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)NbO
3
(KNN) thin film with a high piezoelectric coefficient (e
31
~ 8-10 C/m
²
) and low dielectric constant (ϵ
r
~ 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 (V
p-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.