High-SPL and Low-Driving-Voltage pMUTs by Sputtered Potassium Sodium Niobate

This work presents an air-coupled piezoelectric micromachined ultrasonic transducer (pMUT) with
high transmitting acoustic pressure by using sputtered potassium sodium niobate (K,Na)NbO3
(KNN) thin film with a high piezoelectric coefficient (e31 ~ 8-10 C/m2) and low dielectric constant
(er ~ 260-300) for the first time. The fabricated KNN pMUT with a resonant frequency at 104.5 kHz
has been tested to exhibit unprecedented results: (1) high sound pressure level (SPL) of 109 dB/V
at a distance of 10 cm, which is 8 times higher than that of AlN-based pMUTs at a similar
frequency; (2) low-voltage operation of only 4 volts peak-to-peak amplitude (Vp-p); and (3) good
receiving sensitivity. As such, this work presents a new class of high-SPL and low-driving-voltage
pMUTs for potential applications in various fields, including consumer electronics, such as but not
limited to haptic feedback, loudspeaker, and AR/VR systems.