An Ultra-Low Total Harmonic Distortion Piezoelectric MEMS Loudspeaker with Double-S Unimorph Actuators

This paper presents an ultra-low total harmonic distortion (THD) piezoelectric MEMS loudspeaker designed for in-ear applications, featuring double-S unimorph piezoelectric actuators. With a square diaphragm of 3 mm in length and a 2.7 μm-thick sputtered PZT, the double-S actuators exhibit piston vibration with THD <0.75% for the sound pressure level (SPL) over 88 dB with 3 Vpp excitation across 1-20 kHz. This design validates the feasibility of achieving ultra-low THD performance in MEMS piezoelectric loudspeakers through a piston-vibration-based structural design.