ISSTT Proceedings

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NbN HEB for THz Radiation: Technological Issues and Proximity Effect

Authors:
Konstantin S. Il'in, Axel Stockhausen, Michael Siegel, Alexei D. Semenov, Heiko Richter, Heinz-Wilhelm Hübers
Abstract:
Superconducting phonon-cooled hot-electron bolometer (HEB) detectors are complex multi-layer devices consisting of an ultra-thin superconducting film (mostly NbN) and a thick normal metal layer. We present results on the development of NbN ultra-thin film technology and the systematic study of superconducting and transport properties of NbN bridge-structures with different thickness (4 - 10 nm) and width (0.1 - 10 µm). The NbN films are deposited onto heated Si substrate by magnetron sputtering of Nb target in the reactive gas mixture of argon and nitrogen. A critical temperature of about 9.5 K is reached for NbN films with a thickness between 5 and 6 nm. Twofold increase of the film thickness increases the critical temperature to 12 K. Reducing the bridge width below 0.5 µm leads to a decrease in its critical temperature that is similar to the effect of the film thickness. The model of intrinsic proximity effect in ultra-thin films explains fairly well the degradation of superconductivity in NbN bridges with the decrease of either film thickness or bridge width. Moreover, the proximity effect theory agrees well with experimental data on the critical temperature variations in NbN/Au bi-layers with different thickness of the Au layer. We have shown that an 18 nm thick buffer layer of NbN under much thicker Au layer is sufficient to ensure a bi-layer critical temperature of 8.5 K that is close to the critical temperature of 5 nm thick HEB devices. Presented results demonstrate challenges of further developing HEB detectors for THz spectral range.
Categories:
HEB Mixers, Poster Session
Year:
2008
Session:
P2
Full-text:
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Page Number(s):
403-408