High-current-density small-area SIS junctions for high-frequency radio astronomy

Eric E. Bloemhof

doi:10.1117/12.180990

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2 July 1994 High-current-density small-area SIS junctions for high-frequency radio astronomy

Eric E. Bloemhof

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Proceedings Volume 2160, Superconductive Devices and Circuits; (1994) https://doi.org/10.1117/12.180990
Event: OE/LASE '94, 1994, Los Angeles, CA, United States

Abstract

At the Smithsonian Astrophysical Observatory, we have been developing expertise in the construction of high-frequency heterodyne receivers using SIS junctions as their first mixing elements. This research has been carried out in support of the Submillimeter Array (SMA), a radio interferometer soon to be built on Mauna Kea that will require multiple reciever systems at a number of bands between 177 GHz and 920 GHz. In this paper, we describe research on the fabrication of all-refractory SIS junctions. To be useful as high-frequency mixers, SIS junctions must have small area and high critical current density. At the lower SMA frequencies, Nb/Al-Oxide/Nb ahs proven to be an ideal material system, and optical photolithography has sufficient resolution for junction definition. At the higher frequencies, NbN/MgO/NbN may enjoy an advantage due to its larger energy gap, and electron-beam lithography may be necessary for defining junctions much smaller than one micron in size. We report good initial results for Nb/Al-Oxide/Nb junctions, fabricated using a self-aligned optical technique, with area $AP 0.5 micrometers ² and critical current density $AP 10,000 Amp/cm².

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Eric E. Bloemhof "High-current-density small-area SIS junctions for high-frequency radio astronomy", Proc. SPIE 2160, Superconductive Devices and Circuits, (2 July 1994); https://doi.org/10.1117/12.180990

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