Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-10-24
2004-12-21
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S098000, C349S106000, C349S113000
Reexamination Certificate
active
06833892
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a liquid crystal display device and electronic apparatus. Particularly, the invention relates to a liquid crystal display device having a cholesteric liquid crystal layer as a reflective layer or a transflective layer, and presenting excellent visibility with a bright display and a wide viewing angle.
2. Description of Related Art
Reflective-type liquid crystal display devices can be applied in a variety of mobile electronic apparatus because they do not have a light source, such as a backlight, and thus they consume less power. Reflective-type liquid crystal display devices take advantage of ambient light, such as natural light or illumination light, but are difficult to view under dark conditions. Liquid crystal display devices have been proposed which use ambient light under light conditions as in an ordinary reflective-type liquid crystal display device, while presenting a display via an internal light source under dark conditions. This type of liquid crystal display device employs a reflective and transmissive display method. Depending on the ambient light level, the device switches between a reflective mode and a transmissive mode. The device presents a distinct display under dark conditions while saving power. In this specification, this type of liquid crystal display device is referred to as a “transflective-type liquid crystal display device.”
In one proposed transflective-type liquid crystal display device, a reflective layer, formed of a metal film of aluminum or the like and having slits (apertures), is arranged on the inner surface of a lower substrate (in this specification, one surface of the substrate facing the liquid crystal is referred to as an “inner surface”, and the other surface of the substrate opposite from the inner surface is referred to as an “outer surface”), and the reflective layer functions as a transflective layer.
FIG. 11
illustrates a related art transflective liquid crystal display device having this type of transflective layer.
The liquid crystal display device
100
includes liquid crystal cells including a liquid crystal
103
between a pair of transparent substrates
101
and
102
. A reflective layer
104
and an insulator
106
are laminated on the lower substrate
101
. A lower electrode
108
, which is an electrically conductive transparent layer fabricated of indium tin oxide (hereinafter referred to ITO), is formed on the insulator
106
. An alignment layer
107
is formed to cover the lower electrode
108
. On the other hand, a color filter
109
having color layers of R (red), G (green), and B (blue) is formed on the upper substrate
102
. A planarization layer
111
is laminated on the color filter
109
. Upper electrodes
112
, fabricated of electrically conductive transparent film, such as of ITO, is formed on the planarization layer
111
. An alignment layer
113
is then deposited to cover the upper electrodes
112
.
The reflective layer
104
is fabricated of a metal, having a high light reflectance, such as aluminum, and has a slit
110
to transmit light for each pixel. Through the slit
110
, the reflective layer
104
can function as a transflective layer (hereinafter, the reflective layer
104
is referred to as a “transflective layer”). Arranged on the outer surface of the upper substrate
102
are a forward diffuser
118
, a retardation film
119
, and an upper polarizer
114
in that order from the upper substrate
102
. Arranged on the outer surface of the lower substrate
101
are a ¼-wave plate
115
, and a lower polarizer
116
in that order from the lower substrate
101
. A backlight
117
(an illumination device) is arranged beneath the lower polarizer
116
below the bottom surface of the lower substrate
101
.
When the liquid crystal display device
100
shown in
FIG. 11
is used in a reflective mode under light conditions, external light, such as sunlight or illumination entering from above the upper substrate
102
, is transmitted through the liquid crystal
103
, is reflected from the surface of the transflective layer
104
on the lower substrate
101
, is transmitted through the liquid crystal
103
again, and then exits toward the upper substrate
102
. When the liquid crystal display device
100
is used in a transmissive mode under dark conditions, light emitted from the backlight
117
arranged below the lower substrate
101
is passed through the slit
110
of the transflective layer
104
, is transmitted through the liquid crystal
103
, and then exits toward the upper substrate
102
. These list rays contribute to image displaying in each mode.
In the transflective-type liquid crystal display device and the reflective-type liquid crystal display device, a metal film having a high light reflectance, such as aluminum or silver, has been used in the related art for the reflective layer or the transflective layer. A dielectric mirror can be formed of a laminate of dielectric thin films having different refractive indices, a reflective cholesteric plate formed of a cholesteric liquid crystal, or a reflective hologram plate using a hologram element is used for the reflective layer in the reflective-type liquid crystal display device. These reflective plates not only reflect light, but also have other functions.
In particular, the cholesteric liquid crystal exhibits a liquid crystal phase above a certain temperature (liquid crystal transition temperature), in which liquid crystal molecules take a cyclical helical structure configuration with a constant pitch. This structure has the property that the cholesteric liquid crystal selectively reflects light having a wavelength coinciding with the helical pitch thereof while transmitting light having other wavelengths. The helical pitch is controlled by the intensity of ultraviolet light or temperature at the curing of the liquid crystal. The color of reflected light is localized, and the cholesteric liquid crystal is thus used as a reflective-type color filter.
If a plurality of cholesteric liquid crystal layers reflecting light rays of different colors are laminated, the cholesteric liquid crystal layers function as a reflective plate that reflects white light.
The reflective plate using the cholesteric liquid crystal has the characteristic functions as described above. In comparison with the widely used metals in the related art, the cholesteric liquid crystal accomplishes a very bright and pure-color display. The reflective plate using the cholesteric liquid crystal can be used to enhance image quality on a reflective-type or transflective-type liquid crystal display device.
SUMMARY OF THE INVENTION
When a reflective cholesteric plate is used as a reflective layer to enhance the image quality on a reflective-type liquid crystal display device, a viewing angle of the screen is narrow compared with a related art display using a metal layer. Since the reflective cholesteric plate exhibits a sharp directivity in reflected light beams, a display much brighter than a related art display is obtained when a user views the screen of the liquid crystal display device within a limited narrow angle range. When a user changes the user's viewing position, the screen suddenly becomes darker.
In a related art transflective liquid crystal display device shown in
FIG. 11
, the user views the display regardless of the presence or absence of ambient light. The lightness level of the screen during the transmissive mode is significantly lower than that during the reflective mode. This is attributed to the fact that the display during the transmissive mode uses only half the light beams emitted from a backlight, that the display during the transmissive mode uses the light beams passed through the slits of the transflective layer, and that the ¼-wave plate and the lower polarizer are arranged on the outer surface of the lower substrate.
In the related art transflective liquid crystal display device, the display mode changes between during reflection and during transmission o
Caley Michael H
Oliff & Berridge
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