Airborne Rangefinding With pMUTs Array Using Differential Structure

Abstract

Here, we report a differential ring array of piezoelectric micromachined ultrasonic transducers (pMUTs) for ultralong-range detection. Among them, the differential structure is used to improve the sensitivity of the device, and the ring array is used to improve the generated sound intensity. The synergy between the differential structure and the ring array improves the acoustic performance of pMUTs. The piezoelectric material adopts aluminum nitride (AlN) thin film compatible with complementary metal–oxide–semiconductor (CMOS) process. The resonant frequency of the device (80 kHz), the piezoelectric film radius ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500 \mu \text{m}$ </tex-math></inline-formula> ), and the top electrode ratio were optimized using the finite element method. Compared to pMUTs with central circular electrodes, the differential structure provides two times the low-frequency drive sensitivity and two times the center displacement at the resonant frequency. Seven elements with differential structure were used to form a ring pMUTs array, and the size of the ring pMUTs array was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times5$ </tex-math></inline-formula> mm2. Further research shows that the ring pMUTs array can achieve a very large range ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\ge 0.6$ </tex-math></inline-formula> m) detection, and the range error is less than 2.4 mm. The differential ring pMUTs array provides a valuable reference for obstacle avoidance, flow measurement, liquid-level measurement, and other fields.