Analysis of I/sub c/ 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/sub c/ and R/sub n/ values. We found that in most cases, the I/sub c/R/sub n/, values of junctions on a wafer scaled with the square root of I/sub c/. The distribution of both the junction I/sub c/ and R/sub n/ were expressed well by the log-normal distribution function with their /spl sigma/ 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/sub c/ and R/sub n/ values. In contrast, we could not observe a universal scaling relation between I/sub c/R/sub n/, and I/sub c/ among junctions processed under different conditions. This indicates that the I/sub c/ variation due to process conditions originates from something other than a simple barrier-thickness variation.