A cochlea bio-inspired tunable piezoelectric cantilever array MEMS microphone: comprehensive study

Abstract This study introduces a bio-inspired AlN-piezoelectric MEMS microphone that showcases a cantilever structure offering adjustable performance, fully emulating the dynamics and tunability observed in the basilar membrane of the mammalian cochlea. Through the incorporation of piezoelectric and converse piezoelectric effects alongside dual parametric modulation mechanisms, the device successfully replicates three crucial aspects of cochlear mechanics: i) sensory transduction characteristic of inner hair cell (IHC); ii) local stiffness modulation enabled by outer hair cell (OHC) somatic motility; and iii) energy redistribution in coupled-system recapitulating the energy transfer of cochlear traveling wave dynamics. The device performance was systematically characterized through electrical characterizations, optical analysis, and acoustic measurements. Experimental results demonstrate a baseline sensitivity of −25.38 dB/Pa and signal-to-noise ratios up to 79.28 dB within an operation bandwidth from 1.755 to 2.261 kHz (3 dB cut-on and cut-off bandwidth), while the quality factor (Q) can be tuned to a value ranging from −55.38% to 180.10% of initial values, representing a 124.72% tuning span. In essence, the critical innovations encompass: i) a MEMS microphone that pioneers the first fully mimicking simultaneous sensing/tuning functionality of the mammalian cochlea, through piezoelectric and converse piezoelectric effects; ii) a combination of two novel tuning mechanisms, i.e., AC (through parametric modulation) and mechanical coupling, are applied without the necessity for mechanical structure modification. It can be envisioned that such a technology enables next-generation hearing aids with bio-inspired auditory adaptation, bridging a critical gap in prosthetic sound processing, while also catering to the ever-increasing demands of intelligent acoustic sensors.