Transmission electron microscopy and atomic force microscopy analysis of Nb-Al-AlOx-Nb superconducting tunnel junction detectors

DOI PDF 被引用文献2件
  • N. Rando
    Astrophysics Division, Space Science Department of the European Space Agency, ESTEC, Noordwijk, The Netherlands
  • P. Videler
    Astrophysics Division, Space Science Department of the European Space Agency, ESTEC, Noordwijk, The Netherlands
  • A. Peacock
    Astrophysics Division, Space Science Department of the European Space Agency, ESTEC, Noordwijk, The Netherlands
  • A. van Dordrecht
    Astrophysics Division, Space Science Department of the European Space Agency, ESTEC, Noordwijk, The Netherlands
  • P. Verhoeve
    Astrophysics Division, Space Science Department of the European Space Agency, ESTEC, Noordwijk, The Netherlands
  • R. Venn
    Cambridge Microfab, Cambridge, United Kingdom
  • A. C. Wright
    Advanced Materials Research Laboratory, MRIC, North East Wales Institute, Mold Road, Wrexham LL11 2AW, United Kingdom
  • J. Lumley
    Oxford Instruments, Scientific Research Division, Cambridge, United Kingdom

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<jats:p>The performance of photon detectors based on superconducting tunnel junctions are related to their current - voltage (I-V) curve characteristics and, ultimately, to the quality of the thin tunnel barriers (of order 1 nm) which separate the two superconducting thin films. Both the optimization of the spectroscopic performance of these detectors and the development of a reproducible and high yield fabrication route, require a better understanding of barrier quality and growth techniques. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) provide valuable tools for the investigation of the barrier region and for the control of the quality of the different thin films and related interfaces. In this paper, the results of a TEM and AFM evaluation of Nb-Al-AlOx-Nb tunnel junctions are reported, together with their interpretation on the basis of the I-V curve performance at low temperature (T≥0.3 K). Thickness disuniformities of the Al plus AlOx overlayer and evidence of barrier defects have been found, which may place constraints on the spectroscopic performance of such devices. Through the use of TEM it has also been possible to confirm the epitaxial nature of the Nb base electrode. The junction counter electrode however appears to be polycrystalline, with a columnar morphology and an average grain width of 40 nm. The overall structure of the various layers may well place constraints on the tunneling characteristics of the device.</jats:p>

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