Fabrication and characterization of PECVD Si3N4 diaphragm-based capacitive-type acoustic sensor for IoT application

A bottom-inlet capacitive acoustic sensor with PECVD-Si3N4 diaphragm is presented for Internet of things (IoT) application which is simple and compatible with the CMOS process. The polyimide sacrificial layer enables the photo-mask to be used at least for 5 photo-masks, resulting a simple fabrication process. For a bottom-inlet-type package, the diaphragm composed of a PECVD-Si3N4 structure layer and a TiN electrode layer was designed to be placed over the back-plate. The sensor has a total chip area of 1 mm(2) and a chip thickness of 0.4 mm, and a 355 mu m-radius diaphragm, respectively. To characterize the open-circuit sensitivity in a static state, an analytical approximately linearized electric-field method (ALEM) capacitor model was applied. The effective radius of the diaphragm was determined to be 316 mu m, and the effective residual stress was modelled to be +61 MPa. From the model, the open-circuit sensitivity was characterized as 3.65 mV/Pa under an 8 V bias condition. (C) 2016 The Authors. Published by Elsevier Ltd.