18 May 2009 A method for improving the drop test performance of a MEMS microphone
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Abstract
Most micro electro mechanical system (MEMS) microphones are designed as capacitive microphones where a thin conductive membrane is located in front of a rigid counter electrode. The membrane is exposed to the environment to convert sound into vibrations of the membrane. The movement of the membrane causes a change in the capacitance between the membrane and the counter electrode. The resonance frequency of the membrane is designed to occur above the acoustic spectrum to achieve a linear frequency response. To obtain a good sensitivity the thickness of the membrane must be as small as possible, typically below 0.5 μm. These fragile membranes may be damaged by rapid pressure changes. For cell phones, drop tests are among the most relevant reliability tests. The extremely high acceleration during the drop impact leads to fast pressure changes in the microphone which could result in a rupture of the membrane. To overcome this problem a stable protection layer can be placed at a small distance to the membrane. The protective layer has small holes to form a low pass filter for air pressure. The low pass filter reduces pressure changes at high frequencies so that damage to the membrane by excitation in resonance will be prevented.
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Matthias Winter, Seifeddine Ben Aoun, Gregor Feiertag, Anton Leidl, Patrick Scheele, Helmut Seidel, "A method for improving the drop test performance of a MEMS microphone", Proc. SPIE 7362, Smart Sensors, Actuators, and MEMS IV, 736214 (18 May 2009); doi: 10.1117/12.821187; https://doi.org/10.1117/12.821187
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