Quality factor improvement of piezoelectric MEMS resonator by the conjunction of frame structure and phononic crystals

Recently, piezoelectric resonators fabricated by using MEMS (i.e., micro-electro-mechanical systems) technology have received increasing attention in a large and diverse set of applications, including sensors, filters and timing references. One of the critical challenges for the actual application of MEMS resonators is further improving their quality factors (Qs) to respond the urgent demand of performance enhancement. Herein, a strategy by employing suspended frame structure and phononic crystals (PnC) was proposed to reduce the energy dissipation, and thus AlN-on-SOI MEMS resonators with high Q were successfully implemented. The suspended frame structure isolates the mechanical vibration between the resonant body and the anchoring substrate, while PnC arrays serve as a frequency-selective reflector to reduce the energy leakage. The multi-physics finite-element-analysis (FEA) and the experimental comparison were employed to systematically investigate the underlying mechanisms of the energy dissipation reduction of the proposed strategy. The unloaded Qs (i.e., Q_u) of proposed resonators achieved maximum 7.8-fold and 1.5-fold improvements compared with that of bared resonators and that of those with only suspended frame structure, respectively.