Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-09-10
2003-05-20
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S147000, C349S148000
Reexamination Certificate
active
06567148
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electrode substrate, in which wires reduce resistance of electrodes for applying voltage to a pixel so as to respond to a large-capacity and high-definition display, and a manufacturing method thereof, and further concerns a liquid crystal display element which is provided with the electrode substrate.
BACKGROUND OF THE INVENTION
Ferroelectric liquid crystal display has superior properties in memory, fast response, and a wide viewing angle. In addition, as for a liquid crystal display device using ferroelectric liquid crystal, when direct matrix method is adopted, in which stripe scanning electrodes and signal electrodes made of transparent conductive films are arranged in a matrix form on a substrate, it is possible to provide a display with a large capacity and high definition as compared with a TN(Twisted Nematic) and an SNT(Super-Twisted Nematic) liquid crystal display devices that also adopt a direct matrix method. This advantage of ferroelectric liquid crystal is described in “Applied Physics Letters 36, (1986) p.899-901” by N. A. Clark and S. T. Lagerwall.
However, as for ferroelectric liquid crystal adopted for a direct matrix method, when merely a transparent conductive film is used for forming the stripe electrodes so as to manufacture a ferroelectric liquid crystal display device having a large capacity and high definition, it is necessary to form long stripe electrodes in accordance with a wider display area, resulting in larger resistance on electrodes. Consequently, problems such as heat, delay of a signal, and a deformed waveform of a signal applied to a pixel area, tend to occur and affect a drive.
The conventional TN and STN liquid crystal display devices form a high contrast screen by adopting a plurality of frame scans which use a multiplexing drive for periodically applying driving voltage. Therefore, delay effect, which causes a delay in applying driving voltage, has hardly degraded display quality. However, recently, as for such a liquid crystal display device, in order to respond to the growing needs for a larger screen and faster response, influence of the delay effect cannot be ignored.
For this reason, when a larger screen is provided in the ferroelectric liquid crystal display device, a method has been adopted, in which low-resistance conductive wires such as a metal film are provided for reducing the entire electrode resistance.
The conductive wires are formed so as to conductively come into contact with the stripe electrodes along the length of the stripe electrodes. Meanwhile, as for the ferroelectric liquid crystal cell and the STN liquid crystal cell that need to be manufactured with a small cell gap, evenness on a substrate surface significantly affects liquid crystal alignment. Therefore, as for such a liquid crystal cell, it is necessary to obtain favorable evenness on the substrate. Hence, the conductive wires need to be arranged so as to realize favorable evenness on a substrate.
In order to form such conductive wires, the following four methods have been conventionally adopted:
A first method adopts a abrading operation as described in “NEPCON West '89, p426-p447, 1989”. This method forms conductive wires in accordance with the steps of FIGS.
13
(
a
) through
13
(
c
). Firstly, metal wires
103
(conductive wires) are formed in stripes on a substrate
101
, which is coated with polyimide
102
(FIG.
13
(
a
)). Next, on the substrate
101
, an insulating film
104
is formed so as to cover the metal wires
103
(FIG.
13
(
b
)). And then, merely bumps of the insulating film
104
, that are located on the metal wires
103
, are abraded so as to expose the upper surface of the metal wires
103
(FIG.
13
(
c
)). Further, a transparent conductive film is formed in stripes on the metal wires
103
.
This method makes it possible to increase the thickness of the metal wires
103
as well as to expose the upper surfaces of the metal wires
103
merely by abrading the insulating film
104
.
A second method adopts photolithography as described in “IEEE/CHMT '89, Japan IEMT Symposium, p128-131”. This method forms conductive wires in accordance with the steps of FIGS.
14
(
a
) through
14
(
d
). The metal wires
103
are formed into stripes on the substrate
101
(FIG.
14
(
a
)). Next, negative photoresist(polyimide negative photoresist) is made into a film so as to cover the metal wires
103
on the substrate
101
; thus, an insulating film
105
is formed (FIG.
14
(
b
)). And then, the insulating film
105
is partly removed on the metal wires
103
by photolithography which uses a photo mask
106
for exposing the upper surfaces of the metal wires
103
(FIG.
14
(
c
)).
As shown in FIGS.
15
(
a
) and
15
(
b
), the photolithography process adopts the photomask
106
which includes a plurality of small holes
106
b
on both sides of a stripe pattern
106
a
. This arrangement makes it possible to remove projecting portions
105
a
of the insulating film
105
, that are located on both sides of the metal wires
103
. Consequently, the surface of the insulating film
105
is evenly formed together with the upper surface of the metal wires
103
(FIG.
14
(
d
)). The small holes
106
b
make it possible to adjust the exposure amount so as to soften and remove merely the projecting portions
105
a
around the metal wires
103
.
This method makes it possible to form the thick metal wires
103
in the same manner as the first method. In addition, photolithography exposes the upper surfaces of the metal wires
103
.
As disclosed in Japanese Published Unexamined Patent Application No. 76134/1996 (Tokukaihei 8-76134, published on Mar. 22, 1996), a third method forms stripe conductive wires on a transparent substrate and fills UV(ultraviolet)cure resin between the conductive wires. This method forms conductive wires in accordance with the steps of FIGS.
16
(
a
) through
16
(
d
).
Firstly, a smoothing mold
108
, which has UV cure resin
107
applied thereon, is disposed so as to oppose the transparent substrate
101
on which the metal wires
103
are formed into stripes(FIG.
16
(
a
)). Next, the UV cure resin
107
is exposed to ultraviolet light from the back of the substrate
101
so as to form an insulating film having the same thickness as the metal wires
103
(FIG.
16
(
b
)). And then, the smoothing mold
108
is separated from the substrate
101
(FIG.
16
(
c
)), and transparent electrodes
109
are formed on the surface of the layer consisting of the metal wires
103
and the UV cure resin
107
(FIG.
16
(
d
)).
In this method, in the step of FIG.
16
(
b
), the smoothing mold
108
having the UV cure resin
107
applied thereon is pressed onto the substrate
101
having the metal wires
103
formed thereon, and then, the UV cure resin
107
is exposed to ultraviolet light; therefore, it is possible to achieve a preferable evenness of the insulating film including UV cure resin
107
.
As described in “J. Electrochem. Soc.; SOLID-STATE SCIENCE TECHNOLOGY August 1988, p2013-p2016”, a fourth method adopts a liquid-phase deposition film forming method(Liquid-phase deposition; LPD) of SiO
2
amorphous film. The LPD method uses solution of hydrosilicofluoric acid(H
2
SiF
6
:HF), and the chemical equilibrium of the solution is shifted to the deposition side of SiO
2
so as to form a film. This method forms conductive wires in accordance with the steps of FIGS.
17
(
a
) through
17
(
d
).
Firstly, a metallic material is formed into a film on the substrate
101
(FIG.
17
(
a
)), and the metallic material is patterned by using photoresists
110
so as to form the metal wires
103
(FIG.
17
(
b
)). Here, after the patterning operation, the photoresists
110
are not removed. And then, SiO
2
films
111
are formed between the metal wires
103
by using the LPD method(FIG.
17
(
c
)), the photoresists
110
are exfoliated from the metal wires
103
(FIG.
17
(
d
)). This method makes it possible to provide an even construction which has no projection or groove on the metal wires
103
and the S
Akiyama Hisashi
Itoh Nobuyuki
Kabe Masaaki
Kim Robert H.
Qi Mike
Renner Otto Boisselle & Sklar
Sharp Kabushiki Kaisha
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