Liquid crystal display

Details Liquid crystal display Liquid crystal display

1997-07-11

2001-01-30

Sikes, William L. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S139000, C349S143000

Reexamination Certificate

active

06181402

ABSTRACT:

BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a liquid crystal display.
(b) Description of the Related Art
Generally, a conventional liquid crystal display (LCD) comprises two substrates having electrodes and liquid crystal injected therebetween. Light transmittance is adjusted by controlling the intensity of voltage being applied to the electrodes.
Hereinafter, the conventional LCD is explained in detail with reference to the accompanying drawings.
FIGS. 1A and 1B
are sectional views of a conventional twisted-nematic liquid crystal display (TN-LCD). The TN-LCD in
FIG. 1A
, comprises: transparent glass substrates
1
and
2
facing each other; a liquid crystal layer
7
inserted between the substrates
1
and
2
; and electrodes
3
and
4
formed respectively on the inner surfaces of the transparent glass substrates
1
and
2
; and two polarizing plates
5
and
6
attached to the outer surface of the glass substrates
1
and
2
respectively for polarizing the light.
The electrode
3
of the lower substrate
1
is a pixel electrode, and the electrode
4
of the upper substrate
2
is a common electrode, and dielectric anisotropy &Dgr;&egr; of the liquid crystal layer
7
is positive.
In the absence of an electric field, the long axis of the liquid crystal molecules
8
of the liquid crystal layer
7
is in parallel with the substrates
1
and
2
, and the liquid crystal molecules
8
are twisted spirally from one substrate to the other substrate.
When a power V is connected to the electrodes
3
and
4
, and sufficient electric field is present in the liquid crystal layer
7
in the direction of the arrow as illustrated in
FIG. 1B
, the major axis of the liquid crystal molecules
8
is in parallel with the direction of the electric field. This type of TN-LCD unfortunately results in having a narrow viewing angle.
To remedy this problem, a new method, an in-plane switching liquid crystal display (IPS-LCD), has been proposed recently.
FIGS. 2A and 2B
are sectional views of a conventional IPS-LCD. The main difference between the TN-LCD and the IPS-LCD lies with the placement of the electrodes
3
and
4
.
Unlike the TN-LCD, both electrodes
3
and
4
of the IPS-LCD are formed on the same substrate, either upper or lower, in parallel to each other. In
FIGS. 2A and 2B
, the electrodes
3
and
4
are formed on the lower substrate
1
as an example. The dielectric anisotropy &Dgr;&egr; of the liquid crystal layer
7
may be positive or negative. The other reference numerals of
FIGS. 2A and 2B
represent the same elements of
FIGS. 1A and 1B
.
In the absence of an electric field, the long axis of the liquid crystal molecules
8
of the liquid crystal layer
7
is parallel with the two substrates
1
and
2
, or has a predetermined angle with respect to the two electrodes
3
and
4
.
When a power V is connected to the two electrodes
3
and
4
, and sufficient electric field is applied, the generated electric field is substantially parallel with the substrates
1
and
2
, and perpendicular to the electrodes
3
and
4
. Accordingly, the long axis of the liquid crystal molecules
8
at the center of the liquid crystal layer
7
is parallel with the electric field.
On the other hand, the liquid crystal molecules
8
, away from the center of the liquid crystal layer
7
, has a spirally twisted substructure since the liquid crystal molecules
8
near the substrates
1
and
2
maintain their initial state due to the alignment force.
However, the IPS-LCD has the undesirable effects of a reduced contrast ratio due to light leakage in the dark state and the decreased response speed of the liquid crystal molecules,
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal display having (LCD) a wide viewing angle to substantially obviate the problems associated with the related art.
An LCD according to embodiments of the present invention is made by injecting a liquid crystal material having dielectric anisotropy between first and second substrates and aligning perpendicularly the liquid crystal molecules with respect to the two substrates. First and second electrodes are formed on one of the two substrates and made parallel with each other.
Alignment films for aligning molecular axes of the liquid crystal molecules perpendicularly with respect to the substrates may be formed on the first or the second substrate, and the alignment films may or may not be rubbed.
In addition, the LCD of the present invention may further include polarizing plates, and the transmission axes of the polarizing plates are parallel or perpendicular to each other.
Here, the dielectric anisotropy of the liquid crystal material may be positive or negative, and may be one among pure nematic liquid crystal, chiral nematic liquid crystal and nematic liquid crystal having chiral dopant.
When voltage is applied to two electrodes of the LCD of the present invention, a parabolic electric field is generated between the two electrodes, and the liquid crystal molecules are driven by the electric field.
The liquid crystal display described above is called an electrically-induced optical compensation liquid crystal display (EOC-LCD).
In the EOC-LCD according to the embodiments of the present invention, the liquid crystal molecules are symmetrically aligned to the surface which is equal distance from each of the electrodes. Accordingly, the phase retardation of the transmitted light is symmetrically caused, thereby obtaining a wide viewing angle.
Additional objects and advantages of the present invention are set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.


REFERENCES:
patent: 5493426 (1996-02-01), Johnson et al.
patent: 5532854 (1996-07-01), Fergason
patent: 5541753 (1996-07-01), Raynes et al.
patent: 5654782 (1997-08-01), Morokawa et al.
patent: 5668651 (1997-09-01), Yamada et al.
patent: 5694188 (1997-12-01), Sano et al.
patent: 5841498 (1998-11-01), Baur et al.
patent: 227 809 A1 (1985-09-01), None
patent: 53-89753 (1978-08-01), None

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