Modeling methods of MEMS micro-speaker with electrostatic working principle

Abstract

The market for mobile devices like tablets, laptops or mobile phones is increasing rapidly. Device hou sings get thinner and energy efficiency is more and more important. Micro-Electro-Mechanical-System (MEMS) loudspeakers, fabricated in complementary metal oxide semiconductor (CMOS) compatible technology merge energy efficient driving technology with cost economical fabrication processes. In most cases, the fabrication of such devices within the design process is a lengthy and costly task. Therefore, the need for co mputer modeling tools capable of precisely simulati ng the multi-field interactions is increasing. The accurate modeling o f such MEMS devices results in a system of coupled partial differential equations (PDEs) describing the intera ction between the electric, mechanical and acoustic field. For the efficient and accurate solution we apply the Finite Element (FE) method. Thereby, we fully take the no nlinear effects into account: electrostatic force, charged moving b ody (loaded membrane) in an electric field, geometr ic nonlinearities and mechanical contact during the snap-in case between loaded membrane and stator. To efficiently hand le the coupling between the mechanical and acoustic fields, we appl y Mortar FE techniques, which allow different grid sizes along the coupling interface. Furthermore, we present a recen tly developed PML (Perfectly Matched Layer) technique, which allows limiting the acoustic computational domain e ven in the near field without getting spurious refl ections. For computations towards the acoustic far field we us a Kirchhoff Helmholtz integral (e.g, to compute the directivity pattern). We will present simulations of a MEMS speaker system based on a single sided driving mechanism as well as an outlook on MEMS speakers using double stator systems (pull-pull-system), and discuss their efficiency (SPL) an d quality (THD) towards the generated acoustic sound.