Development of Low-Noise Terahertz SIS Mixers with High Current Density NbN/AlN/NbN Tunnel Junctions

Zhen WANG  Yoshinori UZAWA  Akira KAWAKAMI  

IEICE TRANSACTIONS on Electronics   Vol.E83-C   No.1   pp.27-33
Publication Date: 2000/01/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Issue on Superconductive Devices and Systems)
Category: Analog Applications
NbN/AlN/NbN tunnel junction,  ultra-high current density,  quasi-optical SIS mixer,  Al/SiO/NbN microstripline,  quantum noise limit,  

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We report on progress in the development of high current density NbN/AlN/NbN tunnel junctions for application as submillimeter wave SIS mixers. A ultra-high current density up to 120 kA/cm2, roughly two orders of magnitude larger than any reported results for all-NbN tunnel junctions, was achieved in the junctions. The magnetic field dependence and temperature dependence of critical supercurrents were measured to investigate the Josephson tunneling behaviour of critical supercurrents in the high-Jc junctions. We have developed a low-noise quasi-optical SIS mixer with the high-current density NbN/AlN/NbN junctions and two-junction tuning circuits which employ Al/SiO/NbN microstriplines. The tuning characteristics of the mixer were investigated by measuring the response in the direct detection mode by using the Fourier Transform Spectrometer (FTS) and measuring the response in the heterodyne detection mode with the standard Y-factor method at frequencies from 670 to 1082 GHz. An uncorrected double sideband receiver noise temperature of 457 K (12hν/kB) was obtained at 783 GHz.