Fabrication and characterization of Nb/Al-AlN /Nb superconducting tunnel junctions

  1. Alexey Pavolotsky,
  2. François Joint,
  3. Udupa Sujit Manjunatha,
  4. Victor Belitsky,
  5. Denis Meledin,
  6. Takafumi Kojima,
  7. Sho Masui,
  8. Ravishankar Narayanan,
  9. and Vincent Desmaris
We report a Nb/Al-AlN /Nb superconducting tunnel junction process in which the AlN barrier is formed by plasma nitridation using a compact microwave electron-cyclotron-resonance (ECR) nitrogen plasma source integrated into a standard sputter cluster. This enables growth of uniform tunnel barriers across a broad range of specific resistances, with RnA down to ≈3,Ω,μm2. Junctions maintain excellent quality, exhibiting Rj/Rn≥25 at the highest barrier transparencies. We characterize resistivity, specific capacitance, and the evolution of junction parameters under room-temperature aging and thermal annealing. A consistent calibration of the junction specific capacitance Cs versus RnA is established and independently validated by the performance of demonstrator SIS mixers designed using the extracted Cs.
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