PVDF - TrFE/SiO 2 Composite Film Bulk Acoustic Resonator for Frequency-Modulated Sensor Application

This paper reports a film bulk acoustic resonator (FBAR) using polyvinylidene fluoride- trifluoroethylene (PVDF-TrFE)/SiO2 composite for frequency-modulated sensing. The PVDF-TrFE/SiO2 composite FBAR was designed, simulated and developed. A Micro Electro Mechanical Systems (MEMS) process was adopted for PVDF-TrFE, including xenon difluoride (XeF2) release etching. After poling PVDF - TrFE, the thickness expansion mode was observed at 387–398 MHz. A modified Butterworth-Van Dyke (MBVD) model for a lossy piezoelectric transducer was used for the characterization of the thickness expansion mode. Impedance ratio, coupling coefficient $(k^{2})$ and mechanical quality factor $(Q_{m})$ increase with the radius of the device. The temperature coefficient of frequency is as large as −1430 ppm/°C due to decrease in the elastic constants of PVDF-TrFE. The maximum $(Q_{m})$ is 33 for 80 um radius of the device at 20°C, decreasing with temperature raise. Allan variance is 1.15 kHz (i.e. 2.96 ppm) at an averaging time of 1.01 s. These results are important for future sensing using the FBAR.