Concept and proof for an all-silicon MEMS micro speaker utilizing air chambers

MEMS-based micro speakers are attractive candidates as sound transducers for smart devices, particularly wearables and hearables. For such devices, high sound pressure levels, low harmonic distortion and low power consumption are required for industrial, consumer and medical applications. The ability to integrate with microelectronic circuitry, as well as scalable batch production to enable low unit costs, are the key factors benchmarking a technology. The Nanoscopic Electrostatic Drive based, novel micro speaker concept presented in this work essentially comprises in-plane, electrostatic bending actuators, and uses the chip volume rather than the its surface for sound generation. We describe the principle, design, fabrication, and first characterization results. Various design options and governing equations are given and discussed. In a standard acoustical test setup (ear simulator), a MEMS micro speaker generated a sound pressure level of 69 dB at 500 Hz with a total harmonic distortion of 4.4%, thus proving the concept. Further potential on sound pressure as well as linearity improvement is outlined. We expect that the described methods can be used to enhance and design other MEMS devices and foster modeling and simulation approaches. A new concept for an all-silicon CMOS compatible microspeaker uses the volume of the chip to generate sound. Microspeakers are used in a range of smart devices, and must provide both high sound pressure levels and low harmonic distortion. The majority of existing devices achieve this by out-of-plane deflection of surfaces, such as membranes or plates. Now, a project run by Bert Kaiser from Fraunhofer-Institute for Photonic Microsystems demonstrates micro speakers that comprise of in-plane electrostatic bending actuators that utilize the volume of the chip to generate sound. They first introduce the concept of their device and then demonstrate a working system, achieving a sound pressure level of 69 dB at 500 Hz and a total harmonic distortion of 4.4%.