Polyimide-On-Silicon 2D Piezoelectric Micromachined Ultrasound Transducer (PMUT) Array

Area of Science:

• Materials Science
• Electrical Engineering
• Acoustics

Background:

• Micromachined ultrasonic transducers (MUTs) are crucial for ultrasound imaging and sensing.
• Developing cost-effective and high-performance MUT arrays remains a key challenge.

Purpose of the Study:

• To present a fully addressable 8x8 rigid piezoelectric micromachined ultrasonic transducer (PMUT) array.
• To demonstrate a low-cost fabrication process for PMUT arrays using standard silicon wafers.
• To characterize the performance of the PMUT array, focusing on frequency, sensitivity, coupling, crosstalk, and bandwidth.

Main Methods:

• Fabrication of PMUTs on a silicon wafer using deep reactive ion etching (DRIE).
• Integration of a polyimide passive layer for frequency tuning.
• Characterization of resonance frequency, sensitivity, effective coupling coefficient, interelement crosstalk, pressure response, and fractional bandwidth.

Main Results:

• A 3.2 MHz in-air frequency and 3 nm/V sensitivity were achieved with a 6 µm polyimide thickness.
• An effective coupling coefficient of 14% was calculated, with approximately 1% interelement crosstalk.
• A 70% -6 dB fractional bandwidth at a 1.7 MHz center frequency was observed underwater.

Conclusions:

• The fabricated PMUT array offers a low-cost solution for ultrasound imaging.
• The design demonstrates significant reduction in interelement crosstalk compared to existing technologies.
• The results indicate potential for imaging and sensing in shallow-depth applications.