rf reactively sputtered superconducting NbN/subx/ films

NbNx films containing various phases have been prepared by the radio frequency (rf) reactive sputtering technique and examined for their superconducting and electrical properties. These films have been found to have a wide range of upper critical magnetic fields, transition temperatures, and normal-state resistivities depending on the partial pressure of nitrogen in the sputtering atmosphere and the substrate temperature. The fcc NbN films exhibit Hc2(4.2°K) ranging 150 to 230 kOe, whereas some of the Nb+Nb2N+NbN and Nb2N+NbN films exhibit high critical fields more than 320 kOe which are probably caused by the existence of thin connected superconducting filaments in the multiphase films at high field.