Low-loss superconducting coplanar waveguide resonators fabricated with TiN

Titanium nitride (TiN) is an attractive superconducting material for superconducting circuits due to its high kinetic inductance. Here, we report low-loss superconducting coplanar waveguide (CPW) resonators fabricated with high-quality TiN thin films. As evidenced in X-ray diffraction analyses, single crystalline TiN film is epitaxially sputtered on c-plane sapphire wafers by optimizing its growth condition. CPW resonators with a center line width of 10 μm are fabricated based on TiN films of various thickness. Microwave characterization is performed at millikelvin temperature in low-power and high-power regimes, respectively. The best internal quality factor Q_i > 3 million in the single-photon limit and Q_i > 12 million in the high power limit. Surprisingly, anomalous film thickness dependence of kinetic inductance is observed, which may originate from varied TiN stoichiometry in the films of different thickness.