Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-10-23
2003-09-09
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S001330, C428S412000, C428S432000, C428S480000, C428S702000, C427S164000, C204S192140, C204S192220
Reexamination Certificate
active
06617056
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a transparent conductive laminate having an In—Sn—O transparent conductive film. More specifically, this invention relates to a low resistant transparent conductive laminate having a crystalline In—Sn—O transparent conductive film on a transparent film substrate made of a thermoplastic polymer, a manufacturing process therefore and a display comprising the laminate.
BACKGROUND ART
As electrodes of various kinds of display devices such as a liquid crystal display, an electroluminescence device or the like, or a solar cell, a thin film material with transparency and conductivity (hereafter, referred as “transparent conductive film”) which shows high visible light transmittance and low electrical resistance is inevitable. Further, accompanying recent rapid popularization of portable mobile terminals, and miniaturization and weight reduction of their terminals, as substrates to be used in display devices or the like by forming a transparent conductive film on its surface, materials having lighter weight, higher flexibility and higher shock resistance than conventional ones are required. Under these circumstances, the use of a transparent conductive laminate having a transparent conductive film mainly composed of In (indium)—Sn (tin)—O (oxygen) (hereafter, referred as “ITO-film) fabricated onto a thermoplastic polymer film substrate having lighter weight, higher flexibility and higher shock resistance than glass used as a substrate, is now growing.
When a color display device is intended to be formed by using a transparent conductive laminate having an ITO-film fabricated onto such a film substrate, a resistivity of the ITO-film is desirably about 2×10
−4
&OHgr;·cm.
However, an ITO-film fabricated onto a film substrate by DC magnetron sputtering, RF magnetron sputtering, vacuum evaporation method, ion-plating method or the like generally has a higher value of sheet resistance than an ITO-film fabricated onto a glass substrate.
One of the reasons is that only an ITO-film having no more than about 300 nm in thickness can be fabricated onto a film substrate due to the fact that the rigidity against the bending of thermoplastic polymer film substrate is smaller than that of glass substrate. That is, when it is intended to increase the thickness of the ITO-film from that thickness, it is not seldom that the film curls or cracks are fabricated onto the ITO-film, due to the stress of the ITO-film.
Another reason is that the heat resistance of thermoplastic polymer film substrate is lower than that of glass, and the process temperature fabricating an ITO film on the film substrate must be set at a lower temperature than that on a glass substrate; therefore, the crystals of the ITO-film do not grow sufficiently during film forming.
Incidentally, the structure of an ITO-film having crystalline parts is analyzed by X-ray diffraction method. In a polycrystalline ITO, three strong diffraction lines are observed in X-ray diffraction method, and they are defined by Miller indices. These are attributable to the diffraction lines from crystal planes (222), (400) and (440), from the lower angle side. It has been reported that these diffraction lines from the crystal planes (222), (400) and (440) appear around 30.5° (2&thgr;), around 35° (2&thgr;) and around 50.5° (2&thgr;), respectively when the X-ray source is Cu—K&agr;. For example, in the literature titled “transparent conductive film” (“HYOUMEN” vol. 18, No. 8 (1980) 440-449), an X-ray diffraction pattern of a crystalline ITO-film which was made by an vacuum evaporation method on a polyester film substrate and heat-treated is shown in FIG.
4
. An X-ray diffraction pattern of a crystalline ITO-film which was fabricated onto a glass substrate by sputtering is shown in “SHINKU” vol. 30, No. 6, 546-554. The X-ray diffraction charts shown in these literatures have peaks attributable to the diffraction from crystal planes. (222), (400) and (440).
It has been commonly known that the structure and electrical properties of an ITO-film fabricated onto a glass substrate by DC magnetron sputtering strongly depend on the film-fabricating temperature; and a film having a state of amorphous or a mixture of amorphous and crystalline is formed when a film formation process is carried out by keeping the glass substrate at room temperature.
Regarding an ITO-film fabricated onto a glass substrate, in order to reduce the resistivity of the film, a method in which crystalline orientation is controlled so that (400) crystal plane becomes parallel to the surface of the substrate has been proposed. For example, JP-A 7-90550 (JP-A means Japanese unexamined patent application) has descried that an ITO-film formed in such a manner that (100) direction, i.e., (400) face, is parallel to the substrate has a decreased resistivity. It becomes important to heat the substrate at a high temperature exceeding 200° C. during ITO-film fabricating in order to realize such a crystalline orientation. Several studies have been carried out regarding crystalline orientation control for decreasing a resistivity in a so-called high temperature process in which film fabricating is carried out while keeping a substrate temperature at 200° C. or higher as mentioned above.
Further, it is known that the structure of an ITO-film fabricated onto a glass substrate largely differs depending on a film fabricating atmosphere. For example, JP-A 9-50712 discloses a method for controlling an ITO film structure, that is, the particle sizes and the number of crystals are controlled by introducing water vapor, an inert gas, into the atmosphere. In addition, JP-A 8-92740 discloses a method for controlling film structure by using a sputtering apparatus, and the method actively removes impurity gas, and at the same time constitutes a vacuum system of 4.0×10
−4
Pa.
However, in an ITO-film formation on a thermoplastic polymer film substrate, since the softening point of a commonly used polymer film is lower than 200° C., the film substrate can not be heated at a high temperature exceeding 200° C.; and thereby such a high process-temperature exceeding 200° C. as in the case of ITO-film formation on glass substrate can not be used. Hence, in a transparent conductive laminate using a thermoplastic polymer film substrate, crystals of an ITO-film can not be sufficiently grown, and as a result, such a low sheet resistance as in the case where a glass substrate is used can not be realized.
That is, in a transparent conductive laminate using a thermoplastic polymer film substrate, an ITO film fabricating at such a high temperature as in the case of a laminate fabricated onto a glass substrate can not be realized, and further the thickness of the ITO-film is limited; and accordingly a laminate having a conductive film of low resistivity has not been provided yet.
Under these circumstances, the main object of the present invention is to provide a laminate in which the resistance of a surface layer is significantly decreased without losing the merits of the laminate having an ITO-film fabricated onto a thermoplastic polymer film substrate.
Another object of the present invention is to provide a process for manufacturing a transparent conductive laminate having a crystalline ITO-film fabricated by sputtering on a polymer film substrate kept at about room temperature. The process is characterized in that the transparent conductive laminate having an extremely lower resistivity and a better light transmittance in its ITO film than a transparent conductive laminate fabricated onto a conventional thermoplastic polymer film substrate is produced by combining the positive controlling of ITO-film's fine structure through the control of film-forming atmosphere during sputtering, with crystal growth through a heat treatment at a relatively low temperature.
A further object of the present invention is to provide a display device using the above-mentioned laminate as an electrode.
DISCLOSURE OF THE INVENTION
The inventors of the present invention pursued
Hara Hiroshi
Tsuboi Seiji
Jones Deborah
Piziali Andrew T
Teijin Ltd.
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