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 Ba0.75Sr0.25TiO3 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 Ba0.75Sr0.25TiO3 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.