Self-Assembled Inorganic Nanomembrane Tubes: Rolled-Up Piezoelectrics for Microacoustic Wave-Based Actuators and Sensors.

Shaping piezoelectrics into innovative 3D microstructures is an emerging field, offering the potential to unlock new functionalities through topological engineering. Existing methods can create 3D piezoelectric composites and origami-inspired structures, but they often reduce electromechanical resonance quality, especially when using organic elastic backbones with low mechanical quality factors. At the same time, 2D free-standing piezoelectric nanomembranes used in acoustic wave resonators require thin film materials with low intrinsic stress to prevent device rupture as lateral dimensions increase. In this work, the first example of 3D self-assembled piezoelectrics composed entirely of inorganic materials is presented. By precisely controlling mechanical stress and the nanomembrane release process, free-standing nanomembranes are shaped into conformably stable tubular structures. The resulting rolled-up piezoelectric (RUP) structures can be tuned in diameter, length, and winding number to optimize their performance for either actuation or sensing applications. Tubes up to 11 mm in length and 3.5 mm in rolling length are demonstrated, with functionality confirmed through 1-port interdigital transducers (IDT) and 2-port delay-line architectures, integrating up to 10 mm