A study of fabrication for oxide-superconductor devices by using transparent-conductive oxides

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The purpose of this study is to investigate properties of superconducting devices composed of a high-T_C superconductor YBa_2Cu_3O_7 (YBCO : S-layr) and a transparent-conductive material In_2O_3 : Sn (ITO : N-layr) . Based on the general equation I*exp (eV/nkT) of semiconducting diodes, we have first analyzed current-voltage (I-V) characteristics of SN bi-layrs consisted of these materials. It has been shown that the exponent n is nearly equal to unity, indicating the Schottky type behavior rather than the pn junction behavior, and that temperature dependence of the barrier height is proportional to temperature, implying the existance of the interfacial layr at the SN boundary. We have also made chemical analyzes for the ITO/substrate interface, and have found that ITO films on oxide substrates are more stable than those on polymer substrates in the sense that diffusion of In atoms into substrates is suppressed in the former case.Next we have investigated characteristics of SNS tri-layrs in which ITO and In_2O_3 are used as N-layrs. In both types of junctions, I-V curves are linear at 290K and nonlinear at 77K showing behavior qualitatively similar to Josephson devices. Quality of the junctions seems to be superior in the case of junctions with In_2O_3. In addition, most of SN bi-layrs with In_2O_3 show differential negative resistance behavior in the reverse direction of I-V curves. This may be attributed from electron avalanche effects in the nonuniform parts of the junctions, and the system is possibly used as a switching device.In conclusion, we have shown that oxide superconducting devices can be made by using ITO films. Since there may exist the Schottky barrier between YBCO and ITO layrs, a new type of superconducting devices is expected to be developed with the aid of this effect.