Characteristics of Nb/Al superconducting tunnel junctions fabricated using ozone gas

doi:10.1088/1674-1056/24/9/093301

Abstract To improve the energy resolution (ΔE) of Nb/Al superconducting tunnel junctions (STJs), an ozone (O₃) oxidation process has been developed to fabricate a thin defect-free tunnel barrier that simultaneously shows high critical current J_C > 1000 A/cm² and high normalized dynamic resistance R_DA > 100 MΩ · μm², where A is the size of the STJ. The 50-μm² STJs produced by O₃ exposure of 0.26 Pa· min with an indirect spray of O₃ gas, which is a much lower level of exposure than the O₂ exposure used in a conventional O₂ oxidation process, exhibit a maximum J_C = 800 A/cm² and a high R_DA= 372 MΩ · μm². The 100-pixel array of the 100-μm² STJs produced using the same O₃ oxidation conditions exhibits a constant leak current I_leak = 14.9 ± 3.2 nA at a bias point around Delta /e (where e is half the energy gap of an STJ), and a high fabrication yield of 87%. Although the I_leak values are slightly larger than those of STJs produced using the conventional O₂ oxidation process, the STJ produced using O₃ oxidation shows a ΔE = 10 eV for the C-Kα line, which is the best value of our Nb/Al STJ x-ray detectors.

Keywords: Nb/Al superconducting tunnel junctions high critical current density high energy resolution ozone

Received: 05 December 2014
Revised: 28 April 2015
Accepted manuscript online:

PACS:	33.20.Kf	(Visible spectra)
	33.70.Jg	(Line and band widths, shapes, and shifts)

Corresponding Authors: Masahiro Ukibe
E-mail: ukibe-m@aist.go.jp

Cite this article:

Masahiro Ukibe, Go Fujii, Masataka Ohkubo Characteristics of Nb/Al superconducting tunnel junctions fabricated using ozone gas 2015 Chin. Phys. B 24 093301

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Characteristics of Nb/Al superconducting tunnel junctions fabricated using ozone gas

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