Effect of Chemical and Plasma Functionalization on the Performance of Microwave Resonators

Charged tunneling defects at the vacuum-dielectric interfaces are known to be deleterious to quantum bits in superconducting quantum computing. In this work, we explored both chemical and plasma based functionalization strategies to substitute siloxane functional groups with Si-H and Si-F on the silicone surface. The chemical used was hydrofluoric acid, which had two effects - removing all residual hydrocarbons left from the surfaces and the aluminium passivation layer deposited on top of the TiN. The plasma functionalization was performed in Ar/SF
6
, Ar/H
2
, Ar/C
4
F
8
and O
2
environments. Best results were obtained after combining the chemical and plasma treatment in Ar/SF
6
. Q-factors of 800k were measured for devices produced with 25 nm TiN thick films with 12 μm spacing and 3 μm line width. We correlate the change in Q factors with chemical, structural and morphological modifications of the TiN and Si surfaces.