Performance Enhancement of Piezoelectric MEMS Microspeaker Using Jointed and Separated Curved Cantilever Array with Modulation Circuits

The monolithic integration of acoustic sensors (microphone) and actuators (speaker) on a single chip holds significant potential for future applications. This study presents a piezoelectric MEMS microspeaker with a suspending area of 5.3 mm² for high-frequency applications. Multiple tweeter units, combined with driving methods, are implemented to enhance the microspeaker performance from 5 kHz to 13 kHz. The proposed design incorporates curved cantilevers and a central joint within the same suspended area to create separate low- and high-resonance tweeters, positioning them between the Helmholtz resonance. However, an SPL zero occurs between the two resonances due to the out-of-phase motion of the tweeter units. To address this issue, gain- and phase-modulation driving methods are introduced to manage the gain and phase of the input signals to the low-resonance tweeter, effectively eliminating the SPL zero. The proposed microspeaker demonstrates performance enhancements through these driving techniques. Measurements were conducted using a 1 V_pp signal with an 8 V_DC bias in a standard ear simulator to evaluate the performance of the proposed design under different driving methods. Compared to the reference design, the proposed microspeaker exhibits better SPL performance above 12 kHz due to the high-resonance tweeter. Additionally, the implementation of both gain- and phase-modulation driving effectively eliminates the SPL zero at 11.2 kHz, resulting in an SPL improvement of over 15 dB. Moreover, the proposed design with both driving methods suppresses the THD peak caused by the SPL zero, further enhancing overall performance. This study demonstrates the effectiveness of the proposed microspeaker design, particularly with phase-modulation driving, in achieving high SPL and low THD across the target frequency range.