Mechanical-thermal noise in CMOS micromachined inductive microphone

In this paper, we present mechanical-thermal noise characterization and calculation for the new state-of-the art monolithically integrated CMOS micromachined inductive microphone. This new acoustic sensor has a suspended moving membrane attached to the substrate with 4 L-shaped arms. This membrane has 1.4times1.4 mm² surface, 22 mug mass and its natural frequency was found to be around 200 kHz. This sensor was analyzed for mechanical-thermal noise by modeling the suspended membrane with its mass-spring oscillator diagram and adding a force generator alongside each damper. The system damping factor was found to be 4times10^-2 N.s/m, which gives a fluctuating force spectral density of 2.57times10^-11 N/radicHz. This noise pressure spectral density corresponds to an A-weighted sound level of about 38 dB(A) SPL. Consequently, this microphone is well suited for recording low-level signals in quiet environments.