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 Al 2 O 3 capping layers on oxide sheets. Using this simple method, over 20 mm 2 of crack-free, deep-ultraviolet transparent electrode La:SrSnO 3 and ferroelectric Ba 0.75 Sr 0.25 TiO 3 flexible sheets were obtained. By contrast, the sheets without any capping layers broke. The obtained sheets showed considerable flexibility and high functionality. The La:SrSnO 3 sheet simultaneously exhibited a wide bandgap (4.4 eV) and high electrical conductivity (>10 3 S/cm). The Ba 0.75 Sr 0.25 TiO 3 sheet exhibited clear room-temperature ferroelectricity with a remnant polarization of 17 μC/cm 2 . Our findings provide a simple transfer method for obtaining large, crack-free, high-quality, single-crystalline sheets.