Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-07-27
2002-11-12
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S147000
Reexamination Certificate
active
06480253
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device and a manufacturing method of the same, and it particularly relates to a ferroelectric liquid crystal display device having a large screen and being capable of high-definition display, as well as relates to a manufacturing method of the same.
BACKGROUND OF THE INVENTION
Ferroelectric liquid crystal has excellent properties such as excellent memory effect, high-speed response, and a wide visual angle, and in the case where it is applied to a display device of a simple matrix type, the display device becomes capable of high-definition large-capacity display (see N. A. Clark and S. T. Lagerwall, Appl. Phys. Lett., 36 (1980), pp. 899 (Date of Publication: Jun. 1, 1980)). An example of a conventional structure of a ferroelectric liquid crystal display device is shown in
FIG. 13
which is a cross-sectional view of the same.
The ferroelectric liquid crystal display device is provided with two glass substrates
112
a
and
112
b
. On the glass substrate
112
a
, a plurality of transparent signal electrodes
113
a
made of indium tin oxide (ITO) or the like are formed so as to be parallel with each other, on which a transparent insulating film
114
a
made of SiO
2
(silicon dioxide) or the like is formed.
On the glass substrate
112
b
facing the glass substrate
112
a
, transparent scanning electrodes
113
b
made of ITO or the like are formed so as to be parallel with each other in a direction crossing the direction of the signal electrodes
113
at a right angle, and the scanning electrodes
113
b
are also covered with a transparent insulating film
114
b
made of SiO
2
.
On the transparent insulating films
114
a
and
114
b
, alignment films
115
a
and
115
b
having been subjected to a uniaxial alignment processing such as a rubbing operation are formed, respectively. As the alignment films
115
a
and
115
b
, an organic polymer film such as a polyimide film, a nylon film, or a polyvinyl alcohol film, a SiO (silicon monoxide) rhombic vapor deposition film, or the like is used. In the case where an organic polymer film is adapted so as to be used as the alignment films
115
a
and
115
b
, such alignment processing as to align the liquid crystal molecules so as to be substantially parallel with respect to the electrode substrates is applied to the alignment films
115
a
and
115
b.
The glass substrate
112
a
on which the signal electrodes
113
a
, the transparent insulating film
114
a
, and the alignment film
115
a
are laminated in this order is hereinafter referred to as an electrode substrate
110
. Likewise, the glass substrate
112
b
on which the scanning electrodes
113
b
, the transparent insulating film
114
b
, and the alignment film
115
b
are laminated in this order is hereinafter referred to as an electrode substrate
111
.
The electrode substrates
110
and
111
are combined to each other with a sealing material
116
which is applied thereto except a part serving as an injection opening, through which subsequently ferroelectric liquid crystal
117
is injected into a space formed between the alignment films
115
a
and
115
b
. Then, the injection opening is sealed with the sealing material
130
.
The electrode substrates
110
and
111
thus assembled are sandwitched between polarization plates
118
a
and
118
b
which are arranged so that polarization axes thereof cross each other at a right angle. In the case where a display area is large, spherical spacers
119
are dispersely provided between the electrode substrates
110
and
111
so that the electrode substrates
110
and
111
are parallel with each other, resulting in that a uniform cell thickness is achieved.
The ferroelectric liquid crystal molecules
120
have spontaneous polarization
121
in a direction orthogonal to a direction of a major axis of the molecule
120
, as shown in FIG.
14
. Therefore, each of the ferroelectric liquid crystal molecules
120
moves along a surface of a conical locus
122
in response to a force proportional to a vector product of the spontaneous polarization
121
and an electric field which is generated by a voltage applied across the signal electrode
113
a
and the scanning electrode
113
b.
Therefore, to the eyes of an observer, the ferroelectric liquid crystal molecule
120
appears to switch between generator positions A and B in the conical locus
122
, as shown in FIG.
15
. Here, in the case where, for example, the polarization plates
118
a
and
118
b
are arranged so that a direction of the polarization axis of one of the polarization plates
118
a
and
118
b
agrees with the molecular major axis direction
138
a
of the molecule
120
at the position A and that a direction of the polarization axis of the other polarization plate agrees with a direction
138
b
, a dark field is obtained when the molecules
120
switch to the position A. A bright field is obtained due to birefringence when the molecules
120
switch to the position B.
Furthermore, respective alignment states of the ferroelectric liquid crystal molecules
120
in the positions A and B are equivalent in elastic energy. Accordingly, after the electric field by the voltage across the signal electrodes
113
a
and the scanning Helectrode
113
b
disappears, the alignment state, or the optical state, of the molecule
120
is maintained. This is a so-called memory effect of ferroelectric liquid crystal. The memory effect is a characteristic that the conventional nematic liquid crystal does not possess, and in combination with the high-speed response due to the spontaneous polarization, enables a display device using the ferroelectric liquid crystal to realize high-definition large-capacity display in a simple matrix arrangement.
On the other hand, the Japanese Publication for Laid-Open Patent Application No. 311213/1997 (Tokukaihei 9-311213, Date of Publication: Dec. 2, 1997) discloses the following manufacturing method: a micell colloid aqueous solution mainly consisting of transparent conductive particles, pigment particles, a surfactant, and a supporting electrolyte, in which the transparent conductive particles and the pigment particles are surrounded by the surfactant, is prepared by the wet electrolytic method, and the micell is broken by electrolysis so that the conductive particles and the pigment particles are separated and deposited on electrodes.
To realize moving picture display by means of a display device with a large screen, it is necessary to lower wire resistances of signal electrodes and scanning electrodes so as to reduce deformation of waveforms of applied voltages. In other words, for high-speed driving of a display device with a large screen, it is necessary to lower wire resistances so that waveforms of voltages applied to each pixel do not deform. A wire resistance required is determined by a capacitance of the display device and a pulse width of a driving waveform. More specifically, it is necessary to set the wire resistance low so as to fall in a predetermined range as shown in the Patent Application No. 361209/1997 (Tokuganhei 9-361209, corresponding to U.S. patent application Ser. No. 09/217,162) which the Applicant of the present invention has filed.
Therefore, metal wires are used as supplementary wires, but such an arrangement undergoes, apart from problems related to fine processing and adhesion to substrates, such problems as line defects, etch selectivity of metal or transparent electrodes (transparent conductive films), and flatness of a substrate.
Furthermore, there exist in transparent electrodes many projections which are caused by nodules of a target used in film formation and in turn cause disorder of alignment and vertical leakage (leakage between upper and lower transparent electrodes). The following description will explain these problems.
[Line Defects]
In the process of forming wires in a liquid crystal display device, dusts, defects in formed resist patterns, metal wiring defects, defects in formed transparent electrodes, etc. cause defects i
Akiyama Hisashi
Itoh Nobuyuki
Miyoshi Shuji
Shigeta Mitsuhiro
Tomikawa Masahiko
Renner , Otto, Boisselle & Sklar, LLP
Schechter Andrew
Sharp Kabushiki Kaisha
Ton Toan
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