Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2001-12-13
2004-06-22
Whitehead, Jr., Carl (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S098000, C349S033000, C349S094000, C349S099000, C349S128000, C349S129000, C349S167000, C349S191000
Reexamination Certificate
active
06753551
ABSTRACT:
This application incorporates by reference Taiwanese application Serial No. 089126649, filed Dec. 13, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a liquid crystal display (LCD) with a wide viewing angle, and more particularly to a LCD having a regulating device for aligning liquid crystal molecules with a negative dielectric constant.
2. Description of the Related Art
Benefited from the advantages of the thinness, lightness and low radiation properties, LCDs (Liquid Crystal Displays) have been widely used in the world. However, the contrast ratio will be decreased as the user sees the display from a larger viewing angle, which causes the viewing angle to be within a very limited range. Therefore, how to increase the viewing angle and improve the property of the LCD has been the critical lesson for the researchers.
Referring to
FIG. 1
, it is a sectional view showing the structure of a conventional LCD. The conventional LCD has an upper plate
102
and a lower plate
104
. An upper analyzer film
106
is positioned above the upper plate
102
and a lower polarizer film
108
is positioned under the lower plate
104
. The polarization direction of the upper analyzer film
106
is perpendicular to that of the lower polarizer film
108
. Moreover, the upper plate
102
includes a glass substrate
110
, a color filter
112
, a transparent electrode
114
, and an alignment film
116
. The lower plate
104
includes a glass substrate
120
, a transparent electrode
122
, and an alignment film
124
. The liquid crystal layer
118
, including a plurality of liquid crystal molecules
118
A, is sandwiched between the upper plate
102
and lower plate
104
. After a rubbing process, these liquid crystal molecules are aligned on the alignment films
116
or
124
.
When a voltage Va is supplied between the transparent electrode
114
and transparent electrode
122
, the alignment of the liquid crystal molecules in the liquid crystal layer
118
will be changed according to the amount of the voltage Va. The direction of light will varied because of different alignment directions of the liquid crystal molecules
118
A. Under this condition, the transmittance of the light will be changed according to the state of the liquid crystal molecules
118
A in the liquid crystal layer
118
. Therefore, the various brightness of the LCD, such as white, dark and gray scale, can be controlled by the various voltage applied between the transparent electrodes
114
,
112
.
In order to get a wide viewing angle, a LCD using an OCB mode (Optically Compensated Bend mode) has been provided. Referring to
FIG. 2
, it shows the relation between the applied voltage Va and the transmittance of the LCD with the OCB mode. As the applied voltage Va is 0, the transmittance is T
1
. If the applied voltage Va equals to the threshold voltage Vc, the transmittance will be the maximum value, T
2
. When the applied voltage Va is V
1
, the transmittance is the minimum value 0.
In the OCB mode, the dielectric constant difference of the liquid crystal used in the LCD is positive, and the liquid crystal molecules are in a horizontal alignment on the alignment films
116
,
124
. The direction of the upper analyzer film
106
is perpendicular to that of the lower polarizer film
108
.
Referring to FIG.
3
A~
3
C, the arrangement of the liquid crystal molecules in the liquid crystal layer
1118
are varied by different voltages Va applied to the LCD with the OCB mode. In
FIG. 3A
,
3
B,
3
C, the applied voltage Va is 0, Vc, and V
1
, respectively. The liquid crystal layer
118
comprises a first liquid crystal layer A, a second liquid crystal layer B and a third liquid crystal layer C. The first liquid crystal layer A is contact with the alignment film
116
, the second liquid crystal layer B is contact with the alignment film
124
, and the third liquid crystal layer C is sandwiched between the first liquid crystal layer A and the second liquid crystal layer B.
In
FIG. 3A
, the applied voltage Va is zero at the initial state, the angle between the first liquid crystal layer A and the alignment film
116
or the second liquid crystal layer B and the alignment film
124
is very small, about 3 to 8 degree. The liquid crystal molecules in the third liquid crystal layer C turn to parallel to the alignment films
116
,
124
. This is in a “splay alignment” state. At this time, angles are formed between the liquid crystal molecules and both of the upper and lower analyzers
106
,
108
, so lights can pass the upper analyzer film
106
through the lower polarizer film
108
. The LCD is in a white state.
In
FIG. 3B
, as the applied voltage Va is Vc, the angle between the first liquid crystal layer A and the alignment film
116
or between the second liquid crystal layer B and the alignment film
124
is increased. The liquid crystal molecules in the third liquid crystal layer C are almost perpendicular to the alignment films
116
,
124
. This is in a “bend alignment” state. At this time, the LCD is in the white state and has a maximum brightness.
In
FIG. 3C
, as the applied voltage Va is V
1
, the angle between the first liquid crystal layer A and the alignment film
116
or between the second liquid crystal layer B and the alignment film
124
is increased to a maximum, about 80 degrees or more. The liquid crystal molecules in the third liquid crystal layer C are substantially perpendicular to the alignment films
116
,
124
. In other words, the aligned direction of all liquid crystal molecules are almost perpendicular to the upper analyzer
106
and lower polarizer
108
, so lights can't pass through these polarizers. At this time, the LCD is in a dark state.
The OCB mode works when the applied voltage Va between the upper and lower plate
102
,
104
is in a range between the threshold voltage Vc and V
1
. The various brightness and the gray scale of the LCD are achieved by various voltage Va. In the OCB mode, the liquid crystal molecules can be arranged well, the liquid crystal molecules rotate in the same direction, and the friction between the liquid crystal molecules is reduced. Therefore, the LCD with OCB mode has the advantages of fast response and the wide viewing angle. However, it is unstable when the applied voltage is in the range between zero and the threshold voltage Vc. In this unstable stage, the LCD with the OCB mode is non-operated. In order to operate the LCD, the applied voltage should be higher than the threshold voltage Vc. It takes a time to increase the applied voltage Va from zero to the threshold voltage Vc. In other words, the response time of the LCD with OCB mode is slow and the applied voltage Va is high.
SUMMARY OF THE INVENTION
From the above description, the object of the present invention is to provide a LCD having a wide viewing angle. The LCD is in the dark state without applied voltage and in a white state with the applied voltage, such that the contrast ratio of the LCD is increased. A plurality of domains are defined by opposite regulating devices on the upper and lower substrates to achieve the advantages of the wide viewing angle, high contrast ratio and high response speed.
According to the present invention, a liquid crystal display having a wide viewing angle includes a first substrate, a first electrode, a first regulating device, a second substrate, a pixel electrode, a second regulating device and a liquid crystal layer. The first substrate includes a first surface thereon. The first electrode and the first regulating device having a first inclined plane are formed on the first surface. The second substrate has a second surface, and the first surface of the first substrate is opposed to the second surface of the second substrate. The pixel electrode and the second regulating device with a second inclined plane are formed on the second substrate. The first regulating device is opposed to the second regulating device. The liquid crystal layer is positioned between the first substrate and the second substrate. The liquid
AU Optronics Corp.
Hogans David L.
Jr. Carl Whitehead
Rabin & Berdo P.C.
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