Photolithography-Only Fabrication of Transmons Using Double-Oblique Evaporation

  1. K. Aoyanagi,
  2. S. Abe,
  3. S. Chen,
  4. T. Inada,
  5. C. Kawai,
  6. Y. Mino,
  7. K. Nakamura,
  8. K. Nakazono,
  9. T. Nitta,
  10. and K. Watanabe
We investigate a photolithography-only fabrication process for transmon Josephson junctions using a modified double-oblique evaporation geometry. Using a bilayer resist process and
Al shadow evaporation, we fabricate junction structures and confirm by optical and scanning electron microscopy that the resulting narrowed crossing region reaches a geometrical area on the order of 104 nm2, which lies in the size range relevant to qubit junction fabrication. Room-temperature resistance screening shows that the junction resistance falls within the target range for the present transmon design over a usable process window and exhibits a clear design dependence. We further implement fabricated junctions in transmon devices and evaluate them in a three-dimensional Al cavity at 20mK, where we observe basic transmon qubit operation with f01=4.865 GHz, T1∼9μs, and T∗2∼0.4μs. These results demonstrate the feasibility of realizing functional transmon devices in a photolithography-only process using double-oblique evaporation.