We demonstrate a low-volume, stress-free, piezoelectric micro-electromechanical system (MEMS) cantilever array for fully implantable hearing aids. The 12-element spiral-matrix is sensitive to the lower part of audible frequency range (300⁻700 Hz) through the proper resonant frequency of the individual spirals tuned by dimensions of the cantilevers. The obtained high Q-factors (117⁻254) provide high frequency selectivity. The generated open circuit voltage signals could be sufficient for the direct analog conversion of the signals for cochlear multielectrode implants. By comparing different geometries we have also demonstrated that the initial stress, which is derived from silicon-dioxide (SiO2) and aluminum-nitride (AlN) layers, could be drastically reduced simply by the spiral geometry. The results of vibration measurements have shown a good agreement with the calculated resonant frequencies.
