Annealing reduces Si 3 N 4 microwave-frequency dielectric loss in superconducting resonators

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 (TLSs), including damping caused by resonant energy exchange with TLSs and by the relaxation of nonresonant TLSs. 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 2 orders of magnitude, and reduces the resonant -type damping by a factor of 3. Employing infrared absorption spectroscopy, we find that annealing reduces the concentration of hydrogen in Si 3 N 4 , suggesting that hydrogen impurities cause substantial dissipation.