Dielectric loss extraction for superconducting microwave resonators

Abstract

The investigation of two-level-state (TLS) loss in dielectric materials and interfaces remains at the forefront of materials research in superconducting quantum circuits. We demonstrate a method of TLS loss extraction of a thin film dielectric by measuring a lumped element resonator fabricated from a superconductor-dielectric-superconductor trilayer. We extract the dielectric loss by formulating a circuit model for a lumped element resonator with TLS loss and then fitting to this model using measurements from a set of three resonator designs: a coplanar waveguide resonator, a lumped element resonator with an interdigitated capacitor, and a lumped element resonator with a parallel plate capacitor that includes the dielectric thin film of interest. Unlike other methods, this allows accurate measurement of materials with TLS loss lower than $10^{-6}$. We demonstrate this method by extracting a TLS loss of $1.02\times 10^{-3}$ for sputtered $\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$ using a set of samples fabricated from an $Al/A{\mathrm{l}}_2{\mathrm{O}}_3/Al$ trilayer. We observe a difference of 11$\%$ between extracted loss of the trilayer with and without the implementation of this method.