Control of disorder and superconductivity in sputtered TiN thin films via substrate RF bias

Titanium nitride thin films are prepared using DC reactive magnetron sputtering at room temperature, with an RF bias applied to the substrate to systematically control film growth. By adjusting the substrate RF bias, the degree and length scale of disorder are tuned, leading to pronounced changes in film microstructure and superconducting properties. A dome-shaped dependence of the superconducting critical temperature, Tc, on RF bias is observed, accompanied by a minimum in the superconducting coherence length near the peak of the Tc dome. This correlated behavior reflects a controlled evolution from point-like disorder to a nanocrystalline microstructure that ultimately develops into well-ordered grains separated by electrically transparent grain boundaries. At intermediate RF bias, the films acquire an optimal grain size that enhances intragrain superconductivity while reducing the effective coherence length. This mesoscopic control of disorder and microstructure provides a pathway for engineering TiN films with superconducting properties that are desirable for applications requiring high normal-state sheet resistance in fully gapped superconductors, such as superconducting resonators and high-kinetic-inductance devices.