Abstract
Facilitated by microelectromechanical systems (MEMS) technology, MEMS speakers or microspeakers have been rapidly developed during the past decade to meet the requirements of the flourishing audio market. With advantages of a small footprint, low cost, and easy assembly, MEMS speakers are drawing extensive attention for potential applications in hearing instruments, portable electronics, and the Internet of Things (IoT). MEMS speakers based on different transduction mechanisms, including piezoelectric, electrodynamic, electrostatic, and thermoacoustic actuation, have been developed and significant progresses have been made in commercialization in the last few years. In this article, the principle and modeling of each MEMS speaker type is briefly introduced first. Then, the development of MEMS speakers is reviewed with key specifications of state-of-the-art MEMS speakers summarized. The advantages and challenges of all four types of MEMS speakers are compared and discussed. New approaches to improve sound pressure levels (SPLs) of MEMS speakers are also proposed. Finally, the remaining challenges and outlook of MEMS speakers are given.
Highlights
With the rapid advancement of consumer electronics, the worldwide audio market has been seeing a growing trend towards smaller devices with lower power consumption and better performance in the last decade
Speakers based on sol-gel or sputtered Piezoelectric based zirconatepiezoelectric titanate (PZT) films with thicknesses of 1–2 μm typically speakers based on sol-gel or sputtered PZT films with thicknesses of 1–2 μm typically have have diaphragm sizes of no more than 4 mm and can generate high sound pressure levels (SPLs) over 90 dB in diaphragm sizes of no more than 4 mm and can generate high SPLs over 90 dB in tubes or tubes or ear simulators for in-ear applications. Their ear simulators for in-ear applications
Approaches to improve the SPLs of MEMS speakers including special structures, new materials, electrode configurations, and speaker arrays are highlighted and discussed, especially for piezoelectric
Summary
With the rapid advancement of consumer electronics, the worldwide audio market has been seeing a growing trend towards smaller devices with lower power consumption and better performance in the last decade. As one of the core components in mobile electronic devices such as laptops, smartphones, wireless earbuds, and humanmachine interfaces, are highly demanded to be smaller, lighter, and more power efficient Speakers in those mobile electronic devices are dominated by conventional speakers with bulky moving coils, which are still challenging to be batch fabricated since voice coils and permanent magnets must be assembled [1]. The simplification of the mechanical suspensions and electromagnetic parts in the miniaturization would lead to reduced bandwidths and increased nonlinearities, deteriorating the sound quality [2,4] It is difficult for conventional manufacturing technologies to achieve high dimensional precision and good reproducibility in the miniaturization of speakers
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