Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-03-15
2002-11-19
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S084000, C349S096000, C349S106000, C349S124000
Reexamination Certificate
active
06483562
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-068420, filed Mar. 15, 1999; and No. 11-068421, filed Mar. 15, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to an electrode substrate for a reflection type liquid crystal display device and to a reflection type liquid crystal display device, and in particular, to an electrode substrate provided with a light scattering film for a reflection type liquid crystal display device, which enables it to obtain a display plane excellent in brightness and in display quality, and wide in viewing angle, and also to a reflection type liquid crystal display device provided with such an electrode substrate.
The main components of a liquid crystal display device are generally constituted by a pair of electrode substrates each provided with a polarizing film and electrodes for driving a liquid crystal, and the liquid crystal filled in a space between these electrode substrates.
On the occasion of displaying an image in this liquid crystal display device, a voltage is impressed between these facing electrodes so as to cause a change in the state of orientation of the liquid crystal molecules filled between the electrode substrates, thereby controlling not only the plane of polarization of the light passing through the liquid crystal but also the transmittance or non-transmittance of the light through the polarizing film.
As for the type of liquid crystal display device, a transmission type liquid display device of a lamp-built-in type such as so-called back-light or light-guide type is widely employed today. In this liquid crystal display device, a light source (lamp) is arranged on the back or side of an electrode substrate disposed on the back of the device (i.e. an electrode substrate which is disposed on the side remote from a viewer among a pair of electrode substrates between which the aforementioned liquid crystal is filled, which is hereinafter referred to as a back electrode substrate), thereby introducing a light from the back electrode substrate into the display plane, thus enabling it to display a bright image.
In view of the advantageous characteristics that power consumption can be minimized and total weight can be reduced, the application of a liquid crystal display device to a portable display device such as a mobile machine has been increasingly expected now.
In the case of lamp-built-in type liquid display device however, the power consumption by the built-in light source (lamp) is relatively large (for example, the lamp consumes almost the same degree of electric power as that of CRT or of plasma display device). Therefore, the lamp-built-in type liquid display device is disadvantageous in that the serviceable time of battery is short, and that the total weight and size of the device would be increased due to a relatively large volume percentage to be occupied by the battery in relative to the entire device. Namely, it cannot be said that the aforementioned advantages that a liquid display device inherently have are fully utilized by the lamp-built-in type liquid display device.
In view of the aforementioned circumstances, a reflection type liquid crystal display device not provided with a light source (lamp) has been proposed. This reflection type liquid crystal display device is provided on the back electrode substrate thereof with a light reflective plate having a light reflecting function or provided with a reflective electrode which functions not only as a liquid crystal driving electrode but also as a light reflective plate. In this case, an external light such as a room light or natural light is allowed to enter into the liquid crystal display device from the viewer's side electrode substrate (i.e. an electrode substrate which is disposed on a viewer's side among a pair of electrode substrates filling a liquid crystal therebetween), and this incident light is then allowed to be reflected by the aforementioned light reflective plate or the reflective electrode, the reflected light being emitted from the electrode substrate disposed on a viewer's side, thus displaying an image.
As for the back electrode substrate to be employed in this reflection type liquid crystal display device, ones shown in
FIGS. 1 and 2
for instance are already known.
The liquid crystal display device shown in
FIG. 1
comprises a viewer's side electrode substrate A, a back electrode substrate B, and a liquid crystal layer
10
interposed therebetween. The viewer's side electrode substrate A is constructed such that a color filter
16
is formed on a glass substrate
11
a
, and a transparent electrode
15
is formed on the color filter
16
.
The back electrode substrate B shown in
FIG. 1
is constructed such that an insulating film
13
having a roughened surface for scattering a light is formed on a glass substrate
11
b
provided on the surface thereof with a TFT (thin film transistor) array
18
, and additionally, a metallic reflective film
12
functioning also as a liquid crystal driving electrode is selectively formed on the insulating film
13
so as to make the location of metallic reflective film
12
coincide with each pixel, the underlying TFT array
18
being subsequently interconnected with the metallic reflective film
12
through via-holes
19
.
The liquid crystal display device shown in
FIG. 2
comprises a viewer's side electrode substrate A, a back electrode substrate B, and a liquid crystal layer
20
interposed therebetween. The viewer's side electrode substrate A is constructed such that a color filter
26
is formed on a glass substrate
21
a
, and a flattening layer
24
and a transparent electrode
25
a
are formed on the color filter
26
. A polarizing film
27
a
is formed on the opposite surface of the glass substrate
21
a.
The back electrode substrate B shown in
FIG. 2
is constructed such that a transparent electrode
25
b
is formed on one surface of a glass substrate
21
b
, and a polarizing film
27
b
and a metallic reflective film
22
are disposed on the opposite surface of the glass substrate
21
b.
However, the reflection type liquid crystal display device of this kind is accompanied with a problem that, since the aforementioned metallic reflective film is employed for reflecting an incident light, the viewing angle is restricted depending on the position of the external light source.
Moreover, the back electrode substrate B shown in
FIG. 1
is also accompanied with problems that the step of forming a roughened surface of the insulating film for securing a sufficient viewing angle as well as the step of forming the via-holes
19
for securing an electric connection between the metallic reflective film
12
and a circuit wiring (the TFT array
18
) are complicated, and at the same time, the surface roughness of the metallic reflective film
12
is prominent, thereby raising a problem with respect to the orientation of liquid crystal.
On the other hand, the back electrode substrate B shown in
FIG. 2
is also accompanied with problems that since the metallic reflective film
22
is disposed on the back surface of the substrate, the light path of the reflected light is caused to differ from that of the incident light due to the thickness of the substrate
21
b
, so that, due to this difference in light path, the light that has passed through a pixel and reflected by the metallic reflective film
22
is caused to enter into a neighboring pixel to generate a display defect such as color mixture, or otherwise, the incident light is caused to be reflected not only from the surface of the transparent electrode
25
b
but also from the metallic reflective film
22
disposed on the back surface of the substrate, thereby generating a dual image.
As means for solving the aforementioned problems, the present inventors have already proposed an idea of providing a light scattering film as set forth in J
Fukuyoshi Kenzo
Imayoshi Koji
Kitamura Satoshi
Ngo Julie
Sikes William L.
Staas & Halsey , LLP
Toppan Printing Co. Ltd.
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