter electrode 15. In addition, the bar 17b extends parallel to the gate bus line.

At this time, the gap between the comb portion 17a and the counter electrode 15 is vertically spaced so that a fringe field can be formed between the comb portion 17a of the pixel electrode and the counter electrode 15 exposed by the comb portion 17a. It is formed smaller than the distance between the substrates, and the width of the comb portion 17a and the exposed counter electrode 15 is formed so that an electric field can extend over the entire electrode.

In addition, although not shown in FIG. 3, an upper substrate is opposed to the lower substrate at a predetermined distance, and a liquid crystal layer including a plurality of liquid crystal molecules is interposed between the lower substrate and the upper substrate.

When voltage is applied to the counter electrode 15 and the pixel electrode 17 of the liquid crystal display device having such a configuration, a fringe field E is formed between the counter electrode 15 and the pixel electrode 17 of each pixel. At this time, since the comb portion 17a of the pixel electrode is symmetrically arranged up, down, left, and right for each of the unit pixel spaces (p1, p2, p3, p4), the fringe field E is also a fringe formed in another pixel adjacent up, down, left, and right. The field E is symmetrical with respect to the gate bus line and 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 vertically, vertically, or horizontally. 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.

As described above in detail, according to the present invention, in the high opening ratio and high transmittance liquid crystal display device, the electric field formed in the selected unit pixel space is based on the electric field and data bus lines formed in the left and right pixel spaces of the pixel. They are symmetrical with each other, and symmetrical with respect to the electric field and gate bus lines formed in the upper and lower pixel spaces. Accordingly, symmetrical electric fields are formed for each unit pixel, and multiple domains are formed in the liquid crystal display. Therefore, the refractive index anisotropy of the liquid crystal molecules is compensated, and color shift is prevented, thereby improving image quality characteristics.

In addition, since the distance between the counter electrode and the data bus line is kept constant, the opening area is not reduced, so that the opening ratio can be prevented from decreasing.

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

Claims (3)

Upper and lower substrates opposed to each other by a predetermined distance; A liquid crystal layer comprising several liquid crystal molecules interposed between the upper and lower substrates; 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 formed to overlap with the counter electrode, the plurality of parallel pixel electrodes being parallel and arranged at equal intervals and a bar electrically connected to the thin film transistor while connecting one end of the comb teeth; The comb portion of one unit pixel selected from the unit pixels forms a predetermined angle with respect to the data bus line direction. The comb portion of the unit pixel adjacent to the selected unit pixel in a horizontal direction is symmetrical with respect to the comb portion of the selected pixel and the data bus line, The comb portions of the unit pixels adjacent in the vertical direction of the selected unit pixel are symmetrical with respect to the comb portion of the selected pixel and the gate bus line. The distance between the counter electrode exposed by the comb and the comb is less than the distance between the upper and lower substrates, The width of the counter electrode exposed by the comb portion and the comb portion is a width such that an electric field can extend to the entire portion of the electrode by the two electrodes, the high aperture ratio and high transmittance liquid crystal display. The liquid crystal display of claim 1, wherein an angle formed between the comb portion and the data bus line direction is about 5 to 15 degrees. The liquid crystal display of claim 1, wherein the bar extends in parallel with the gate bus line.