High-quality sub-micron Nb trilayer tunnel junctions for a 100 GHz SIS receiver

• Published in: IEEE Transactions on Magnetics (Institute of Electrical and Electronics Engineers); (United States) 1991-03, Vol.27 (2), p.3165-3167
• Main Authors: Worsham, A.H., Prober, D.E., Kang, J.H., Przybysz, J.X., Rooks, M.J.
• Format: Article
• Language: English
• Subjects: 665300 > Interactions Between Beams & Condensed Matter-- (1992-); 665411 > Basic Superconductivity Studies-- (1992-); Aging; Applied sciences; Capacitance; CHALCOGENIDES; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Contact resistance; CURRENT DENSITY; ELECTRIC CONDUCTIVITY; ELECTRICAL INSULATION; ELECTRICAL PROPERTIES; Electronics; ELEMENTS; Exact sciences and technology; FABRICATION; Insulation; JUNCTIONS; LAYERS; METALS; MINERALS; NIOBIUM; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; PHYSICAL PROPERTIES; Physics; QUALITY FACTOR; QUARTZ; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; SILICON COMPOUNDS; SILICON OXIDES; SUBSTRATES; Superconducting device noise; Superconducting devices; SUPERCONDUCTING JUNCTIONS; SUPERCONDUCTIVITY; TRANSITION ELEMENTS 665412 > Superconducting Devices-- (1992-); TUNNEL EFFECT; Voltage; Wiring
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/20.133883

A modified SNIP process was used to fabricate high-quality 0.5, 2, and 4 mu m/sup 2/ small-area Nb/AlO/sub x//Nb trilayer tunnel junctions with current densities as large as 5000 A/cm/sup 2/. The average junction quality factors for the junctions at 4.4 K were V/sub m/(2 mV)=39 mV for J/sub c/=3000 A/cm/sup 2/ and V/sub m/ (2 mV)=27 mV for J/sub c/=5000 A/cm/sup 2/. The best values of V/sub m/ obtained were 50 mV for J/sub c/=3000 A/cm/sup 2/ and 41 mV for J/sub c/=5000 A/cm/sup 2/. These devices were designed and fabricated for use in a W-band mixer receiver. The substrate was 50- mu m-thick fused or crystal quartz. Special methods were developed for handling such thin insulating substrates and patterning films. The fabrication process was self-aligned and used SiO/sub 2/ instead of anodized Nb as the thick insulator. SiO/sub 2/ isolated the junction area and defined the opening for contact to the Nb wiring layer. The authors have fabricated series arrays of up to 12 junctions, with individual junction areas of 0.5 mu m/sup 2/. The array I-V quality was not degraded compared to that of an individual junction.