Obtaining High SPL Piezoelectric MEMS Speaker via a Rigid-Flexible Vibration Coupling Mechanism

Among the main problems affecting the sound pressure level (SPL) of piezoelectric microelectromechanical systems (MEMS) speakers is that the membrane vibration displacement of those with sealed membranes is small, while those with unsealed membranes suffer from acoustic loss. Presented here is a high-SPL piezoelectric MEMS speaker via a rigid-flexible coupling mechanism, which can maintain large vibration displacement of the unsealed membranes without acoustic loss. The ingenious deposition of Parylene C on the upper surface before etching the back cavity is the key process forming the rigid–flexible-coupling sealed vibration membrane. Compared with that of the proposed speaker without the flexible sealed Parylene C at 2 V, the SPL generated by that with the rigid–flexible-coupling sealed vibration membrane is 3.0–26.1% higher, the frequency range of the speaker with the sealed membrane is widened from 250 Hz–20 kHz to the human hearing frequency range of 20 Hz–20 kHz for SPLs exceeding 59 dB, and a 101.2-dB SPL is obtained at the resonance frequency of 6.7 kHz. This simple strategy represents a significant step toward practical applications of piezoelectric MEMS speakers, given the wide frequency band, high SPL, and low power consumption. [2021-0041]