Effects of rf bias on the superconducting and structural properties of rf magnetron sputtered NbN

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Abstract
The superconducting and structure properties of rf magnetron sputtered NbN films prepared at elevated substrate temperatures were investigated as a function of rf substrate bias. The superconducting transition temperature was observed to be independent of bias up to approximately −60 V after which it decreased and broadened. An increase of up to 60% in deposition rate over the unbiased case was observed. Substrate bias produced little effect on the low-temperature resistivity, resistivity ratio, and the film composition. The major structure change observed was a strong dependence of the preferred crystallite orientation on bias. At low bias the orientation was (200) which changed to (111) as the bias was increased. These materials are of excellent quality for use in all refractory tunnel junctions.