Performance of Aluminum Nitride Curved PMUT Arrays Fabricated Using Glass Blowing Technique

We present the initial characterization results of curved piezoelectric micromachined ultrasound transducer (PMUT) arrays fabricated using the chip-scale glass-blowing method. The three-dimensional PMUTs are realized by depositing 750 nm thick 30% scandium-doped aluminum nitride (Sc-AlN) on curved suspended glass diaphragms of 150 μm diameter. The performance of a 13 × 13 row-column-addressable curved PMUT array was characterized using electrical impedance, Laser Doppler vibrometer (LDV), and hydrophone. The electrical impedance and LDV measurements showed the device resonance frequency of ~4.2 MHz in air, and the hydrophone measurement showed a resonance frequency of ~2.58 MHz in water. The low-frequency response measured with LDV was 0.3 nm/V. Using 54.1 Vpp electrical input to the curved PMUT array, the acoustic field profile mapped by the hydrophone showed a focal length of 4.27 mm, a focal width of 2.1 mm, and a peak pressure of 0.4353 kPa/V/cell at 7 mm, and corresponding spatial-peak-temporal-average intensity ISPTA = 476 mW/cm2.