TiN/PECVD-Si3N4/TiN diaphragm-based capacitive-type MEMS acoustic sensor

Abstract

A capacitive-type MEMS acoustic sensor with a planarised TiN/plasma-enhanced chemical vapour deposition -Si3N4/TiN diaphragm based on a polyimide sacrificial layer is presented. The multi-layer diaphragm has the effective residual stress of +31.5 MPa. Furthermore, this sensor features a 21% lower parasitic capacitance and a 56% lower air-gap resistance in comparison with those of a sensor fabricated without planarisation. Five photomasks were used. In addition, to evaluate the frequency response, both an effective capacitance model and an equivalent circuit model equipped with a voltage-controlled voltage source are newly proposed and compared with conventional models. The open-circuit sensitivity is modelled to -45.4 dBV/Pa at 1 kHz with 9.6 V, indicating a difference of 0.9 dB in comparison with the open-circuit sensitivity of the conventional model