3D FEM Analysis of High-Frequency AlN-Based PMUT Arrays on Cavity SOI

Area of Science:

• Materials Science
• Mechanical Engineering
• Electrical Engineering

Background:

• High-frequency piezoelectric micromachined ultrasonic transducers (PMUTs) are crucial for miniaturized ultrasonic systems.
• Accurate modeling is essential for predicting and optimizing PMUT performance.
• Existing analytical models may lack precision for complex 3D structures.

Purpose of the Study:

• To develop and validate three-dimensional (3D) finite element method (FEM) models for high-frequency PMUTs.
• To simulate and analyze the resonant frequencies, mode shapes, electrical impedance, and acoustic fields of PMUTs.
• To verify the model's accuracy against experimental measurements of fabricated devices.

Main Methods:

• Development of a 3D FEM model incorporating a sandwiched piezoelectric structure, silicon passive layer, and silicon substrate with a cavity.
• Application of periodic boundary conditions for simulating PMUT characteristics.
• Experimental verification using fabricated aluminum nitride (AlN)-based PMUT arrays and a laser Doppler vibrometer (LDV).

Main Results:

• The 3D FEM simulation showed a resonant frequency difference within 6% compared to experimental measurements for a 16-MHz PMUT.
• This accuracy is significantly better than that achieved with analytical methods.
• Simulated electrical impedance in air and water closely matched experimental results, validating the model's predictive capability.

Conclusions:

• The developed 3D FEM model accurately predicts the electrical and acoustic performance of high-frequency PMUTs.
• The model is suitable for optimizing PMUT structures and design.
• This approach holds potential for analyzing transmission and reception in PMUT arrays for future compact ultrasonic applications.