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

TL;DR

This study shows that high-temperature annealing of silicon nitride significantly reduces microwave-frequency dielectric loss in superconducting resonators, mainly by decreasing hydrogen impurities that cause dissipation, thus improving device performance.

Contribution

It demonstrates that annealing effectively reduces dielectric loss in Si₃N₄ by lowering hydrogen impurity levels, with detailed analysis of loss mechanisms and impurity effects.

Findings

Annealing reduces the loss tangent of Si₃N₄ by over two orders of magnitude.

Annealed Si₃N₄ shows less power-dependent loss at cryogenic temperatures.

Hydrogen impurity reduction correlates with decreased dielectric dissipation.

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.