Wearable Flexible Piezoelectric Sensors Enhanced by Sequential Induction and Functional Synergy for Monitoring Human Motion

Abstract Wearable flexible piezoelectric sensors based on ZnO piezoelectric films demonstrate broad application potential in motion detection for human‐computer interaction. In this study, ZnO‐based piezoelectric films with a multilayer orientation‐inducing layer (M‐OIL) structure are developed via the magnetron sputtering technique that employs a hierarchical deposition strategy combining sequential induction and functional synergy. This multilayer design favorably addresses the film's orientation limitations and thus enhances the piezoelectric performance significantly. The developed ZnO M‐OIL piezoelectric films are integrated onto flexible polyimide (PI) substrates to construct a ZnO M‐OIL sensor with excellent mechanical flexibility and enhanced piezoelectric output performance. Under a load force of 0.98 N, the sensor achieves a maximum open‐circuit voltage (V _oc ) of 2.25 V (threefold improvement), a maximum piezoelectric constant (d ₃₃ ) of 173.05 Pm V ⁻¹ (5.8‐fold improvement), a rapid response/recovery time of 2.1/2.7 ms, and a voltage sensitivity ( S _v ) of up to 1.47 V·N ⁻¹ (2.3‐fold improvement), while maintaining exceptional output stability during both impact and bending cycles either in normal or extreme environmental conditions such as artificial sweat immersion and thermal treatment. Owing to its exceptional electromechanical conversion performance, the ZnO M‐OIL sensor precisely captures biomechanical signals associated with diverse human motions, showcasing its feasibility for intelligent wearable systems in practical applications.