ABSTRACT
The refractory nitride Josephson tunnel junctions with NbN superconducting thin-film base electrode were studied after 1982 using thermal or plasma oxide tunnel barriers, showing attractive I-V nonlinear characteristics only when a superconducting soft metal was used as counterelectrode. Experimentally the insulating tunnel barrier of a SIS junction could be a native oxide formed thermally or in an oxidizing plasma on the base electrode or an oxide layer formed on a very thin "overlayer" deposited on the base electrode such as Nb-Al-AlOx-Nb trilayer junctions. In situ elaboration of a SIS trilayers in a sputtering or other physical vacuum deposition (PVD) equipment without breaking the vacuum is a big advantage to achieve uniform and reproducible junction barrier nanolayers interfacing with electrodes films. The study of the role of sputtering conditions and substrate material on NbN cubic film texture and epitaxy at low enough substrate temperature was a clue in the 1980s.
