Reduced leakage current in Josephson tunnel junctions with codeposited barriers

Josephson junctions were fabricated using two different methods of barrier formation. The trilayers employed were Nb/Al-AlOx/Nb on sapphire, where the first two layers were epitaxial. The oxide barrier was formed either by exposing the Al surface to O-2 or by codepositing Al in an O-2 background. The codeposition process yielded tunnel junctions that showed the theoretically predicted subgap current and no measurable shunt conductance. In contrast, devices with barriers formed by thermal oxidation showed a small shunt conductance in addition to the predicted subgap current. (C) 2010 American Institute of Physics. [doi:10.1063/1.3518983]