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Characteristics of Nb/Al superconducting tunnel junctions fabricated using ozone gas |
Masahiro Ukibe, Go Fujii, Masataka Ohkubo |
Nanoelectronics Research Institute (nano), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan |
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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 JC > 1000 A/cm2 and high normalized dynamic resistance RDA > 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 JC = 800 A/cm2 and a high RDA= 372 MΩ · μm2. The 100-pixel array of the 100-μm2 STJs produced using the same O3 oxidation conditions exhibits a constant leak current Ileak = 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 Ileak 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.
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Received: 05 December 2014
Revised: 28 April 2015
Accepted manuscript online:
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PACS:
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33.20.Kf
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(Visible spectra)
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33.70.Jg
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(Line and band widths, shapes, and shifts)
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Corresponding Authors:
Masahiro Ukibe
E-mail: ukibe-m@aist.go.jp
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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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