Freestanding ferroelectric membranes via ionic unlocking van der Waals interface

Freestanding oxide films have attracted significant interest for their potential applications in flexible electronics. However, the common use of sacrificial layers hinders the development of freestanding oxide films that meet industrial demands for larger area, device-scalable thickness and low cost. Here, we present a water-assisted ionic unlocking strategy that enables the rapid exfoliation of centimeter-scale, freestanding ferroelectric Pb(Zr,Ti)O₃ membranes from Pb(Zr,Ti)O₃/Pt/Mica. Leveraging density functional theory and ab initio molecular dynamics simulations, we identify water-induced potassium ion leaching from the Mica substrate as a key interfacial weakening pathway that substantially reduces the Pt/Mica interfacial binding energy, thereby enabling crack propagation driven by capillary forces along the weakened interface. The resulting 1×1 cm² Pb(Zr,Ti)O₃ membranes demonstrate a remarkable piezoelectric coefficient of 528 pC N^-1, approximately twice that of their clamped counterparts on Mica. Moreover, by incorporating these membranes, we fabricate self-powered flexible acoustic sensors for high-fidelity sound recording and speech recognition, achieving a speech recognition accuracy exceeding 93%. This work represents a significant advance in both the scalable fabrication of freestanding ferroelectric membranes and the engineering of high-performance flexible sensors.