Niobium trilayer process for superconducting circuits

A Nb-AlO_x-Nb trilayer process was developed that consistently produces junctions with V_m>40 mV. Critical current density was controlled reproducibly from 200 to 7000 A/cm² by controlling the oxygen pressure in the process chamber during thermal oxidation of the aluminum. A multilayer AlO_x barrier was used to produce junctions for Josephson circuit applications requiring low critical currents (<50 A/cm²). A second Al deposition and oxidation was able to reproducibly control the critical current density from 6 to 200 A/cm². High quality (V_m>40 mV) Josephson junctions have been fabricated with low stress (<1 Gdyne/cm²) by an appropriate choice of niobium deposition rate (8 to 9 Å/s) and argon sputtering pressure (4 mtorr)