Superconductive Transition Temperatures of Reactively Sputtered Niobium Films

Niobium films have been examined with respect to their electrical and superconductive properties. The films were deposited by dc and asymmetric ac sputtering techniques in argon with addition of a small amount of nitrogen gas. The films obtained had a wide range of resistivities and transition temperatures depending on the partial nitrogen pressure in the argon atomosphere. The maximum transition temperature of films obtained was 15.3°K, which very close to those reported for bulk NbN. It was found that the asymmetric ac sputtering technique is useful to increase the transition temperature of niobium films sputtered reactively in the presence of a nitrogen gas.