Alternating Bias Assisted Annealing of Amorphous Oxide Tunnel Junctions

  1. David P. Pappas,
  2. Mark Field,
  3. Cameron Kopas,
  4. Joel A. Howard,
  5. Xiqiao Wang,
  6. Ella Lachman,
  7. Lin Zhou,
  8. Jinsu Oh,
  9. Kameshwar Yadavalli,
  10. Eyob A. Sete,
  11. Andrew Bestwick,
  12. Matthew J. Kramer,
  13. and Joshua Y. Mutus
We demonstrate a transformational technique for controllably tuning the electrical properties of fabricated thermally oxidized amorphous aluminum-oxide tunnel junctions. Using conventional test equipment to apply an alternating bias to a heated tunnel barrier, giant increases in the room temperature resistance, greater than 70%, can be achieved. The rate of resistance change is shown to be strongly temperature-dependent, and is independent of junction size in the sub-micron regime. In order to measure their tunneling properties at mK temperatures, we characterized transmon qubit junctions treated with this alternating-bias assisted annealing (ABAA) technique. The measured frequencies follow the Ambegaokar-Baratoff relation between the shifted resistance and critical current. Further, these studies show a reduction of junction-contributed loss on the order of ≈2×10−6, along with a significant reduction in resonant- and off-resonant-two level system defects when compared to untreated samples. Imaging with high-resolution TEM shows that the barrier is still predominantly amorphous with a more uniform distribution of aluminum coordination across the barrier relative to untreated junctions. This new approach is expected to be widely applicable to a broad range of devices that rely on amorphous aluminum oxide, as well as the many other metal-insulator-metal structures used in modern electronics.
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