Improvements in silicon oxide dielectric loss for superconducting microwave detector circuits
Dale Li, Jason Austermann, James A. Beall, Daniel T. Becker, Hsiao-Mei Cho, Anna E. Fox, Nils Halverson, Jason Henning, Gene C. Hilton, Johannes Hubmayr, Jeffrey L. Van Lanen, John P. Nibarger, Michael D. Niemack, Kent D. Irwin
Dielectric loss in low-temperature superconducting integrated circuits can cause lower overall efficiency, particularly in the 90 to 220 GHz regime. We present a method to tune the dielectric loss for silicon oxide deposited by plasma-enhanced chemical-vapor deposition at ambient temperatures. Deposition in an environment with a higher silane-to-oxygen ratio produces silicon oxide films with a lower loss-tangent and a slightly higher optical index of refraction, while contributing no appreciable change in film stress. We measured the dielectric loss by fabricating a series of Nb- SiOx-Nb microstrip resonators in the frequency range of 6 to 9 GHz and comparing their temperature dependence to a model of parasitic two-level-system fluctuators. The dielectric loss-tangent of silicon oxide was improved from 6 × 10-3 for stoichiometric silicon dioxide to 2 × 10-3 for a more silicon-rich silicon oxide. We present details of the fabrication process and measurements of microstrip resonators.