Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-01-22
2004-06-08
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06747718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a reflection-type liquid crystal display having a reflecting plate for reflecting out a light transmitted through a liquid crystal layer from an outside and a method for manufacturing a same.
2. Description of the Related Art
Reflection-type liquid crystal displays have been used mainly in a portable terminal because they can be made thinner, less power consuming, and lighter in weight than transmission-type ones. Specifically, a reflecting plate in the reflection-type liquid crystal display reflects an incident light transmitted from the outside, and it is therefore available as a light source for display, thus eliminating a necessity of a back-light.
A recent reflection-type liquid crystal display includes basically a liquid crystal of, for example, a TN (Twisted Nematic)-type, a single polarizing plate-type, a STN (Super Twisted Nematic)-type, a GH (guest host)-type, or a PDLC (Polymer Dispersion)-type, a Cholesteric-type, or alike, a switching element for driving the liquid crystal, and a reflecting plate provided inside or outside a liquid crystal cell. Such a typical reflection-type liquid crystal display employs an active matrix scheme which realizes high definition and high picture quality by using a TFT (TFT) or metal/insulator film/metal-structured diode (MIM) as the switching element and also has the reflecting plate attached thereto.
The following will describe a conventional liquid crystal display of the single polarizing plate-type with reference to FIG.
19
.
An opposed-side substrate
1
includes a polarizing plate
2
, a phase-difference plate
3
, a glass substrate
4
, a color filter
5
, and a transparent electrode
6
. A lower side substrate
7
includes, on the other hand, a glass substrate
8
, a reverse stagger-structured TFT
9
formed as a switching element on the glass substrate
8
, a protrusion shape
10
made up of a first insulating layer which provides an unevenly-structured base, a polyimide film
11
formed thereon as a second insulating layer, and a reflecting electrode
13
which is connected to a source electrode
12
of the TFT
9
and also which functions as a reflecting plate-and-pixel electrode.
Between the opposed-side substrate
1
and the lower side substrate
7
is located a liquid crystal layer
14
.
A reflected light
16
is utilized for display. The reflected light
16
is given by an incident light
15
from outside when it passes through the polarizing plate
2
, the phase-difference plate
3
, the glass substrate
4
, the color filter
5
, the transparent electrode
6
, and the liquid crystal layer
14
and then is reflected by the reflecting electrode
13
.
This reflection-type liquid crystal display needs to have such display performance that it would give bright and white display when the liquid crystal is in a light-transmitting state. To achieve this display performance, the incident light
15
transmitted in various orientations needs to be efficiently emitted to the outside. To do so, an uneven structure can be formed on the polyimide film
11
to thereby provide the reflecting electrode
13
located thereon with a light-scattering function. Therefore, the display performance of the reflection-type liquid crystal display largely depends on how to control the uneven structure of the reflecting electrode
13
.
The following will describe a conventional method for manufacturing a reflecting electrode used in the conventional reflection-type liquid crystal display with reference to FIG.
20
A and FIG.
21
J.
In steps for manufacturing a TFT, first a gate electrode
21
is formed on a glass substrate
20
(FIG.
20
A). Subsequently, a gate insulator film
22
, a semiconductor layer
23
, and a doping layer
24
are formed (FIG.
20
B). Subsequently, an island
25
of the semiconductor layer
23
and the doping layer
24
is formed (FIG.
20
C), thereby forming a source electrode
26
and a drain electrode
27
(FIG.
20
D). Next, a reflecting electrode
34
is formed.
In steps for manufacturing the reflecting electrode, first an organic insulator film
28
is formed which has photosensitivity (FIG.
20
E). Subsequently, protrusions
29
are formed by photolithography in a region for forming the reflecting electrode (
FIG. 20F
) and melted into a smooth protrusion shape
30
(
FIG. 21
G). Subsequently, the smooth protrusion shape
30
is covered with an organic insulator film
31
to form a further smoother uneven surface
32
(FIG.
21
H). Subsequently, to electrically connect the reflecting electrode to the source electrode of the TFT, a contact portion
33
is formed (FIG.
21
I), to then form a reflecting electrode
34
(FIG.
21
J). This method for manufacturing reflecting electrodes is disclosed for example in Japanese Examined Patent Application No. Sho 61-6390 and in Proceedings of the SID (Tohru Koizumi and Tatsuo Uchida, Vol. 29, p. 157, 1988).
FIG. 22
is a plan view of a pattern of the protrusions
29
in the FIG.
20
F. The following will describe the process with reference to FIG.
22
F.
Protrusions
29
are not in contact with each other, that is mutually isolated. The protrusions
29
are each extremely small, measuring 1-20 &mgr;m in diameter and 0.5-5.0 &mgr;m in height. Therefore, during a subsequent substrate washing process, a heating process, or a film forming process, adherence between the protrusions
29
and underlying layer may deteriorate, thus causing the protrusions
29
to problematically flake off.
With this, therefore, a desired uneven structure cannot be formed in a reflecting electrode region, so that a desired optical property cannot be obtained for the reflecting electrode. That is, such the reflection electrode, if used in the reflection-type liquid crystal display, would give dark display or irregularities in brightness.
To prevent flake-off of the protrusions, also, it may be suggested that a coupling material be applied under the protrusions
29
to improve adherence. Under and below the protrusions
29
, however, the TFT, the wiring lines, and a like are arranged, so that they may be adversely influenced by the coupling material, thus deteriorating reliability of the switching element. Therefore, the coupling material should not be used.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide a reflection-type liquid crystal display which prevents flake-off of protrusions which provide a base for the uneven structure of a reflecting electrode to thereby achieve high brightness and high definition display performance, and a method for manufacturing same.
According to a first aspect of the present invention, there is provided a reflection-type liquid crystal display including:
a transparent first substrate;
a transparent electrode provided on the transparent first substrate;
a second substrate;
an insulator film which is provided on the second substrate and also on a surface of which is formed an uneven structure;
a reflecting electrode which is provided on the insulator film in such a shape as reflecting the uneven structure; and
a liquid crystal layer sandwiched by a side of the transparent electrode formed on the first substrate and a side of the reflecting electrode provided on the second substrate;
wherein the insulator film includes a first insulating layer in which a large number of depressions are irregularly arranged which are isolated as surrounded by protrusions and a second insulating layer which covers the first insulating layer entirely.
In the foregoing first aspect, the depressions refer to portions where there is essentially no film thickness present and so may be called apertures, through-holes or a like instead.
Protrusions on the first insulating layer according to a prior art are not in contact with each other, that is, are isolated. Therefore, if some of all the protrusions have weaker adherence with the underlying layer, they easily flake off. The protrusions on the first insulating layer according to the first aspect are all connected in a network. T
Kanou Hiroshi
Kikkawa Hironori
Suzuki Teruaki
Yamaguchi Yuichi
Dudek James A.
NEC Corporation
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