Characterization of an advanced MEMS artificial basilar membrane using XeF2 etching in the air and fluid

Abstract

Cochlear implants (CIs) are implanted electronic devices for hearing recover of patients who have profoundly hearing loss caused by damaged hair cells in the cochlea. Although CIs have been conventionally successful, it has some limitations: necessity of extracorporeal devices, exposure of a disability by extracorporeal devices, requirement of large power, frequent recharging, and complicated signal processing circuits. To overcome these limitations, many researchers proposed the artificial basilar membranes (ABMs) to develop fully implantable CIs using microelectromechanical system (MEMS) technology. The ABM mimics the function of cochlea such as frequency selectivity and acoustic to electrical energy conversion. In the previous studies of our group, Kim et al. developed an ABM consisting of an aluminum nitride (AlN) beam array with narrow supports. However, the piezoelectric voltage output was noise level because the narrow supports lead to a rigid body motion of beams. To increase the piezoelectric output of an ABM, Jang et al. proposed an ABM fabricated by using a silicon-on-insulator (SOI) wafer and deep reactive ion etching (DRIE). Although the Jang et al.’s ABM showed the enhanced piezoelectric output performance, their fabrication process was too complicated with relatively high production cost. In this paper, we fabricated an advanced MEMS ABM based on XeF2 etching technology. The XeF2 etching enable the total fabrication process to very simple with relatively low production costs in comparison with DRIE. Also, the low-pressure chemical vapor deposition silicon nitride (LPCVD Si3N4) was used to reduce the lateral bending of beam which was caused by residual stress. In addition to fabrication process, the all beams of ABM were designed to continuous beam structure without narrow supports to avoid rigid body motion of beam. The displacement and piezoelectric output of each beam were measured using a scanning laser-Doppler vibrometer (SLDV) for acoustic or electric stimulus. During acoustic stimulus, the fabricated ABM showed a frequency selectivity in the range 10.5 - 36.5 kHz and the piezoelectric voltage output in the range 2 - 5 µV. It also showed a frequency selectivity in the range 11.1 - 47.7 kHz for electric stimulus. Also, the frequency selectivity of the fabricated ABM was estimated in the fluid. Since the viscous-damping effect of water, the resonance frequency was shifted from 11.1 - 47.7 kHz in air to 3.1 - 11.9 kHz in fluid. From these results, the fabricated ABM has the two functions of cochlea which are frequency selectivity and acoustic-to-electric energy conversion. Also, we identified the feasibility as substitute of the conventional CIs and the potential as fully implantable device. ⓒ 2016 DGIST