Abstract
Piezoelectric microelectromechanical systems (MEMS) microphones have been researched for over 30 yr because they are relatively easy to build, output a signal without any biasing circuitry, and are relatively linear. The primary impediment to mass utilization of piezoelectric MEMS microphones has been the noise levels of these devices, which have been unacceptably high. The input referred noise of most piezoelectric MEMS microphones is greater than or equal to 55 dB(A) while commercial capacitive MEMS microphones typically have noise floors between 32 and 38 dB(A), roughly ten times lower. In order to achieve competitive noise levels in a piezoelectric MEMS microphone, a systematic approach to mechanical and electrical optimizations must be used. A key microphone metric for this optimization is acoustically generated electrical energy, as opposed to sensitivity. This optimization can be used to determine the minimum achievable noise floor for piezoelectric sensors with relatively few assumptions. Further, this optimization allows for the determination of materials, electrode patterns, layer thicknesses, and mechanical structures that minimize the noise. These models have been used to design and build piezoelectric MEMS microphones with a noise floor of 34 dB(A) and indicate that further improvements can be achieved.
Published Version
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