A THz SIS Mixer With a NbTiN-Ground Plane and SIS Microtrilayers Directly Grown on a Quartz Substrate

A new structure and a fabrication process for multi-material THz-SIS mixers are proposed. In this design, both the micrometer-sized SIS trilayers (MTLs: microtrilayers) and the ground plane are deposited directly onto the substrate. This structure is expected to possess a number of unique features, e.g., (1) the quality of the SIS junction is not affected by the physical nature of the ground plane film; (2) the heat can escape directly from the junction into the substrate. The influence of the MTL-structure on the junction quality and circuit characteristics have been investigated. Numerical calculation suggests that the extra rf loss around the junction can be kept small if the offset between the junction and the ground plane is less than 1 mum. MTL-SIS mixers have been fabricated using Nb/Al-AlN(or Al-AlO_x)/Nb SIS junctions and NbTiN/Al microstrip lines. The leakage current of the SIS junction can be made as small as that of the best all-Nb devices. The MTL-SIS structure will be useful in the development of future THz SIS mixers. The abstract goes here.