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

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 O₃ 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.