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Chin. Phys. B, 2015, Vol. 24(9): 093301    DOI: 10.1088/1674-1056/24/9/093301

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
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.
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:

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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