KR100306806B1 - Liquid crystal display - Google Patents

Abstract

The present invention discloses a liquid crystal display device capable of improving transmittance and aperture ratio. The disclosed liquid crystal display includes an upper and lower substrates opposed to each other at a predetermined distance, a liquid crystal interposed between the upper and lower substrates, a pixel electrode and a counter electrode disposed on an inner side of the lower substrate, and the pixel electrode and the counter electrode A pixel electrode and a counter electrode formed of a transparent conductive material and spaced apart from each other by a width smaller than the distance between the upper and lower substrates, and a horizontal alignment layer disposed on the lower substrate surface on which the electrodes are formed, and an electric field to be formed between the electrodes and a predetermined angle. A first polarizing plate having a horizontal alignment film rubbed to form a surface, a vertical alignment film disposed on an inner side surface of the upper substrate, a first axis disposed on an outer surface of the lower substrate, and having a rubbing axis coincident with a rubbing direction of the horizontal alignment layer; A second polarizing plate disposed on an outer side of the substrate and having a polarizing axis in a direction crossing the polarizing axis of the first polarizing plate; It includes a phase compensating film which is interposed between the substrate portion and the second polarizing plate.

Description

Liquid crystal display

The present invention relates to a wide viewing angle liquid crystal display device, and more particularly, to a hybrid alignment (HAN) mode liquid crystal display device having improved transmittance.

In general, the liquid crystal display of in-plane switching (IPS) mode is a liquid crystal display for driving a transverse electric field developed by Hitachi, Japan, to compensate for viewing angle characteristics of a twisted nematic (TN) mode liquid crystal display. (Principle and characteristic of electro-optical behavior with in-plane switching mode, Asia display 95, p577-580)

In the liquid crystal display of the IPS mode, both the pixel electrode and the counter electrode for driving the liquid crystal are formed on the lower substrate, and the horizontal alignment film is formed on the upper and lower substrate surfaces. Accordingly, the molecules in the liquid crystal are arranged such that the surface of the substrate and its long axis are parallel, and when an electric field is formed between the pixel electrode and the counter electrode, the optical axis of the electric field and the liquid crystal molecules are aligned so that the substrate and the long axis are parallel, It penetrates.

However, the IPS mode has a disadvantage in that the response speed is slow because the liquid crystal molecules move in a horizontally aligned state.

In order to improve such a response speed, as another conventional method, a method has been proposed in which electrodes are arranged in the same manner as the IPS mode, and the state of the alignment film is arranged in the same manner as the conventional HAN mode.

That is, as shown in FIG. 1, in the conventional liquid crystal display device, the lower substrate 1 and the upper substrate 5 are opposed to each other at a predetermined interval. On the lower substrate 1, the pixel electrode 2a and the counter electrode 2b for driving the liquid crystal are made of an opaque material and have a predetermined width and are spaced apart at predetermined intervals. A horizontal alignment film 6a is formed on the surface of the lower substrate 1 on which the electrodes 2a and 2b are formed, and a vertical alignment film 6b is formed on the surface of the upper substrate 5. At this time, the horizontal alignment layer 6a is rubbed to form an angle of about 45 degrees with a predetermined direction, that is, an electric field to be formed between the electrodes 2a and 2b. In addition, a nematic liquid crystal 3 is interposed between the lower substrate 1 and the upper substrate 5.

The first polarizing plate 7a is formed on the rear surface of the lower substrate 1, and the second polarizing plate 7b is formed on the rear surface of the upper substrate 5. Here, the polarization axis of the first polarizing plate 7a is attached to coincide with the rubbing direction of the horizontal alignment layer 6a, and the polarization axis of the second polarizing plate 7b is attached so as to cross the first polarizing plate 7a.

In the conventional liquid crystal display having such a configuration, before the electric field is formed between the pixel electrode 2a and the counter electrode 2b (the OFF region), the liquid crystal molecules 3a are arranged in the horizontal alignment layer 6a and the vertical alignment layer 6b. Under the influence of), it lays down on the lower substrate 1 side and stands still toward the upper substrate 5 side.

On the other hand, when an electric field is formed between the pixel electrode 2a and the counter electrode 2b (ON region), the liquid crystal molecules 3a are twisted in parallel with the direction of the electric field to leak light.

However, the IPS mode liquid crystal display adopting the HAN mode arrangement as described above has the following problems.

First, since the pixel electrode 2a and the counter electrode 2b for driving the liquid crystal are formed of an opaque metal film, the aperture ratio and the transmittance are reduced.

At this time, even if the electrodes 2a and 2b are formed of a transparent metal film, the liquid crystal molecules 3a are displaced in a direction parallel to the electric field between the pixel electrode 2a and the counter electrode 2b. The liquid crystal molecules 3a on the top of 2a, 2b maintain the initial arrangement, so that the transmittance is still low.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of improving both transmittance and aperture ratio by operating all of the liquid crystal molecules on an electrode, thereby solving the above-mentioned problems.

1 is a cross-sectional view of an IPS mode liquid crystal display adopting a conventional HAN mode.

2 is a cross-sectional view of a HAN mode liquid crystal display device according to the present invention;

Figure 3 shows a phase compensation film according to the present invention.

4 is a graph comparing transmittance according to voltage in the liquid crystal display of the present invention.

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

10-lower substrate 11a-pixel electrode

11b-counter electrode 13-horizontal alignment layer

14-first polarizer 15-liquid crystal

15a-liquid crystal molecules 20-upper substrate

22-vertical alignment layer 24-second polarizer

26-phase compensation film

In order to achieve the above object of the present invention, the HAN liquid crystal display device of the present invention, the upper and lower substrates opposed to each other at a predetermined distance, the liquid crystal interposed between the upper and lower substrates, and disposed on the inner surface of the lower substrate The pixel electrode and the counter electrode, the pixel electrode and the counter electrode are formed of a transparent conductive material, the pixel electrode and the counter electrode spaced apart by a width narrower than the distance between the upper and lower substrates, disposed on the lower substrate surface formed with the electrode A horizontal alignment layer, the horizontal alignment film rubbed to form a predetermined angle with the electric field to be formed between the electrodes, the vertical alignment film disposed on the inner surface of the upper substrate, and the outer surface of the lower substrate, the rubbing of the horizontal alignment film A first polarizing plate having a rubbing axis coincident with the direction, and disposed on an outer surface of the upper substrate, and crossing the polarizing axis of the first polarizing plate; And a second polarizing plate having a polarization axis in a direction to be inclined, and a phase compensation film interposed between the upper substrate and the second polarizing plate.

According to the present invention, in the HAN mode liquid crystal display, an electrode for driving a liquid crystal is formed of a transparent material, and the gap between the electrodes is narrower than the cell gap of the upper and lower substrates, thereby forming a fringe field. Accordingly, when the electric field is applied, the liquid crystal molecules are also distorted in the upper part of the electrode, thereby greatly improving the transmittance and aperture ratio.

(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 HAN mode liquid crystal display device according to the present invention, FIG. 3 is a view showing a phase compensation film according to the present invention, and FIG. 4 is a transmittance according to voltage in the liquid crystal display device of the present invention. This is a graph comparing.

First, referring to FIG. 2, the lower substrate 10 and the upper substrate 20 are opposed to each other with a predetermined cell gap d. The pixel electrode 11a and the counter electrode 11b are spaced apart from each other by a predetermined distance on the lower substrate 10. In this case, the pixel electrode 11a and the counter electrode 11b of the present invention are formed of a transparent material, for example, an indium tin oxide (ITO) material, and the distance between the pixel electrode 11a and the counter electrode 11b is The distance is smaller than the cell gap d. Preferably, the distance between the pixel electrode 11a and the counter electrode 11b is about 1 to 5 μm from the thickness of the gate insulating film, although not described in detail, and the width of the pixel electrode 11a and the counter electrode 11b is about. It is about 1-7 micrometers.

A horizontal alignment layer 13 is formed on the lower substrate 10 on which the pixel electrode 11a and the counter electrode 11b are formed to implement the HAN mode, and a vertical alignment layer 22 is formed on the opposite surface of the upper substrate 20. Formed. The horizontal alignment layer 13 has a pretilt angle of 10 ° or less, and the vertical alignment layer 22 has a pretilt angle of about 85 ° to 90 °. Here, the horizontal alignment layer 13 is rubbed to form a predetermined angle, preferably about ± 45 °, with the electric field to be formed between the pixel electrode 11a and the counter electrode 11b, and rubbing is applied to the vertical alignment layer 22. Not done. In addition, the liquid crystal 15 having several liquid crystal molecules is interposed in the space between the lower substrate 10 and the upper substrate 20. Here, the liquid crystal is a nematic liquid crystal, and it is excellent in the transmittance to use a material having negative dielectric anisotropy. In addition, the product of the birefringence Δn of the liquid crystal 15 and the thickness (d: same as the cell gap between the upper and lower substrates) of the liquid crystal 15 (hereinafter referred to as a retardation value) may be about 0.2 to 0.6 μm. This is preferred.

Meanwhile, the first polarizer 14 is disposed on the rear surface of the lower substrate 10, and the second polarizer 24 is disposed on the rear surface of the upper substrate 20. Here, the polarization axis of the first polarizing plate 14 is attached to coincide with the rubbing direction of the horizontal alignment layer 13, and the polarization axis of the second polarizing plate 24 is attached to cross the polarization axis of the first polarizing plate 14. In addition, a phase compensation film 26 is disposed between the upper substrate 20 and the second polarizing plate 24 to compensate for the refractive anisotropy of the liquid crystal 15. At this time, the phase compensation film 26 is made of a disk type, that is, the liquid crystal molecules having negative refractive anisotropy as shown in FIG. 3 in order to compensate the refractive anisotropy of the rod-shaped liquid crystal molecules 15a. The liquid crystal molecules 26a in 26 are arranged to be 90 degrees symmetric with the initial arrangement of the liquid crystal molecules 15a. In addition, the retardation value (the product of the birefringence of the liquid crystal constituting the phase compensation film and the thickness of the phase compensation film) of the phase compensation film 26 is preferably equal to the retardation value of the liquid crystal 15.

In the liquid crystal display having such a configuration, before the electric field is formed between the pixel electrode 11a and the counter electrode 11b (the OFF region), the liquid crystal molecules 15a are formed of the horizontal alignment layer 13 and the vertical alignment layer 22. Under the influence, they are laid on the lower substrate 10 side and stand still toward the upper substrate 5 side. At this time, since the long axes of the liquid crystal molecules 15a lying on the lower substrate 10 side follow the rubbing direction, the light passing through the first polarizing plate 14 passes through the liquid crystal 15. However, the second polarizing plate 24 intersected with the first polarizing plate 14 does not pass, and the screen is dark. At this time, since the phase compensation film for compensating the refractive index anisotropy of the liquid crystal molecules 15a is disposed outside the upper substrate 20, complete dark can be realized.

On the other hand, if a predetermined voltage is applied between the pixel electrode 11a and the counter electrode 11b, the interval l between the electrodes 11a and 11b is smaller than the cell gap d, so that only the edges of the electrodes 11a and 11b are used. In addition, an electric field is also formed on the electrode (ON region). Accordingly, not only the liquid crystal molecules present between the electrodes 11a and 11b but also the liquid crystal molecules above the electrodes 11a and 11b are twisted in the direction of the electric field. Accordingly, the transmittance can be greatly increased. In addition, since the rubbing direction of the initial horizontal alignment layer 13 was processed so that the angle between the electric field and the electric field was 45 degrees, the liquid crystal molecules 15a were twisted by 45 degrees when the electric field was applied, thereby leaking light while satisfying the maximum transmittance. Done. In addition, the pixel electrode 11a and the counter electrode 11b are formed of a transparent material, thereby improving the aperture ratio.

Here, the use of a negative dielectric anisotropy as the liquid crystal is because, as shown in the graph of Figure 4, the transmittance according to the voltage is superior to the positive material of the negative dielectric anisotropy.

As described in detail above, according to the present invention, in the HAN mode liquid crystal display device, an electrode for driving the liquid crystal is formed of a transparent material, and the gap between the electrodes is narrower than the cell gap of the upper and lower substrates so that a fringe field is formed. do. Accordingly, when the electric field is applied, the liquid crystal molecules are also distorted in the upper part of the electrode, thereby greatly improving the transmittance and aperture ratio.

In addition, since the HAN mode itself has a fast response speed, it is possible to solve the problem of response characteristics of the IPS mode.

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; A liquid crystal interposed between the upper and lower substrates; A pixel electrode and a counter electrode disposed on an inner side of the lower substrate, wherein the pixel electrode and the counter electrode are formed of a transparent conductive material and are spaced apart from each other by a width narrower than the distance between the upper and lower substrates; A horizontal alignment layer disposed on a lower substrate surface on which the electrode is formed and rubbed to form a predetermined angle with an electric field to be formed between the electrodes; A vertical alignment layer disposed on an inner side surface of the upper substrate; A first polarizer disposed on an outer surface of the lower substrate and having a rubbing axis coincident with a rubbing direction of the horizontal alignment layer; A second polarizer disposed on an outer surface of the upper substrate and having a polarization axis in a direction crossing the polarization axis of the first polarizer; And a phase compensation film interposed between the upper substrate and the second polarizing plate. The liquid crystal display of claim 1, wherein the liquid crystal is a material having a negative dielectric anisotropy. The liquid crystal display device of claim 1, wherein an angle formed between the horizontal alignment layer, the rubbing direction, and the electric field formed between the pixel electrode and the counter electrode is about ± 45 °. The liquid crystal display device according to claim 1, wherein the phase compensation film is composed of disk type liquid crystal molecules having negative refractive anisotropy. The liquid crystal display device according to claim 1, wherein the retardation value of the phase compensation film and the retardation value of the liquid crystal are substantially the same. The liquid crystal display device according to claim 1, wherein the retardation value is about 0.2 to 0.6 mu m.