Identifying and Mitigating Fabrication-Induced Losses in Superconducting Quantum Devices
SQMS researchers characterize niobium hydride formation from wet chemical processing and associated noise sources in superconducting devices for quantum information science applications
The Science:
Native surface oxides are a major contributor to decoherence in superconducting qubits. Common fabrication protocols use wet chemical fluoride-based etchants, such as hydrofluoric acid and the associated buffered oxide etchant, to minimize these oxides. However, these treatments introduce hydrogen into niobium, leading to the formation of niobium hydrides. By characterizing the formation mechanism of niobium hydrides and associated loss pathways in superconducting devices, we are developing hydride mitigation strategies, which have direct implications for qubit manufacturing.
Impact:
This study reveals that niobium hydrides are not linked to two-level system noise but are correlated to power-independent loss channels. This work also provides evidence that the rate of hydrogen incorporation into niobium is determined by the etch rate of the passivating surface oxide and the concentration of hydrogen in solution. These data have immediate impact on production protocols that both minimize the presence of lossy surface oxides and mitigate the formation of detrimental hydrides in superconducting quantum devices.
Summary:
We have conducted a comprehensive materials characterization of niobium hydrides formed in niobium thin films under various etchant treatments, including hydrofluoric acid, buffered oxide etch, and ammonium fluoride. Leveraging various techniques, including secondary-ion mass spectrometry, X-ray scattering, and transmission electron microscopy, we have examined the spatial distribution and phase transformation of niobium hydrides. We found that the rate of hydride formation is dependent on both the hydrogen concentration in the solution and the etch rate of the native surface oxide, Nb2O5, which acts as a diffusion barrier for hydrogen incorporation. Through correlative device measurements, we have demonstrated that niobium hydrides introduced by wet chemical etching are detrimental to superconducting properties and result in increased power-independent microwave loss in coplanar waveguide resonators. Resonator results revealed no correlation between niobium hydrides and two-level system loss or with device aging mechanisms.
Contacts:
Mark Hersam: m-hersam@northwestern.edu; Michael Bedzyk: bedzyk@northwestern.edu
Focus Areas:
Materials, devices
Institutions:
Northwestern University, NIST Boulder, University of Colorado-Boulder, Colorado School of Mines, University of Oregon, Rigetti Computing, Louisiana State University
Citation:
C. G. Torres-Castanedo, D. P. Goronzy, T. Pham, A. McFadden, N. Materise, P. Masih Das, M. Cheng, D. Lebedev, S. M. Ribet, M. J. Walker, D. A. Garcia-Wetten, C. J. Kopas, J. Marshall, E. Lachman, N. Zhelev, J. A. Sauls, J. Y. Mutus, C. H. McRae, V. P. Dravid, M. J. Bedzyk, and M. C. Hersam, “Formation and microwave losses of hydrides in superconducting niobium thin films resulting from fluoride chemical processing,” Advanced Functional Materials, DOI: 10.1002/adfm.202401365 (2024)
Funding:
This work was primarily supported by the U.S. Department of Energy, the Office of Science, the National Quantum Information Science Research Centers, the Superconducting Quantum Materials and Systems Center (SQMS) under contract No. DE-AC02-07CH11359. This work made use of the Jerome B. Cohen X-Ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (DMR-2308691) at the Materials Research Center of Northwestern University and the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205). This work also made use of the EPIC and Keck-II facilities of the Northwestern University NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and the Northwestern MRSEC program (NSF DMR-2308691).