Recently, a new approach for an all-silicon MEMS-based microspeaker has been presented for in-ear applications. The volume displacement is generated by multiple electrostatic actuated beams called “Nanoscopic Electrostatic Drives” (NED) that move in lateral direction between a top and a bottom silicon wafer. The top and the bottom wafers are provided with openings through which air can flow in and out. Two fundamentally different actuator designs have been realized: An asymmetric electrostatic pull-actuator and an electrostatic push-pull actuator. While the push-pull actuator can be actively displaced in both directions, the pull actuator can only be displaced actively in one direction and therefore requires an offset voltage to oscillate around a working point. These different driving schemes have a major impact on stability and harmonic distortions. In this presentation, MEMS speakers realized using both approaches will be compared and the impact on acoustic performance will be demonstrated.

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