Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-06-25
2001-04-10
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S146000
Reexamination Certificate
active
06215542
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a liquid crystal display(LCD), and more particularly to a LCD having an improved viewing angle and transmittance.
2. Related Art
A liquid crystal display(LCD) has an optical aniostropy owing to a structure thereof. The optical anisotropy(or refraction index anisotropy) means that a refraction index at a major axis of a liquid crystal molecule is different from that at a minor axis of the liquid crystal molecule. Because of the optical aniostropy, a polarization of the light passing through the liquid crystal molecule and oscillating direction of the polarized light are varied. The refraction index is represented as a difference between a refraction index in a direction parallel to the major axis of the liquid crystal molecule(ordinary refraction index) and a refraction index in another direction perpendicular to the major axis thereof(extraordinary refraction index), which is called as a birefringence. On the other hand, in applying a voltage to the liquid crystal cell, the liquid crystal molecules are rearranged owing to a dielectric anisotropy of the liquid crystal and light passes through the rearranged liquid crystal molecules.
FIGS. 1A and 1B
show an electrically controlled birefringence(ECB) mode liquid crystal display(LCD) using the birefringence of the liquid crystal molecule, wherein the LCD in
FIG. 1A
is under no voltage applied thereto and the LCD in
FIG. 1B
is subjected to the applied voltage.
The liquid crystal molecules
8
are formed between a upper substrate
1
and a lower substrate
4
. On an opposite surface of the upper substrate
1
and an opposite surface of the lower substrate
1
, are respectively formed a counter electrode
2
and a pixel electrode
5
on which vertical alignment layers
3
and
6
are disposed. On a non-opposite surface of the upper substrate
1
and a non-opposite surface of the lower substrate
4
, are disposed the respective polarization layers
7
a
and
7
b
. The vertical alignment layers
3
and
6
are rubbed so as to have a pretilt angle of about 85 to 89 degrees.
In no applied voltage, as shown in
FIG. 1A
, all the liquid crystal molecules of the ECB mode LCD are vertically arranged to the upper substrate and the lower substrate. In applying voltage to the LCD, as shown in
FIG. 1B
, the liquid crystal molecules which are directly contacted with the vertical alignment layers of the upper substrate and the lower substrate maintain their original state and the liquid crystal molecules between the most outer liquid crystal molecules are slantly arranged in a given direction.
The ECB mode LCD has a merit of high contrast ratio. However, since when applying voltage, the liquid crystal molecules in the middle part of the liquid crystal layer are oriented in one direction, a phase retardation is different according to the viewing angle. Accordingly, the transmittance is varied responsive to the viewing angle and thus the viewing angle becomes narrow. On the other hand, when no voltage is applied to the LCD, a complete dark state can be realized at a just front of the liquid crystal cell. However, at a side of the liquid crystal cell there is the phase retardation with respect to the front, so a leakage current of the LCD is generated.
SUMMARY OF THE INVENTION
Accordingly, an aim of a present invention is to improve a viewing angle when voltage is applied to a liquid crystal display(LCD) while preventing a leakage current of the LCD in no applied voltage.
In order to accomplish an aim of the present invention, a liquid crystal display(LCD) comprises a first substrate, a first electrode formed on the first substrate and being a plate shape, a second substrate opposite the first substrate, and a second electrode formed on the second substrate and being a plate shape provided with a given opening part. Here, one of the first electrode and the second electrode is a counter electrode and the other is a pixel electrode. The opening part shape is rectangular. The second electrode has at least one opening part therein. In case where the opening part is two or more, a width of the opening part is less than a distance between the opening part and the adjacent opening part. The width of the opening part is preferably 3 to 5 &mgr;m. The liquid crystal used in the LCD has a type of negative dielectric anisotropy.
In another case, the second electrode includes a rectangular frame, a first part vertically and inwardly protruded from one side of the rectangular frame and a second part inwardly protruded from an end of the first part in a circle shape. The opening part is defined by the rectangular frame, the first part and the second part. A width of the rectangular frame, a width of the first part, a radius of the second part are larger than a width of the opening part.
So as to prevent a light leakage current of the LCD, the LCD further comprises a first polarization layer formed on the non-opposite surface of the first substrate, a second polarization layer formed on the non-opposite surface of the second substrate and a optical phase retardation compensation film formed at least between the first substrate and the first polarization layer and between the second substrate and the second polarization layer. Further, the LCD comprises a storage electrode, over the second substrate, overlapping the second electrode at a selected portion, the border of the pixel electrode.
The electric field generated between the pixel electrode and the counter electrode is an ellipse shape and symmetrically formed centering around a center of the opening part between the pixel electrode and the counter electrode. Therefore, the viewing angle of the LCD is increased when voltage is applied to the LCD. The light leakage under no applied voltage, is prevented by compensating the phase retardation using the optical phase retardation compensation film.
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patent: 4490015 (1984-12-01), Kawarada et al.
patent: 5136407 (1992-08-01), Clerc
patent: 5182664 (1993-01-01), Clerc et al.
patent: 5229873 (1993-07-01), Hirose et al.
patent: 5309264 (1994-05-01), Lien et al.
patent: 5339181 (1994-08-01), Kim et al.
patent: 5589965 (1996-12-01), Bahadur et al.
patent: 5615028 (1997-03-01), Ishiguro et al.
patent: 728063 (1995-01-01), None
Lee Seung Hee
Park Han Jun
Rho Bong Gyu
Dudek James A.
Hyundai Electronics Industries Co,. Ltd.
Selitto & Associates, P.C.
Ton Toan
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