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

Flexible electronics strongly demand the integration of flexible and large‐scale multifunctional oxides. BiFeO3 is one of the most essential multifunctional oxides that could be used in memories, logics, sensors, and actuators. Recently, freestanding single‐crystalline BiFeO3 membranes exhibited superior elasticity and flexibility. However, fabrication and integration of large‐scale freestanding BiFeO3 membranes into flexible electronics remain elusive. In this study, inch‐scale freestanding single‐crystalline BiFeO3 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 SiTiO3/Sr3Al2O6/(SrRuO3/)BiFeO3 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 BiFeO3 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 BiFeO3 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. [ABSTRACT FROM AUTHOR]