SnO²-induced rutile TiO²fabrication for high-k dielectric films using sol-gel process

As optical and electronic devices continue to scale down, the demand for high-k dielectric thin films that can be processed under strict thermal budget constraints has increased significantly. Rutile-phase TiO2 is a promising high-k material due to its high dielectric constant; however, its formation typically requires annealing temperatures above 800 °C, which limits its integration into thermally sensitive systems. Developing a low-temperature route for stabilizing rutile-phase TiO2 remains a critical challenge. In this study, a SnO2 buffer-layer-assisted strategy is proposed to enable the low-temperature formation of rutile-phase TiO2 thin films. SnO2, which intrinsically possesses a rutile crystal structure and a lattice constant closely matched to that of rutile TiO2, was employed as a buffer layer to promote phase stabilization. SnO2/TiO2 bilayer thin films were fabricated using a solution-based sol-gel process combined with spin coating, followed by thermal annealing. X-ray diffraction analysis revealed that TiO2 single-layer films annealed at 550 °C exhibited only the anatase phase, whereas TiO2 films deposited on SnO2 buffer layers showed clear rutile-phase diffraction peaks under the same annealing conditions. This indicates that the SnO2 buffer layer effectively promotes the anatase-to-rutile phase transition at reduced temperatures. Morphological characterization using FE-SEM confirmed uniform film thicknesses of approximately 100 nm, while atomic force microscopy revealed an exceptionally smooth surface with a root-mean-square roughness of 0.43 nm. These results demonstrate that the introduction of a SnO2 buffer layer enables stable rutile-phase TiO2 formation at 550 °C without compromising film quality. The proposed approach provides a practical pathway for integrating high-k TiO2 thin films into optical and electronic devices requiring low-temperature processing.