Abstract
This study demonstrates a piezoelectric MEMS microspeaker featuring a parylene-spring connecting the cantilever-actuator and central-diaphragm to maintain the low-frequency responses and extend the bandwidth. Through wafer-level parylene coating, the proposed design achieves the following features and merits: (1) Central-diaphragm fully supported by flexible parylene spring: achieving larger linear piston displacement to ensure good THD (Total-Harmonic-Distortion) and maintain SPL (Sound-Pressure-Level) in flat area, (2) Four cantilever-actuators fully coated with and constrained by parylene film: increasing their equivalent stiffness to elevate the resonant frequency to avoid SPL zero; (3) Slits between cantilever-actuators fully sealed by parylene: avoiding acoustic short circuit; In summary, measurements under 0.707 Vrms (10 Vdc) driving voltage in standard ear simulator, proposed design achieves bandwidth enhancement (>65 dB, 100 Hz~17.7 kHz), and THD bandwidth (<8%, 100 Hz~13.3 kHz).