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

Bert Kaiser,Hermann Schenk,Klaus Schimmanz,Holger Conrad,David Schuffenhauer,Sergiu Langa,Lutz Ehrig,Harald Schenk,Michael Stolz

doi:10.1038/s41378-019-0095-9

Abstract

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.

Highlights

There is great demand for high performance micro electromechanical systems (MEMS) micro speakers by the consumer and by the hearing aid industry
In this paper we present a novel design concept for MEMS micro speakers based on the fabrication technologies referred to as silicon bulk micro machining, which is fully CMOS compatible
The device comprises clamped-clamped electrostatic bending actuators, the NED13, placed pairwise in rows and columns within the device layer of a bonded silicon on insulator (SOI) wafer and covered by another wafer bonded to the SOI wafer with a tiny separation

Summary

Introduction

There is great demand for high performance micro electromechanical systems (MEMS) micro speakers by the consumer and by the hearing aid industry. A prominent example is smartphones, which have all the types of MEMS mentioned above They include acoustic transducers, most likely appearing as multiple MEMS microphones, to Several concepts for MEMS-based micro speakers have been reported in the literature. Chen et al.[2] used a 3.5 mm Kaiser et al Microsystems & Nanoengineering (2019)5:43 diameter polymer membrane on a silicon substrate, incorporating a single loop copper coil and two magnets for electromagnetic driving of the speaker. They were able to demonstrate 106 dB at 1 kHz in a 2 cm[3] closed cavity, with an input power of 1.76 mW. For a driving voltage of 2 Vpp they were able to measure a peak SPL of 86 dB (2 cm[3] closed cavity) with a THD of less than

Methods

Results

Conclusion