Analysis of Ic spreads in interface engineered junctions

We have investigated the electrical properties of interface engineered junctions fabricated under various process conditions to clarify the possible origin of the spreads in I_c and R_n values. We found that in most cases, the I_cR_n , values of junctions on a wafer scaled with the square root of I _c. The distribution of both the junction I_c and R _n were expressed well by the log-normal distribution function with their σ values being different by a factor of two. These results indicate that Cooper pairs and quasiparticles in the junctions transfer through different transport channels, i.e., direct tunneling for the former and resonant tunneling for the latter, and that a variation in the tunnel barrier thickness among junctions dominates the spreads in the I_c and R_n values. In contrast, we could not observe a universal scaling relation between I_cR _n, and I_c among junctions processed under different conditions. This indicates that the I_c variation due to process conditions originates from something other than a simple barrier-thickness variation