New scaling relation for sputtered NbN films

A scaling relationship has been discovered between the sputtering rate and the partial pressure of argon PAr, which leaves the superconducting properties of NbN films invariant. As PAr increases for a given sputtering rate, there is a linear reduction of Tc together with a rapid increase, followed eventually by saturation, in Hc2 at 4.2 K. These produce a maximum in Jc (measured at 19 T and 4.2 K) at a particular value of PAr. Films exhibiting nearly the same set of superconducting properties and microstructures can be made at a higher fixed sputtering rate if the values of PAr are multiplied by a constant scale factor. This scaling relation is found to hold for two separate sputtering systems, one of which uses a standard diffusion pump while the other uses an oilless turbo pump. Additional comparisons with the results of others reinforces the conclusion that the scaling relationship is universal and thus may provide some insight into those factors in the sputtering process which are important for determ...