S. Massar

Ultra-high Q-factor superconducting tantalum resonators on 300 mm Si wafers

  1. R. Acharya,
  2. D. Perez Lozano,
  3. Ts. Ivanov,
  4. S. Massar,
  5. C. Vrancken,
  6. Y. Canvel,
  7. Y. Li,
  8. A. M. Vadiraj,
  9. J. Van Damme,
  10. S. Aghaeimeibodi,
  11. A. Khalajhedayati,
  12. M. Mongillo,
  13. O. Painter,
  14. D. Wan,
  15. A. Potočnik,
  16. and K. De Greve
Superconducting resonators are central to superconducting quantum information technologies and essential for bosonic qubit architectures, where long-lived storage modes enable hardware-efficient
error correction. Achieving ultra-high quality factors in scalable planar circuits is challenging because multiple dissipation channels contribute to the total loss. Here we report planar α-Ta resonators fabricated on 300 mm ultra-high-resistivity (>10 kΩ cm) intrinsic silicon using industrial processes, achieving median internal Q factors exceeding 40 million and maxima above 60 million. Energy-participation-ratio analysis identifies a dominant participation-controlled interface loss mechanism and places conservative upper bounds on substrate-associated dissipation. For the best-performing substrate, the inferred substrate loss tangent is below 1.0×10−8, establishing industrial MCZ silicon among the lowest-loss substrate platforms reported for superconducting resonators. At the same time, the exceptionally low losses show no clear correlation with commonly cited silicon substrate metrics such as room-temperature resistivity or impurity concentrations. More broadly, these studies establish industrial 300 mm processing, careful interface engineering, and 300 mm MCZ silicon substrates as a promising platform for resonator-heavy superconducting quantum architectures with ultra-high quality factors.
arxiv pdf

Reversing Hydrogen-Related Loss in α-Ta Thin Films for Quantum Device Fabrication

  1. D. P. Lozano,
  2. M. Mongillo,
  3. B. Raes,
  4. Y. Canvel,
  5. S. Massar,
  6. A. M. Vadiraj,
  7. Ts. Ivanov,
  8. R. Acharya,
  9. J. Van Damme,
  10. J. Van de Vondel,
  11. D. Wan,
  12. A. Potocnik,
  13. and K. De Greve
α-Tantalum (α-Ta) is an emerging material for superconducting qubit fabrication due to the low microwave loss of its stable native oxide. However, hydrogen absorption during fabrication,
particularly when removing the native oxide, can degrade performance by increasing microwave loss. In this work, we demonstrate that hydrogen can enter α-Ta thin films when exposed to 10 vol% hydrofluoric acid for 3 minutes or longer, leading to an increase in power-independent ohmic loss in high-Q resonators at millikelvin temperatures. Reduced resonator performance is likely caused by the formation of non-superconducting tantalum hydride (TaHx) precipitates. We further show that annealing at 500°C in ultra-high vacuum (10−8 Torr) for one hour fully removes hydrogen and restores the resonators‘ intrinsic quality factors to ~4 million at the single-photon level. These findings identify a previously unreported loss mechanism in α-Ta and offer a pathway to reverse hydrogen-induced degradation in quantum devices based on Ta and, by extension also Nb, enabling more robust fabrication processes for superconducting qubits.
arxiv pdf