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Fabrication and DC-Characterization of NbTiN Based SIS Mixers for Use Between 600 and 1200 GHz

Authors:
J. A. Stern, B. Bumble, H. G. LeDuc, J. W. Kooi, J. Zmuidzinas
Abstract:
SIS mixers incorporating two-junction, NbTiN tuning-circuits have been designed and fabricated using two different types of tunnel-junctions. The first type of tunnel junction- NbTiN/MgO/NbTiN--has the advantage of a large gap voltage (5 mV), but has a relatively soft I-V characteristic and high specific capacitance as compared to Nb/Al-Ox/Nb tunnel-junctions. The second type of junction—Nb/Al-AlNx/NbTiN, is a hybrid structure, which has many of the advantages of Nb junctions, with a slightly larger energy gap voltage (3.5 mV) and more robust thermal properties. A detailed description of the deposition techniques used in making the AlNx devices will be given in a separate paper. In this paper, we discuss the deposition of high-quality NbTiN films, and the trade-off between stress and quality in these films. We also discuss the deposition details for the NbTiN/MgO/NbTiN junctions. We measured the magnetic-penetration-depth of our NbTiN films with SQUID circuits. Using long resonators coupled to Josephson junctions, we measured propagation velocities for our microstrip-line circuits; this measurement gave us an independent estimate of the NbTiN magnetic-penetration-depth and a qualitative measure of RF-losses in the microstrip-lines.
Categories:
Devices, Receivers
Year:
1998
Session:
7
Full-text:
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Page Number(s):
305-313