Machine Aligned Fabrication of Submicron Nb/Al-AlOX/Nb Junctions using a Focused Ion Beam

In this abstract, a process is described that we are developing which uses a Ga focused ion beam (FIB) for the fabrication of Nb/AlAlOx/Nb superconductive-insulatingsuperconductive (SIS) tunnel junctions. The objective is to use a machine alignment scheme for the definition and insulation of junctions with diameters as small as 0.5μm for high critical current density (JC) applications. The fabrication of such ultra-small area SIS junctions has typically only been achieved using electron beam lithography and a multi-resist layer scheme [1]. Typical techniques for the fabrication of SIS junctions use a self-aligned resist lift-off process. The resist pattern is used to define both the junction counter electrode and the subsequent insulation field that insulates the base electrode from the wiring layer. The wiring layer contacts the junction counter electrode through a via in the insulation field that is created during resist lift-off.