Unexpected geometrical anodization effect in the fabrication of Nb/Al-oxide/Nb junctions

In our research on the fabrication of Nb/Al-oxide/Nb mixer elements, we have discovered an unexpected effect which is attributable to the geometry of the mixer. We have found that the electrical quality of anodically sealed junctions fabricated in our laboratory depends strongly on the geometry of the base electrode. For example, it is possible to design a series array of junctions using two geometries of base electrode features and obtain poor junction electrical characteristics with one type of base feature and excellent characteristics with the other. The role of Nb film stress, junction size and placement on the base electrode feature, wiring interconnection process and anodization conditions in this effect have been studied.