First resonance frequency and high sensitivity for MEMS acoustic sensors

In this paper, the first resonance frequency of the clamped square diaphragm of the capacitive acoustic sensor has been calculated using variational iteration method (VIM). The equivalent electrical circuit model using lumped parameters has been used to obtain the sensitivity of the sensor. The aim is to develop the microphones with high sensitivity and flat frequency response in hearing range. The high sensitivity can be obtained by changing the initial stress of diaphragm, sigma_r, diaphragm size, a, diaphragm thickness, t, back plate thickness, h, air gap thickness, d, back plate hole radius, r, surface area fraction occupied by the holes, a., and bias voltage. The optimized structure has a diaphragm thickness of 0.8 mum, a diaphragm area of 2.43 mm², an air gap of 4.0 mum and a 1.0 mum thick back plate with acoustical ports. The device shows maximum sensitivity 47.9mV/Pa, with a high frequency response extending to 18 kHz.