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.