Review Paper: MEMS Audio Speakers

Abstract Miniaturization of electro-mechanical sensors and actuators has benefited from an advancement in CMOS technology over the years. However, miniaturization of audio speakers has seen considerable development only in the recent times. This paper reviews the developments in MEMS audio speaker research and the initial commercial products available in the market. At first glance, it appears that the relatively slow development of MEMS speakers can be attributed to the fact that the principle of actuation has remained unchanged for several decades. Unfortunately, the physics behind audible sound production holds us back from exclusively adopting miniaturized speakers — sound pressure level is directly proportional to the area of the sound radiating surface. Nevertheless, researchers are continuing to explore new avenues for designing and developing MEMS speakers, without limiting themselves to the existing actuation principles. With newly discovered materials and improving technology, the research in MEMS speakers is gaining attention and new products are emerging. A speaker design based on piezoelectric actuation or electrostatics actuation is favourable at MEMS scale. Indian research community is also contributing to advances in MEMS speakers and near-ultrasonic devices. This paper reviews the development in MEMS audio speakers in India and in the world. The tabulated review findings aim to offer readers an overview of the development of micro-speakers and to provide guidance for designing new micro-speakers.