Development of high-quality factor thin tantalum superconducting microwave coplanar waveguide resonators for coherent quantum circuits

We designed, calculated, simulated, fabricated and measured thin film (40 nm) arrays of α-Ta coplanar waveguide (CPW) microwave resonators with a niobium (Nb) seed layer on the unheated high resistivity silicon (Si) substrate. The chip is made of three quarter-wavelength (λ/4) microwave resonators which are capacitively coupled to a common transmission line. We performed microwave frequency spectroscopy at ultralow cryogenic temperatures and found the resonance frequencies of the resonators between f= 3-8 GHz. In fact, we observed resonance frequency shift due to kinetic inductance which was calculated as L_K= 2.5×10^-7 (H/m). Moreover, power sweep measurement showed an internal quality factor Q_i (at f_r= 3.65 GHz) exceeding 10⁶ at high power and 2.7×10⁵ at the single photon regime at base temperature T= 77 mK.