Low-Temperature Route to Direct Amorphous to Rutile Crystallization of TiO2 Thin Films Grown by Atomic Layer Deposition

High Resolution Image Download MS PowerPoint Slide The physicochemical properties of titanium dioxide (TiO 2 ) depend strongly on the crystal structure. Compared to anatase, rutile TiO 2 has a smaller bandgap, a higher dielectric constant, and a higher refractive index, which are desired properties for TiO 2 thin films in many photonic applications. Unfortunately, the fabrication of rutile thin films usually requires temperatures that are too high (>400 °C, often even 600–800 °C) for applications involving, e.g., temperature-sensitive substrate materials. Here, we demonstrate atomic layer deposition (ALD)-based fabrication of anatase and rutile TiO 2 thin films mediated by precursor traces and oxide defects, which are controlled by the ALD growth temperature when using tetrakis(dimethylamido)titanium(IV) (TDMAT) and water as precursors. Nitrogen traces within amorphous titania grown at 100 °C inhibit the crystal nucleation until 375 °C and stabilize the anatase phase. In contrast, a higher growth temperature (200 °C) leads to a low nitrogen concentration, a high degree of oxide defects, and high mass density facilitating direct amorphous to rutile crystal nucleation at an exceptionally low post deposition annealing (PDA) temperature of 250 °C. The mixed-phase (rutile–brookite) TiO 2 thin film with rutile as the primary phase forms upon the PDA at 250–500 °C that allows utilization in broad range of TiO 2 thin film applications.