Liquid crystal ITO connector having a metal layer

A liquid crystal apparatus includes a liquid crystal panel side electrode extending from a liquid crystal panel and an external circuit side electrode extending from an external circuit and connected to the liquid crystal panel side electrode for driving the liquid crystal panel, by using conductive material. The liquid crystal panel side electrode includes a laminated film made of an indium tin oxide film having a surface and a metal film on the surface. The metal film is selected from one of a molybdenum film and an aluminum film. The liquid crystal panel side electrode has a left portion of the metal film and an indium tin oxide film opening area, at a connection area between the liquid crystal panel side electrode and the external circuit side electrode. The indium tin oxide film of the liquid crystal panel side electrode is covered with the metal film over the entire surface thereof. The liquid crystal panel side electrode is formed in a stripe shape, and the left portion of the metal film of the liquid crystal panel side electrode at the connection area is formed to have a width 1/30 to 1/3 times as narrow as a width of the stripe.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a liquid crystal apparatus having an 
external drive circuit connected thereto. 
2. Related Background Art 
Conventionally, a liquid crystal panel and an external drive circuit are 
mechanically and electrically connected together by a widely known method 
whereby a connection electrode of a film carrier tape on which a drive IC 
for example is mounted, is positioned facing an indium tin oxide (ITO) 
electrode of a liquid crystal panel, and both of the electrodes are 
mechanically and electrically connected together by thermocompression 
bonding using an isotropic conductive adhesive agent made of resin 
particles coated with metal particles or metal plated. 
Another method is also known whereby a metal bump is formed on a connection 
electrode of a drive IC, and conductive paste or metal particles are 
interposed between the metal bump and the ITO electrode of a liquid 
crystal panel to mechanically and electrically connect together the metal 
bump and the ITO thin film. 
According to the conventional technique, the wiring resistance from the 
external drive circuit to the liquid crystal material mainly depends on 
the wiring resistance of the ITO electrode itself. 
A drive signal supplied to the liquid crystal material is subject to a 
delay .tau.=RC where R is a wiring resistance from the external drive 
circuit to the liquid crystal material, and C is an electrostatic 
capacitance between the upper and lower electrodes. This delay leads to a 
small drive margin. A liquid crystal, particularly a ferroelectric liquid 
crystal, which requires a small cell gap such as about 2 microns, 
inevitably makes the electrostatic capacitance C very large. It therefore 
becomes necessary to reduce the wiring resistance as small as possible. 
In view of the above circumstances, according to a conventional technique, 
a method has been used whereby a narrow stripe metal film made of 
molybdenum, aluminum or the like is provided on the ITO thin film of a 
transparent stripe conductive film wired within a liquid crystal. 
Such a metal film on the ITO thin film is provided also at the area outside 
of the liquid crystal cell because even such a small area has a large 
wiring resistance. If a fine wire made of molybdenum film or aluminum film 
is used, electrolysis action may occur under the condition of, e.g., a 
presence of water contents so that the fine molybdenum or aluminum film is 
subject to corrosion and broken out. From this reason, the whole area of 
the ITS electrode outside of the liquid crystal cell is covered with the 
metal film. 
The metal film is likely to have surface oxidation. Therefore, the surface 
is covered with a thin metal oxide film having a thickness of, e.g., about 
1000 to 3000 angstroms. This metal oxide film is generally an insulating 
material. Therefore, in order to ensure electrical connection between the 
connection electrode of a film carrier tape and the metal film facing the 
connection electrode, hard metal particles (e.g., nickel) have been used 
which can break the oxide metal film. Use of nickel particles causes point 
contacts between the particles and the connection electrode, resulting in 
variations of wiring resistance. Furthermore, nickel particles may 
sometimes break the metal film together with the metal oxide film, 
lowering the reliability of electrical connection. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an electrical 
connection method capable of reducing a wiring resistance from an external 
drive circuit to a liquid crystal material while improving the reliability 
of electrical connection. 
The above object of the present invention can be achieved by a provision of 
a liquid crystal apparatus wherein a liquid crystal panel side electrode 
extending from a liquid crystal panel is connected to an external circuit 
side electrode extending from an external circuit for driving the liquid 
crystal panel, by using conductive material, and wherein the liquid 
crystal panel side electrode is a laminated film made of an indium tin 
oxide film and a metal film, and the liquid crystal panel side electrode 
has a left portion of the metal film and an indium tin oxide film opening 
area, at a connection area between the liquid crystal panel side electrode 
and the external circuit side electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1A is a schematic diagram showing the electrical system for driving a 
ferroelectric liquid crystal cell in the manner as illustrated in FIG. 2. 
A clock signal (CS) generated by a clock generator is supplied to a scan 
electrode selector for selecting a scan electrode. A signal outputted from 
the scan electrode selector is supplied to a scan electrode driver to 
generate a signal to be supplied to a scan electrode group. 
A data modulator capable of generating an information signal and an 
auxiliary signal is supplied with the clock signal (CS) and a data signal 
(DS) outputted from a data generator. The data modulator generates a data 
modulated signal (DM) which is supplied to a signal electrode driver and 
then to a signal electrode group. 
FIG. 1B shows examples of signals inputted to and outputted from the data 
modulator. The output signal corresponds to the signal I.sub.1 shown in 
FIG. 2. 
FIG. 1C is a circuit diagram of the data modulator for outputting the data 
modulated signal (DM) shown in FIG. 1B. The modulator is constructed of 
two inverters 11 and 12, two AND gates 13 and 14, and an OR gate 15. 
Signals S.sub.1 to S.sub.5 shown in FIG. 2 are scan signals applied to the 
scan electrodes of the matrix electrode group, and correspond to the 
signals outputted from the scan electrode driver shown in FIG. 1A. Signals 
I.sub.1 to I.sub.3 are information signals or data modulated signals 
applied to the information electrodes or signal electrodes of the matrix 
electrode group, and correspond to the signals outputted from the 
information electrode driver or signal electrode driver shown in FIG. 1A. 
Letter A represents a voltage waveform of a signal at an intersection 
point for the signals S.sub.1 and I.sub.1, and letter C represents a 
voltage waveform of a signal at an intersection point for the signals 
S.sub.3 and I.sub.3. 
The external drive circuit of the liquid crystal apparatus shown in FIG. 1A 
includes a scan side drive circuit having the scan electrode selector and 
scan electrode driver, and an information side drive circuit having the 
data generator, data modulator, and signal electrode driver. 
FIG. 3 is a plan view of a substrate 8 of a liquid crystal panel 111 as 
viewed in the direction indicated by an arrow 114, the plan view showing 
the connection arrangement of the present invention. FIG. 4 is a cross 
section taken along line Y--Y' of FIG. 3. FIG. 7 is a plan view showing 
the connection arrangement to which the present invention is not applied 
(as viewed in the same direction as in FIG. 3). 
A connection electrode 1 of the liquid crystal panel 111 (parallel 
electrodes each having a line width of 100 microns and a line space of 100 
microns, the plan view being shown in FIG. 5) has a two-layer structure 
constructed of an ITO (indium tin oxide) thin film 2a of about 500 to 1500 
angstroms, and a metal thin film 3a (e.g., molybdenum, aluminum) of about 
1000 to 3000 angstroms. The metal thin film may be a laminated film having 
two or more layers. An ITO opening area 4 having a width of 80 microns is 
formed in the electrode 1 at the central area thereof, and the metal thin 
film 3a is left at opposite ends (side edge portions). 
The liquid crystal panel 111 used in the present invention is provided with 
liquid crystal cells integrally formed with the substrate 8. 
The cell structure of the liquid crystal cells is provided with the 
substrate 8 laminated with the metal thin film 3b and ITO thin film 2b, 
another substrate 118 facing the substrate 8, and liquid crystal material 
115. The substrate 118 facing the substrate 8 is formed with a metal thin 
film 113 intersecting with the metal thin film 3b, and ITO thin film 112. 
The cell structure is sealed with sealing material 116 at the peripheral 
portion between the two substrates 118 and 8. An isotropic conductive film 
is interposed between the connection electrode 1 of the liquid crystal 
panel 111 and a connection electrode 5 of an external drive circuit. The 
connection electrode 5 may be, for example, a connection electrode on a 
film carrier having a base film 9, the electrode being made of copper. The 
isotropic conductive film is made of, for example, epoxy-based adhesive 
agent with solder particles being dispersed. Both of the electrodes are 
connected together by thermocompression bonding. Fine solder particles are 
melted and pressed through thermocompression so that they diffuse in the 
direction parallel to the substrate. It is therefore possible to obtain 
electrical contact of a large area as indicated at 7a in FIG. 3. In this 
case, solder particles present between the connection electrode 5 and the 
ITO thin film 2a (or 4) become electrical contacts 7a of a shape extending 
in the direction parallel to the substrate. However, solder particles not 
present between the connection electrode 5 and the ITO thin film are not 
pressed and left as solder particles 7b which do not contribute at all to 
electrical connection. 
The connection electrode 1 of the liquid crystal panel 111 and the 
connection electrode 5 of the film carrier become in area contact with the 
solder particles 7a, providing a highly reliable electrical connection. 
The wiring resistance from the external drive circuit to the liquid 
crystal material 115 is reduced to a low value because of the metal thin 
film 3b on the connection electrode 1 of the liquid crystal panel 111. 
The blank portion 31 shown in FIG. 3 corresponds to the area where the 
epoxy-based adhesive agent 6 indicated by hatched lines cannot be observed 
when the portion with the substrate 8 and base film 9 are facing each 
other is viewed in the direction indicated by the arrow 114, because the 
metal thin film 3a formed on the substrate 8 is opaque. 
FIG. 6 shows another preferred embodiment of the present invention. The 
structure of this embodiment is the same as shown in FIG. 5 except that 
there are provided three narrow metal thin films 3a on an ITO thin film 
2a. 
The line width of a narrow metal thin film 3a used in the present invention 
is preferably about 1/3 to 1/30 time as narrow as the width W of the 
stripe metal thin film 3c. The width W is generally about 50 to 500 
microns. 
According to the present invention, as shown in FIGS. 5A and 5B and FIG. 6, 
the metal thin film 3c at the area outside of the liquid crystal cell 
preferably covers the whole area of the ITO thin film. The problem of 
corrosion or breakage to be caused by electrolysis action under a presence 
of water contents can be eliminated. 
FIGS. 7A and 7B show an apparatus to which the present invention is not 
applied. This apparatus uses the same substrate 8 shown in FIG. 5A except 
that the narrow metal thin film 3a used in the present invention is 
omitted. 
FIG. 8 is an equivalent circuit of the apparatuses shown in FIGS. 3, 4, 5A 
and 5B. R2 represents a wiring resistance of the connection electrode 5 
from the external drive circuit 10 to the solder particle No. 2 nearest to 
the external circuit 10, R3 represents a wiring resistance of the 
connection electrode 5 between two adjacent solder particles, R4 
represents a wiring resistance of the ITO thin film between two adjacent 
solder particles, Rb represents a wiring resistance of the narrow metal 
thin film 3a between two adjacent solder particles, R7 represents a wiring 
resistance of the ITO thin film from the point A to the liquid crystal 
material, and R8 represents a wiring resistance of the metal thin film 3c 
from the point A to the liquid crystal. The values of these resistances 
are the same both for the apparatus of the present invention and the 
apparatus to which the present invention is not applied. 
According to the method to which the present invention is not applied, a 
wiring resistance R12 from the external drive circuit 10 and the liquid 
crystal material is greatly dependent upon the distance a from the point A 
of the metal thin film 3c to the solder particle No. 1 nearest to the 
metal thin film 3c and the resistance Rito of the ITO electrode 2a. The 
sheet resistance value of the ITO electrode 2a is several tens times as 
large as that of the metal thin film 3c. The distance a varies with the 
dispersion degree of solder particles, and it is inevitable in many cases 
that the distance a takes a maximum of about 500 microns. According to the 
connection arrangement of the present invention, electrical connection is 
reliably obtained by means of the ITO opening area 4, and the metal thin 
film 3a is left at the opposite ends (side edge portions) of the 
connection electrode 1 of the liquid crystal panel so that the distance 
from the solder particle 7a to the metal thin film 3a is made several 
microns or less. Therefore, the above-described two problems can be 
eliminated. FIG. 10 shows the case where the connection electrode 1 of the 
liquid crystal panel 111 is positioned facing the connection electrode 5 
of the film carrier, both the electrodes being displaced in the direction 
indicated by X. 
Consider the case where the ITO opening area 4 having a width of, e.g., 80 
microns is formed in the connection electrode 1 of the liquid crystal 
panel 111 at the central area thereof, and a parallel pattern of metal 
thin films of about 10 microns runs at the opposite side edge portions of 
the electrode. In such a case, even if the connection electrode 1 of the 
liquid panel 111 and the connection electrode 5 of the external drive 
circuit displace from each other by 10 microns for example in the 
direction indicated by X in FIG. 10, it is possible to obtain electrical 
connection without reducing the contact area and prevent the wiring 
resistance R1 from increasing. 
FIGS. 11 and 12 show an electrical connection between a connection 
electrode 111 of a liquid crystal panel and a drive IC 112 of a bare chip 
state. FIG. 12 is a cross section taken along line y--y' of FIG. 11. The 
connection electrode 111 of the liquid crystal panel has a two-layer 
structure including an ITO thin film 113 and metal thin film 114. An ITO 
opening area 116 is formed in the connection electrode 111 at the central 
area thereof facing the connection electrode 115 of the drive IC 112. A 
metal bump (gold, silver, copper, or the like) 17 is formed between the 
ITO opening area 116 and the connection electrode 115 of the drive IC 112. 
Both the electrodes (the ITO opening area 116 and the connection electrode 
115) are connected together using conductive paste 118 interposed 
therebetween. Electrical connection is obtained at the ITO opening area 
116 so that the connection reliability can be improved, and because of a 
presence of the metal thin film 114 near the ITO opening area the wiring 
resistance from the drive IC 112 to the liquid crystal material can be 
made small. In FIG. 12, reference numeral 120 represents an epoxy-based 
adhesive agent, and reference numeral 121 represents an insulating film 
such as SiO.sub.2 and polyimide. 
As described above, the connection electrode of a liquid crystal panel is 
made to have a two-layer structure of an ITO thin film and metal thin 
film, and an ITO opening area is formed. Therefore, connection to the 
connection electrode of an external drive circuit can be obtained with 
high reliability, and the wiring resistance from the external drive 
circuit to the liquid crystal material can be made small. 
The ITO opening area is formed in the connection electrode of a liquid 
crystal panel at the central area thereof. Therefore, even a positional 
displacement relative to the external drive circuit occurs during 
connection work, the connection reliability can be prevented from being 
lowered due to a reduction of contact area.