In nuclear radiation detection, superconductors have the inherent advantage of better energy resolution than that of semiconductors. The ultimate energy resolution has never been accomplished by the conventional method of fabricating the tunnel junctions. In this study, lithographic technique for Josephson LSI circuits is applied to the production of a superconducting tunnel junction for radiation detection. Nb-Al/aluminum oxide/Nb tunnel junctions with different junction sizes and barrier oxidation times have been fabricated to study their characteristics. The current-voltage curves were measured in the temperature range from 4.2 to 0.45 K. The junctions showed some amount of leakage current which remained below 2 K. The behavior of the leakage current was successfully understood from its experimental dependence on the junction size.
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