Impact of substrate and resonator surface treatments on microwave loss of high-Q titanium nitride superconducting resonators
This work explores the influence of surface treatments on the resonator performance of single-crystal titanium nitride (TiN) films grown on sapphire substrates using plasma-assisted molecular beam epitaxy. Various surface treatments are performed on the substrate prior to growth, and on the complete resonator devices prior to wire bonding in order to reduce two level system loss.
The impact of sapphire surface cleaning prior to thin film growth is investigated through six wafers. The set of wafers are cleaned using an ex-situ cleaning of either organic solvents or a Piranha etch and an in-situ treatment consisting of a thermal anneal under either UHV, atomic-nitrogen, or atomic-oxygen conditions. The finished resonators are treated with either a hydrofluoric or piranha etch.
The effect of various cleaning treatments on the sapphire wafers and the TiN thin film are characterized using AFM, SEM and HRXRD. XPS analysis of the acid-cleaned resonator surfaces indicate that both acid etches reduces the O-1s peak intensity. Acid-cleaning the resonators consistently doubles the internal quality factor, with a mean quality factor close to 1 million, compared to control samples that are cleaned with organic solvents.