Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-12-15
2001-11-06
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06313898
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates a liquid crystal displaying apparatus, and more particularly, to an active matrix type liquid crystal displaying apparatus.
An array substrate to be used in the liquid crystal displaying apparatus of the conventional active matrix type liquid crystal apparatus is arranged in a plurality of scanning wirings and a plurality of signal wirings respectively in a row direction and a column direction on an insulating substrate. One pixel composed of a thin film transistor (hereinafter referred to as TFT) as active element to be controlled by the scanning wiring and the signal wiring and a pixel electrode to be connected with TFT are formed in the crossing position between the scanning wiring and the signal wiring with an alignment film (first alignment film) being formed on the pixel. Another substrate (hereinafter referred to as counter substrate) for interposing the liquid crystal has a common electrode on an insulating substrate, and an alignment film (second alignment film) is formed on it. An array substrate and an counter substrate interposes a liquid crystal composition in a gap between the array substrate and the counter substrate with a face where the aforementioned pixel electrode is formed and a face where the common electrode is formed being confronted with each other. A “TN” liquid crystal where a liquid crystal molecules are twisted by 90 degrees in a thickness direction, because the alignment film is normally aligned in a direction deviated by 90 degrees on the array substrate side and the counter substrate side.
In a liquid crystal displaying apparatus of such a TN type, leaking light comes out from a gap; which is located between the pixel electrode, and the scanning wiring and the signal wiring in the periphery thereof. In order to prevent the leaking light by removing the gap, and at the same time, a disclination to be caused by the lateral direction electric field from the scanning wiring and the signal wiring, and the level difference of the pixel electrode end portion, the transparent insulating film is formed of a thick film of 1 &mgr;m or more. There is disclosed an art of forming the pixel electrode on the scanning wiring and the signal wiring through the transparent insulating film. Thus, the disclination by the lateral direction electric field from the scanning wiring and the signal wiring is prevented from being caused, and at the same time, the pixel electrode can be superposed on the scanning wiring and the signal wiring, whereby the aperture ratio of one pixel can be made larger.
FIG. 23
shows a sectional view of one pixel of the liquid crystal displaying apparatus using an art of forming on the scanning wiring and the signal wiring through the transparent insulating film the conventional pixel electrode described in, for example, Japanese Unexamined Patent Publication No. 84284/1995. In
FIG. 23
, reference numeral
1
is a transparent substrate, reference numeral
2
is a scanning wiring, reference numeral
3
is a storage capacitance wiring (hereinafter referred to as Cs wiring), reference numeral
4
is a gate insulating film, reference numeral
5
is a semiconductor layer serving as a channel, reference numeral
6
is a semiconductor layer for ohmic contact, reference numeral
7
is a signal wiring, reference numeral
8
is a drain electrode, reference numeral
9
is a passivation film, reference numeral
10
is a transparent resin film made of an organic material, reference numeral
12
is a pixel electrode, reference numeral
14
is a liquid crystal molecule. Reference numeral
18
is a common electrode on the side of the counter substrate. The alignment film exists on both the array substrate side and the counter substrate side. A glass substrate for composing the counter substrate, a black matrix and the coloring layer are omitted for simplification.
In the conventional liquid crystal displaying apparatus shown in
FIG. 23
, the space of the adjacent pixel electrodes becomes approximately several micro meters on the signal wiring
7
. In the conventional example, the relationship of the space between the liquid crystal thickness d and the pixel electrode is preferable to have the following relation;
L/d≦0.9 through 0.4
When the thickness d of, for example, the liquid crystal is 5 &mgr;m, L becomes 2 through 5 &mgr;m. When the space between the pixel electrodes becomes narrow, the liquid crystal molecule of the pixel end portion receives the influences of the lateral electric field from the adjacent pixel electrode. Especially, when a driving system of reversing the polarity of the signal for each column, the lateral electric field twice the longitudinal electric field to be added to the pixel electrode and the opposite electrode is added. In the conventional liquid crystal displaying apparatus shown in
FIG. 23
, an arrow mark shows the alignment direction when the array substrate surface of the aligning (hereinafter referred to as rubbing treatment) for aligning the liquid crystal is made upward. When the aligning in such one direction is conducted, a phenomenon called reverse tilt domain in the liquid crystal molecule in a direction different from that of the direction of the pretilt when the lateral electric field is added between the adjacent pixels. The disclination is caused on the boundary to the normal tilt region by the reverse tilt. The disclination is decided in the producing position by physical values such as lateral electric field strength between the adjacent pixel electrodes, anchoring strength by the aligning, pretilt angle, and viscosity of the liquid crystal molecule
14
. By the condition, the superposing amount between the pixel electrode on the side where the disclination is easy to be caused and the wiring has to be made larger. When the superposing between the pixel electrode and the wiring is made larger, an area for transmitting the light for increasing the light shielding area become smaller, and the aperture ratio is reduced. When only the superposing amount between the pixel electrode on the side where the disclination is easy to cause and the wiring are made larger, a coupling capacitance (hereinafter referred to as Cds) to be caused by the superposing portion between the pixel electrode and the signal wiring becomes different in the right and left superposing portion especially with the superposing amount between the signal wiring and the pixel electrode being made larger only on the side where the disclination is easy to cause. The electric potential of the pixel electrode receives more through the Cds the influences in the signal changes in the signal wiring where the superposing amount is larger. In the TFT-LCD for displaying the TN mode liquid crystal in a normally white mode concretely by the influences of signal changes in the signal wiring through the Cds, the brightness of the pixel of the gray displaying portion connected with the signal line for displaying the black window becomes lower as compared with that of the portion where the black window is not displayed in a case where the black window is displayed with the gray display as background, with a problem of causing the cross talk.
In the conventional liquid crystal displaying apparatus as described, it is necessary to make larger the superposing amount between the wiring and the pixel electrode on the side where the disclination is easy to produce, the disclination being caused by the production of the reverse tilt region due to the lateral electric field between the pixel electrodes when the disclination is restrained by shielding light.
Thus, the aperture ratio of the pixel is reduced, and there arises a problem of causing the cross talk.
Considering the problems of the conventional active matrix type liquid crystal displaying apparatus, an object of the present invention is to provide a liquid crystal displaying apparatus of high displaying quality, which is high in aperture ratio and is free from the cross talk.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present
Iwasa Toshinori
Mizunuma Masaya
Numano Yoshinori
Tsumura Akira
Dudek James A.
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Schechter Andrew
LandOfFree
Liquid crystal display device having intermediate alignment... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display device having intermediate alignment..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device having intermediate alignment... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2605028