Evaluation of kinetic-inductance nonlinearity in a single-crystal NbTiN-based coplanar waveguide

Abstract

We have developed a kinetic inductance travelling-wave amplifier toward the THz-band operation. In this paper, we discuss the nonlinear kinetic inductance of single-crystal niobium titanium nitride (NbTiN) thin film in response to the application of current to the film. In our calculation, it is found that single-crystal NbTiN films have a large current variation in the kinetic inductance compared with that of polycrystalline NbTiN films. To evaluate the nonlinearity, we fabricated a superconducting coplanar waveguide with a 0.2-m line length and measured the transmittance. We observed a variation of the electrical length of the line caused by the modulation of the kinetic inductance as a function of the value of the current applied to the strip.