An ultra-high low-frequency SPL piezoelectric MEMS loudspeaker based on sputtered PZT

Piezoelectric MEMS loudspeakers with quasi-closed diaphragm structures have been shown to effectively prevent air leakage and enhance low-frequency sound pressure level (SPL). However, achieving an SPL over 90 dB at 20 Hz for in-ear applications remains challenging due to limitations in excitation voltage and diaphragm size. This work presents a piezoelectric MEMS loudspeaker featuring a 2.7 µm-thick sputtered PZT film and a circular quasi-closed diaphragm with 6 slits, capable of withstanding up to 100 Vpp excitation without mechanical rupture or piezoelectric breakdown. Acoustic characterization using a 711-ear simulator demonstrates that the fabricated loudspeaker achieves an SPL of over 90.4 dB at 20 Hz under 100 Vpp excitation with active power of 0.98 mW. Long-term operation under 100 Vpp excitation shows that after 3 hours, the SPL at 20 Hz remains at 92.4 dB, and after 6 hours, it is 84 dB, demonstrating the reliability of the design. Additionally, free-field testing at a distance of 1 cm reveals an SPL of 91 dB at 400 Hz under 100 Vpp excitation. This study provides an effective approach for enhancing low-frequency SPL in MEMS loudspeakers, paving the way for future applications.