Possible quasiparticle localization induced by substrate treatment in superconducting TiN film resonators

TiN is of recent interest in devices for quantum-information processing and for astronomy photon-detection. This has led to a number of studies on the growth of advantageous superconductors, such as TiN. In thin TiN films, we observe stronger disorder when the substrate is exposed to an oxygen plasma before TiN deposition than when we grow without. The addition of the oxide layer changes the film properties for thicknesses less than 25nm, including the preferred growth mode from the [200] phase to the [111] phase. Transmission is measured in a dilution refrigerator on TiN coplanar waveguide resonators. Resonator data of thin films on oxygen prepared substrates show an order of magnitude decrease in internal quality factor (Qi) compared to the base films and corresponds with the preferred growth direction. The thin films from oxygen prepared substrates are also further in the dirty and disordered limit. A phenomenological modification of the MB theory with quasiparticle inelastic scattering describes the temperature dependence data. This data suggests as an increased quasiparticle effect in the films, and possibly indicates some localization transition for the quasiparticles.