Nonlinear damping effects in MEMS-based microspeakers

Miniaturized microelectromechanical systems (MEMS) microspeakers are a current development trend for in-ear audio applications. However, when a transducer shrinks to a size that fits on a microelectronic chip, its physics begins to differ from the effects governing the macroscopic world. On the one hand, the electrostatic drive benefits from small electrode gaps, which lead to high driving forces. On the other hand, the fluid dynamics of the air in the microscopic cavities of a microspeaker chip can cause strong damping forces, including severe nonlinearities. Adequate damping is considered beneficial for wideband audio applications, however, nonlinear damping effects introduce unwanted harmonic distortion and should therefore be avoided, or at least taken into account, throughout the development process. In this presentation we will discuss the source and nature of such effects and give an outlook on how to reduce them in designs.