Quantitative Analysis of Surface Losses in Coplanar Waveguide Resonators Part 2: Anisotropic Trenching*

Deep anisotropic etching into the substrate drastically alters the surface participation ratios of coplanar waveguide resonators. This technique provides one method to mitigate losses by reducing overall participation or to shift losses between interfaces for comparison to modeling. Here we demonstrate titanium nitride coplanar waveguide resonators with mean quality factors exceeding two million and controlled trenching reaching 2.2 µm into the silicon substrate. We measure sets of resonators with a range of sizes and trench depths and compare these results with finite-element simulations to demonstrate quantitative agreement with a model of interface dielectric loss. We then apply this analysis to determine the extent to which trenching can improve resonator performance. Furthermore, we report progress on understanding other loss contributions in these systems and the application of trenching to superconducting qubit devices.