A Flexible Film Bulk Acoustic Resonator Radio-Frequency Sensor Based on β-Type PVDF Films for Tactile Perception

A flexible Film bulk acoustic resonator (FBAR) radio-frequency (RF) sensor based on a flexible substrate and β-type polyvinylidene fluoride (PVDF) film is proposed for tactile perception. The molecule chains of the β-type PVDF film have a spontaneously polarized structure, showing the high piezoelectric characteristic. The FBAR structure is a sandwiched Al/β-type PVDF/Al structure on a flexible polyimide (PI) film substrate. Experimental results show that the resonance frequency of the RF sensor is around 250 MHz, and it shows high bending and pressure sensitivities with a bending sensitivity of –330 kHz/mm –1, a compressive pressure sensitivity of 4.7 kHz/Pa, and a lower temperature drift temperature coefficient of frequency (TCF) of −63 ppm/K. This research integrates multiphysics finite element analysis and the modified Butterworth–Van Dyke (MBVD) model to elucidate the interaction mechanisms between bulk acoustic waves (BAW) and PVDF molecules within the FBAR piezoelectric layer. It theoretically and experimentally explains the regulation mechanisms of BAW excitation by mechanical and thermal fields in the FBAR. It is expected to have potential applications in wearable devices, robots, soft touch, and medical diagnosis.