Ta/Al Bilayers for Coherent Superconducting Quantum Devices

Reducing materials and processing-induced losses in superconducting qubit circuits remains a critical focus in the effort to decrease qubit decoherence and improve overall performance. When considering the superconducting base metallization of a qubit, the interfaces, surfaces, and interior microstructure may all be expected to play a role in the final device performance. In this work we examine the use of Ta, Al, and combined Ta/Al bilayers to examine the impact of base metal material, structure, and interfaces on the performance of coplanar waveguide superconducting resonators. An in-depth materials examination of the bilayer films used in resonator fabrication will be presented, including microstructural, surface, and superconducting critical temperature characterization. Resonator performance will be correlated to differences in Ta/Al bilayer structure, properties, and resonator fabrication.