Study of the residual surface resistance of niobium films at 1.5 GHz

Potential contributions to the residual surface resistance of niobium films exposed to 1.5 GHz microwaves are reviewed and studied. These include the oxidation of the film surface, the formation of hydride precipitates, the c ontamination by noble gas atoms and the presence of macroscopic film defect s such as those resulting from the roughness of the substrate. Particular a ttention is given to the dependence of the residual resistance on the ampli tude of the microwave. Results similar to those obtained for bulk niobium p rovide strong evidence against the conjecture that the small size of the fi lm grains should be a fundamental limitation to the production of films hav ing a low residual resistance. (C) 2001 Elsevier Science B.V. All rights re served.