Fabrication of SIS junctions for space borne submillimeter wave mixers using negative resist e-beam lithography

We report on the development of a new process for the fabrication of Nb/Al-AlO/sub x//Nb tunnel junctions for channel 1 (480-640 GHz) Superconductor-Insulator-Superconductor (SIS) mixers of HIFI, the Heterodyne Instrument for FIRST (Far InfraRed & Submillimeter Telescope). The process is derived from a standard self-aligned lift-off process but uses negative resist electron beam lithography (EBL) for junction definition. The junction area is tightly controlled down to below 1 /spl mu/m/sup 2/ without the complexity of processes using positive electron beam resists. We describe process parameters and experimental results: DC-tests and Fourier Transform Spectrometer (FTS) measurements.