Piezoelectric ultrasonic transducer based on flexible AlN

• A piezoelectric transducer is realized on flexible highly oriented Aluminum Nitride.
• Compressive residual stress due to Aluminum Nitride deposited on polymeric substrate is the origin of a dome shape.
• Flexural behavior of actuated domes is studied by Laser Doppler Vibrometer.
• Significant mechanical displacement to generate ultrasound waves is measured.

This work presents a promising ultrasound wearable technology based on a piezoelectric transducer, realized on flexible highly oriented Aluminum Nitride, with significant mechanical displacement in spite of being attached on a rigid support. Circular membranes with different radius sizes, based on 1-μm-thick AlN thin film as the active piezoelectric layer, are designed, fabricated, and characterized. The AlN is deposited on kapton HN substrate with a low sputtering deposition temperature that allows the integration and the compatibility with flexible electronics. Mechanical and thermal stability of kapton makes this polyimide based sheet a potential substrate for flexible piezoelectric thin film technology. The actuation at low voltage (1–10 V) of the AlN membranes is studied in air in the range of ultrasound frequencies, from 0 Hz up to 2 MHz; the voltage amplitude, the shape and displacement of the flexure mode (0, 1) is studied by a Laser Doppler Vibrometer to characterize the mechanical properties of the device.

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