Metastable Rutile TiO2 Growth on Non-Lattice-Matched Substrates via a Sacrificial Layer Strategy

Abstract

Metastable materials possess unique properties critical for advanced technologies; however, their synthesis is significantly challenging. Among the TiO2 polymorphs, rutile TiO2 stands out for its exceptional dielectric properties; however, its film growth typically requires high-temperatures or lattice-matched substrates, limiting its practical applications. This article presents a novel sacrificial layer strategy for the atomic layer deposition (ALD) of pure-phase rutile TiO2 films on diverse substrates, including amorphous Al2O3, HfO2, and ZrO2. This approach employs ultrathin Ru sacrificial layers to facilitate the formation of rutile TiO2 seed layers via the in situ generation of a rutile-matched RuO2 lattice. At the same time, it is completely removed as volatile RuO4 under exposure to O-3 during the ALD process. This approach eliminates the need for high-temperature annealing and substrate restrictions, enabling low-temperature formation of rutile TiO2 on diverse substrates, including amorphous oxides. Comprehensive characterization reveals the structural stability of the films and their enhanced dielectric performance. Stabilizing rutile TiO2 independently of the underlying layer opens new possibilities for its integration into memory capacitors. Furthermore, this strategy provides a versatile framework for stabilizing other metastable material phases, thereby offering opportunities for diverse applications.