IEEE Transactions on Applied Superconductivity

High current density NbN/AlN/NbN tunnel junctions for submillimeter wave SIS mixers

Z. Wang, Yoshinori Uzawa, Akira Kawakami

Published Jun 1, 1997• 38 citations

Abstract

We report on the fabrication and properties of high current density NbN/AlN/NbN tunnel junctions for the application of superconducting SIS mixers in the submillimeter wave regions. Junctions having current densities as high as 50 kA/cm/sup 2/ exhibited a good Josephson tunneling behaviour, excellent terahertz response, and sensitive heterodyne mixing properties. Accurate values of junction capacitance were estimated by measuring dc-SQUID resonant steps for the design of tuning circuits. The measured specific capacitance gives values in the range of 20-200 fF//spl mu/m/sup 2/ for the current density range of 1-100 kA/cm/sup 2/. The NbN/AlN/NbN tunnel junctions were integrated with a NbN thin film antenna to investigate the terahertz responses and mixing tests in a quasi-optical testing system. Photon-assisted tunneling steps were clearly observed on the I-V curve with irradiation up to 1.02 THz, and a low-noise heterodyne mixing was demonstrated in the 300-GHz band.

DOI: 10.1109/77.621818

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