Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-09-02
2001-05-22
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S122000
Reexamination Certificate
active
06236441
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to liquid crystal display apparatus.
A display method, wherein an electric field is supplied to a liquid crystal in a direction approximately parallel to the surface of a substrate using a pair of comb-shaped electrodes, has been disclosed in JP-B-63-21907 (1988), U.S. Pat. No. 4,345,249, W091/10936, JP-A-6-222397 (1994), and JP-A-6-160878 (1994). In this type of display method, the electrode is not required to be transparent, and so an opaque metallic electrode having a high electro-conductivity is used.
The display method disclosed in the above-referenced prior art, i.e. the display method wherein an electric field is supplied to a liquid crystal in a direction approximately parallel to the surface of a substrate (hereinafter called an in-plane switching method), has the feature of providing a wide viewing angle. However, none of the prior art teaches how to make a high contrast ratio and a decreased nonuniformity of display compatible.
In accordance with the in-plane switching method, the electric field is supplied in a direction approximately parallel to the surface of the substrate. Therefore, in contrast to the conventional twisted nematic display method, the driving voltage depends on the cell gap, and the threshold voltage, Ec, is approximately expressed by the following equation (math. 1).
Ec
=
π
d
LC
K
2
ϵ
0
Δϵ
(
math
.
1
)
where,
d
LC
: Cell gap
K
2
: Elastic constant of twist of the liquid crystal
&Dgr;∈: Dielectric anisotropy of the liquid crystal
∈
0
: Dielectric constant in vacuum
Investigation by the present inventors has revealed that, in accordance with the in-plane switching method, the driving voltage depends on the cell gap, and accordingly, variation of the cell gap in the display plane is readily expressed as a variation of the surface brightness, and nonuniformity of display occurs readily. The term nonuniformity of display refers to a nonuniformity in brightness caused by variation of the cell gaps.
If the dispersing amount of the spacer beads is increased as a countermeasure against the nonuniformity of display, the nonuniformity of display can be decreased by an increase in the amount of the spacer beads, which contributes to formation of the cell gap. However, it also has been revealed that a leakage of light caused by variation in the liquid crystal orientation in the vicinity of the spacer beads is increased with an increase in the amount of the spacer beads at an aperture portion of the display, creating the problem that the contrast is decreased.
If a planarization film composed of organic high polymers is formed as another countermeasure on the whole surface of a substrate having a group of electrodes, the nonuniformity of display can be decreased with a decrease of the surface nonuniformity. However, it also has been revealed that the contrast ratio is decreased because the driving voltage is increased, and so a problem arises in that a sufficient voltage can not be supplied to the liquid crystal.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a liquid crystal display apparatus having a wide viewing angle, a high contrast ratio, and a small nonuniformity of display, and a method for manufacturing the same.
The liquid crystal display apparatus relating to the present invention comprises a pair of substrates, and a liquid crystal layer interposed between the pair of substrates, wherein at least one substrate of the pair of substrates comprises a plurality of electrodes, a passivation film formed on the plurality of electrodes, and an insulating layer formed at concave portions on the passivation layer for making the thickness of the liquid crystal layer uniform. The variation in the thickness of the liquid crystal layer is preferably at the utmost 0.3 &mgr;m.
Furthermore, another form of the liquid crystal display apparatus relating to the present invention comprises a pair of substrates, and a liquid crystal layer interposed between the pair of substrates, wherein at least one substrate of the pair of substrates comprises a plurality of electrodes, a passivation film formed on the plurality of electrodes, and an insulating layer formed on the passivation layer, wherein the thickness of the insulating layer in regions other than a region on the electrodes is made larger than the thickness of the passivation layer in the region on the electrodes.
The size of the light leakage region varies depending on whether the spacer beads contribute to the formation of the gap or not. The light leakage around the spacer beads contributing to the formation of the gap is remarkably small in comparison with the light leakage around the spacer beads which do not contribute to the formation of the gap. With a view toward making the thickness of the liquid crystal layer uniform, the dispersing amount of the spacer beads can be decreased, whereby the light leakage around the spacer beads becomes small because almost all of the spacer beads can contribute to the formation of the gap. Accordingly, a decrease in contrast due to light leakage around the spacer beads is prevented, and the nonuniformity of display can be decreased.
The advantages of the present invention are remarkable in the use of the in-plane switching method. In comparison with twisted nematic display methods, the in-plane switching method has a feature to reveal readily the variation in the cell gap as a variation of the surface brightness because the driving voltage depends on the cell gap.
REFERENCES:
patent: 4345249 (1982-08-01), Togashi
patent: 4728176 (1988-03-01), Tsubayama et al.
patent: 5042920 (1991-08-01), Yoshino et al.
patent: 5132816 (1992-07-01), Itoh et al.
patent: 5585951 (1996-12-01), Noda et al.
patent: 5598285 (1997-01-01), Kondo et al.
patent: 5600464 (1997-02-01), Ohe et al.
patent: 5641974 (1997-06-01), den Boer et al.
patent: 5818550 (1998-10-01), Kadota et al.
patent: 63-21907 (1988-05-01), None
patent: 6-160878 (1994-06-01), None
patent: 6-222397 (1994-08-01), None
patent: WO 91/10936 (1991-07-01), None
Aratani Sukekazu
Kagawa Hiroyuki
Kondo Katsumi
Matsuyama Shigeru
Oh-e Masahito
Antonelli Terry Stout & Kraus LLP
Duong Tai V.
Hitachi , Ltd.
Parker Kenneth
LandOfFree
Liquid crystal display apparatus and a method for... 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 apparatus and a method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display apparatus and a method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2496319