Design of multi-bandwidth piezoelectric microelectromechanical systems accelerometers for totally implantable auditory prostheses: How many bandwidths are enough?

Hearing aids and cochlear implants help patients treat their hearing loss, but have limitations impacting their use rates. Completely implantable auditory prostheses would expand the range of activities a prosthesis user could engage in and enable 24/7 use. However, the lack of a completely implantable microphone that is robust, lightweight, and low noise prevents the wide adoption of implantable devices. Current implantable sensors struggle to meet or exceed the performance necessary for this application. This work develops a discretized and exhaustive design optimization approach to identify multi-bandwidth transducers that meet the 20-phon noise floor over 100 Hz-8 kHz. The design procedure is based on an experimentally validated analytical model that simulates the response of miniature piezoelectric microelectromechanical systems (MEMS) accelerometers. A four-bandwidth accelerometer with constrained proof mass thicknesses is selected as the design that best balances area minimization with ease of manufacturability. The estimated MEMS die dimensions are 825 μm × 575 μm, which is a 23% MEMS die area reduction compared to the previously published dual-bandwidth sensor [A. E. Hake, P. Kitsopoulos, and K. Grosh, IEEE Sens. J., 23(13), 13957-13965 (2023)].