A fully-integrated CMOS-MEMS audio microphone

We report on the construction of a microphone and associated electronics fabricated entirely within a standard CMOS (complementary metal oxide semiconductor) die. An A-weighted noise level of 46 dB SPL was achieved with a total diaphragm area of 0.61 mm/sup 2/. Because the microphone uses the same processing sequence as CMOS-MEMS (microelectromechanical systems) microspeakers it is now possible to create acoustic systems-on-chip for applications in such areas as hearing aids, in-ear translators, and active noise cancellation. Because electret materials are not used, the microphone can withstand temperatures up to 250/spl deg/C with no degradation in performance. The frequency-modulated output provides a convenient, low-noise way to transmit the signal off chip, and is directly compatible with digital circuitry and FM radios.