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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]

Integration of magnetic materials into bio‐integrated flexible electronics will bring multi‐functionality, such as magnetoception and wireless communication. In practical application, the performance of magnetic materials and devices should remain stable during cyclic bending–unbending and they can be degradable within a designated lifetime. However, direct integration of magnetic materials with flexible and biocompatible materials and maintaining mechanically stable microwave performance have not been achieved yet. Here, ultrathin (5–50 nm) permalloy (NiFe) films deposited on biocompatible silk fibroin (SF) films are shown to be bending stable, and dissolvable. The ferromagnetic properties of NiFe films deposited on SF, Kapton, and silicon are studied and compared by ferromagnetic resonance. Benefiting from the low surface roughness of fibroin, which is only ≈0.8 nm, SF/NiFe films exhibit comparable ferromagnetic properties to Si/NiFe, better than that of Kapton/NiFe films. Moreover, the ferromagnetic resonance field of SF/NiFe films remains highly stable during cyclic bending that is exposed to both compressive and tensile strain/stress, and its temperature stability is very close to that of Si/NiFe. Finally, the whole SF/NiFe films are demonstrated to be dissolvable and biocompatible. Therefore, SF/NiFe films can be a useful and stable platform for flexible and biocompatible microwave applications. [ABSTRACT FROM AUTHOR]

Magnonics or spin waves have the potential to serve as the carrier for future information communication. A controllable spin wave resonance (SWR) device is demonstrated in a Au/[DEME]+[TFSI]−/LSMO/STO capacitor heterostructure, which could be regulated by ionic liquid gating (ILG) method. The SWR critical angle φC, excitation position to perform uniform precession, is shifted in a reversible manner (thus recording "off" and "on") with +1.5 V gating voltage (Vg), measured by quantitative angular dependent electron spin resonance (ESR) spectroscopy. Based on the modified Puszkarski's surface inhomogeneity model, the ILG control SWR at low Vg (Vg < 1.5 V) can be explained by a charge‐doping‐induced effective surface magnetic anisotropy change. Applying a higher Vg (Vg > 1.5 V) enhances the surface mode SWR and gradually diminishes the body mode SWR. Oxygen vacancies generate at higher Vg (Vg > 1.5 V) resulting in the modulation of superexchange between the Mn ions, evidenced by X‐ray photoelectron spectroscopy and secondary ion mass spectroscopy characterization. This ILG control SWR presents a solution for energy efficient and low‐voltage control of magnonics and spin wave devices. [ABSTRACT FROM AUTHOR]