KR20000027764A - Lcd with high aperture rate and high transmissivity - Google Patents

Abstract

PURPOSE: An LCD with high aperture rate and high transmissitive is provided to remove a color shift by rubbing an orientation film and warping the orientation film according to a height of a liquid crystal layer when forming an electric field. CONSTITUTION: A upper substrate(20) and a lower substrate(30) are opposed and replaced at a certain distance. A liquid crystal layer(35) having several liquid crystal molecules(35a) is inserted into between the upper substrate(20) and the lower substrate(30). A counter electrode(23) is separated and arranged on the lower substrate(20). A gate insulating film(25) is formed on a upper portion of the lower substrate(20). A pixel electrode(27) is formed to a portion between the counter electrode(23). Orientation films(29,32) are arranged to a boundary portion of the lower substrate(20) and the liquid crystal layer(35) and between the upper substrate(30) and the liquid crystal layer(35). First and second polarizers(40a,40b) are installed to a peripheral surface of the lower substrate and a peripheral surface of the upper substrate(30).

Description

High Opening and High Transmittance Liquid Crystal Display

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly, to a high opening ratio and a high transmittance liquid crystal display (Fringe Field Switching mode) capable of preventing color shift.

In general, a high aperture ratio and a high transmittance liquid crystal display have been proposed to improve a low aperture ratio and a 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. As shown in the figure, the lower substrate 1 and the upper substrate 10 are opposed to each other at a predetermined distance. Here, the distance between the lower substrate 1 and the upper substrate 10 is referred to as a cell gap d hereinafter. The liquid crystal layer 15 is interposed between the lower substrate 1 and the upper substrate 10. On the lower substrate 1, the counter electrodes 3 are spaced apart at regular intervals with a predetermined width. Here, the counter electrode 3 is formed of a transparent conductor, for example, indium tin oxide (ITO). The gate insulating film 5 is formed on the lower substrate 1 on which the counter electrode 3 is formed, and the pixel electrode 7 is formed between the counter electrodes 3 on the gate insulating film 5. In this case, the pixel electrode 7 is also formed of a transparent conductor, and the distance l between the pixel electrode 5 and the counter electrode 3 is smaller than the cell gap d.

Alignment films 8 and 11 are formed on the uppermost opposing surface of the lower substrate 1 and on the opposing surface of the upper substrate 10 to uniformly arrange liquid crystal molecules in the liquid crystal layer 15 before an electric field is formed. have. At this time, the alignment layers 8 and 11 have a low pretilt angle (about 2 ° or less) and are rubbed in an anti-parallel state to form a predetermined angle with the direction in which the electric field is formed.

The high aperture ratio and high transmittance liquid crystal display having such a configuration is such that, before the electric field is formed between the counter electrode 3 and the pixel electrode 7, the substrate is almost horizontal to the substrate under the influence of the alignment films 8 and 11. Are arranged.

On the other hand, when an electric field is formed between the counter electrode 3 and the pixel electrode 7, a fringe field is formed in which the shape of the electric field includes a vertical component, and the liquid crystal molecules have their optical axis perpendicular or horizontal to the electric field direction. It turns out and leaks light.

However, the high-aperture and high-permeability liquid crystal display device as described above is twisted so that the liquid crystal molecules are parallel to the electric field direction and the long axis (or short axis) of the liquid crystal molecules at the time of applying the electric field, so that a predetermined color is determined according to the direction of the screen. Is expressed.

That is, specifically, since the liquid crystal molecules have a rod shape in shape, the refractive indexes in the major axis direction and the refractive indexes in the minor axis direction are different from each other. Thus, as described above, when the liquid crystal molecules are aligned in the electric field direction, the white state, when the electric field is applied, has a predetermined color according to the viewing angle direction when viewed from the tilt angle of the screen.

This will be described in more detail with reference to Equation 1.

T ≒ T ₀ sin ² (2χ) · sin ² (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, when Δnd is changed, the light wavelength λ of the maximum light transmittance is changed, and as the Δnd is changed, color shift occurs in the white state. That is, since Δn is different in the direction looking at the long axis of the liquid crystal molecules and the direction looking at the short axis of the liquid crystal molecules, the light wavelength λ is changed to obtain the maximum transmittance, and the color corresponding to the changed wavelength is expressed. .

As described above, when a white screen is to be displayed, color is expressed at a predetermined azimuth angle, which is called color shift. This color shift phenomenon decreases the image quality of the liquid crystal display and decreases the uniformity of transmitted light according to the azimuth angle.

Accordingly, an object of the present invention is to solve the above-mentioned conventional problems, and to improve image quality characteristics of a high aperture ratio and a high transmittance liquid crystal display.

1 is a cross-sectional view of a conventional high opening ratio and high transmittance liquid crystal display device.

2 is a cross-sectional view of a high aperture ratio and high transmittance liquid crystal display device according to the present invention;

3 is a view showing a rubbing axis of a high opening ratio and a high transmittance liquid crystal display according to the present invention;

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

20: lower substrate 23: counter electrode

25 gate insulating film 27 pixel electrode

29, 32: alignment layer 30: upper substrate

35 liquid crystal layer 40a first polarizing plate

40b: second polarizing plate

In order to achieve the above object of the present invention, according to an embodiment of the present invention, the present invention is formed on the inner surface of the upper and lower substrates opposed to, and opposed to a predetermined distance with the liquid crystal interposed therebetween, A transparent pixel electrode which forms a fringe field for driving molecules in the liquid crystal together with a counter electrode spaced apart at a distance smaller than a distance between the counter electrode and the upper and lower substrates, and the counter electrode and the pixel electrode are formed. In a high aperture and high transmittance liquid crystal display device comprising an alignment film formed between a lower substrate and a liquid crystal layer and between the upper substrate and a liquid crystal layer, the rubbing axis of the alignment layer of the lower substrate and the rubbing axis of the alignment layer of the upper substrate And rubbed to cross each other.

Here, the first polarizing plate is further attached to the rear surface of the lower substrate, and the second polarizing plate is further attached to the rear surface of the upper substrate, and the polarization axis of the first polarizing plate and the polarization axis of the second polarizing plate are disposed in parallel to each other. do.

According to the present invention, in the high opening ratio and the high transmittance liquid crystal display device, the alignment layer is rubbed so as to cross up and down, and when the electric field is formed, the angle at which the liquid crystal molecules are distorted according to the height of the liquid crystal layer is different. Accordingly, the refractive index anisotropy of the liquid crystal molecules can be compensated for, and color shift can be eliminated.

(Example)

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

2 is a cross-sectional view of a high aperture ratio and high transmittance liquid crystal display according to the present invention, and FIG. 3 is a view illustrating a rubbing axis of the high aperture ratio and high transmittance liquid crystal display according to the present invention.

First, as shown in FIG. 2, in the high opening ratio and high transmittance liquid crystal display according to the present invention, the lower substrate 20 and the upper substrate 30 are opposed to each other at a predetermined distance and are disposed on the lower substrate 20. ) And the upper substrate 30 are interposed between the liquid crystal layer 35 including several liquid crystal molecules 35a. Here, the distance (cell gap) between the upper and lower substrates 30 and 20, that is, the thickness of the liquid crystal layer 35 is referred to as D. In addition, the liquid crystal layer 35 may selectively use positive or negative dielectric anisotropy. In the present embodiment, for example, a liquid crystal having a negative dielectric anisotropy is used. In this case, the product of the refractive index anisotropy and the cell gap (Δnd) of the liquid crystal molecules is about 0.2 to 1.2 μm, which is appropriate for realizing proper image quality of the high aperture ratio and high transmittance liquid crystal display of the present invention.

On the lower substrate 20, a counter conductor 23 made of a transparent conductor, for example, ITO, is formed in a strip form, spaced at regular intervals and having a predetermined width. The gate insulating layer 25 is formed on the lower substrate 20 on which the counter electrode 23 is formed. In the portion between the counter electrodes 23 on the gate insulating film 25, a pixel electrode 27 having a strip shape and made of a transparent conductor is formed. In this case, the distance L between the pixel electrode 27 and the counter electrode 23 is smaller than the cell gap D so as to form a fringe field, and the widths of the counter electrode 23 and the pixel electrode 27 are pixels. An electric field formed between the electrode 27 and the counter electrode 23 is formed to have a width enough to extend over the upper electrodes 23 and 27.

Alignment layers 29 and 32 for determining an initial arrangement of liquid crystal molecules are disposed between the boundary portion between the lower substrate 20 and the liquid crystal layer 35 and between the upper substrate 30 and the liquid crystal layer 35. The alignment film has a pretilt angle of about 1 to 15 degrees.

In addition, in order to prevent color shift occurring in a high aperture ratio and a high transmittance liquid crystal display, which are conventional problems, in the present invention, as shown in FIG. 3, the rubbing axes 29a and 32a of the vertical alignment layers 29 and 32 are mutually different. Place them to intersect. In addition, the rubbing axis 29a of the lower alignment layer is then formed between the counter electrode 23 and the pixel electrode 32 with an electric field formed at a predetermined angle θ, preferably 70 to 110 ° when using a negative liquid crystal. To achieve an angle of degree, when using a positive liquid crystal is rubbed to achieve an angle of -20 to 20 degrees.

First and second polarizing plates 40a and 40b are disposed on the outer circumferential surface of the lower substrate 20 and the outer circumferential surface of the upper substrate 30, respectively, to polarize light incident from the bottom surface of the lower substrate 20 in a predetermined direction. Here, polarization axes (not shown) of the first and second polarizing plates 40a and 40b are attached to the substrates 20 and 30 so as to be parallel to each other, and the polarization axes of the first polarizing plate 40a and the alignment of the lower alignment layer 29 are The axes 29a are attached coincidentally or vertically.

In the high aperture and high transmittance liquid crystal display having such a configuration, before the electric field is formed between the counter electrode 23 and the pixel electrode 27, the liquid crystal molecules are twisted 90 degrees under the influence of the alignment layers 29 and 32. Arranged in the form At this time, the polarization axes of the first and second polarizing plates 40a and 40b are arranged in parallel to each other, so that light passing through the liquid crystal layer 35 does not pass through the polarization axes of the second polarizing plate 40b, so that the screen is dark. Becomes

On the other hand, when a potential difference is generated between the counter electrode 23 and the pixel electrode 27, a fringe field is formed between the counter electrode 23 and the pixel electrode 27. Then, the liquid crystal molecules that have been twisted are arranged to coincide with the fringe field and their short axis. In this case, the liquid crystal molecules are not uniformly twisted in the same direction as in the related art, but are twisted at different angles according to the height of the liquid crystal layer. Accordingly, the refractive index anisotropy of the liquid crystal molecules is compensated, and the color shift phenomenon is eliminated.

As described in detail above, according to the present invention, in the high opening ratio and the high transmittance liquid crystal display device, the alignment layer is rubbed so as to cross up and down, so as to be distorted at different angles according to the height of the liquid crystal layer when forming an electric field. Accordingly, the refractive index anisotropy of the liquid crystal molecules can be compensated for, and color shift can be eliminated.

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

Claims (6)

Upper and lower substrates opposed to each other by a predetermined distance with the liquid crystal interposed therebetween; A transparent counter electrode formed on an inner side surface of the lower substrate; A transparent pixel electrode spaced apart from each other by a distance smaller than the distance between the counter electrode and the upper and lower substrates to form a fringe field for driving molecules in the liquid crystal together with the counter electrode; A high aperture and high transmittance liquid crystal display device comprising an alignment layer formed between a lower substrate and a liquid crystal layer on which the counter electrode and a pixel electrode are formed, and between the upper substrate and the liquid crystal layer, respectively. And a rubbing axis of the alignment layer of the lower substrate and a rubbing axis of the alignment layer of the upper substrate so as to cross each other. The polarizer of claim 1, wherein a first polarizer is further attached to a rear surface of the lower substrate, and a second polarizer is further attached to a rear surface of the upper substrate, and a polarization axis of the first polarizer and a polarizer of the second polarizer are A high opening ratio and a high transmittance liquid crystal display, characterized in that arranged in parallel to each other. The rubbing axis of the lower substrate-side alignment layer has an angle of about 70 to 110 ° with an electric field formed between the counter electrode and the pixel electrode when a liquid crystal having a negative dielectric anisotropy is used. When the material having a positive dielectric anisotropy is used to achieve an angle of about -20 to 20 °, high opening ratio and high transmittance liquid crystal display device. The liquid crystal display of claim 3, wherein the polarization axis of the first polarizing plate is coincident with or perpendicular to the rubbing axis of the lower substrate side alignment layer. 2. The liquid crystal display of claim 1, wherein the pretilt angle is 1 to 15 degrees. The liquid crystal display of claim 1, wherein a product (Δnd) of the refractive index anisotropy of the liquid crystal molecules in the liquid crystal and the cell gap is 0.2 to 1.2 µm.