Millimeter-Sized Epitaxial Ferroelectric BaTiO3 Freestanding Sheets Peeled from Al2O3 Substrates

Freestanding ferroelectric perovskite-structured oxide sheets with a high degree of orientation are promising for next-generation electronic devices, including optical communication technologies. A widely used method employs a water-soluble Sr₃Al₂O₆ sacrificial layer to obtain freestanding epitaxial sheets. However, the SrTiO₃ substrate used in this process is unsuitable for large-area fabrication, necessitating alternative materials. In this study, we fabricated crack-free, epitaxial BaTiO₃ freestanding films using a cost-effective and scalable r-plane Al₂O₃ substrate and a water-soluble CaO sacrificial layer. The BaTiO₃ epitaxial sheets, which were released via pure water immersion, exhibited c-axis orientation, with ferroelectric polarization aligned in the out-of-plane direction. The sheet exhibits room-temperature ferroelectricity, with a remanent polarization of 21 μC/cm² and minimal leakage current. This approach reduces the fabrication costs and allows the production of larger freestanding sheets, making it promising for flexible electronics and advanced applications.