At the 2022 IEEE International Ultrasonics Symposium, imec, a world-leading research and innovation center in nanoelectronics and digital technologies, presented a piezoelectric Micromachined Ultrasound Transducer (pMUT) array that is compatible with flat-panel-displays (FPD) process technologies. The array demonstrates acoustic pressures in mid-air above 1kPa, a pressure level relevant for enabling mid-air haptics and directed sound. Moving from wafer-based to FPD-compatible processes prepares the pMUT technology for the integration of future mid-air applications, such as vibro-haptics, time-of-flight (3D) sensing or gesture recognition, in novel form factors like smartphones and car dashboards. This technology can be used to create touchless, interactive, screens in automotive and consumer applications, or used in gaming.

(A) A large-area pMUT array consisting of 22 phased annular rings of 500 µm diameter pMUTs (B) Detail.

Ultrasound technology can be used to equip smart systems with haptic feedback, giving the user a sense of touch. In the case of mid-air haptics, ultrasonic waves produce a local pressure field causing the user to ‘feel’ a light sensation without touching the object. Such applications require high-pressures at low ultrasonic frequencies. Current solutions include, on the one hand, large standard piezoelectric elements that produce relatively high frequencies impeding a precise interaction with the user. On the other hand, small silicon-based micromachined transducer arrays can enable haptic feedback at short distance in a small area only. Our FPD-compatible thin-film pMUT technology is inherently more compatible with display manufacturing techniques. As such, it paves the way to applications with unprecedented area and depth of experience.

Measured peak focal pressure at a height of 30 mm above the center of the pMUT array

Imec’s FPD-compatible thin-film pMUT array now fills the niche for low-frequency, high-pressure devices for large volume mid-air applications. We demonstrate peak pressures of ~1.5 kPa in air at resonant frequencies in the range of 200 to 400 kHz, replicating the performance metrics successfully demonstrated mid-air haptic feedback on its Si wafer-based platform.

“We currently offer wafer-level demonstrations of our FPD-technology and prototyping solutions for interested parties. Additionally, we are looking into partnerships for volume manufacturing on large-area panels and plates,” says Erwin Hijzen, Program Director MEMS Ultrasound at imec.

“The possibility to integrate our pMUT technology into large panels and displays is a key milestone in realization of our vision on large area sensor surfaces. We started with ultrasound transducers for in-body imaging and now moved to mid-air applications such as haptics.” concludes Xavier Rottenberg, Fellow Sensors and Actuators at imec.

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