Tunable Microwave Resonators Composed of Stoichiometric Titanium Nitride and Multilayer Titanium Nitride/Titanium

Low-temperature high-Q frequency tunable microwave resonators were fabricated and measured. Two different types of material were fabricated and tested: Titanium nitride/titanium (TiN/Ti) multilayers and stoichiometric titanium nitride (sTiN). The multilayer resonators had a tunable resonant frequency and still maintained a high internal quality factor at temperatures around 50 mK. Multilayer TiN/Ti resonators had a T_c of 1.5K and sTiN resonators had a T_c of 4.5K. Biasing was accomplished using lithographically etched lines and an external power supply. The frequency tunability, as before [1], was achieved by injecting a DC through a current-directing circuit into the nonlinear inductor whose kinetic inductance is current dependent. We were able to achieve a frequency tunability of up to 20MHz, or .5 % fractional frequency shift, while maintaining a base temperature of less than 50 mK, without measurable heating of the device. Different lengths and widths of bias lines were compared to determine the effect on the microwave resonators. We were able to achieve an internal quality factor of Q_i > 250,000 for certain designs.
[1] M. R. Vissers, J. Hubmayr, M. Sandberg, et al. Appl. Phys. Let. 107, 062601 (2015).