Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-12-11
2002-09-17
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06452658
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a reflective liquid crystal display (hereinafter “LCD”) and a method for manufacturing the same, more particularly to a reflective LCD having high transmittance.
BACKGROUND OF THE INVENTION
The reflective LCD generally uses natural light as a light source rather than additional light source. In this reflective LCD, a natural light is radiated from an upper substrate, and then the light is reflected via a reflecting plate disposed at a bottom position of a lower substrate. At this time, the light is absorbed or transmitted according to the arrangement of liquid crystal molecules.
The general twisted nematic(TN) mode reflective LCD has the drawback of narrow viewing angle. Therefore, conventionally the hybrid mode reflective LCD capable of displaying full color and having a fast response time in the low voltage condition has been suggested. However, the hybrid mode reflective LCD only uses the birefringence effect of liquid crystal molecules, accordingly the contrast ratio is degraded since the gray scale inversion is easily occurred depending on the viewing direction. To solve foregoing problem, a bi-axial compensating film is applied to the hybrid mode reflective LCD. However, the bi-axial compensating film is difficult to produce and it is also difficult to apply to cells.
Therefore, conventionally the reflective LCD without using any optical compensating film has been suggested to solve the problem of gray scale inversion and to obtain high transmittance and wide viewing angle.
FIG. 1
is a cross-sectional view showing a conventional reflective LCD having high transmittance.
First of all, a metal layer is deposited on a lower substrate
1
and a selected portion of the same is patterned, thereby forming a gate bus line(not shown) and a common signal line (not shown). After an ITO layer is deposited on the lower substrate
1
, the ITO layer is patterned to be contacted with the common signal line so that the ITO layer has a shape of comb, thereby forming a counter electrode
2
. At this time, each tooth of the comb of the counter electrode
2
is separated by a selected distance. Afterward, a gate insulating layer
4
is deposited on the lower substrate
1
in which the counter electrode
2
, the gate bus line and the common signal line are formed. A channel layer(not shown) and an ohmic layer(not shown) are formed on a selected portion of the gate insulating layer
4
, thereby defining an active region. A metal layer is deposited on the gate insulating layer
4
in which the channel layer and the ohmic layer are formed, and a selected portion of the metal layer is patterned, thereby forming a source electrode(not shown), a drain electrode(not shown) and a data bus line(not shown). Consequently, a thin film transistor(not shown) is completed. Another ITO layer is deposited over the gate insulating layer in which the thin film transistor is formed, and the ITO layer is patterned so as to contact with the drain electrode, thereby forming a pixel electrode
6
. The pixel electrode
6
also has a shape of comb and its teeth are disposed between those teeth of the counter electrode
2
. A first homogeneous alignment layer
8
is formed on the gate insulating layer in which the pixel electrode
6
and the thin film transistor(not shown) are formed. In the meantime, a color filter
12
is attached to one face of an upper substrate
10
and a second homogeneous alignment layer
14
is formed on a surface of the color filter
12
. The lower substrate
1
and the upper substrate
10
are attached by intervening a selected distance therebetween so that the first and the second homogeneous alignment layers
8
,
14
are opposed each other. A liquid crystal layer
15
is sandwiched between the lower substrate
1
and the upper substrate
10
. A polarizer
17
is attached to an outer face of the upper substrate
10
, and a quarter wave plate
18
and a reflecting plate
19
are attached to an outer face of the lower substrate
1
.
Herein, a distance l
1
between the tooth of the counter electrode
2
and that of the pixel electrode
6
is preferably narrower than a distance d
1
between both substrates
1
,
10
, i.e. the cell gap. It is preferable that a width P
1
of the counter electrode
2
and a width P
2
of the pixel electrode
6
are formed such that liquid crystal molecules in upper portions of the electrodes are sufficiently driven in the presence of electric field.
In this reflective LCD, there is formed a fringe field Ef between the counter electrode
2
and the pixel electrode
6
as shown in the drawing when voltage is applied to the counter electrode
2
and the pixel electrode
6
. Therefore, liquid crystal molecules on and between both electrodes
2
,
6
are all driven, thereby greatly improving the transmittance.
However, the conventional reflective LCD having high transmittance has following drawbacks.
First of all, the conventional reflective LCD having high transmittance has the counter electrode
2
and the pixel electrode
6
, both made of a transparent conductor such as the ITO layer. Therefore, the counter electrode
2
is not formed at the same time with the gate bus line, and the pixel electrode
6
is not formed at the same time with the data bus line.
That is to say, the counter electrode
2
is formed after the gate bus line is formed, and the pixel electrode
6
is formed after the data bus line is formed. Accordingly, there may be added a mask pattern and manufacturing process is complicated.
Furthermore, compared with a general reflective TN LCD, the conventional reflective liquid crystal display having high transmittance has no topology which is formed on the lower substrate for scattering light. Therefore, an incident light is not scattered with a wide angle when electric field is applied. Further, excellent viewing angle characteristic is obtained at front side of a screen, while poor viewing angle characteristic is found at the sides of the screen.
SUMMARY OF THE INVENTION
Accordingly, it is one object of the present invention to provide a method for manufacturing a reflective LCD having high transmittance, which is capable of simplifying a manufacturing process by simultaneously forming the counter electrode and the pixel electrode.
It is another object of the present invention to provide the LCD having high transmittance that can obtain wide viewing angle.
To accomplish foregoing objects, the reflective LCD comprises:
an upper and a lower substrates opposed each other by intervening a liquid crystal layer;
a first insulating layer formed on the lower substrate;
a second insulating layer formed on the first insulating layer, wherein the second insulating layer has a uniform topology on its surface; and
a first and a second electrodes disposed alternatively at a sidewall of the topology in the second insulating layer,
wherein a distance between the first and the second electrodes is narrower than a distance between the upper and the lower substrates so that a fringe field is formed between the first and the second electrodes.
The present invention further comprises:
a lower substrate comprising a gate bus line and a common signal line extended in a selected direction; a gate insulating layer formed on the lower substrate in which the gate bus line and the common signal lines are formed; a thin film transistor having a channel layer formed at a selected portion on the gate insulating layer having the gate bus line, and a source electrode overlapped with one side of the channel layer, and a drain electrode overlapped with the other side of the channel layer; an intermetal insulating layer formed on the gate insulating layer in which the thin film transistor is formed, and having a plurality of uniform topology on its surface; a counter electrode disposed at one sidewall of the topology of the intermetal insulating layer, and contacted with the common signal line; and a pixel electrode disposed at the other sidewall of the topology of the intermetal insulating layer and between the counter electro
Lee Seung Hee
Lee Won Geon
Park In Cheol
Hyundai Display Technology Inc.
Ladas & Parry
Ngo Julie
Sikes William L.
LandOfFree
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