Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1996-05-31
2001-07-31
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S038000
Reexamination Certificate
active
06268894
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active matrix type liquid crystal display apparatus with a high aperture ratio of a pixel portion.
2. Description of the Related Art
Liquid crystal display apparatuses have been widely used as display devices for TV sets and graphics display devices due to their advantageous features of thin structure and low power consumption. Among liquid crystal display, an active matrix type liquid crystal display apparatus using thin film transistors (referred to as TFTS) as switching devices has high speed response characteristic and high precision characteristics, making it an attractive choice for high picture quality, large size, and color pictures.
Each display device portion of such an active matrix type liquid crystal display apparatus is generally composed of a switching active device (such as a TFT), an active device array substrate, an opposite substrate, a liquid crystal material, and polarizing plates. The active device array substrate has a pixel electrode connected to the switching active device. The opposite substrate has an opposite electrode disposed opposite to the active device array substrate. The liquid crystal material is disposed between the active device array substrate and the opposite substrate. The polarizing plates are disposed outside of the two substrates. In the active matrix type liquid crystal display apparatus, each liquid crystal pixel cell corresponding to each pixel is composed of the pixel electrode, the opposite electrode, and the liquid crystal layer.
By varying a voltage supplied to each pixel electrode, the optical state of liquid crystal molecules in the liquid crystal pixel cell is changed and thereby a picture is displayed on the screen. An electric field corresponding to a picture signal voltage is not supplied to a liquid crystal layer disposed outside the pixel electrodes (namely, the non-pixel region). Thus, the non-pixel region is optically shielded. By varying an electric field of a pixel portion in which a pixel electrode is formed, the optical state of the liquid crystal layer of the pixel portion is changed and thereby a picture is displayed.
To reduce the entire power consumption of the liquid crystal display apparatus, the non-pixel region that is optically shielded should be minimized and thereby the aperture ratio of the pixel portion should be maximized to improve the optical use efficiency of the display apparatus.
As a related art reference, a technology for improving the aperture ratio of a pixel portion has been disclosed as Japanese Patent Laid-Open Publication No. 1-73324. In this related art reference, one auxiliary capacitor line is disposed between two adjacent pixel electrodes. The auxiliary capacitor line is shared by the two adjacent pixel electrodes.
However, the liquid crystal pixel cell corresponding to each pixel tends to be affected by the electric field that takes place between signal lines and scanning lines disposed on pixel electrodes and the vicinity thereof. As a result, the liquid crystal molecules in the vicinity of a peripheral portion of the pixel electrode are reversed. (This situation is referred to as edge reverse phenomenon.) In other words, the liquid crystal molecules in the vicinity of the peripheral portion of the pixel electrode are affected by the electric field that takes place between signal lines and scanning lines as well as by the electric field that precisely corresponds to a picture signal voltage of a picture signal supplied from the pixel electrode. As a result, the optical state of each pixel portion does not precisely correspond to the picture signal. Consequently, light leaks out at the peripheral portion of each pixel portion, thereby decreasing the contrast of the picture. Thus, the display quality of the screen is remarkably deteriorated.
SUMMARY OF THE INVENTION
The present invention is made from the above-described point of view.
A first object of the present invention is to provide a liquid crystal display apparatus that has a high aperture ratio of the pixel portion, suppresses the edge reverse phenomenon, and thereby decreases power consumption and improves of the display quality of the screen.
A second object of the present invention is to provide a liquid crystal display apparatus that prevents the aperture ratio of the pixel portion from decreasing against an alignment process in an array forming step and a cell forming step.
A third object of the present invention is to provide a liquid crystal display apparatus that prevents a penetration voltage corresponding to a voltage supplied to each scanning line from taking place, thereby improving display quality and reliability.
A fourth object of the present invention is to provide a liquid crystal display apparatus that does not need to form a light shielding layer, thereby remarkably simplifying a fabrication process thereof.
A fifth object of the present invention is to provide a liquid crystal display apparatus that prevents a cross-talk from taking place, thereby remarkably improving the display quality thereof.
To accomplish the above-described objects, a first aspect of the present invention is a liquid crystal display apparatus having a plurality of pixel cells, each of which comprise a scanning line and a signal line disposed on an insulation substrate such that the scanning line intersects with the signal line, a switching device disposed at the intersection of the scanning line and the signal line, a display pixel electrode electrically connected to the switching device, an opposite electrode disposed opposite to the display pixel electrode through a liquid crystal layer, and an auxiliary capacitor line disposed in a space between two adjacent display pixel electrodes and capacitively coupled with the display pixel electrode to form an auxiliary capacitor, wherein the scanning line overlaps with the display pixel electrode.
A second aspect of the present invention is a liquid crystal display apparatus having a plurality of pixel cells, each of which comprises a scanning line and a signal line disposed on an insulation substrate such that the scanning line intersects with the signal line, a switching device disposed at the intersection of the scanning line and the signal line, a display pixel electrode electrically connected to the switching device, an opposite electrode disposed opposite to the display pixel electrode through a liquid crystal layer, and an auxiliary capacitor line disposed in a space between two adjacent display pixel electrodes and capacitively coupled with the display pixel electrode to form an auxiliary capacitor, wherein the display pixel electrode capacitively couples with the auxiliary capacitor electrode disposed corresponding to the opposite side of the display pixel electrode and electrically shielded therefrom.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of best mode embodiments thereof, as illustrated in the accompanying drawings.
REFERENCES:
patent: 4582395 (1986-04-01), Morozumi
patent: 5159476 (1992-10-01), Hayashi
patent: 5305128 (1994-04-01), Stupp et al.
patent: 5394258 (1995-02-01), Morin et al.
patent: 5453857 (1995-09-01), Takahara
patent: 5457553 (1995-10-01), Mori
patent: 5517342 (1996-05-01), Kim et al.
patent: 64-73324 (1989-03-01), None
Aoki Yoshiro
Sato Hajime
Kabushiki Kaisha Toshiba
Pillsbury Madison & Sutro LLP
Sikes William L.
Ton Toan
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