Performance of Terahertz Waveguide SIS Mixers Employing Epitaxial NbN Films and Nb Junctions
- 30 June 2009
- journal article
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Applied Superconductivity
- Vol. 19 (3), 405-408
- https://doi.org/10.1109/tasc.2009.2018232
Abstract
We have designed, fabricated, and tested terahertz waveguide superconductor-insulator-superconductor (SIS) mixers with Nb/AlOx/Nb junctions and NbN/SiO2/Al microstriplines. The NbN ground plane used was an epitaxial film grown on a single-crystal MgO substrate. A two-junction tuning circuit, which was directly placed at the feed point of a bow-tie waveguide probe without impedance transformers, was used. A full-height waveguide, hammer-type choke filter, and zero-depth backshort were adopted for the design of the microstrip-waveguide transition structure. The Nb junctions in which the current density was 6.5 kA/cm2 showed good I-V characteristics, yielding a subgap-to-normal-state resistance ratio greater than 20. The results obtained for the mixer performance showed a receiver noise temperature of 440 K (DSB) at 1 THz; the results were corrected for losses in the beam splitter and the vacuum window. A detailed analysis of the mixers suggested that the waveguide mixers composed of epitaxial NbN films and Nb junctions were effective in the terahertz band.Keywords
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