Critical current variation in YBa₂Cu₃O_7−x step-edge junction arrays on MgO substrates

The dc transport properties of high-temperature superconducting Josephson junction arrays were investigated. Each array had the same design of 50 junctions in series, with each junction formed from a Y Ba₂Cu₃O_7−x (YBCO) grain boundary grown on an engineered MgO step-edge substrate. The variation of critical current was analysed and modelled. Comparisons were made on the average and one sigma standard deviation, σ, of I_c values for arrays fabricated both on the same chip and a different chip. For arrays containing 2 μm wide junctions, the typical values of σ were 20–35%. Increasing the junction width reduces σ to 8–15% in arrays with 4 μm wide junctions, qualitatively consistent with the prediction using a model of multiple channels across the width of the junction. (paper)