NbN/AIN/NbN Tunnel Junctions Applied as Terahertz SIS Mixers

Zhen WANG  Yoshinori UZAWA  Akira KAWAKAMI  

IEICE TRANSACTIONS on Electronics   Vol.E80-C   No.10   pp.1258-1264
Publication Date: 1997/10/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Issue on Basic Properties and Applications of Superconductive Electron Devices)
NbN/AlN/NbN junction,  high current density,  SIS mixer,  terahertz response,  heterodyne mixing,  

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We report on progress in the development of high-current-density all-NbN tunnel junctions for application as submillimeter wave SIS mixers. A very high current density up to 54 kA/cm2, roughly an order of magnitude larger than any reported results for all-NbN tunnel junctions, was achieved in the junctions with a thin aluminum nitride (AIN) tunnel barrier. Even though the junctions have a very high current density, they showed high-quality junction characteristics with a large gap voltage, sharp quasipartical current rise, and small subgap leakage current. The junctions also exhibited good Josephson tunneling behavior, excellent terahertz response, and sensitive heterodyne mixing properties. NbN/AIN/NbN tunnel junctions were integrated with a NbN thin-film antenna to investigate the terahertz responses and the heterodyne mixing properties in a quasioptical mixer testing system. Photon-assisted tunneling steps were clearly observed on the I-V curve with irradiation up to 1 THz, and low-noise heterodyne mixing was demonstrated in the 300-GHz band.