Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2001-07-20
2004-02-03
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192260
Reexamination Certificate
active
06685805
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a substrate having a transparent conductive film, a substrate having a transparent conductive film manufactured using the method, and a touch panel using the substrate.
2. Prior Art
Conventionally, glass substrates having a tin-oxide-containing indium oxide (hereinafter referred to as ‘ITO’) film are widely used as the substrates having a transparent conductive film of liquid crystal display panels (hereinafter referred to as ‘LCDs’) and the like. In recent years, such glass substrates having an ITO film have also come to be used in resistive film type touch panels.
As shown in
FIG. 3
, a resistive film type touch panel is composed of a transparent upper electrode
1
and a lower electrode
3
, with the lower electrode
3
and the upper electrode
1
being arranged in facing relation to one another with spacers
2
therebetween; when the upper electrode
1
is pushed with a pen
4
, a finger or the like, the upper electrode
1
comes into contact with the lower electrode
3
.
The method of detection of the input position in such a resistive film type touch panel may be analog or digital, with the method selectively used depending on the application. The analog detection method, which gives a higher detection resolution, is used in a wider range of applications. In the case of an analog detection type touch panel, a voltage is applied between two parallel electrodes, one at each end in a prescribed direction of the touch panel, as shown in
FIG. 4A
, thus forming a linear potential gradient as shown in
FIG. 4B
, and by measuring the voltage Ec corresponding to an input contact point, the input position c is detected.
It is required that such a resistive film type touch panel transmits light well, and so the ITO film formed on the substrate is extremely thin, usually not more than 30 nm (see for example Japanese Laid-open Patent Publication (Kokai) No. 11-167827). Moreover, in the case of an analog detection type touch panel, the ITO film on the glass substrate usually has a surface resistance of 300 to 2000&OHgr;, and moreover since this ITO film is used as the electrode for determining the input position, there is a strict requirement for the surface resistance to be uniform.
The steps in manufacturing a resistive film type touch panel are to subject a lower electrode
3
comprised of a glass substrate having an ITO film to resist printing, etching, silver ink printing, insulating ink printing, micro dot spacer formation, scribing and so on, next bond the lower electrode
3
to an upper electrode
1
that has been prepared in a separate manufacturing step, and then seal around the upper electrode
1
and the lower electrode
3
by heat sealing. Of these steps, in a printing step such as silver ink printing or insulating ink printing and in the heat sealing step, heat treatment at a maximum temperature of 160° C. is carried out, and during this heat treatment the surface resistance of the ITO film changes; as a result, in some cases a touch panel manufactured using such a substrate will not function properly.
Specifically, when the surface resistance of the ITO film has dropped due to heat treatment, the detected voltage drops and thus a discrepancy arises between the input position and the detected position; when the surface resistance has risen, the detected voltage rises and thus the same kind of discrepancy again becomes prone to occur. Moreover, if the surface resistance distribution is not uniform, then the potential gradient loses its linearity as shown in
FIG. 4B
, that is, there is no longer a linear relationship between distance and potential, and hence it becomes impossible to detect the input position accurately.
A description will now be given, with reference to
FIG. 5
, of the reason why heat treatment causes the surface resistance of an ITO film to change.
The ITO film is polycrystalline, and the more film deposition is carried out at a high temperature above about 160° C., which is the crystallization temperature of ITO, the more crystallization proceeds and the more stable the crystal structure becomes. However, impurity-containing ITO and non-crystalline ITO, for which the crystal structure changes easily during subsequent heat treatment, are inevitably formed near the substrate surface during the initial stage of the film deposition (FIG.
5
A), and in particular since the lattice constant of ITO is high, i.e. about 1 nm, at a film thickness of less than 30 nm the proportion of crystallized ITO is low and the proportion of impurity-containing ITO and non-crystalline ITO high (FIG.
5
B). When such an ITO film containing a lot of impurity-containing ITO and non-crystalline ITO is subsequently subjected to heat treatment, the crystal structure changes due to the progression of crystallization of the film and the occurrence of oxidation, and hence the electrical properties, and thus the surface properties, of the ITO film change. This change in the surface properties becomes greater as the ITO film is made thinner and hence the proportion of the crystal structure that is unstable increases (FIG.
5
A).
Considering the effects of the heat treatment that must inevitably be carried out during the manufacturing of a touch panel, it is desirable for the percentage change between the surface resistance of the ITO film before heat treatment and the surface resistance of the ITO film after heat treatment to be not more than ±10%.
The ITO film is formed on the surface of the glass substrate using an in-line type or batch type sputtering device that uses magnetron sputtering (hereinafter referred to merely as ‘sputtering’).
With such an existing sputtering device, it is difficult to keep the above-mentioned percentage change in the surface resistance of the ITO film down to no more than ±10% under typical conditions used conventionally when manufacturing a transparent conductive film for an LCD (for example, substrate temperature: 200 to 400° C.; sputtering pressure: 0.27 to 1.33 Pa; ratio of oxygen to argon in the mixed gas: 0 to 0.04), particularly when the thickness of the ITO film is less than 30 nm.
Methods proposed in the past for reducing the percentage change in the surface resistance have been, in the case of sputtering, to make the nitrogen doping amount in the ITO film 0.01 to 0.6 mass % and the film thickness 5 to 25 nm or to use no nitrogen doping in the ITO film and make the tin doping amount 4.2 to 8.3 at % (see Japanese Laid-open Patent Publication (Kokai) No. 2000-113732), and, in the case of applying a coating solution that forms an ITO film upon pyrolysis, to apply two such coating solutions having different pyrolysis temperatures onto the glass substrate, and then, to improve the stability of the resistance to heat treatment, carry out baking first under an oxidizing atmosphere and then under a non-oxidizing atmosphere (see Japanese Laid-open Patent Publication (Kokai) No. 2000-100263).
However, in the case of the former of the above methods, it was found in 200° C. 60-minute heat resistance tests that the percentage change in the surface resistance was kept down to within −10% to +19%, but there is a problem that this is still insufficient. Moreover, in the case of the latter of the above methods, there is a problem in that during the application of the coating solutions it is impossible to avoid foreign particles getting into the coating solutions and then during the baking there is a high probability of these foreign particles sticking, and a problem in that the percentage change in the surface resistance cannot be kept down to within ±20%, which is insufficient.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of manufacturing a substrate having a transparent conductive film, which is capable of suppressing change in the surface resistance of the film upon the substrate being subjected to prescribed heat treatment, a substrate having a transparent conductive film m
Katoh Yukihiro
Kiyota Shogo
McDonald Rodney G.
Nippon Sheet Glass Co. Ltd.
Rossi & Associates
LandOfFree
Method of manufacturing substrate having transparent... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of manufacturing substrate having transparent..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of manufacturing substrate having transparent... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3335138