Design and Modeling of Piezoelectric-AlN-based Acoustic Sensor for Sound Pressure Level Measurements

This paper illustrates the design of a piezoelectric acoustic sensor based on AlN to be used for aero-acoustic measurements. A significant prerequisite for such sensors is a large sound pressure level (SPL) and flat frequency response in the auditory band (20 Hz to 20 kHz). That is why this sensor has been designed to measure upto an SPL of 180 dB. The design of the device has been achieved through the MEMS-CAD tool Coventorware. The Si-diaphragm thickness has been optimized for the desired SPL range using Coventorware for three different sizes of the device, namely 1.5 mm x 1.5 mm, 1.75 mm x 1.75 mm and 2 mm x 2 mm. The cavity developed after the diaphragm formation is connected to the exterior environment through a microchannel. The microchannel was designed for low cut-off frequency. The complete frequency response of all the three sensor structures has been determined. Moreover, a comparison has been drawn among the three devices in terms of parameters such as low cut-off frequency, resonance frequency, and sensitivity to find the optimized device size. The low cut-off frequency, resonance frequency, and flat band sensitivity of the optimized device are 35 Hz, 83 kHz, and 170 mu V/Pa, respectively. In addition to this, a proposed fabrication process flow of the device has been presented.