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DOE OSTI · 1979035

Nitrogen plasma passivated niobium resonators for superconducting quantum circuits

Zheng, K.·Kowsari, D.·Thobaben, N. J.·Du, X.·Song, X.·Ran, S.·Henriksen, E. A.·Wisbey, D. S.·Murch, K. W.
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Abstract

Microwave loss in niobium metallic structures used for superconducting quantum circuits is limited by a native surface oxide layer formed over a timescale of minutes when exposed to an ambient environment. Here, in this work, we show that nitrogen plasma treatment forms a niobium nitride layer at the metal–air interface, which prevents such oxidation. X-ray photoelectron spectroscopy confirms the doping of nitrogen more than 5 nm into the surface and a suppressed oxygen presence. This passivation remains stable after aging for 15 days in an ambient environment. Cryogenic microwave characterization shows an average filling-factor-adjusted two-level-system loss tangent Fδ TLS of (2.9±0.5)·10 –7 for resonators with a 3 μm center strip and (1.0±0.3)·10 –7 for a 20 μm center strip, exceeding the performance of unpassivated samples by a factor of four.

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71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICSDepth profiling techniquesDielectric propertiesPlasma processingQuantum computingSuperconductivitySuperconductorsThin filmsX-ray photoelectron spectroscopy

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Zheng, K., Kowsari, D., Thobaben, N. J., Du, X., Song, X., Ran, S., Henriksen, E. A., Wisbey, D. S., Murch, K. W.. 2022-03-11. Nitrogen plasma passivated niobium resonators for superconducting quantum circuits. https://doi.org/10.1063/5.0082755

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