Design and Optimization of MEMS based AlN Sensor for Acoustic Application

The market for MEMS sensors based on Aluminum Nitride (AlN) is developing because of AlN material's capacity to produce CMOS-compatible, highly reliable, and self-powered devices. Utilizing the COMSOL software tool, the sensors parameters are designed and optimized in accordance with the dimension and thickness of AlN thin film layer. The proposed design technique is applicable to any piezoelectric diaphragm-based acoustic sensors, regardless of the cavity and hole structures in the silicon or SOI (silicon on insulator) based substrate. The diaphragm consists fixed 25 µm Si layer and variable (0.5 µm to 2.5 µm) Al/AlN/Al layer. The AlN layer is sandwiched between top and bottom Aluminum electrodes of thickness 0.3 µm. The diaphragm area is varying from 1.75 mm x 1.75 mm to 3.5 mm x 3.5 mm. Prior to engaging in expensive fabrication methods, this work optimizes the AlN layer with regard to resonance frequency, deflection at the diaphragm's center, and sensor response. The simulated results demonstrate the trade-off between the diaphragm deflection at the center and a workable frequency range in accordance with the design parameters that were specified. For a frequency range of 0.5 kHz to 18 kHz, the device's optimal design has a simulated sensitivity of 2.5 µV/Pa and at resonance the sensitivity is 200 µV/Pa.