Epitaxial Growth of CaTiO3 Thin Films by Metal Organic Vapor Phase Epitaxy for Potential Applications in Memristive Devices.

Abstract

Calcium titanate thin films with high structural quality were grown heteroepitaxially on perovskite oxide substrates using the liquid-delivery spin metal-organic vapor phase epitaxy (MOVPE) technique. To determine the growth window, suitable metal-organic precursors were selected, and their evaporation conditions were established. Initially, the thermal decomposition behavior of the precursors was studied using thermogravimetric analysis, which showed that full pyrolysis at 460 °C is possible for both the Ca and Ti precursors. This enabled the growth of fully strained, stoichiometric CaTiO₃ films on SrTiO₃ and NdGaO₃ substrates, and potentially on other perovskite oxide substrates, within the diffusion-limited regime. The influence of vaporization temperatures, substrate temperature, oxygen-to-argon ratio, and Ca-to-Ti ratio on the structural properties of the CaTiO₃ thin films was investigated using high-resolution X-ray diffraction, atomic force microscopy, and transmission electron microscopy. Structural analysis was ultimately correlated with electrical properties measured via IV curves. Intrinsic resistive switching was observed for stoichiometric and slightly off-stoichiometric CaTiO₃ films grown on SrTiO₃ substrates with ≈2.2% tensile strain. Relative to our previous work on resistive switching in SrTiO₃ (Baki., Sci. Rep., 2021, 11 (1), 1-11), the underlying mechanism is discussed in the context of CaTiO₃. This highlights the potential of CaTiO₃ for technological applications such as resistive random-access memory (ReRAM) and neuromorphic computing.