Abstract

Potential of bismuth oxide (Bi2O3), which has a low melting point and is expected to have good surface coverage nature on other materials, has been examined for an.artificial insulator barrier material in tunnel junctions with a cuprate superconductor electrode. We have evaluated Bi2O3 barrier through constructing Nd1.85Ce0.15CuO4 base electrode/Bi2O3 barrier/Ag top electrode superconductor-insulator-normal metal (SIN) junctions. Our results indicate that Bi2O3 is possible to be a good barrier material when it is formed at substrate temperatures below 400°C and is around 30A thick. From normalized conductance curve fitting to the BCS theory taking account of gap broadening Г, the best SIN junction in this study (Bi2O3 barrier formed at 350°C and 30A thick) gives Г/Δ ratio of 0.52 (Δ: gap energy), which proves the Bi2O3 layer functions well as a barrier in this tunnel junction. Higher quality in junction electrical characteristics will be attainable through improvements in oxygen stoichiometry and surface coverage of Bi2O3 barrier layer as well as in surface morphology and superconductivity of base electodes.

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