Abstract
This study presents the design of a rib-reinforced diaphragm to minimize the performance impact by residual stress in the piezoelectric film. The proposed design features three advantages. First of all, the design of a cross-rib structure minimizes the resonant frequency shift caused by residual stress, which is critical to the low-frequency performance of MEMS speakers. Secondly, the rib-reinforced diaphragm benefiting by small deformation attains larger acoustic resistance to achieve minor sound pressure level (SPL) attenuation at low frequencies. Last but not the least, the cross-rib design suppresses the asymmetric diaphragm deformation due to the directional residual stress induced by crystal structure of PZT, and therefore maintains the flatness of the diaphragm during vibration resulting in better acoustic efficiency. Measurement results of the proposed design in the standard ear simulator demonstrate a maximum SPL of 94.0 dB with only 0.7 V rms driving voltage and 1.67 mm 2 diaphragm. In addition, more than 13 dB SPL improvement is realized below 1 kHz, and the low frequency limit of 20 dB attenuation from the SPL peak is lowered to only one-third of the reference type.