Niobium trilayer process for superconducting circuits

A Nb-AlO/sub x/-Nb trilayer process was developed that consistently produces junctions with V/sub m/>40 mV. Critical current density was controlled reproducibly from 200 to 7000 A/cm/sup 2/ by controlling the oxygen pressure in the process chamber during thermal oxidation of the aluminum. A multilayer AlO/sub x/ barrier was used to produce junctions for Josephson circuit applications requiring low critical currents (<50 A/cm/sup 2/). A second Al deposition and oxidation was able to reproducibly control the critical current density from 6 to 200 A/cm/sup 2/. High quality (V/sub m/>40 mV) Josephson junctions have been fabricated with low stress (<1 Gdyne/cm/sup 2/) by an appropriate choice of niobium deposition rate (8 to 9 AA/s) and argon sputtering pressure (4 mtorr).<
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