Properties of RF-sputtered Nb/Al-AlOx/Nb Josephson SNAPjunctions

摘要

A detailed analysis of the properties of Nb/Al-AlOx/Nb Josephson tunnel junctions fabricated with a modified SNAP process is presented. Selective niobium anodization has been used not only as on-line monitoring of the junction quality, through depth profiling anodization spectroscopy, but also to achieve a controlled reduction of the junction area at micrometer level by a proper choice of the anodization current. The dependence of the most relevant junction electrical parameters on fabrication variables has been investigated. With this fabrication process, junctions with Vm as high as 60 mV and current densities Jc⩽2000 A/cm2 at 4.2 K are routinely obtained, thus demonstrating its feasibility for high frequency mixer and voltage standard applications