10 MHz Thin-Film PZT-Based Flexible PMUT Array: Finite Element Design and Characterization

Area of Science:

• Materials Science
• Acoustics
• Electrical Engineering

Background:

• Miniaturized high-frequency ultrasound systems require advanced transducer designs.
• Flexible piezoelectric micromachined ultrasound transducer (PMUT) arrays offer new possibilities.
• Lead zirconate titanate (PbZr0.52Ti0.48O3) (PZT) thin films are key components in PMUTs.

Purpose of the Study:

• To improve the design of flexible PMUT arrays using finite element method (FEM) software.
• To design and characterize a 10 MHz PMUT 2D array operating in the 3-1 mode.
• To optimize figures of merit including center frequency, bandwidth, depth of field, and crosstalk.

Main Methods:

• Utilized PZFlex, a finite element method software package, for virtual prototyping.
• Designed a circular unit-cell with concentric Pt/PZT/Pt/Ti layers on a polyimide (PI) substrate.
• Created and characterized a 256-unit (16x16) 2D PMUT array, analyzing pulse-echo and spectral responses.

Main Results:

• Predicted a 10 MHz center frequency and 87% bandwidth under water load and air backing.
• Observed a mechanical focal length of 2.9 mm and a -6 dB depth of field of 3.7 mm.
• Measured crosstalk at -55.6 dB, with decreased bandwidth attributed to oscillation decay and guided waves.

Conclusions:

• Finite element-based virtual prototyping is effective for designing robust, flexible PMUT arrays.
• Optimization of key performance metrics is crucial for advanced ultrasound applications.
• The study provides a pathway for developing next-generation miniaturized high-frequency ultrasound systems.