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

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.

Large-Signal Equivalent-Circuit Model of Asymmetric Electrostatic Transducers

“…The displacementdependent capacitor is constructed with a current-dependent voltage source in series with a linear capacitor. The reader may verify that U in = u 0 (1 − x/g 0 ), and therefore the charge entering the capacitor follows (1). Notice that the displacement is read out from the force ("current") of the linear component of the spring (k 1 ).…”

“…devices. Kaiser et al [1], for instance, report the fabrication of an all-silicon, CMOS-compatible electrostatic microloudspeaker based on the nano e-drive (NED) actuation principle [2]. Electrostatic MEMS microphones have already found widespread use [26].…”

“…This circuit representation is done in such a way that no code-specific "derivative" or "integral" elements are used, enabling thus its implementation in a standard circuit simulator-it only requires using controlled sources that compute algebraic equations. We also apply this network model to simulate the behavior of the MEMS loudspeaker designed by Kaiser et al [1], which has been shown to exhibit nonlinear stiffening effects [3]- [5], and also make a prediction of its behavior as a microphone. Although laid out for the case of electrostatic transducers, the procedure that we follow here can also be applied to build nonlinear network models of other systems, such as piezoelectric or electrodynamic transducers.…”

Spray-coated electret materials with enhanced stability in a harsh environment for an MEMS energy harvesting device

“…Therefore, charge flows between the electrodes and can be collected as harvested energy to provide sustainable power for wireless sensors with low power consumption. Compared with other types of energy harvesting principles, such as piezoelectric [15][16][17][18][19][20] , triboelectric [21][22][23][24] , and electromagnetic [25][26][27][28][29] methods, electrostatic energy harvesters have been increasingly studied for their good compatibility with MEMS technology and integrated circuit (IC) fabrication processes 8,[30][31][32][33][34][35] , which reduces the size and cost of devices and improves device reliability.…”

Investigation of a new method for sound generation – Advanced Digital Sound Reconstruction

“…It has to be noted, that the overall power consumption is not yet lower than the one of classical analog loudspeaker principles but the problem is rather shifted to the driving circuit. Nevertheless, smaller form factors as well as the low power consumption pave the way for a new generation of micro-speakers [4].…”