Preliminary Modeling of an Intracochlear Piezoelectric Microphone

Abstract

A preliminary model of an intracochlear piezoelectric microphone is proposed that mimics the structure of stereocilia in the cochlea. Its purpose is to determine the crucial system parameters prior to fabrication of an actual testing set up via a mathematical model. As a first approximation, the system is modeled as a 1-D, periodic beam with N identical substructures. Each one consists of a nanorod grown on an Si substrate, a bottom electrode, piezoelectric thin film, and two top electrodes. The model consists of: a finite element analysis of a single substructure to obtain its flexibility matrix and differential voltage (DV) under unit loads; and a mapping of these results through the structure to predict displacement and DV of each substructure. A parametric study is then conducted based on this model. It was determined that the nanorod length was the most critical parameter in improving sensitivity. By increasing the amount of drag force on the nanorods the sensitivity grows. Substructures near fixed boundaries generate higher DV thus leading to better sensitivity too. The number of substructure in the microphone would also affect signal-to-noise ratio.

On the theoretical maximum achievable signal-to-noise ratio (SNR) of piezoelectric microphones

“…Historically, potential advantages cited for piezoelectric MEMS microphones include no backplate, no required bias voltage, and a relatively large capacitance compared to capacitively transduced MEMS microphones. More recently, piezoelectric sensing has proven useful for prototyping microphones with unconventional geometries, such as microphones mimicking the hearing organs of insects [5–7] and human cochleas [8], and microphones employing dense cantilever arrays for “pre-filtering” captured sound [9]. …”