Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-07-19
2002-09-17
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C359S459000
Reexamination Certificate
active
06452653
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a reflector for use in a reflective liquid crystal display device which displays an image by reflecting external light when used in OA equipment, a personal computer, a mobile phone, a mobile data terminal, or the like, to a method of fabricating the same, to the reflective display device, and a method of fabricating the same.
BACKGROUND OF THE INVENTION
As AV equipment and data equipment has been scaled down to have a reduced thickness in recent years, there has been growing demand for a liquid crystal display device as a light-receiving display device. For the data equipment, a liquid crystal display device that can be mounted on a notebook personal computer with higher portability has been in increasing demand with the advent of a multimedia society. In the field of mobile data terminals, a liquid crystal display device which is lower in profile, weight, and power consumption has been required.
Such liquid crystal display devices are subdivided into a transmissive type having a backlight disposed on the rear surface of a liquid crystal panel and a reflective type having a reflector disposed therein and using external light as illuminating light. There is also a semitransmissive type comprising a half mirror, which uses ex al light reflected by a reflector as illuminating light in a bright environment, while using a backlight in combination in a dark environment. Since a reflective liquid crystal display device and a semitransmissive liquid crystal display device use a mode of displaying an image by reflecting external light and normally do not need a light source such as a backlight unit, they can be reduced particularly in power consumption, profile, and weight compared with a conventional transmissive liquid crystal display device. In a typical reflective liquid crystal display device, a scattering reflector made of aluminum or silver is disposed behind a liquid crystal panel. In a monochrome display device used in a wrist watch, a scattering reflector with a sheet polarizer is bonded to the outside of glass. As a display mode of the reflective liquid crystal display device, a TN (Twisted Nematic) mode, a STN (Super Twisted Nematic) mode, a GH (Guest-Host) mode involving the use of a dichroic dye have been used predominantly.
To achieve brighter and more satisfactory display in the reflective liquid crystal display device, it is required to reflect and scatter incident light in the normal viewing angle direction which is perpendicular to a display screen and thereby increase the intensity of the light. In addition to reflecting and scattering, in the normal viewing angle direction, external light incident at a specified angle from a specified direction, it is also desirable to similarly reflect and scatter, in the normal viewing angle direction, external light incident at arbitrary angles from different directions. As a result, it becomes necessary to fabricate a reflector having optimum reflecting properties which allow external light incident from an arbitrary direction to be used efficiently as display light. The optimum reflecting properties used here indicate the properties of the reflector with which incident light is reflected in a wide range and with a high reflectance.
In the case of using a conventional reflector such as one having a specular metal film formed on a substrate, incident light is reflected only in the direction of regular reflection so that the reflectance is low in a direction other than the regular reflection direction. This causes the problem that a screen displayed is extremely dark in a direction of visual recognition of a viewer, such as the normal viewing angle direction, which significantly degrades the display quality.
To solve the problem, a reflective liquid crystal display panel comprising a scattering reflector having a rough configuration is disclosed in, e.g., Japanese Unexamined Patent Publication No. HEI 4-243226. The scattering reflector disclosed in the publication is fabricated in accordance with the following method such that a reflecting surface thereof has a uniform configuration and is formed with high reproducibility. That is, as shown in
FIG. 33A
, a resist film
202
is coated on a glass substrate
201
. Then, as shown in
FIG. 33B
, the resist film
202
is covered with a photomask
203
patterned into a specified configuration and exposed to light. Subsequently, the exposed resist film
202
is developed with a developing solution, whereby numerous projecting portions
204
as shown in
FIG. 33C
are formed. Since the projecting portions
204
have generally right-angled edges in cross section, the edges of the projecting portions
204
should be rounded off. By performing a heat treatment, therefore, a configuration as shown in
FIG. 33D
is obtained. Further, Ag is vapor-deposited over the glass substrate
201
formed with the projecting portions
204
to form a metal reflective film
206
(FIG.
33
E). By the foregoing process, the scattering reflector has been fabricated.
To solve the foregoing problem, a pixel electrode having reflecting properties with which reflection of incident light in the region of regular reflection is reduced is also disclosed in, e.g., Japanese Unexamined Patent Publication No. HEI 6-27481. According to the publication, a reflector
210
comprises: a substrate
211
formed with a plurality of projecting portions
212
a
and
212
b
; a polymer resin film
214
provided over the substrate
211
; and a pixel electrode
215
disposed on the polymer resin film
214
, as shown in FIG.
34
. The surface of the pixel electrode
215
has a continuously undulating configuration.
To form the reflector
210
, the following method has been used (FIGS.
35
). First, as shown in
FIG. 35A
, a resist film
212
made of a photosensitive resin is coated on the substrate
211
by spin coating and pre-baked at a specified processing temperature. Subsequently, the resist film
212
is exposed to light by using a photomask
213
positioned thereabove, as shown in FIG.
35
B. Then, development is performed by using a developing solution to form the projecting portions
212
a
and
212
b
having different heights on the substrate
211
, as shown in FIG.
35
C. Subsequently, a heat treatment is performed by heating the projecting portions
212
a
and
212
b
for one hour at a specified temperature, as shown in FIG.
35
D. The heat treatment rounds off the respective angular edge portions of the projecting portions
212
a
and
212
b
to form projecting portions
212
a
and
212
b
with rounded edge portions. Then, as shown in
FIG. 35E
, a polymer resin is spin-coated on the substrate
211
after the heat treatment to form the polymer resin film
214
. Finally, the pixel electrode
215
is formed by sputtering on the polymer resin film
214
(FIG.
35
F).
On the other hand, Japanese Unexamined Patent Publication No. HEI 9-292504 disclosed that, if the angle formed between an extremely small surface at the surface of a pixel electrode having a projecting and depressed configuration and a substrate surface is defined as a slope angle, the reflecting properties of a reflector, i.e., the reflectance and brightness thereof in a direction normal to a substrate, are determined by the slope angle distribution.
However, since the conventional reflector has formed the projecting and depressed configuration by forming the projecting portions by using the photoresist and melting and rounding the projecting portions with the application of heat, the configuration is determined by the roundness of the projecting portions shaped naturally by the heat-melting process so that it is difficult to precisely control the configuration. It is therefore evident that the slope angle distribution of the projecting portions has not been produced actually such that specified reflecting properties are provided. As a result, the light reflected by the conventional reflector in the regular reflection direction is increased so that brightness in the viewing angle direction is insufficient
Karasawa Takeshi
Kawaguri Mariko
Nishiyama Seiji
Wakita Naohide
Yamanaka Yasuhiko
Chowdhury Tarifur R.
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel LLP
Sikes William L.
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