Photolithography-Only Fabrication of Transmons Using Double-Oblique Evaporation

TL;DR

This paper demonstrates a photolithography-only process for fabricating transmon qubits with double-oblique evaporation, achieving functional devices with promising quantum coherence properties.

Contribution

It introduces a novel fabrication method for transmon Josephson junctions using a modified double-oblique evaporation technique, eliminating the need for electron-beam lithography.

Findings

Junctions with geometrical areas around 10^4 nm^2 were successfully fabricated.

Junction resistance falls within the target range for transmon design.

Transmon devices exhibit basic quantum operation with T1 ~ 9 μs and T2* ~ 0.4 μs.

Abstract

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 $10^4~\mathrm{nm}^2$, 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 $20 \, \mathrm{mK}$, where we observe basic transmon qubit operation with $f_{01}$=4.865 GHz, $T_1 \sim 9 \, \mu \mathrm{s}$, and $T_2^* \sim 0.4 \, \mu \mathrm{s}$. These results demonstrate the feasibility of realizing functional transmon devices in a photolithography-only process using double-oblique evaporation.