Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-08-05
2001-11-06
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S129000
Reexamination Certificate
active
06313899
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to a liquid crystal display (LCD), especially to a TFT (thin film transistors) active matrix LCD having satisfactory visibility in a wide viewing angle range.
B. Description of the Prior Art
Compared with the conventional cathode-ray tube (CRT), the LCD has many advantages, such as, thinner in size and lighter in weight. Nevertheless, the viewing angle characteristic of the LCD is very narrow. To relieve the viewing angle dependence of the LCD, various types of LCD have been developed, for example, IPS (In-Plane Switching) LCD. However, IPS LCD is restricted to the application of desktop computers rather than notebooks since the optical transmission rate of IPS LCD is much lower than that of conventional TN (Twisted Nematic) LCD.
To improve the viewing angle dependence, a conventional method is to provide a LCD wherein there are many orientation directions for the liquid crystal molecules in the liquid crystal layer. For instance, a conventional LCD developed by Fujitsu company is illustrated in
FIGS. 6A and 6B
. Refer to
FIG. 6A
, the LCD includes an upper glass substrate
1
, a lower glass substrate
2
, and a liquid crystal layer
5
interposed therebetween. A pixel electrode
3
is disposed on the upper glass substrate
1
while a partial common electrode
4
is disposed on the lower glass substrate
2
. More particularly, there are multiple protrusions
6
on the pixel electrode
3
and the partial common electrode
4
. An orientation layer
7
overlays the homeotropic surface which covers the pixel electrode
3
and the protrusions
6
. The other orientation layer
7
overlays the homeotropic surface which covers the partial common electrode
4
and the protrusion
6
.
The structure as shown in
FIG. 6A
illustrates the situation when no voltage is applied between the pixel electrode
3
and the partial common electrode
4
or when the voltage applied between the pixel electrode
3
and the partial common electrode
4
is lower than a threshold voltage. Under the circumstance, all liquid crystal molecules have the same orientation direction (the vertical direction in FIG.
6
A). On the other hand, when the voltages applied between the pixel electrode
3
and the partial common electrode
4
exceeds the threshold voltage, the behavior of the liquid crystal molecules will vary in a manner as shown in FIG.
6
B. Under the circumstance, the orientation directions of the liquid crystal molecules will be affected by the protrusions
6
. Consequently, the viewing angle can be widened utilizing the LCD structure as illustrated in
FIGS. 6A and 6B
.
Another approach is developed by IBM and is illustrated in
FIGS. 7A and 7B
. Refer to
FIG. 7A
, the partial structure of the LCD includes an upper glass substrate
1
, a lower glass substrate
2
, a pixel electrode
3
, a partial common electrode
4
, a liquid crystal layer
5
and two orientation layers
7
.
A groove
9
is formed on the partial common electrode
4
, which causes discontinuities of the partial common electrode
4
. When no voltage is applied between the pixel electrode
3
and the partial common electrode
4
, or when the voltage applied between the pixel electrode
3
and the partial common electrode
4
does not exceed a threshold voltage, the liquid crystal molecules in the liquid crystal layer
5
have the same orientation direction, as illustrated in FIG.
7
A. On the other hand, when the voltage applied between the pixel electrode
3
and the partial common electrode
4
exceeds the threshold voltage, the orientation direction of the liquid crystal molecules near the groove
9
will vary in a manner as illustrated in FIG.
7
B. It is due to the non-uniform electric fields (as shown by the arrows in
FIG. 7B
) caused by the existence of the groove
9
. Consequently, the viewing angle can also be widened utilizing the LCD structure as illustrated in
FIGS. 7A and 7B
.
Yet another approach is also developed by IBM and illustrated in FIG.
8
. The LCD includes: an upper glass substrate
1
, a lower glass substrate
2
, a liquid crystal layer
5
interposed therebetween, a pixel electrode
3
, a partial common electrode
4
, a protrusion
6
, and two orientation layers
7
. The structure described in
FIG. 8
can be considered to be a combination of the structures described in
FIGS. 6A
,
6
B and
FIGS. 7A
,
7
B. Specifically, the orientation directions of the liquid crystal molecules can be further diversified because of the two reasons: (1) the liquid crystal molecules near the protrusion
6
tend to align perpendicular to the homeotropic surface which covers the partial common electrode
4
and the protrusions
6
; (2) the fringing field effect (as shown by the arrows in
FIG. 8
) appears at the edges of the pixel electrode
3
. Consequently, the viewing angle can also be widened utilizing the LCD structure as illustrated in FIG.
8
.
In summary, for the prior art as illustrated in
FIGS. 6A
,
6
B and
FIG. 8
, the dielectric materials constituting the protrusions
6
must satisfy some requirements such as resistivity, dielectric constant, and shape. As for the prior art illustrated in
FIGS. 7A
,
7
B, the fabrication processes is somewhat complicated because the groove
9
need to be formed on the partial common electrode
4
.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a LCD having wide viewing angle by providing a structure capable of providing various orientation directions of liquid crystal molecules.
It is another object of the present invention to provide a LCD having wide viewing angle by utilizing a simple fabrication processes.
A preferred embodiment of the present invention includes a first substrate, a second substrate, a liquid crystal layer, a plurality of pixels, a common electrode, a plurality of protrusions, a plurality of control electrodes, a first orientation layer and a second orientation layer.
The liquid crystal layer is interposed between the first substrate and the second substrate. The plurality of pixels are arranged in a matrix and disposed on the first substrate, each pixel has a pixel electrode and a switching means connected to it. The common electrode is disposed on the second substrate. The plurality of protrusions are composed of dielectric material and at least one of the plurality of protrusions is disposed on each pixel electrode. Each of the plurality of control electrodes is disposed on top of one of the plurality of protrusions. The first orientation layer overlays the homeotropic surface which covers the plurality of pixel electrodes, the plurality of protrusions, and the plurality of control electrodes. The second orientation layer overlays the surface of the common electrode.
The plurality of protrusions, the voltage applied to the plurality of control electrodes, and the fringing field effect appears at the edges of the plurality of pixel electrodes altogether make the liquid crystal molecules in the liquid crystal layer have many orientation directions, which widens the viewing angle of the LCD.
Another preferred embodiment of the present invention includes a first substrate, a second substrate, a liquid crystal layer, a plurality of pixels, a common electrode, a plurality of protrusions, a plurality of control electrodes, a first orientation layer and a second orientation layer.
The liquid crystal layer is interposed between the first substrate and the second substrate. The plurality of pixels are arranged in a matrix and disposed on the first substrate, each pixel has a pixel electrode and a switching means connected to it. The common electrode is disposed on the second substrate. The plurality of protrusions are composed of dielectric material and at least one of the plurality of protrusions is disposed on the region of the common electrode corresponding to each of the plurality of pixels. Each of the plurality of control electrodes is disposed on top of one of the plurality of protrusions. The first orientation layer overlays th
Kuo Chen-Lung
Wei Chung-Kuang
Wu Biing-Seng
Bacon & Thomas PLLC
Chi Mei Electronics Corporation
Chung David
Sikes William L.
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