# An argon ion beam milling process for native $\text{AlO}_\text{x}$ layers enabling coherent superconducting contacts

## TL;DR

This paper introduces an argon ion beam milling process to effectively remove native aluminum oxide layers, enabling high-quality, coherent superconducting contacts compatible with quantum circuit fabrication.

## Contribution

The study demonstrates a novel ion beam milling technique that preserves superconducting properties and integrates seamlessly with existing Josephson junction fabrication processes.

## Key findings

- Residual resistance of ion beam milled contacts is below 50 mΩ·μm².
- Resonators with 6% ion beam exposure maintain quality factors above 10^6.
- No degradation observed in superconducting resonators after ion beam treatment.

## Abstract

We present an argon ion beam milling process to remove the native oxide layer forming on aluminum thin films due to their exposure to atmosphere in between lithographic steps. Our cleaning process is readily integrable with conventional fabrication of Josephson junction quantum circuits. From measurements of the internal quality factors of superconducting microwave resonators with and without contacts, we place an upper bound on the residual resistance of an ion beam milled contact of 50$\,\mathrm{m}\Omega \cdot \mu \mathrm{m}^2$ at a frequency of 4.5 GHz. Resonators for which only $6\%$ of the total foot-print was exposed to the ion beam milling, in areas of low electric and high magnetic field, showed quality factors above $10^6$ in the single photon regime, and no degradation compared to single layer samples. We believe these results will enable the development of increasingly complex superconducting circuits for quantum information processing.