Related papers: Krypton-sputtered tantalum films for scalable high-performance quantum devices

Krypton-sputtered tantalum films for scalable high-performance quantum devices

URL: http://arxiv.org/abs/2601.20091v1
Date: Tue, 27 Jan 2026 22:24:40 GMT
Title: Krypton-sputtered tantalum films for scalable high-performance quantum devices
Authors: Maciej W. Olszewski, Lingda Kong, Simon Reinhardt, Daniel Tong, Xinyi Du, Gabriele Di Gianluca, Haoran Lu, Saswata Roy, Luojia Zhang, Aleksandra B. Biedron, David A. Muller, Valla Fatemi,
Abstract summary: Superconducting qubits based on tantalum (Ta) thin films have demonstrated the highest-performing microwave resonators and qubits.<n>Here, we show that changing the sputter gas from argon to krypton (Kr) promotes BCC Ta synthesis on silicon (Si) at temperatures as low as SI200celsius.<n>We find these films to have substantially higher electronic conductivity, consistent with clean-limit superconductivity.
Score: 31.35573202055024
License: http://creativecommons.org/licenses/by/4.0/
Abstract: Superconducting qubits based on tantalum (Ta) thin films have demonstrated the highest-performing microwave resonators and qubits. This makes Ta an attractive material for superconducting quantum computing applications, but, so far, direct deposition has largely relied on high substrate temperatures exceeding \SI{400}{\celsius} to achieve the body-centered cubic phase, BCC (\textalpha-Ta). This leads to compatibility issues for scalable fabrication leveraging standard semiconductor fabrication lines. Here, we show that changing the sputter gas from argon (Ar) to krypton (Kr) promotes BCC Ta synthesis on silicon (Si) at temperatures as low as \SI{200}{\celsius}, providing a wide process window compatible with back-end-of-the-line fabrication standards. Furthermore, we find these films to have substantially higher electronic conductivity, consistent with clean-limit superconductivity. We validated the microwave performance through coplanar waveguide resonator measurements, finding that films deposited at \SI{250}{\celsius} and \SI{350}{\celsius} exhibit a tight performance distribution at the state of the art. Higher temperature-grown films exhibit higher losses, in correlation with the degree of Ta/Si intermixing revealed by cross-sectional transmission electron microscopy. Finally, with these films, we demonstrate transmon qubits with a relatively compact, \SI{20}{\micro\meter} capacitor gap, achieving a median quality factor up to 14 million.

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