Structure-based equivalent circuit modeling of a capacitive-type MEMS microphone

Structure-based equivalent circuit modeling for a capacitive-type MEMS acoustic sensor is presented. The model is subsequently divided into three main areas: acoustic, mechanical, and electrical domains. Furthermore, it is composed of three different parameter groups: empirical, theoretical, and mixed data. With an extraction method using measured values, the compliance of a diaphragm and the zero-bias intrinsic capacitance were evaluated to 3.430 × 10-3 m/N and 1.02 pF, respectively, whereas the viscous resistance of acoustic holes and an equivalent mass were calculated to be 2.958 × 108 kg/s·m4 and 7.856 × 10-10 kg, respectively, with theoretical calculation from geological dimension. To verify the proposed model, the open-circuit sensitivities were compared between the modeled and measured values. The MEMS microphone had an open-circuit sensitivity of -48.5 dBV/Pa at 1 kHz with a bias of 10.4 V, while the modeled open-circuit sensitivity was -48.6 dBV/Pa, which shows good agreement in the range from 100 Hz to 18 kHz. That indicates the validation of the structure-based equivalent circuit model to predict and design the MEMS microphone.

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