Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-02-25
2003-07-29
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06600535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflector incorporated in a reflective liquid crystal display device with no backlight, a method for fabricating the same, and a reflective liquid crystal display device incorporating the same.
2. Description of the Related Art
In recent years, liquid crystal display devices have been increasingly used in personal computers, TVs, word processors, video cameras, etc. There has been demands for further improvements of these appliances such as miniaturization, power-saving, cost reduction, etc. In an attempt to meet these demands, reflective liquid crystal display devices having no backlight which display images by reflecting ambient light incident thereupon have been developed.
In order to achieve bright display with a reflective liquid crystal display device having no backlight, it is important to efficiently utilize ambient light. Accordingly, a reflector incorporated in such a reflective liquid crystal display device plays a very important roll. It is thus necessary to design a reflector having the most suitable reflection characteristic and which efficiently utilizes ambient light incident upon the device from every direction, and to develop a technique for fabricating such a reflector with high accuracy and high reproducibility.
Japanese Laid-Open Patent Publication No 6-75238 discloses a reflective liquid crystal display device. The reflector incorporated in the liquid crystal display device includes convex/concave portions formed of a photosensitive resin and a film thinner than the convex/concave portions deposited over the convex/concave portions, thereby smoothing the surface of the reflector including the convex/concave portions. The reflector is used in the liquid crystal display device in combination with a guest-host mode (referred to as simply a “GH” mode hereinafter).
FIGS. 20G
to
20
L are top views each illustrating one of the fabrication steps for a conventional reflector
106
, whereas
FIGS. 20A
to
20
F are each cross-sectional views taken along the line A to A′ in FIGS.
20
G to
20
L, respectively. In
FIG. 20L
, dashed lines represent contour lines of the reflector
106
.
First, as shown in
FIGS. 20A and 20G
, a photosensitive resin is deposited on a glass substrate
101
so as to form a photosensitive resin layer
102
a
. Then, a photomask
103
including circular regions is placed over the glass substrate
101
as shown in
FIGS. 20B and 20H
. Then, the substrate is exposed to light and developed, thus forming cylindrical protrusions
102
b
on the substrate
101
as shown in
FIGS. 20C and 20I
. Then, the entire substrate is subjected to a heat treatment so that the protrusions
102
b are adequately melted and form smooth convex portions
102
c
as shown in
FIGS. 20D and 20J
. Then, a photosensitive resin is again deposited over the entire surface of the substrate
101
including the smooth convex portions
102
c
so as to form a photosensitive resin layer
104
thinner than the layer
102
a
, thereby obtaining a surface including smooth convex/concave portions as shown in
FIGS. 20E and 20K
. Finally, a thin metal film is deposited on the layer
104
so as to form a reflection film
105
as shown in
FIGS. 20F and 20L
. A conventional reflector
106
is thus fabricated.
As shown in
FIG. 20L
, the reflector
106
fabricated by the conventional fabrication process includes a lot of flat regions. The optical characteristic of the reflector
106
is such that, although no interference occurs, a large portion of light incident upon the reflector
106
is reflected to a direction of regular reflection. For example, when light is incident upon the conventional reflector
106
from a direction perpendicular thereto, a large portion of the light is reflected to the direction perpendicular to the reflector
106
which corresponds to the direction of the regular reflection. Accordingly, there is only a very limited range of directions in which high-intensity reflected light is obtained. In other words, with such a conventional reflector
106
, it is not possible to obtain high-intensity reflected light in -a wide range of directions. Therefore, when such a reflector is used in a reflective liquid crystal display device performing multi-color display, the brightness of display would not be sufficient for practical use.
Conventional liquid crystal display devices are produced without sufficient consideration for compatibility among the liquid crystal display mode, the color filter, and the reflector. Therefore, there are undesirable situations such as where the display is bright but with low contrast; the contrast is high but with low brightness; or the brightness and the contrast are both high but with a slow response rate, a high threshold voltage, or non-uniformity in display due to inferior orientation of the liquid crystal molecules.
In order to ensure the display quality required for practical use, the application of such a conventional reflective liquid crystal display device is limited to a black-and-white display or, at the best, a 4-color display. Thus, the growing demand for multi-color displays with the growing variety of information has not been satisfied.
In order to realize a multi-color display which can be practically used, the compatibility among the reflector, the liquid crystal display mode, the color filter, and other factors need to be considered while improving the reflection characteristic of the reflector. Unlike a transmission type liquid crystal display device provided with a backlight, the reflective liquid crystal. display device greatly depends upon ambient light. Thus, it is necessary to suitably design the optical characteristic and the convex/concave structure of the reflector, appropriately select a display mode from a number of display modes to best match the optical characteristic of the reflector, optimize various parameters of the display mode, and appropriately design a color filter. However, it has not been possible to realize a multi-color display even with these factors being optimized since the reflection characteristics of the reflector are not sufficient.
SUMMARY OF THE INVENTION
According to one aspect of this invention, a reflector includes a substrate, a plurality of convex/concave portions formed on the substrate, and a thin reflective film formed over the convex/concave portions. When light is incident upon the reflector at a first incident angle with respect to a normal direction thereof, an intensity of reflected light in a viewing angle range of about −45° to +45° with respect to a regular reflection direction of the incident light is about 60% or more of a reference intensity, where the reference intensity is an intensity of light which is incident upon a standard white plate at a second incident angle with respect to a normal direction thereof and is reflected to the normal direction.
In one embodiment of the invention, each of the convex/concave portions at least partially includes a continuous curved surface. A total area of the portions of the substrate whose inclination at a surface of the reflector is less than 2° accounts for about 40% or less with respect to a total area of the substrate.
In another embodiment of the invention, the convex/concave portions are formed of a photosensitive resin.
In still another embodiment of the invention, the convex/concave portions are formed of an inorganic oxide and a photosensitive resin.
In still another embodiment of the invention, the convex/concave portions are formed of minute particles and a photosensitive resin.
In still another embodiment of the invention, the convex/concave portions are formed by forming a plurality of cylindrical depressions in a photosensitive resin layer formed on the substrate and heating the plurality of cylindrical depressions.
According to another aspect of this invention, a method for fabricating a reflector including a substrate, a plurality of convex/concave portions formed on the substrate, and a thin reflective film f
Ban Mariko
Fujii Akiyoshi
Itoh Yasuhisa
Kimura Naofumi
Nakamura Kozo
Edwards & Angell LLP
Neuner George W.
Roos Richard J.
Sharp Kabushiki Kaisha
Ton Toan
LandOfFree
Reflector, method for fabricating the same and reflective... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reflector, method for fabricating the same and reflective..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reflector, method for fabricating the same and reflective... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3000842