Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-04-18
2003-08-12
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S113000, C349S117000, C349S096000
Reexamination Certificate
active
06606139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device including a reflector, and a portable electronic apparatus. More particularly, the present invention relates to a liquid crystal display device which has a viewing angle property that allows a display to appear brighter when a viewer looks at the display from a direction close to a direction of a normal line with respect to a display surface of the liquid crystal display device than when the viewer looks at the display from other viewing angles; and a portable electronic apparatus including at its display section the liquid crystal display device with such a viewing angle property.
2. Description of the Related Art
In general, liquid crystal display devices are called semi-transmissive liquid crystal display devices or transmissive liquid crystal display devices, which include backlights, or reflective liquid crystal display devices, depending upon the form of display of the liquid crystal display devices. To display images, reflective liquid crystal display devices use only outside light, such as sunlight or light from indoor illumination sources, and, thus, do not use a backlight. Reflective liquid crystal display devices are frequently used in, for example, portable information terminals that are under constant stress to be made thinner and lighter and to have decreasing power consumption.
When semi-transmissive liquid crystal display devices are in an environment that does not provided sufficient outside light, a backlight is turned on for operation in a transmission mode. On the other hand, when semi-transmissive liquid crystal display devices are in an environment that provides sufficient outside light, the backlight is not turned on, so that they operate in a reflection mode thereby saving power. Semi-transmissive liquid crystal display devices are frequently used in portable electronic apparatuses, such as cellular phones or notebook-size personal computers (PC).
FIG. 12
is a sectional view of an example of a related transflective liquid crystal display device.
In the general structure of the transflective liquid crystal display device, a reflection mode STN (super-twisted nematic) liquid crystal cell
72
, a forward scattering plate
90
, an upper retardation plate
73
b
, and an upper polarizing plate
74
are placed upon each other on a lower retardation plate
73
a
of a reflective plate
71
in that order from the side of the lower retardation plate
73
a
; and a backlight
95
, serving as a light source, is provided below the reflective plate
71
. The reflective plate
71
has a lower polarizing plate
70
and the lower retardation plate
73
a
provided thereat.
In the general structure of the liquid crystal cell
72
, a lower glass substrate
75
, a color filter
76
, a lower transparent electrode layer
78
, a lower alignment film
79
, an upper alignment film
80
disposed so as to be separated from and to oppose the lower alignment film
79
, an upper transparent electrode layer
81
, and an upper glass substrate
82
are placed upon each other in that order from the side of the lower polarizing plate
70
. A super-twisted nematic liquid crystal layer
83
is disposed between the lower and upper alignment films
79
and
80
. An overcoat layer (not shown), formed of silica or acrylic resin, is provided between the color filter
76
and the lower transparent electrode layer
78
.
The reflective plate
71
has an Al film whose surface is in a specular state, and has holes
71
a
for passing light from the backlight
95
when the backlight
95
is used.
The retardation plates
73
a
and
73
b
are provided to prevent coloring of the display into blue or yellow by compensating for phase differences of light that passes through the STN liquid crystals.
The forward scattering plate
90
is causes the incident light to be reflected not only in a specular reflection direction by the surface of the reflective plate
71
, but also in a direction close to the specular reflection direction by the surface of the reflector
71
. The forward scattering plate
90
achieves this by scattering light (outside light) passing through the upper polarizing plate
74
and the upper retardation plate
73
b
and incident upon the forward scattering plate
90
towards the liquid crystal cell
72
.
FIG. 13
illustrates another example of a related transflective liquid crystal display device.
In the general structure of the transflective liquid crystal display device, a first retardation plate
173
a
, a second retardation plate
173
b
, and a polarizing plate
174
are placed upon each other on a reflection mode STN (super-twisted nematic) liquid crystal cell
172
in that order from the side of an upper glass substrate
182
; and a backlight
195
, serving as a light source, is provided below the liquid crystal cell
172
.
In the general structure of the liquid crystal cell
172
, a lower glass substrate
175
, a reflector
171
, an overcoat layer
171
c
, a color filter
176
, an overcoat layer
177
a
, a lower transparent electrode layer
178
, a lower alignment film
179
, an upper alignment film
180
disposed so as to be separated from and to oppose the lower alignment film
179
, a topcoat layer
177
b
, an upper transparent electrode layer
181
, and an upper glass substrate
182
are placed upon each other in that order.
Many minute bumpy portions (recesses
171
e
in
FIG. 13
) are formed adjacent each other in an irregular manner at a reflective surface of the reflector
171
. The bumpy portions can be formed by, for example, conventional photolithography methods. In one such method, a surface of a resin base material
171
a
, such as a photosensitive resin layer, is irradiated with light through a mask pattern, the exposed resin is developed to form many minute adjacent spherical recesses, and the surface of the resin base material
171
a
having the spherical recesses is subjected to evaporation or plating using, for example, aluminum or silver in order to form a metallic film
171
b
having the bumpy portions (the recesses
171
e
).
The metallic film
171
b
can be made thin (to a thickness of the order of 30 nm) so that light from the backlight
195
can pass therethrough when the transflective liquid crystal display device is in a transmission mode.
The inside surfaces of the recesses
171
e
are spherical, and have an inclination angle distribution in a range of from −20 degrees to +20 degrees and a depth within a range of from 0.1 &mgr;m to 3 &mgr;m. Distances between the recesses
171
e
are set so that pitches between adjacent recesses (center-to-center distance) differ within a range of from 5 &mgr;m to 50 &mgr;m.
To achieve satisfactory display performance of a liquid crystal display device, it is ordinarily necessary for factors such as (1) resolution, (2) contrast, (3) brightness of a screen, (4) brightness of color, and (5) visibility (viewing angle wideness) to be satisfactory.
As shown in
FIG. 14
, a liquid crystal display device which is incorporated in an apparatus which is used with its display surface inclined, such as a portable information terminal including a cellular phone or a notebook-size personal computer, is frequently viewed from a direction close to a normal line direction P with respect to the display surface. More particularly, the information terminal is frequently viewed from a direction within a range of about 10 degrees from the normal line direction P. In general, an angle &thgr; between a main viewing direction &agr; when a viewer (user) views the display surface (screen) and the normal line direction P is frequently within a range of from about 0 degrees to about 20 degrees.
FIG. 14
illustrates a state in which a cellular phone including a display section
100
which comprises a liquid crystal display device and which is provided in a body
105
is being used. In
FIG. 14
, reference character P denotes the normal line with respect to the display surface of the display section
100
, reference character
Kano Mitsuru
Moriike Tatsuya
Yoshii Katsumasa
Alps Electric Co. ,Ltd.
Chowdhury Tarifur R.
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