Annealing reduces Si${}_3$N${}_4$ microwave-frequency dielectric loss in superconducting resonators

Abstract

The dielectric loss of silicon nitride (Si${}_3$N${}_4$) limits the performance of microwave-frequency devices that rely on this material for sensing, signal processing, and quantum communication. Using superconducting resonant circuits, we measure the cryogenic loss tangent of either as-deposited or high-temperature annealed stoichiometric Si${}_3$N${}_4$ as a function of drive strength and temperature. The internal loss behavior of the electrical resonators is largely consistent with the standard tunneling model of two-level systems (TLS), including damping caused by resonant energy exchange with TLS and by the relaxation of non-resonant TLS. We further supplement the TLS model with a self-heating effect to explain an increase in the loss observed in as-deposited films at large drive powers. Critically, we demonstrate that annealing remedies this anomalous power-induced loss, reduces the relaxation-type damping by more than two orders of magnitude, and reduces the resonant-type damping by a factor of three. Employing infrared absorption spectroscopy, we find that annealing reduces the concentration of hydrogen in the Si${}_3$N${}_4$, suggesting that hydrogen impurities cause substantial dissipation.

11 pages, 7 figures

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• Impact of Absorption due to Zero-Field Splitting on Loss in Dielectrics: A Case Study in Sapphire
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