Fabrication of niobium-lead tunnel junctions using a self aligned masking technique

The use of suspended stencils in the self aligned fabrication of niobium lead tunnel junctions has been investigated. It is shown that while all-polymer masks are unsatisfactory for this application, suspended aluminum stencils supported on polyimide can be used to make these junctions with good current-voltage characteristics. This stencil, which can be baked to at least 200°C, is made using e-beam lithography, lift off and plasma etching in oxygen. With this technique, junctions with submicron dimensions have been fabricated in a single masking step without any surface cleaning of the niobium film. The current-voltage characteristic of these junctions do not show the knee structure which is generally attributed to a contamination or damaged layer on the niobium surface.