High quality Nb-based tunnel junctions for high frequency and digital applications

摘要

A number of new fabrication techniques are developed and optimized in order to fit the requirements of contemporary superconducting electronics. To achieve ultimate performance of integrated submm receivers with operational frequency of 1 THz, tunnel junctions with AlN tunnel barrier having a RnS value as low as 1 Ωμm2 have been developed. High quality characteristics of Nb/AlN/Nb tunnel junctions with Rj/Rn=16 and RnS=10 Ωμm2 have been demonstrated. Electron Beam Lithography (EBL) in combination with Chemical Mechanical Polishing (CMP) has been incorporated to produce Nb/AlN/Nb junctions with 0.03 μm2 area. A new approach to obtain overdamped Nb/AlOx/Nb tunnel junctions has been proposed and realized. The dependencies of the main parameters of novel junctions on the current density and circuit geometry have been studied. These junctions may have a good potential in Josephson junction arrays and Single-Flux-Quantum applications (RSFQ).