Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-10-24
2004-09-21
Nguyen, Dung T. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S113000, C349S106000
Reexamination Certificate
active
06795148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to liquid crystal display devices and to electronic apparatuses. In particular, the invention relates to a structure of transflective liquid crystal display devices having excellent visibility, and which can display sufficiently bright images not only in a reflective display mode but also in a transmissive display mode.
2. Description of Related Art
Reflective liquid crystal display devices reduce power consumption because they do not have any light sources, such as a backlight. These devices have therefore been used for various portable electronic apparatuses or the like. However, since the reflective liquid crystal display devices use outside light, such as natural light or illumination light to display images, it is difficult to view the images in dark places. Accordingly, another type of liquid crystal display device has been proposed which uses outside light in bright places, as in the conventional reflective liquid crystal display devices, and uses an internal light source to make displayed images visible in dark places. Hence, this type of liquid crystal display device uses a display system serving as both a reflective display and a transmissive display. In this system, a reflective display mode or a transmissive display mode is selected according to the ambient brightness, thereby displaying clear images even in dark places while reducing power consumption. Hereinafter, this type of liquid crystal display device is referred to as a “transflective liquid crystal display device”, in this application.
A transflective liquid crystal display device has been proposed which has a reflecting layer having slits (apertures) to transmit light and formed of a metal, such as aluminum on the inner surface of a lower substrate (hereinafter, the liquid crystal side surfaces of substrates is referred to as “inner surfaces”, and the opposite surfaces are referred to as “outer surfaces”) and which allows the reflecting layer to serve as a transflective layer. In this liquid crystal display device, by providing the metallic film on the inner surface of the lower substrate, the parallax effect due to the thickness of the lower substrate is reduced. In particular, color mixture is prevented in a structure having color filters.
FIG. 13
shows an example of a related art transflective liquid crystal display device using the transflective layer.
The liquid crystal display device
100
has liquid crystal
103
held between a pair of transparent substrates
101
and
102
. A reflecting layer
104
and an insulating layer
106
are deposited on the lower substrate
101
. A lower electrode
108
is formed of a transparent conductive film, such as an indium tin oxide (hereinafter referred to as ITO) film, on the insulating layer
106
, and the lower electrode
108
is covered with an alignment layer
107
. On the other hand, on the upper substrate
102
, a color filter
109
including R (red), G (green), and B (blue) pigmented films are formed. A planarizing layer
111
is deposited on the color filter
109
. Upper electrodes
112
are formed of a transparent conductive film, such as an ITO film, on the planarizing film
111
, and the upper electrodes
112
are covered with an alignment layer
113
.
The reflecting layer
104
is formed of a metal having a high optical reflectivity, such as aluminum, and the reflecting layer
104
has a slit
110
to transmit light in each pixel. The slits
110
allow the reflecting layer
104
to serve as a “transflective layer” (therefore, hereinafter, the reflecting layer
104
is referred to as a transflective layer). In addition, the upper substrate
102
is provided with a front diffuser
118
, a retardation layer
119
, and an upper polarizer
114
on the outer surface thereof, in that order from the upper substrate
102
side. The lower substrate
101
is provided with a quarter wave plate
115
and a lower polarizer
116
on the outer surface thereof, in that order. Also, a backlight
117
(illumination device) is disposed under the lower surface of the lower substrate
101
, that is, under the lower polarizer
116
.
When the liquid crystal display device
100
shown in
FIG. 13
is used in a reflective mode in a bright place, outside light entering through the upper substrate
102
from above, such as sunlight or illumination light, passes through the liquid crystal
103
to be reflected at the surface of the transflective layer
104
on the lower substrate
101
, and then passes through the liquid crystal
103
again to be emitted to the upper substrate
102
side. On the other hand, when the liquid crystal display device
100
is used in a transmissive mode in a dark place, light emitted from the backlight
117
under the lower substrate
101
passes through the slits
110
of the reflecting layer
104
, and then passes through the liquid crystal
103
to be emitted to the upper substrate
102
side. This light contributes to displaying images in the respective modes.
In such a transflective liquid crystal display device, a metallic film having a high optical reflectivity, such as an aluminum or silver film, can be used as the reflecting layer. On the other hand, a dielectric mirror formed by alternately laminating dielectric thin layers having different refractive indexes, a cholesteric reflector using a cholesteric liquid crystal, a hologram reflector using a hologram element, can be used. These new types of reflectors not only serve as reflectors to reflect light, making use of the characteristics of the constituents thereof, but also have a particular function.
In particular, the cholesteric liquid crystal exhibits a liquid crystal phase at a specific temperature (liquid crystal transition temperature) or more, in which liquid crystal molecules are arranged in a regular helical manner with a constant pitch. This structure allows the cholesteric liquid crystal to selectively reflect only light having a wavelength corresponding to the pitch of the helix, and thus to transmit the other light. Since the pitch of the helix can be controlled by, for example, changing the ultraviolet light intensity or the temperature when the liquid crystal is hardened, the color of reflected light is locally changeable, and the cholesteric liquid crystal can therefore be used as a reflective color filter. Also, by laminating a plurality of cholesteric liquid crystal layers to selectively reflect light of different colors, the resulting laminate can serve as a reflector to reflect white light.
SUMMARY OF THE INVENTION
However, the related art transflective liquid crystal display device as shown in
FIG. 13
has a problem in that, while displayed images can be viewed, regardless of the presence or absence of outside light, the brightness of images in a transmissive mode is degraded a lot in comparison with in a reflective mode. This is because, in the transmissive mode, no more than substantially half of light emitted from the backlight is used to display images, and only the light passing through the slits of the transflective layer contributes to displaying images. This problem is also caused by the quarter wave plate and the lower polarizer disposed under the outer surface of the lower substrate and other reasons.
The related art transflective liquid crystal display device has two display modes which are used separately according to whether light is reflected or transmitted. In particular, when the light is transmitted, substantially half of light emitted from the backlight is absorbed by the upper polarizer, and thus only the rest half light is used to display images. Specifically, in a reflective mode, almost all of the linearly polarized light entering from the upper substrate side is used to display bright images. In contrast, in a transmissive mode, the light traveling from the lower surface of the liquid crystal layer toward the upper substrate side must be circularly polarized in order to display images as in the reflective mode. However, half of the circularly polarized light is adso
Okumura Osamu
Ozawa Kinya
Caley Michael H
Nguyen Dung T.
Oliff & Berridg,e PLC
Seiko Epson Corporation
LandOfFree
Liquid crystal display device and electronic apparatus... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display device and electronic apparatus..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device and electronic apparatus... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3211589