Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-03-09
2002-06-18
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000, C349S051000
Reexamination Certificate
active
06407784
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a reflection type liquid crystal display and a method of fabricating the same.
2. Description of the Related Art
A reflection type liquid crystal display includes a light-reflection plate therein, and reflects external lights entering the liquid crystal display, at the light-reflection plate. The thus reflected external lights are used as a light source. Hence, a reflection type liquid crystal display does not need backlight as a light source. For this reason, a reflection type liquid crystal display is generally adopted as a display in a portable terminal device such as a pager. A reflection type liquid crystal display is superior to a transmission type liquid crystal display with respect to power consumption, thickness, and weight.
A reflection type liquid crystal display includes a light-reflection plate therein, and reflects external lights entering the liquid crystal display, at the light-reflection plate. The thus reflected external light is used as a light source. Hence, a reflection type liquid crystal display does not need backlight as a light source. For this reason, a reflection type liquid crystal display is generally adopted as a display in a portable terminal device such as a pager. A reflection type liquid crystal display is superior to a transmission type liquid crystal display with respect to power consumption, thickness, and weight.
FIG. 1
is a cross-sectional view illustrating a structure of a conventional reflection type liquid crystal display.
The illustrated conventional liquid crystal display
10
is comprised of a lower substance
1
A, an upper substrate
1
B facing the lower substrate
1
A, and a liquid crystal layer
14
sandwiched between the lower and upper substrate
1
A and
1
B. For instance, the liquid crystal layer
14
contains GH liquid crystal. In this specification, the upper substrate
1
B is a substrate through which external lights pass and on which characters such as figures and letters are displayed by reflected external lights, and the lower substrate
1
A is a substrate at which external lights having passed through the upper substrate
1
B are reflected.
The lower substrate
1
A is comprised of a glass substrate
2
A, a thin film transistor
6
acting as an active matrix drive device, formed on the glass substrate
2
A, and having a reverse stagger structure, an interlayer insulating film
11
formed over the thin film transistor
6
and composed of polyimide, and a light-reflective electrode plate
24
in electrical connection with a source electrode
21
or a drain electrode
22
of the thin film transistor
6
, acting as a light-reflective plate and a pixel electrode.
The upper electrode
1
B is comprised of a glass substrate
2
B, a color filter
3
formed on the glass substrate
2
B, and a transparent electrode
4
formed over the color filter
3
.
In the illustrated reflection type liquid crystal display
10
, external light
15
pass through the glass substrate
2
B, the color filter
3
, the transparent electrode
4
, and the liquid crystal layer
14
, and are reflected at the light-reflective electrode plate
24
. The reflection type liquid crystal display
10
uses the thus reflected light
16
as a light source.
The reflection type liquid crystal display
10
is required to present bright and white display when a light is transmitted through the liquid crystal layer
14
. To meet with this requirement, it is necessary for the reflection type liquid crystal display
10
to reflect the external light
15
having passed through the upper electrode
1
B in various directions, outwardly through the upper electrode
1
B. Hence, the polyimide film
11
is designed to have raised and recessed portions at a surface thereof to thereby form similar raised and recessed portions at a surface of the light-reflective electrode plate
24
formed on the polyimide film
11
. A shape of the raised and recessed portions of the polyimide film
11
is a key for determining display performance of the reflection type liquid crystal display
10
.
A method of fabricating the reflection type liquid crystal display
10
is explained hereinbelow with reference to
FIGS. 2A
to
2
H. In
FIGS. 2A
to
2
H, the term “PR” means that photolithography is carried out in that step, and a figure at the head of the term “PR” means a total number of photolithography steps. For instance, “2PR” means that the second photolithography is carried out in the step illustrated in an associated Figure.
First, as illustrated in
FIG. 2A
, a gate electrode
17
is formed on a glass substrate
2
.
Then, as illustrated in
FIG. 2B
, an insulating film
18
, a semiconductor layer
19
, and a doped layer
20
are formed in this order over the glass substrate
2
.
Then, as illustrated in
FIG. 2C
, the semiconductor layer
19
and the doped layer
20
are patterned to thereby form an island on the insulating film
18
.
Then, as illustrated in
FIG. 2D
, a source electrode
21
and a drain electrode
22
are formed around the island to thereby fabricate a transistor.
Then, as illustrated in
FIG. 2E
, an insulating film
18
is deposited entirely over the product.
Then, an organic insulating film
25
is deposited entirely over the insulating film
18
, and is patterned so as to form raised and recessed portions
26
above a region where a light-reflective plate is to be formed, as illustrated in FIG.
2
F.
Then, as illustrated in
FIG. 2G
, there is formed a contact hole
23
reaching the source electrode
21
through the organic insulating film
25
and the insulating film
18
.
Then, as illustrated in
FIG. 2H
, the light-reflective electrode plate
24
is formed over the organic insulating film
25
so that the contact hole
23
is filled with the material of which the reflection type liquid crystal display
10
is composed.
As shown in
FIGS. 2A
,
2
C,
2
D,
2
F,
2
G and
2
H, photolithography is carried out six times in the method.
The method having been explained with reference to
FIGS. 2A
to
2
H is suggested in Japanese Patent Publication No. 61-6390, and by T. Koizumi and T. Uchida in Proceedings of the SID, Vol. 29, pp. 157, 1988.
In order to fabricate a reflection type liquid crystal display capable of presenting bright and high-grade display, it has been conventionally necessary to form a high-performance switching device and a high-performance reflective plate on a common insulating substrate. The formation of them on a common substrate requires carrying out a lot of steps for film deposition, photolithography steps, and etching steps. Accordingly, the conventional method of fabricating a reflection type liquid crystal display cannot avoid including a lot of fabrication steps, taking much time, and needing much cost.
Japanese Unexamined Patent Publication No. 6-75238 has suggested a method of fabricating a reflection type liquid crystal display, including the steps of fabricating a thin film transistor on a substrate, forming an organic insulating film entirely over the substrate and the transistor, concurrently forming a contact hole, and a raised portion, and forming a reflective electrode over the contact hole and the raised portion. A drain electrode of the transistor is electrically connected to the reflective electrode through the contact hole.
Japanese Unexamined Patent Publication No. 6-273800 has suggested a reflection type liquid crystal display. In the suggested reflection type liquid crystal display, a gate bus, a source bus, and a thin film transistor are formed on a substrate. An organic insulating film having raised portions is formed over the substrate, covering the thin film transistor therewith. A light-impermeable film is formed on the organic insulating film above the thin film transistor, and a reflective electrode is formed above a region other than the thin film transistor. A gap is formed between the reflective electrode and the light-impermeable film. An alignment film is formed over the product. A liquid crystal layer is sandwiched between the substrate
Kanou Hiroshi
Yamaguchi Yuichi
NEC Corporation
Qi Mike
Sikes William L.
Sughrue & Mion, PLLC
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