Synthesis and estimation of NbN - Nb multilayers

An important role in the future of superconducting electronics will be the development of key technology to synthesize a multilayer structure made of superconducting thin film (S) and normal metal (N) or dielectric thin film. An S - N - S Josephson junction is applicable as a superconducting quantum well device and a superconducting microstrip line is promising in submillimetre wave-transmission technology. In this paper, NbN - Nb multilayers were synthesized in situ by using off-axial DC magnetron sputtering apparatus. Structures of the multilayer samples were analysed using Auger electron spectroscopy (AES). The AES analysis showed that an N atom in an NbN layer rarely diffused into the Nb layer during growth of NbN on the Nb layer at arbitrary substrate temperatures. It was found by x-ray diffraction (XRD) analysis that NbN(111) could grow on Nb(110) even though the substrate temperature was low. XRD analysis also showed that the grain size of NbN thin film on Nb thin film monotonically increased with increase of the substrate temperature.