A flexible film bulk acoustic resonator based on β-phase polyvinylidene fluoride polymer

Abstract

This paper reports a novel flexible film bulk acoustic resonator (FBAR) based on β-phase polyvinylidene fluoride (PVDF) piezoelectric polymer. The proposed device was simulated and evaluated; then, a low-temperature photolithography process with a double exposure method was developed to pattern the electrodes for the device, which enabled the device to retain the piezoelectric properties of the β-phase PVDF film. Results showed that the β-phase PVDF FBARs had a resonant frequency round 9.212 MHz with a high electromechanical coupling coefficient (k2) of 12.76% ± 0.56%. The device performed well over a wide bending-strain range up to 2400 με owing to its excellent flexibility. It showed good stability as a strain sensor with a sensitivity of 80 Hz/με, and no visible deterioration was observed after cyclic bending tests. The PVDF FBAR also exhibited an exceptionally large temperature coefficient of frequency (TCF) of −4630 ppm/K, two orders of magnitude larger than those of other FBARs based on common inorganic piezoelectric materials, extraordinarily high sensitivity for temperature sensing. All results showed that β-phase PVDF FBARs have the potential to expand the application scope for future flexible electronics.