Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-04-20
2002-09-17
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S138000, C349S147000, C430S020000
Reexamination Certificate
active
06452659
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device adopting ferroelectric liquid crystal capable of detailed displaying, particularly, in a large screen, and a manufacturing method the same.
BACKGROUND OF THE INVENTION
Conventionally, as a liquid crystal display device, a liquid crystal display device using STN (Super-Twisted Nematic) liquid crystal or TN (Twisted Nematic) liquid crystal has been known. In recent years, as a liquid crystal display device capable of highly detailed and large capacity displaying, a liquid crystal display device using ferroelectric liquid crystal has been getting an attention.
As disclosed in Appl. Phys. Lett. 36(1980) pp. 899-901 (N. A. Clark and S. T. Lagerwall), ferroelectric liquid crystal has desirable-characteristics. such as memory effect, high response, and wide viewing angle.
Further, as in the conventional liquid crystal display device of TN system. or STN system, ferroelectric liquid crystal is capable of highly detailed and large capacity displaying by the simple matrix system wherein two electrode substrates are faced each other. Note that, the electrode substrate has an arrangement wherein scanning electrodes and signal electrodes, respectively made of a transparent conducting film in stripes, are positioned in matrix. on a transparent substrate.
However, in the case of adopting the ferroelectric liquid crystal in the liquid crystal display device of simple matrix system, when a ferroelectric liquid crystal display device having a large screen with a highly detailed image is manufactured by providing the stripe electrodes which are made of only the transparent conducting film, the electrode resistance is increased as the stripe electrodes are extended in the lengthwise direction in accordance with the increased displaying area. As a result, driving problems are generated such as generation of heat, delaying of a signal, and rounding of a signal wave which is applied to the pixel region.
Note that, since the conventional liquid crystal display device of TN system or STN system adopts the multi-plexing driving wherein a high contrast image is formed by scanning of a plurality of frames by application of a periodic driving voltage, a problem of lowering of displaying due to the delaying effect of the applied-voltage is not presented. However, in the ferroelectric liquid crystal display device, since it is required that a high contrast image be formed by scanning of a single frame, the delaying effect of the applied voltage becomes a problem.
For the described reason, in the case of adopting a larger screen in the ferroelectric liquid crystal display device, it has been a conventional practice to adopt a method in which the entire electrode resistance is lowered by providing metal electrodes made of a low resistant metal in the lengthwise direction of the scanning electrodes and the signal electrodes. It is required that the metal electrodes are formed along the stripe transparent electrodes (scanning electrodes or signal electrodes) in the lengthwise direction, and that the metal electrodes are electrically connected to the stripe transparent electrodes.
As a first method for forming such metal electrodes, a method for forming the stripe transparent electrodes on a transparent substrate, and then forming the metal electrodes which are electrically connected to the transparent electrodes is available. Specifically, the following methods are available. (1) As shown in
FIG. 8
, a method for forming metal electrodes
103
on stripe transparent electrodes
102
formed on a transparent substrate
101
, along an edge
102
b
in the lengthwise direction on the upper surface
102
a
of the transparent electrodes
102
, (2) as shown in
FIG. 9
, a method for forming the metal electrodes
103
on the stripe transparent electrodes
102
formed on the transparent substrate
101
, along the edge
102
b
in the lengthwise direction on the upper surface
102
a
of the transparent electrodes
102
such that the metal electrodes
103
protrude from the edge
102
b
to a side surface
102
c
of the transparent electrodes
102
(Japanese Unexamined Patent publication No. 280724/1989 (Tokukaihei 1-280724)), and (3) as shown in
FIG. 10
, a method in which the stripe transparent electrodes
102
formed on the transparent substrate
101
are made contact with the metal electrodes
103
on an insulating film
104
via a through hall
105
provided on the insulating film
104
covering the transparent electrodes
102
(Japanese Unexamined Patent publication No. 280724/1989 (Tokukaihei 1-280724)).
However, in the case of adopting the first method, the metal electrodes
103
project out of the upper surface
102
a
of the transparent electrodes
102
or the upper surface of the insulating film
104
at least by the thickness of the transparent electrodes
102
or the insulating film
104
. Here, in the case where the ferroelectric liquid crystal display device is adopted in a large screen panel, it is required that the metal electrodes
103
, as a low resistant conducting film for suppressing delaying of the applied voltage, have a film thickness of not less than 0.1 &mgr;m, more preferably not less than 0.4 &mgr;m. Thus, the metal electrodes
103
project out of the upper surface of the transparent electrodes
102
or the insulating film
104
by at least 0.1 &mgr;m. Further, when adopted in a yet larger screen panel, the film thickness of the metal electrodes
103
is required to be thicker.
Also, in order to realize a surface-stabilized ferroelectric liquid crystal. display device, it is preferable that the gap between the facing electrode substrates is set in a range of substantially 1.0 &mgr;m to 3 &mgr;m. Thus, when adopted in a larger screen panel, a problem is presented that short-circuiting of the metal electrodes
103
projecting out of the upper surface of the transparent electrodes
102
or the insulating film
104
is likely to occur between the upper and lower electrode substrates facing each other.
Furthermore, since the metal electrodes
103
project out of the surface of the transparent electrodes
102
or the insulating film
104
, a step-difference is created where the metal electrodes
103
are provided. This presents a problem that the alignment of the liquid crystal is changed where the step-difference is created, and as a result, uniform displaying is not realized.
In order to solve the problems of the first method, the following second through fourth methods are available.
In the second method, stripe metal electrodes are formed on a transparent substrate, and transparent electrodes are formed thereon so as to be electrically connected to the metal electrodes. As the second method, for example, the following method is available. As shown in
FIG. 11
, after forming the metal electrodes
103
in stripes on the transparent substrate
101
, the transparent electrodes
102
are formed in stripes via the insulating film
104
so that the metal electrodes
103
and the transparent electrodes
102
are made contact with each other via the through hall
105
provided on the insulating film
104
(Japanese Unexamined Patent publication No. 63019/1990 (Tokukaihei 2-63019)). In the case of adopting the second method, compared with the case of adopting the first method, the thickness of the metal electrodes
103
can be made thicker, allowing the electrode resistance to be reduced further.
However, in the second method, it is required to provide a manufacturing step for forming the insulating film
104
between the metal electrode
103
and the transparent electrode
102
, and thereafter a step for forming the through hall
105
for connecting the metal electrodes
103
and the transparent electrodes
102
to the insulating film
104
. This increases the number of manufacturing steps.
Also, in the case of adopting the second method, a function of a black matrix is given to the metal electrodes
103
. When the metal electrodes
103
function as a black matrix, it is required that a region A (meshed region in
FIG
Akiyama Hisashi
Shigeta Mitsuhiro
Chowdhury Tarifur R.
Renner Otto Boisselle & Sklar
Sharp Kabushiki Kaisha
Sikes William L.
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