A high-SPL piezoelectric MEMS loud speaker based on thin ceramic PZT

MEMS speakers are attracting more and more interests due to their potential applications in portable and wearable electronics. However, insufficient sound pressure level (SPL) associated with the reduced size is a main challenge for most existing MEMS speakers. This paper presents the design, fabrication and characterization of a high-SPL piezoelectric MEMS speaker based on high-piezoelectric constant ceramic PZT. The ceramic PZT, bonded on an SOI substrate, was thinned down to only 5 μm successfully. The microfabricated piezoelectric MEMS speakers exhibited significantly enhanced SPLs. At a distance of 10 mm, a maximum SPL of 119 dB was achieved in open air by such a single MEMS speaker with a footprint of 6.7 mm × 6.7 mm under a low driving voltage of only 10 Vpp. The SPLs at frequencies as low as 400 Hz still reached over 90 dB. These SPLs are comparable to those of conventional loud speakers or micro-speaker arrays with significantly larger sizes.