Inch‐Scale Freestanding Single‐Crystalline BiFeO3 Membranes for Multifunctional Flexible Electronics

Abstract Flexible electronics strongly demand the integration of flexible and large‐scale multifunctional oxides. BiFeO 3 is one of the most essential multifunctional oxides that could be used in memories, logics, sensors, and actuators. Recently, freestanding single‐crystalline BiFeO 3 membranes exhibited superior elasticity and flexibility. However, fabrication and integration of large‐scale freestanding BiFeO 3 membranes into flexible electronics remain elusive. In this study, inch‐scale freestanding single‐crystalline BiFeO 3 membranes are fabricated with assistance from a water‐soluble sacrificial layer. To transfer flat and crack‐free membranes, all the existing methods are first followed but fail. Then the study introduces a temporary supporting Cu layer on the surface of the as‐grown SiTiO 3 /Sr 3 Al 2 O 6 /(SrRuO 3 /)BiFeO 3 heterostructure and successfully obtains full and crack‐free 5 mm × 5 mm freestanding membranes on various substrates. The residual strain within the heterostructure releases gradually under the protection of the Cu layer. The freestanding BiFeO 3 membranes are relatively uniform among different regions and exhibit good dielectric, ferroelectric, and ferromagnetic properties. Finally, flexible ferroelectric photovoltaic devices are patterned based on those BiFeO 3 membranes, and they have open circuit voltage and short circuit current density up to −0.25 ± 0.03 V and 0.82 ± 0.09 µA cm −2 , respectively.