Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-05-26
2003-01-28
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S141000, C349S128000
Reexamination Certificate
active
06512565
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display, more particularly to a homeotropic alignment liquid crystal display of active matrix type.
BACKGROUND OF THE INVENTION
Generally, the In-plane Switching(hereinafter IPS) mode liquid crystal display has been suggested to improve narrow viewing angle characteristics of the Twisted Nematic (hereinafter TN) mode liquid crystal display. However, the IPS mode liquid crystal display makes an electric field parallel to substrates thereby improving the viewing angle characteristics. The IPS mode liquid crystal display has also a slow response time and a complicated manufacturing process is required to make a dual-domain. U.S. patent application Ser. No. 09/050,292 discloses a vertically aligned IPS (hereinafter IPS-VA) mode liquid crystal display to solve the foregoing problems.
The conventional IPS-VA mode liquid crystal display has following constitution.
Referring to
FIGS. 1A and 1B
, a counter electrode
51
a
and a pixel electrode
51
b
are disposed parallel to each other at an inner surface of a lower substrate
50
in a stripe manner. A first homeotropic alignment layer
53
is formed over the lower substrate
50
where the counter and pixel electrodes
51
a
,
51
b
are formed.
A color filter(not shown) is formed at an inner surface of an upper substrate
55
and a second homeotropic alignment layer
56
is formed on a surface of the color filter.
A liquid crystal layer
57
having a plurality of liquid crystal molecules
57
a
is interposed between the lower substrate
50
and the upper substrate
55
. Herein, the liquid crystal molecules
57
a
are nematic molecules and have both dielectric and refractive anisotropic properties.
A first polarizing plate
58
is disposed at an outer surface of the lower substrate
50
and a second polarizing plate
59
is disposed at an outer surface of the upper substrate
55
. Polarizing axes of the first and second polarizing plates
58
,
59
are crossed each other, and they make an angle of approximately ±45° with an electric field being generated between the counter electrode
51
a
and the pixel electrode
51
b
. A phase compensating film
60
is interposed between the upper substrate
55
and the second polarizing plate
59
so as to compensate the refractive anisotropy of liquid crystal molecules
57
a.
In the absence of electric field between the counter electrode
51
a
and the pixel electrode
51
b
, as shown in
FIG. 1A
, the liquid crystal molecules
57
a
are arranged such that their long axes are disposed almost perpendicular to the substrates
50
,
55
according to the influence of the first and second homeotropic alignment layers
53
,
56
. Consequently, since an incident light to pass the first polarizing plate
58
does not change its polarizing state while passing the liquid crystal molecules
57
a
, the incident light does not pass the second polarizing plate
59
. The screen according to viewing angles shows a complete dark state since the refractive anisotropy of the liquid crystal molecules
57
a
according to the viewing angles is compensated by the phase compensating film
60
.
On the other hand, a predetermined voltage is applied between the counter electrode
51
a
and the pixel electrode
51
b
, as shown in
FIG. 1B
, an electric field E is formed almost parallel to the lower substrate
50
. And then, the liquid crystal molecules
57
a
which are disposed perpendicular to the substrates, are arranged such that their long axes are arranged to be parallel to the electric field E in case a liquid crystal of positive dielectric anisotropy is used. At this time, liquid crystal molecules
57
a
in the left side of the center of the electric field E are aligned in a clockwise direction and liquid crystal molecules
57
a
in the right side of the center of the electric field E are aligned in a counter-clockwise direction thereby forming two domains without incurring additional manufacturing process. Herein, liquid crystal molecules
57
b
in the center of the electric field E are affected by both sided liquid crystal molecules
57
a
having the same intensity in opposite directions. Therefore, they maintain their initial vertically aligned state. At this time, the liquid crystal molecules
57
b
keeping their initial vertically aligned state become a boundary of the two domains.
As described, since the liquid crystal molecules
57
a
are arranged parallel to the electric field E, an incident light to pass the first polarizing plate
58
changes its polarizing state while passing the liquid crystal layer
57
. Accordingly, the light can pass the second polarizing plate
59
, whereby the screen can be shown in a white state.
The IPS-VA mode liquid crystal display as constituted above improves the response time characteristics of display devices since the devices employ homeotropic alignment layers, and there is no need to perform any rubbing process to form two domains.
However, the IPS-VA mode liquid crystal display incurs following problems.
Since an electric field in one direction is formed within a pixel, the viewing angle characteristic of a region where the electric field is formed is superior to that of other regions where no electric field is formed.
In other words, as shown in
FIG. 2
, liquid crystal molecules in a horizontal direction where the electric field is formed, i.e. at 0° and 180° make a complete symmetry in their left side and right side since the liquid crystal molecules are arranged symmetrical themselves. However, liquid crystal molecules in perpendicular and oblique directions where no electric field is formed, i.e. at 90°, 270° and at 45°, 135°, do not make any symmetry. Especially, in the oblique directions, there is even occurred a color shift that a selected color is shown in the white state screen.
Accordingly, it is one object of the present invention to provide a homeotropic alignment liquid crystal display having a multi-domain capable of obtaining a complete viewing angle characteristic at all azimuth angles in the screen.
It is another object of the present invention to provide a homeotropic alignment liquid crystal display having fast response time.
It is still object of the present invention to provide a homeotropic alignment liquid crystal display capable of preventing color shift in all azimuth angles in the screen.
SUMMARY OF THE INVENTION
So as to accomplish the forgoing objects, the present invention provides a homeotropic alignment liquid crystal display having a multi-domain comprising:
an upper substrate and a lower substrate opposed each other to be spaced apart;
a liquid crystal layer interposed between inner surfaces of the upper and lower substrates, the liquid crystal layer including a plurality of liquid crystal molecules;
a first electrode formed on the inner surface of the lower substrate; and
a second electrode formed on the inner surface of the upper substrate, wherein the first electrode and the second electrode form an electric field for driving the liquid crystal molecules;
wherein in the absence of electric field between the first and second electrodes, the liquid crystal molecules are aligned such that their long axes are vertical to surfaces of the substrates,
wherein after applying a selected voltage to the first and second electrodes, first and second electric fields are formed simultaneously, the first electric field having a selected angle with a first direction and the second electric field having a symmetry with the first electric field with respect to the first direction;
wherein the selected angle between the first electric field and the first direction is in the range of 20~70°.
The present invention further provides a homeotropic alignment liquid crystal display having a multi-domain comprising:
an upper substrate and a lower substrate opposed each other to be spaced apart;
a liquid crystal layer interposed between inner surfaces of the upper and lower substrates, the liquid crystal layer including a plurality of liquid crystal molecules;
a gate bus line and a dat
Lee Seung Hee
Lee Yun Hee
Park In Cheol
Hyundai Display Technology Inc.
Ladas & Parry
Qi Mike
Ton Toan
LandOfFree
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