Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-01-10
2003-04-01
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C249S151000, C249S113000
Reexamination Certificate
active
06542214
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a reflection-type liquid crystal display device, more specifically, to a reflection-type color liquid crystal display device containing a color filter therein, capable of displaying in multiple colors.
BACKGROUND TECHNOLOGY
As a conventional reflection-type liquid crystal display device, a reflection-type liquid crystal display device of a monochrome display using a TN (twisted nematic) liquid crystal cell or an STN (super twisted nematic) liquid crystal cell, is mainly used.
For the growing demand of displaying in colors in recent years, however, reflection-type color liquid crystal display devices containing color filters therein have been vigorously developed.
The reflection-type liquid crystal display devices containing color filters therein are broadly classified into the following three types.
The first type is a reflection-type color liquid crystal display device using no polarizing films. There are several devices belonging to this type, one using Guest-Host liquid crystal in which a dichroic pigment or a black dye is mixed in a liquid crystal material to fill a liquid crystal cell with, another using polymer-dispersion liquid crystal in which a liquid crystal material is dispersed in a polymer, and so on. Since any one of them does not use a polarizing film, it is excellent in brightness but low in contrast, and thus it has not been realized for practical use yet.
The second type is a reflection-type color liquid crystal display device having a color filter provided in a liquid crystal cell of a typical monochrome liquid crystal display device using two polarizing films.
Since this type uses two polarizing films, it is excellent in contrast, but it has a disadvantage of a dark display as well as a problem that its chroma is not good because of occurrence of color mixture caused by a reflective layer provided outside its glass substrate.
The third type is a reflection-type color liquid crystal display device using one polarizing film and containing a reflective layer inside a liquid crystal cell.
This reflection-type color liquid crystal display device is excellent in chroma with little color mixture because light is reflected by an inner surface of the liquid crystal cell. Accordingly, the liquid crystal display devices of this type have been vigorously developed.
Hereinafter, the structure of the reflection-type color liquid crystal display device of this type will be briefly explained using FIG.
7
.
FIG. 7
is a schematic sectional view showing a part of the conventional reflection-type color liquid crystal display device considerably enlarged.
In this liquid crystal display device, a reflective layer
103
is first formed on a first substrate
101
which is a transparent glass substrate, and a color filter
104
composed of three color filters of red (R), green (G) and blue (B) is formed thereon. Further, a protective film
105
is formed on the color filter
104
, and many first electrodes
106
in a stripe-shape are formed thereon. The first electrodes
106
are extended to form row side wiring patterns
126
and row side input patterns
128
simultaneously.
On the other hand, many second electrodes
107
in a stripe-shape are formed on the lower surface of the second substrate
102
which is a transparent glass substrate. The second electrodes
107
are extended to form column side wiring patterns (not shown) and column side input patterns (not shown) simultaneously.
The first substrate
101
and the second substrate
102
are opposed such that the first electrodes
106
and the second electrodes
107
are perpendicular to each other, and coupled to have a predetermined gap therebetween with a seal
123
. Then, the gap between the two substrates
101
and
102
is filled with liquid crystal to form a liquid crystal layer
108
.
Thereby, a liquid crystal cell
100
is constituted in which the (STN) liquid crystal layer
108
is sandwiched between the two transparent substrates
101
and
102
.
Both the first electrodes
106
and the second electrodes
107
in the liquid crystal cell
100
are transparent electrodes made of indium tin oxide (ITO), and many electrodes are arranged side by side in directions perpendicular to each other to form pixels at respective intersections thereof. At a position corresponding to each pixel, each color filter of the color filter
104
is arranged in such an order of R, G, and B in both the directions perpendicular to each other.
Further, a row side driving IC
21
and a column side driving IC (not shown) are mounted, as liquid crystal driving ICs which are semiconductor integrated circuit devices (referred to as “IC”), at desired positions on the first substrate
101
and the second substrate
102
of this liquid crystal cell
100
, respectively. This is referred to as a chip-on-glass.
In this event, protruding electrodes (bumps)
21
a
serving as input/output terminals of the row side driving IC
21
are aligned with and bonded to wires of the row side wiring patterns
126
and the row side input patterns
128
with an anisotropic conductive adhesive
30
, and further the each protruding electrode
21
a
is electrically connected to each wire. As for the not shown column side driving IC, its each protruding electrode is similarly bonded to as well as electrically connected to each wire of the column side wiring patterns and the column side input patterns with an anisotropic conductive adhesive.
Finally, a retardation film
111
and a polarizing film
113
(absorption-type polarizing film) are provided outside the second substrate
102
to complete a liquid crystal display device.
However, the conventional reflection-type color liquid crystal display device configured as above has some problems described below.
First of all, since the reflective layer
103
needs to have a high reflectance, aluminum (Al) or silver (Ag) is used as its material. Both of them, however, have poor chemical resistance.
Therefore, in the case of using aluminum or silver as the reflective layer
103
, it is necessary to form a film for protecting aluminum or silver on its top surface. In other words, it is necessary to use aluminum or silver together with the protective film on its top surface as the reflective layer
103
.
Typically, a silicon oxide (SiO
2
) film is formed as the protective film by a sputtering method or a vacuum evaporation method, and further the formation of the aluminum film or the silver film on the first substrate
101
and the formation of the silicon oxide film thereon are sequentially performed in order to prevent the reflectance from decreasing due to oxidation of the surface of the aluminum film or the silver film.
The silicon oxide film has good compatibility with the color filter
104
which is to be formed thereon, and thus the color filter
104
can stably be formed thereon.
However, when silicon oxide exists on aluminum or silver, it is very difficult to pattern the reflective layer
103
because silicon oxide has excellent chemical resistance.
As countermeasures against this problem, it can be considered that the aluminum film or the silver film and the silicon oxide film are formed on the entire surface of the first substrate
101
as the reflective layer
103
.
This eliminates the need to pattern the reflective layer
103
. This makes it impossible, however, to observe the row side wiring patterns
126
and the row side input patterns
128
from the outside of the first substrate
101
because the reflective layer
103
is opaque.
Further, it is also impossible to observe the row side wiring patterns
126
and the row side input patterns
128
through the row side driving IC
21
because the row side driving IC
21
and the column side driving IC, which are semiconductor integrated circuit devices made of silicon, are opaque.
For this reason, it becomes impossible to align the protruding electrodes
21
a
on the lower surface of the row side driving IC
21
with the row side wiring patterns
126
and the row side input patterns
128
. As a result, accurate electrica
Citizen Watch Co. Ltd.
Dudek James
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