Lift-Off Processing and Superconducting Circuit Coherence

As superconducting circuit coherence continues to increase, careful attention must be paid to device fabrication techniques. Substantial evidence points to dielectric loss from two-level state defects in thin amorphous interfacial regions as a limiting relaxation mechanism for superconducting qubits. Transmon qubits have traditionally been fabricated using lift-off aluminum deposited together with their Josephson junctions; however, improved coherence times have recently been found in transmons which use lift-off metal for only a small fraction of the qubit. To better understand this improvement and predict any remaining limits imposed by the incorporation of lift-off, we characterize the increased loss found in coplanar waveguide resonators formed with lift-off metal. We vary surface treatment such as oxygen ashing and ion milling, and study the effects of double-angle evaporation, e-beam resist residue, and surface roughness on resonator quality factors.