Design and Characterization of a MEMS Piezoresistive Cochlear-Like Acoustic Sensor

Abstract

The mammalian cochlea achieves excellent acoustic transduction though the use of mechanical signal processing. The device presented in this paper mimics the structure of the cochlea with a micromachined array of nearly 3000 0.34 μm thick silicon beams suspended between two wafer-high ducts. Piezoresistive strain gauges are incorporated into the beams to produce 38 channels of realtime frequency information. Device mechanical and electrical models are presented. Initial mechanical measurements in air demonstrate good agreement with predicted frequency sensitive and response amplitude. Device sensitivity in air is tentatively measured to be 30 mm/s of beam center velocity response per Pascal of input pressure, corresponding to a predicted piezoresistor sensitivity of 7000 ppm/Pa. This gives an expected achievable resolution of 250 μParms in a 100 kHz band in air. Note that this differs from the intended operating mode of the transducer, which is in fluid over a 20 kHz band.