Piezoelectric Micromachined Ultrasonic Transducer with a Universal Bottom-Up Fabrication Approach Implemented on a Foil as Doppler Radar for Gesture Recognition

This paper presents a state-of-the-art piezoelectric micromachined ultrasonic transducer (PMUT) array fabricated on a 10 μm thick metal foil. Using a bottom-up micromachining technique, the PMUTs of electrode/piezoelectric film/ electrode sandwiched structures with versatile patterns can be implemented on a large-area foil with thickness even thinner than a hair. The proposed microfabrication easily allows the PMUT to generate ultrasonic waves with demanded resonances. The higher- order resonances of PMUT are functionally operated due to self-released residual stress fabrication. The developed PMUT array foil can be attached to the surface/substrate of arbitrary curvature. The integrated stereolithographic process can tune the operation frequencies of processed PMUTs. We successfully demonstrated the developed PMUT as a ranging transmitter and a Doppler radar to perform the hand gesture recognition.