Bandwidth Enhancement of Piezoelectric MEMS Microspeaker Using Reverse-Trapezoid Cantilever with Combined Piston and Bending Motion

This study presents a piezoelectric MEMS microspeaker address high-frequency SPL decay, the design adopts a dual-motion strategy: two actuators directly coupled to the diaphragm generate piston motion for low-frequency performance, while two additional independent actuators introduce a high-frequency bending mode to enhance output via out-of-phase driving. The reverse-trapezoidal cantilever-plate actuator with a relatively large movable area is exploited in this study. The key design features consist of employing only two diaphragm-connected actuators to achieve piston motion, maintaining low-frequency performance compared with the four-actuator configuration and incorporating two independent actuators to create a bending mode, thereby improving high-frequency response with out-of-phase driving. Under$0.7 \text{Vrms}+5 \text{Vdc}$excitation, the proposed design achieves an SPL bandwidth of$160 \text{Hz} \sim 22.3 \text{kHz} (>70 \text{dB})$, outperforming the reference$(130 \text{Hz} \sim 18.3 \text{kHz})$. Furthermore, the design demonstrates improved THD bandwidth of$8.6 \text{kHz} \sim 16.3 \text{kHz}$($(7.7 \text{kHz} \sim 13.7 \text{kHz})$. Table 1 summarizes the results and corresponding comparisons.