On the Design of Piezoelectric MEMS Speakers for High Resolution Audio Applications

Building upon the structural design in the previous work [1], this study introduces fan-shape cantilever plate actuators in order to enhance electroacoustic efficiency. The proposed structure offers three major benefits. To begin with, the fan-shaped actuators generate larger out-of-plane displacement of central diaphragm resulting in a higher sound pressure level (SPL). Secondly, the piston motion of central diaphragm provides superior total harmonic distortion (THD) performance. Last but not the least, by optimizing the ratio of passive components (meandering springs and central diaphragm) to active components (cantilever-plate actuators), the optimized design extends applicable SPL bandwidth to 40 kHz, meeting the requirements for high-resolution audio applications. Measurements of the optimized MEMS speaker in the standard ear simulator GRAS RA0404 illustrate maximum SPL of 92.0 dB at 8.9 kHz with 0.707 $\mathrm{V}_{\text{rms}}+8\mathrm{V}_{\text{DC}}$ input voltage. The bandwidth of SPL ≥ 70 dB is 4.2 ~ 20.0 kHz, while the bandwidth of THD≤ 2% is 5.3 ~ 20.0 kHz.