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P. Udvardi, J. Radó, A. Straszner, J. Ferencz, Z. Hajnal, S. Soleimani, M. Schneider, U. Schmid, P. Révész, J. Volk:
"Spiral-Shaped Piezoelectric MEMS Cantilever Array for Fully Implantable Hearing Systems";
Micromachines, 8 (2017), 311; 1 - 13.

Fully implantable, self-powered hearing aids with no external unit could significantly
increase the life quality of patients suffering severe hearing loss. This highly demanding concept,
however, requires a strongly miniaturized device which is fully implantable in the middle/inner ear
and includes the following components: frequency selective microphone or accelerometer, energy
harvesting device, speech processor, and cochlear multielectrode. Here we demonstrate a low volume,
piezoelectric micro-electromechanical system (MEMS) cantilever array which is sensitive, even in
the lower part of the voice frequency range (300-700 Hz). The test array consisting of 16 cantilevers
has been fabricated by standard bulk micromachining using a Si-on-Insulator (SOI) wafer and
aluminum nitride (AlN) as a complementary metal-oxide-semiconductor (CMOS) and biocompatible
piezoelectric material. The low frequency and low device footprint are ensured by Archimedean
spiral geometry and Si seismic mass. Experimentally detected resonance frequencies were validated
by an analytical model. The generated open circuit voltage (3-10 mV) is sufficient for the direct
analog conversion of the signals for cochlear multielectrode implants.

Fully implantable, self-powered hearing aids with no external unit could significantly
increase the life quality of patients suffering severe hearing loss. This highly demanding concept,
however, requires a strongly miniaturized device which is fully implantable in the middle/inner ear
and includes the following components: frequency selective microphone or accelerometer, energy
harvesting device, speech processor, and cochlear multielectrode. Here we demonstrate a low volume,
piezoelectric micro-electromechanical system (MEMS) cantilever array which is sensitive, even in
the lower part of the voice frequency range (300-700 Hz). The test array consisting of 16 cantilevers
has been fabricated by standard bulk micromachining using a Si-on-Insulator (SOI) wafer and
aluminum nitride (AlN) as a complementary metal-oxide-semiconductor (CMOS) and biocompatible
piezoelectric material. The low frequency and low device footprint are ensured by Archimedean
spiral geometry and Si seismic mass. Experimentally detected resonance frequencies were validated
by an analytical model. The generated open circuit voltage (3-10 mV) is sufficient for the direct
analog conversion of the signals for cochlear multielectrode implants.

http://dx.doi.org/10.3390/mi8100311