Properties of RF-sputtered Nb/Al-AlOx/Nb Josephson SNAP junctions

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 V-m as high as 60 mV and current densities J(C) less than or equal to 2000 A/cm(2) at 4.2 K are routinely obtained, thus demonstrating its feasibility for high frequency mixer and voltage standard applications.