Active-matrix display screen

Details Active-matrix display screen Active-matrix display screen

1999-03-31

2003-08-26

Kim, Robert H. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S147000

Reexamination Certificate

active

06611311

ABSTRACT:

FIELD OF INVENTION
The present invention relates to active-matrix display screens and more particularly to a pixel structure for these screens which allows a high open aperture ratio to be obtained.
BACKGROUND
In a known manner, an active-matrix display screen consists of a number of liquid-crystal cells or pixels arranged in a matrix array. The cells are formed from two substrates, preferably made of glass, which are bonded together via a peripheral seal which provides a thin cavity in which the liquid crystal lies. The first substrate is coated with a back electrode while the second substrate contains the pixel electrodes and, in the case of active-matrix screens, the solid-state drive devices placed between the electrodes to which they are connected as well as an array of selection lines and of data lines placed in two different directions.
The pixel electrodes of liquid-crystal screens are made of a transparent conductive material, such as indium-tin oxide (ITO). However, the selection lines, the data lines and the solid-state drive devices which are used for connecting the data lines to the pixel electrodes are made of an opaque conductive material. Moreover, in order to improve the contrast of the screen, an opaque mask or “black matrix” is usually deposited on the non-driven parts of the pixel. However, when the size of the pixels is reduced in order to limit the manufacturing costs, the opaque elements of the screen keep the same size approximately. This therefore affects the open aperture ratio or OAR which is defined as the transparent area of the panel divided by the total area. Thus, in high-density display screens such as the screens used in projection, the opaque elements of the screen may occupy more than 70% of the total area, leaving only a transparent area of approximately 30%. This results in a very significant loss of brightness and a reduction in picture quality. Moreover, when the size of the pixel electrodes is small, edge effects caused by the non-planar surfaces and perturbations due to the electric field are observed. These edge effects cause the contrast to suffer and result in a non-uniform display.
In order to remedy this drawback, the article IEDM 93, page 401 et seq. proposes a novel pixel structure comprising a transparent electrode between the data line and the pixel electrode, which screens the capacitive coupling between the data line and the pixel electrode and reduces the effects caused by the transverse electric field.
SUMMARY OF THE INVENTION
The subject of the present invention is a novel pixel structure which makes it possible to obtain a very high open aperture ratio with small pixel spacings. This novel structure is particularly advantageous in the manufacture of small active-matrix liquid-crystal display screens requiring high resolution combined with high transmission. The structure includes a transparent earth plane that contains a cut-away portion that is positioned between two adjacent pixel electrodes of the sane polarity and an aperture for connecting each pixel electrode to the corresponding switching device.


REFERENCES:
patent: 5654731 (1997-08-01), Stewart et al.
patent: 5953092 (1999-09-01), Sung et al.
patent: 6115090 (2000-09-01), Yamazaki

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