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TT: Fachverband Tiefe Temperaturen
TT 1: Superconductivity - Fabrication and Characterization
TT 1.2: Talk
Monday, March 26, 2007, 09:45–10:00, H18
Optimization of superconducting/normal metal bi-layers for antenna structures of Hot-Electron Mixers — •Axel Stockhausen1, Konstantin Ilin1, Michael Siegel1, Alexei Semenov2, Andrey Smirnov2, and Heinz-Wilhelm Huebers2 — 1Institute of Micro- and Nano-Electronic Systems, University of Karlsruhe, Karlsruhe, Germany — 2DLR e.V. Institute of Planetary Research, Berlin-Adlershof, Germany
Hot-Electron Mixers operational in the THz frequency range are made from an ultra-thin (< 5 nm) NbN superconducting film, which is in direct contact with an antenna structure from a thick (about 300 nm) gold layer. Usually titanium or chromium in-situ deposited films are used as a buffer layer for the gold film. This leads to suppression of superconductivity in the ultra-thin NbN film due to the proximity effect and worsening of the device performance. To support the superconducting energy gap in the ultra-thin NbN film a buffer layer of superconducting material can be used instead of a normal metal. We report results on the development of deposition processes of superconducting Nb, NbN thin films, and Nb/Au and NbN/Au bi-layer structures. The superconducting films of Nb and NbN were deposited by magnetron or reactive magnetron sputtering of Nb target onto Si substrate kept at room temperature. In-situ Ar ion milling technique was used for pre-cleaning of the substrate surface before deposition. The dependencies of superconducting and normal state properties of the Nb and NbN films and multi-layer structures on deposition conditions will be presented and discussed.