Characterization of NbN/AlN/NbN tunnel junctions fabricated without intentional heating

We have fabricated by SNEP process Nb/Al/NbN/AlN/NbN Josephson junctions with the gap voltage V-g = 2 Delta/e approximate to 4.0 mV, subgap leakage R-sg/R-n = 6.0, current density measured at the gap current rise J(g) approximate to 1.5 kA/cm(2). The (111)-textured NbN with transition temperature T-c approximate to 16 K have been deposited at ambient substrate temperature, Phase composition and structure of the NbN films were investigated by X-ray diffraction analysis (XRD). It was found that the films have a structure close to the cubic delta-NbN (JCPDS card N38-11556) and the phase composition and intrinsic stress in NbN depend on Ar and N-2 partial pressure during DC magnetron sputtering, Cross-sectional TEM analysis showed that in-situ deposition of thin Al layer in the base Nb/Al/NbN electrode provides effective planarization of its surface and the result in improvement of tunnel junction parameters.