Comparison of temperature cycling stability of Pb-alloy Josephson junctions with various counter electrode materials

The stability of Pb-alloy Josephson junctions upon repeated temperature cycling between 300 K and 6 K has been investigated. Various size cross type junctions were fabricated with PbInAu base electrodes and PbAu, PbBi or PbSb counter electrodes. The Pb alloy electrodes were deposited on room temperature substrates by either sequential deposition or evaporation to completion of predetermined alloys. The films were patterned by a lift-off stencil and the tunneling barriers were formed using dc slow discharge in oxygen. The junctions were then passivated with sequentially deposited layers of Ge and SiO and annealed at 80°C for various periods of time. The critical current stability and the junction failure due to shorts as a function of temperature cycling are compared for junctions with different counter electrodes. In the most favorable case, 40 μm square junctions have been thermally cycled for over 6000 times and no failures were observed among a population of more than 1000 junctions.