Operational Characteristics of CPW Microwave Resonator Fabricated with High Kinetic Inductance Superconducting TiN Thin Film

Abstract

High kinetic inductance superconducting materials are intriguing due to their nonlinear nature modu-lated by the applied microwave power, making them suitable for practical active devices such as lumped-element kinetic inductance detector (LEKID) [1] and kinetic inductance traveling wave am-plifier (KIT) [2]. Furthermore, it has been suggested that they may be adopted as a substitute for Jo-sephson junction essential to construct superconducting quantum processors. Besides their nonlinear characteristics, the kinetic inductance itself increases the total inductance of resonantor. This is equivalent to an effective increase in the surface reactance of superconducting thin film, which slows down the phase velocity of transmitted quasi-TEM wave and red-shifts the resonant frequency. This aspect of high kinetic inductance superconducting film can bear some critical advantages in designing microwave circuits. In particular, we can significantly reduce the size of each circuit component if the kinetic inductance is not much lower than the geometrically-determined magnetic inductance. In this work, we characterize the material properties of polycrystalline titanium nitride (TiN, Tc ~4.27 K) thin film deposited by reactive DC magnetron sputtering and analyze the operational characteristics of a superconducting coplanar waveguide (CPW) resonator fabricated with it. The sheet kinetic in-ductance L¬k of TiN film estimated from its normal state resistivity is ~ 6.0810 pH/sq, ~144 times larger than that of Nb (Tc ~9.01 K, L¬k ~42.1071 fH/sq) film. This leads to a remarkable red-shift in the resonant frequency, amounting to ~2.52 GHz for a resonator whose target frequency is designed to be 6 GHz. Meanwhile a Nb resonator with the same geometry shows little difference with a deviation of ~0.61% from its designed value. In the HFSS simulation, it is confirmed that the measured shift is consistent with the simulated output obtained by specifying 2ωLk(ω: angular frequency of microwave) to be the surface reactance of TiN superconducting film.

References [1] L. J. Swenson et al., J. App. Phys. 113, 104501 (2013). [2] M. R. Vissers et al., Appl. Phys. Lett. 108, 012601 (2016).