Electrical characterization of MEMS microphones

Abstract

A reliable characterization of a MEMS microphone is essential for a better understanding of the device physics, for estimating the device performance and for guidance during the research, for better microphones. The work presented in this report focuses on the investigation and comparison of different measurement principles and techniques used to measure the key device parameters resonance frequency and compliance. The first generation MEMS microphones that are developed by NXP are influenced by mechanical vibrations that reduces the device performance. Therefore, new techniques will be implemented to reduce this noise and these techniques are based upon matching the frequencies of two flexible plates in the microphone sensor, we investigate these resonance frequencies in this thesis. This investigation is performed with two different measurement techniques : electrical impedance measurements and laser vibrometer experiments. These measurements are performed in air and vacuum conditions and the influence of ambient pressure, bias voltage and back volume on the resonance frequency is investigated. The vacuum measurements are in good agreement with the finite element simulation results. Additionally the results obtained from different measurements are compared and the difference between the results are analyzed. Finally, recommendations are made for future measurement conditions and setups.