A PZT MEMS loudspeaker with a quasi-closed diaphragm

Piezoelectric MEMS speakers with non-closed diaphragms are promising to generate high sound pressure levels (SPLs), but a serious diaphragm breakage issue exists. In this work, a novel piezoelectric MEMS loudspeaker with a quasi-closed diaphragm is proposed. The quasi-closed diaphragm consists of a diagonally-cut but center-linked diaphragm, that is coated with a thin layer of Parylene-C. Under the combined action of the stress dispersion structure, the application of the Parylene-C film prevents the diaphragm from breakage and significantly reduces the air loss. The MEMS loudspeaker with a small size of 2.5 × 2.5 mm2 has been successfully fabricated and the acoustic performance has been characterized in an 711 ear simulator. The measured SPL reaches its maximum value of 124 dB at 11.8 kHz under a drive voltage of 4 Vpp. The SPL is further increased to 88 dB in the low-frequency range (20–500 Hz) under a voltage of 35 Vpp.