PVDF-TrFE/SiO2 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/degrees C due to decrease in the elastic constants of PVDF-TrFE. The maximum Q(m) is 33 for 80 mu m radius of the device at 20 degrees 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.