Miniature implantable low noise piezoelectric diaphragm sound sensor

Piezoelectric diaphragm sound sensors must be miniaturized and environmentally toughened for use in biomedical applications. We study two disparate applications of the sensor, first as the front end of a completely implantable cochlear implant and the second as an intracardiac pressure sensor. The sensor, which is fabricated using micro-electrical-mechanical-system (MEMS) techniques, consists of a circular diaphragm with at least one aluminum nitride (AlN) based piezoelectric layer backed by an air-filled cavity. The sensors are designed to have a lower input referred noise (IRN) compared to other miniaturized piezoelectric diaphragm hydrophones with similar diaphragm size via structural design and electrode area optimization. Sensors are fabricated with varying diaphragm diameters from 300 to 450 μm to test the effect of residual stresses due to the manufacturing process on the frequency bandwidth and IRN. The sensor works in air and underwater with the same sensitivity, but the frequency bandwidth is re...