FABRICATION OF HIGH-QUALITY SUPERCONDUCTING TUNNEL-JUNCTIONS

High quality Nb/AlOx/Nb superconducting tunnel junctions (STJs) are fa bricated for the radiation detection. The fabrication process includes a MgO thin film, an underlayer method, a control of critical current, a nitrogen plasma passivation, and a SiO2 insulating layer. Subgap cu rrent characteristics of STJs have been investigated in the temperatur e range of 0.35K to 4.2K in order to evaluate the junction quality for the radiation detection. The STJs fabricated by present process show extremely high quality junction characteristics with a leakage current density of 0.1 pA/mu m(2), a resistance ratio R-d/R-n of 6x10(6) for a 200x200-mu m(2) STJ with a critical current density of (7)200A/cm(2) .