Thermal annealing of Nb/Al-AlOx/Nb Josephson junctions

We thermally annealed single un-shunted Josephson junctions at temperatures of 110 to 270°C for durations of 2.5 to 90 minutes. We also exposed some junctions for three separate 15-minute periods in order to compare the result with that of a continuous 45-minute exposure. After annealing, we measured the changes in junction properties such as critical current I_C, normal state resistance R_N, and junction quality parameter V_M. I_C decreases with increased exposure, (starting at approximately 125°C) and R_N increases, such that the I_CR_N product remains roughly constant up to 200°C, at which point I_CR_N also begins to decrease. V_M declines slightly with increased exposure, but with a large amount of scatter. Samples with interrupted exposures degraded less than if annealed continuously. Based on our results, we find that junctions can tolerate an exposure of up to 90 minutes at temperatures as high as 200°C without significant degradation in performance, though allowances will need to be made for shifts in critical current. Junctions exposed for up to 15 minutes at 225°C are degraded further but may still function well enough for some applications.