Very high-current-density Nb/AlN/Nb tunnel junctions for low-noise submillimeter mixers

作者：Jonathan H. Kawamura, David A. B. Miller, Jian Chen, Jonas Stasys Zmuidzinas, B. Bumble, Henry George LeDuc, Jeff A. Stern · 发表于：Applied Physics Letters · 年份：2000 · DOI：10.1063/1.126272 · 被引用次数：55 · 研究领域：Superconducting and THz Device Technology、Physics of Superconductivity and Magnetism、Radio Frequency Integrated Circuit Design

We have fabricated and tested submillimeter-wave superconductor–insulator–superconductor (SIS) mixers using very high-current-density Nb/AlN/Nb tunnel junctions (Jc≈30 kA cm−2). The junctions have low-resistance-area products (RNA≈5.6 Ω μm2), good subgap-to-normal resistance ratios Rsg/RN≈10, and good run-to-run reproducibility. From Fourier transform spectrometer measurements, we infer that ωRNC=1 at 270 GHz. This is a factor of 2.5 improvement over what is generally available with Nb/AlOx/Nb junctions suitable for low-noise mixers. The AlN-barrier junctions are indeed capable of low-noise operation: we measure an uncorrected double-sideband receiver noise temperature of TRX=110 K at 533 GHz for an unoptimized device. In addition to providing wider bandwidth operation at lower frequencies, the AlN-barrier junctions will considerably improve the performance of THz SIS mixers by reducing rf loss in the tuning circuits.