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Open Access Publications from the University of California

Controlling Tcof iridium films using the proximity effect

  • Author(s): Hennings-Yeomans, R
  • Chang, CL
  • Ding, J
  • Drobizhev, A
  • Fujikawa, BK
  • Han, S
  • Karapetrov, G
  • Kolomensky, YG
  • Novosad, V
  • O'Donnell, T
  • Ouellet, JL
  • Pearson, J
  • Polakovic, T
  • Reggio, D
  • Schmidt, B
  • Sheff, B
  • Singh, V
  • Smith, RJ
  • Wang, G
  • Welliver, B
  • Yefremenko, VG
  • Zhang, J
  • et al.

Published Web Location

A superconducting Transition-Edge Sensor (TES) with low- T c is essential in high resolution calorimetric detection. With the motivation of developing sensitive calorimeters for applications in cryogenic neutrinoless double beta decay searches, we have been investigating methods to reduce the T c of an Ir film down to 20 mK. Utilizing the proximity effect between a superconductor and a normal metal, we found two room temperature fabrication recipes for making Ir-based low- T c films. In the first approach, an Ir film sandwiched between two Au films, a Au/Ir/Au trilayer, has a tunable T c in the range of 20-100 mK depending on the relative thicknesses. In the second approach, a paramagnetic Pt thin film is used to create the Ir/Pt bilayer with a tunable T c in the same range. We present a detailed study of fabrication and characterization of Ir-based low- T c films and compare the experimental results to the theoretical models. We show that Ir-based films with a predictable and reproducible critical temperature can be consistently fabricated for use in large scale detector applications.

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