Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-12-26
2004-09-07
Qi, Mike (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S114000, C349S146000, C359S529000, C359S530000
Reexamination Certificate
active
06788366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device including a corner cube array.
2. Description of the Related Art
A reflective liquid crystal display device for conducting a display operation by utilizing ambient light as its light source has been known in the art. Unlike a transmissive liquid crystal display device, the reflective liquid crystal display device needs no backlight, thus saving the power for light source and allowing the user to carry a downsized battery. Also, the space to be left for the backlight in a transmissive device or the weight of the device itself can be saved. For that reason, the reflective liquid crystal display device is not only effectively applicable to various types of mobile electronic units that should be as lightweight and as thin as possible but also allows the use of a battery of an increased size when a unit including the reflective display device is designed to have the same size or weight as a unit including the transmissive device. This is because the space to be left for a backlight in the transmissive device can be used for other purposes in the reflective display device. Thus, the reflective liquid crystal display device is expected to increase the longest operating time of those units by leaps and bounds.
Also, an image displayed by a reflective liquid crystal display device has a better contrast than an image displayed by a display device of any other type even when the display device is used outdoors in the sun. For example, when a CRT, i.e., a self-light-emitting display device, is used outdoors in the sun, the contrast ratio of an image displayed thereon decreases considerably. Likewise, even a transmissive liquid crystal display device, subjected to low reflection treatment, also displays an image at a significantly decreased contrast ratio when the device is operated in an environment in which the ambient light is much intenser than the display light (e.g., in direct sunshine). On the other hand, a reflective liquid crystal display device increases the intensity of the display light proportionally to the quantity of the ambient light, thus avoiding the significant decrease in contrast ratio. For that reason, a reflective liquid crystal display device can be used particularly effectively in mobile electronic units that are often used outdoors, e.g., cell phones, notebook computers, digital cameras and camcorders.
Even though the reflective liquid crystal display devices have these advantageous features that are very useful in various applications, the reflective devices currently available are not fully satisfactory yet in terms of their contrast ratio in dark places, definition, and full-color and moving picture display capabilities, for example. Thus, the development of more practically useful, reflective color liquid crystal display devices is awaited.
A technique of combining a scattering type liquid crystal display mode and a retroreflector is one of known measures to improve the display performance of such a reflective color liquid crystal display device. A conventional reflective liquid crystal display device of such a type will be described with reference to FIG.
14
.
As shown in
FIG. 14
, the reflective liquid crystal display device
900
includes a transparent front substrate
1
, including color filters
9
and a counter electrode
8
thereon, and a rear substrate
2
, which is disposed so as to face the front substrate
1
. A scattering type liquid crystal layer
3
, which switches between a scattering state and a transmitting state, is provided between these substrates
1
and
2
.
On one surface of the rear substrate
2
, thin-film transistors (TFTs, not shown) as switching elements, a retroreflector
5
, transparent pixel electrodes
50
and so on are provided so as to face the liquid crystal layer
3
. By controlling the voltage to be applied to the liquid crystal layer
3
by way of the TFTs and pixel electrodes
50
, each pixel region of the liquid crystal layer
3
can be switched from its scattering state into its transmitting state, or vice versa.
The retroreflector
5
has a reflective film
5
a
with a predetermined surface shape, which is covered with a planarized layer
5
b
. The pixel electrodes
50
are provided on the planarized layer
5
b
. The predetermined surface shape of the reflective film
5
a
is defined by a great number of unit elements, which are arranged in a regular pattern at a pitch that is smaller than that of the color filters
9
. Each of the unit elements is defined by three planes that are opposed substantially perpendicularly to each other. By using the retroreflector
5
having such a configuration, a light ray that has been incident onto this display device
900
can be reflected back toward its source.
Hereinafter, it will be described with reference to
FIGS. 15A and 15B
how this reflective liquid crystal display device
900
operates.
FIGS. 15A and 15B
schematically illustrate the black and white display modes of the display device
900
.
As shown in
FIG. 15A
, while the liquid crystal layer
3
is controlled to exhibit the transmitting state, an incoming light ray
54
, which has been emitted from an external light source
52
, is transmitted through the liquid crystal layer
3
and then reflected back by the retroreflector
5
toward its light source
52
as indicated by the arrow
60
. Thus, the light ray
54
that has been emitted from the light source
52
does not reach the eyes of a viewer
56
. In such a state, the image reaching the eyes of the viewer
56
from this display device
900
is the image of his or her own eyes. In this manner, the “black” display mode is realized.
On the other hand, while the liquid crystal layer
3
is controlled to exhibit the scattering state, the incoming light ray
54
that has been emitted from the light source
52
is scattered and reflected by the liquid crystal layer
3
as indicated by the arrows
62
in FIG.
15
B. That is to say, the retroreflector
5
reflects the incoming light ray
54
not just toward its light source
52
but also toward many other directions. As a result, a portion of the incoming light ray
54
reaches the eyes of the viewer
56
. In this manner, the “white” display mode is realized.
Unlike a twisted nematic (TN) mode liquid crystal display device, for example, the reflective liquid crystal display device
900
, conducting a display operation under such operating principles, can display the colors black and white without using any polarizer. Using no polarizers, this reflective liquid crystal display device
900
is not affected by a decreased optical efficiency, which is normally unavoidable when polarizers are used, and can display a highly bright image thereon. However, to get a high contrast ratio realized by this reflective liquid crystal display device
900
, it is important to maximize the retro-reflectivity of the retroreflector
5
and thereby minimize the amount of unwanted reflected light reaching the viewer's eyes in the black display mode.
A corner cube reflector, which is implemented as an array of corner cubes, is one of known retroreflectors having highest retro-reflectivities. In the corner cube reflector, each of those corner cubes is made up of three planes that are opposed substantially perpendicularly to each other and has a shape corresponding to one corner of a cube. Reflective liquid crystal display devices using a corner cube array of a very small size (which will be herein referred to as a “micro corner cube array (MCCA)”) as their retroreflector are disclosed, for example, in U.S. Pat. No. 5,182,663 and Japanese Patent Application No. 2001-090908 that was filed by the applicant of the present application. The MCCA may be formed by the manufacturing processing step of etching the surface of a crystalline substrate anisotropically (see Japanese Patent Application No. 2001-306052 that was also filed by the applicant of the present application).
The conventional reflective liquid crystal display device including t
Fujiwara Sayuri
Ihara Ichiro
Minoura Kiyoshi
Sawayama Yutaka
Taniguchi Koji
Nixon & Vanderhye P.C.
Qi Mike
Sharp Kabushiki Kaisha
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