Overdamped Nb∕Al–AlOx∕Nb Josephson junctions

We report the fabrication and characterization of overdamped Nb∕Al–AlOx∕Nb superconductor–insulator–superconductor Josephson junction whose fabrication process derives from that of the well-known hysteretic junctions. These junctions are an intermediate state between the superconductor–normal metal–superconductor and the superconductor–insulator–superconductor Josephson junctions. Stable and reproducible nonhysteretic current–voltage characteristics are obtained with a proper choice of the fabrication parameters. We have measured critical current densities JC from 103 up to 2×104A∕cm2, with characteristic voltages from 80 to nearly 450μV. The junctions are stable against time and repeated thermal cycling.