Abstract
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 mm2 and a chip thickness of 0.4mm, and a 355 μm-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 μm, and the effective residual stress was modelled to be +61 MPa. From the model, the open-circuit sensitivity was characterized as 3.65mV/Pa under an 8 V bias condition.
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