Effects of interlayer electrode thickness in Nb/(MoSi2/Nb)N stacked Josephson junctions

Abstract

Dense, vertically stacked Josephson junction arrays are being developed for voltage metrology applications. We present measurements of the uniformity and reproducibility of Nb/(MoSi2/Nb)N vertically stacked junctions that clarify the superconducting properties of the middle Nb superconducting electrode. Middle electrode thicknesses down to 20 nm have shown minimal suppression of the superconducting order parameter as measured through the critical current density. Even with a middle electrode thickness of 5 nm, excellent junction uniformity has been observed as demonstrated by the measurement of large Shapiro steps when the arrays are biased with microwaves. We also discuss the role of the superconducting coherence length in these arrays of high-density junctions.