MEMS middle ear acoustic sensor for a fully implantable cochlear prosthesis

A MEMS accelerometer is proposed as an implantable middle ear microphone for a future fully implantable cochlear prosthesis. Vibration characterization of human temporal bones indicates that a MEMS accelerometer needs to achieve a sensing resolution of 75 mug_rms/radicHz with a bandwidth of 10 kHz to detect normal conversation. A prototype MEMS accelerometer is designed and fabricated. The device exhibits a nominal capacitance value of 2.4 pF with a differential sensitivity of 4 fF/g. When interfaced with a low noise CMOS capacitance-to-voltage converter, the sensor achieves a sensing resolution of 78 mug_rms/radicHz at 500 Hz with a sensitivity of 11.5 mV/g and bandwidth of 6.4 kHz. The overall system attached on umbo demonstrates the capability of detecting normal conversation.