Annealing stability in superconducting Nb wiring with nitrogen plasma treatment

Abstract

We improved the annealing stability in superconducting Nb wiring used in Josephson circuits. Nb film was exposed to nitrogen plasma just after sputtering. We measured the critical current of the Nb wiring before and after annealing. Even before annealing, the critical current with nitrogen plasma treatment is 50% higher than that without treatment. The decrease in critical current after annealing is markedly suppressed. We confirmed using secondary-ion mass spectroscopy profiles that very little oxygen diffuses into Nb films treated using the nitrogen plasma.