Development of PVDF-TrFE/SiO2 composite film bulk acoustic resonator

Abstract

This paper reports a film bulk acoustic resonator (FBAR) using polyvinylidene fluoride- trifluoroethylene (PVDF-TrFE)/SiO2 composite. The PVDF-TrFE/SiO2 composite FBAR was designed, simulated and developed. A Micro Electro Mechanical Systems (MEMS) process including xenon difluoride (XeF2) release etching was adopted with some tuning for PVDF-TrFE. The influences of the process on the surface morphology and crystal orientation of PVDF-TrFE were evaluated for RIE, gold sputtering and XeF2 etching. After poling PVDF-TrFE, the thickness expansion mode was observed at 387–398 MHz. Impedance characteristics was evaluated using a modified Butterworth-Van Dyke (MBVD) model for a lossy piezoelectric transducer. Impedance ratio, coupling coefficient (k2), mechanical quality factor (Qm) and figure of merit increase with the radius of the device. The maximum Qm is 33 for 80 μm radius of the device. The residual film stress of PVDF-TrFE was estimated as 34.8 MPa in tensile mean stress and −79.7 kPa in gradient stress. Elastic stiffness constants c33D and c33E at electrical displacement D = 0 and electric field E = 0 were obtained as 4.45 GPa and 4.46 GPa, respectively.