Significant Suppression of Cracks in Freestanding Perovskite Oxide Flexible Sheets Using a Capping Oxide Layer

Flexible and functional perovskite oxide sheets with high orientation and crystallization are the next step in the development of next-generation devices. One promising synthesis method is the lift-off and transfer method using a water-soluble sacrificial layer. However, the suppression of cracks during lift-off is a crucial problem that remains unsolved. In this study, we demonstrated that this problem can be solved by depositing amorphous Al₂O₃ capping layers on oxide sheets. Using this simple method, over 20 mm² of crack-free, deep-ultraviolet transparent electrode La:SrSnO₃ and ferroelectric Ba_0.75Sr_0.25TiO₃ flexible sheets were obtained. By contrast, the sheets without any capping layers broke. The obtained sheets showed considerable flexibility and high functionality. The La:SrSnO₃ sheet simultaneously exhibited a wide bandgap (4.4 eV) and high electrical conductivity (>10³ S/cm). The Ba_0.75Sr_0.25TiO₃ sheet exhibited clear room-temperature ferroelectricity with a remnant polarization of 17 μC/cm². Our findings provide a simple transfer method for obtaining large, crack-free, high-quality, single-crystalline sheets.