Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-01-23
2004-11-09
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S119000, C349S102000, C349S113000
Reexamination Certificate
active
06816217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to transflective liquid-crystal display devices of the super twisted nematic (STN) type, and more particularly, the present invention relates to a transflective liquid-crystal display device having excellent display features not only in a reflection mode but also in a transmission mode.
2. Description of the Related Art
Almost all portable phones and portable information terminals are currently equipped with a liquid crystal display device, and most of these portable electronic apparatuses are currently equipped with a transflective liquid-crystal display device.
Known transflective liquid-crystal display devices, either of the active matrix type or the passive matrix type, are liquid crystal display devices having an external transflector and having a structure in which one of a pair of mutually opposing glass substrates (i.e., the substrate away from the observer) sandwiching a liquid crystal layer therebetween has a transflective sheet, a retardation film, and a polarizer on the lower surface thereof in this order, and the other glass substrate (i.e., the substrate close to the observer) has another retardation film and another polarizer on the upper surface thereof in this order.
Since developments to make color displays and requirements for higher density of display pixels, in particular, cause the above liquid crystal display devices to suffer from blurred display problems due to parallax, color mixing with unwanted colors, and the like, a liquid crystal display device having a built-in transflector, where the transflector is provided on the inner surface of one of the pair of glass substrates (i.e., the substrate away from the observer), has been mainly used.
FIG. 9
illustrates a partial sectional structure of the known liquid crystal display device having a built-in transflector. This transflective liquid-crystal display device has a pair of glass substrates
71
and
72
and a transflector
75
, on the upper surface of the lower glass substrate
71
(away from the observer ob), formed by a layer
73
having a concave-convex upper surface so as to provide a diffuse reflection and a high-reflectivity film
74
which is made of Al-based or Ag-based metal film, or the like, and which is stacked on the layer
73
. Furthermore, the transflector
75
has a color filter layer
76
, a planarizing layer
77
, transparent electrodes
78
a
, and an alignment film
79
a
formed on the upper surface thereof. The foregoing layer
73
having a concave-convex upper surface has fine concavities and convexities formed in a random manner by treating the upper surface of a transparent substrate such as a glass substrate by sand blasting, etching, or the like. Also, the high-reflectivity film
74
formed on the foregoing layer
73
has fine concavities and convexities
74
c
on its surface, whose sectional shape exhibits a continuous curve having continuous slopes.
While the lower glass substrate
71
has such a transflector, the upper glass substrate
72
(close to the observer ob) has transparent electrodes
78
b
and an alignment film
79
b
formed on the lower surface thereof so as to serve as a counter substrate. The substrate
71
with the transflector and the counter substrate
72
are bonded to each other with a sealant having a loop-like shape in plan view (not shown), and a liquid crystal layer
80
is formed by injecting liquid crystal inside and sealing it in the space enclosed by the pair of glass substrates
71
and
72
and the sealant, so as to provide a liquid crystal cell
81
. The upper and lower alignment films
79
b
and
79
a
are aligned so that the alignment directions of liquid crystal molecules in the liquid crystal layer
80
are twisted by about 220 to 250 degrees.
Also, the liquid crystal cell
81
has an optical film
82
b
, made of at least one retardation film, and a polarizer
83
b
stacked on the upper surface thereof (close to the observer ob) in that order. In addition, the liquid crystal cell
81
has an optical film
82
a
, formed by a plurality of retardation films, and a polarizer
83
a
stacked on the lower surface thereof (away from the observer ob) in that order. Furthermore, a backlight unit
100
is disposed below the polarizer
83
a.
The backlight unit
100
is formed by a transparent light guide plate
101
, a reflecting tube
103
which has a U-shaped cross section and which is disposed so as to oppose one of the side surfaces of the light guide plate
101
, a white light source
102
, such as a cold cathode fluorescent lamp (CCFL), a white light emitting diode, or the like, housed in the reflecting tube
103
, and a reflecting plate
104
disposed on an external surface (the lower surface in the figure) of the light guide plate
101
.
The transflective liquid-crystal display device having the above-mentioned backlight unit
100
is used as, for example, a display portion of a portable phone, and the display portion is used by switching between a reflection mode and a transmission mode, wherein, in the reflecting mode, the reflective liquid-crystal display device uses sunlight or external light as a light source and, in the transmission mode, the transmissive liquid-crystal display device uses the backlight unit
100
as a light source.
The transflector
75
exhibiting the foregoing diffuse reflection has the above-described fine concavities formed in a random manner so as to provide a reflected luminance characteristic, shown by a curve (
1
) in
FIG. 10
, which exhibits an approximately symmetric distribution with respect to the angle of its specular reflecting direction (an approximate Gaussian distribution), or by another curve (
2
) in
FIG. 10
which exhibits a combined distribution in which the above distribution is added with its specular reflection component. In the transflector
75
having the diffuse reflection exhibiting the foregoing approximately symmetric distribution (approximate Gaussian distribution), the metal thin film high-reflectivity film
74
formed on the foregoing layer
73
has the fine concavities and convexities
74
c
formed in a random manner on the surface thereof, as shown in
FIG. 14
, whose sectional shape exhibits a continuous curve having continuous slopes, that is, joining portions (boundaries)
74
d
between adjacent concavities are formed so as to be convex curves. In the transflector
75
having the diffuse reflection exhibiting the foregoing combined distribution, the foregoing layer
73
has a flat portion formed at a part of the fine concavities formed on the upper surface thereof so that the metal thin film on the flat portion has a reflection characteristic.
FIG. 11
illustrates a method for measuring the reflected luminance characteristic of the transflector shown in FIG.
10
. With this method, when the upper surface of the transflector
75
is irradiated with incident light (external light) L
1
at an incident angle &thgr;
1
(an angle from the normal H), a photo detector
105
detects reflected light R
1
, which is part of the incident light L
1
reflected at the foregoing surface, at an acceptance angle &thgr;
a
from the normal H (0°). A curve (
7
) in
FIG. 13
shows the measured relationship between the reflected luminance vs. an acceptance angle, measured by varying the acceptance angle &thgr;
a
from the normal H (0°) to, for example, 60° while the angle &thgr;
1
, which indicates the specular reflecting direction with respect to the surface of the transflector, is set as a center angle.
An example reflector having transflectivity and used in the transflective liquid-crystal display devices is a) the transflector
75
using the metal thin film (high-reflectivity film)
74
with a film thickness of 5 to 40 nm, as shown in
FIG. 9
, so as to provide an appropriate transmittivity in the visible light region; b) a transflector having a plurality of apertures in a metal film; or the like.
FIG. 12A
illustrates a partial sectional structure of another example liquid-crystal display device having the foregoi
Alps Electric Co. ,Ltd.
Ton Toan
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