Enhancing Stability in Superconducting Quantum Circuits via In Situ Al2O3 Deposition
Yi-Ting Cheng1*, Hsien-Wen Wan1, Yen-Hsun Glen Lin1, Lawrence Boyu Young1, Wan-Sin Chen1, Kuan-Hui Lai1, Wei-Jie Yan2, Chao-Kai Cheng1, Yen-Hsiang Lin2, Jueinai Kwo2, Minghwei Hong1
1Graduate Institute of Applied Physics and Dept. of Physics, National Taiwan University, Taipei, Taiwan
2Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:Yi-Ting Cheng, email:d06245005@ntu.edu.tw
Effective passivation of superconducting films is essential for fabricating quantum circuits with enhanced stability. Currently, superconducting films of Al, Ta, and Nb are either exposed to air or subjected to an O₂-rich environment after film deposition, leading to native oxide formation that contributes to dielectric loss at low temperatures and under microwave excitation. Although internal quality factors have improved by removing native oxides and surface contaminants from environmental exposure, these oxides frequently regrow upon re-exposure to air, resulting in gradual degradation over time. In this presentation, we demonstrate superconducting microstrip resonators fabricated with heterostructures featuring in situ-deposited Al₂O₃ thin films on freshly grown Ta and Al films with pristine surfaces. These films were epitaxially deposited on chemically cleaned and ultra-high vacuum (UHV) annealed sapphire substrates. The Al₂O₃ layer effectively shields the underlying Ta and Al films from reactions with atmospheric oxygen-containing species during the device processing and air exposure. The resonators showed minimal to no degradation after two weeks and, in some cases, retained stability even after ten months of air exposure. In conclusion, in situ Al₂O₃ deposition on freshly grown Ta and Al films offers a promising pathway for fabricating superconducting quantum circuits with enhanced long-term stability, applicable to a wide range of superconducting materials.

We acknowledge the support from Natl. Sci. Technol. Council in Taiwan through NSTC 113-2119-M-007-008-.


Keywords: superconducting quantum circuits, in situ oxide deposition, long-term stability, tantalum, aluminum