An electrode substrate in which a lower electrode and an upper electrode face each other with an insulating film interposing therebetween includes, for example, an electrode substrate used in a thin film transistor in an active matrix driving liquid crystal display device. In this electrode substrate, the lower electrode to be a gate wiring/electrode, a gate insulating film, and the upper electrode to be a source/drain electrode and signal wiring are formed in this mentioned order through lamination on a substrate formed of glass or the like. High-precision formation, on a large-area substrate, of a thin film transistor and a display device driven by the thin film transistor requires that the lower electrode and upper electrode to constitute wirings/electrodes and others each be fabricated into a fine pattern and be disposed so as to be accurately aligned with each other. Accordingly, as a general method for fabricating the lower and upper electrodes, there is applied a so-called photolithography technique to use separate photomasks for the upper and lower electrodes. In this method, a photomask that has been beforehand finely fabricated is placed on a (positive type) photoresist deposited on an electrode; the photoresist is irradiated with light to remove the photoresist in the exposed area; the electrode is removed from the region not covered with the photoresist to fabricate the electrode; and finally the photoresist is removed. Accurate alignment of the photomask to be used in fabricating each of the electrodes, with respect to the substrate, makes it possible to accurately align the pattern of each of the electrodes.
A backside exposure method is known as a method for accurately aligning a lower electrode and an upper electrode. The method concerned is a method which auxiliarily utilizes “a part” of the lower metal electrode as a photomask for specifying “a part” of the pattern of the upper electrode. Details of this method are described, for example, in Japanese Patent No. 3,304,671 of the present inventor.
In these years, a method for producing electrodes by using a printing method, in place of a photolithography method, to be a so-called direct-drawing method, such as inkjet, plating, or offset printing, has been actively studied as a method for forming the electrodes for use in these electrode substrates, as described, for example, in Nikkei Electronics, No. 6.17, pp. 67-78, 2002. In these printing methods, required materials are disposed for electrode formation in required positions. Accordingly, these printing methods are less in number of production steps and higher in utilization efficiency of materials than a photolithography method, promising such an advantage that an electrode substrate can be formed at a low cost. The above cited reference describes a case where a metal wiring of 5 μm or less in wiring width was formed by an inkjet method, as a case of a fine electrode pattern formed by a printing method.
A thin film transistor using the above described electrode substrate is applied to an active matrix driving display device, and applied to a flat image-display device such as a display device in a laptop personal computer, a cellular phone or a flat television set so that used as display elements are, for example, liquid crystal elements, organic electroluminescence elements, electrophoresis elements or the like. In addition, there is a trend to apply a thin film transistor using the above described electrode substrate to RFID typified by a contactless IC card as a contactless information medium. In any one of these cases, such a thin film transistor is applied as a man-machine interface device, through the intermediary of images and communication information, to fundamental products that support the highly information-based society.
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