Effect of geometry on the performance of MEMS aluminum nitride trampoline resonators in longitudinal resonance

The performance of a MEMS aluminum nitride trampoline-shape piezoelectric resonator is analyzed using three-dimensional finite element simulations. The device, targeted to operate at frequencies in the 3 GHz range is suitable for ultra-high-frequency (UHF) filtering applications. Material damping is accounted for in the model. The simulations are used to predict the effects of various geometric parameters on the resonator overall performance which is evaluated with the effective acoustic coupling coefficient (K²) and the quality factor (Q) and extracted from the electrical impedance frequency response plots. The results indicate that (i) K² is insensitive to geometry (K²~6.5%), (ii) Q increases linearly with the AlN thickness and (iii) a trampoline resonator with three legs is slightly more efficient than those with more.