Airborne Piezoelectric Micromachined Ultrasonic Transducers for Long-Range Detection

• Published in: Journal of microelectromechanical systems Vol. 30; no. 1; pp. 81 - 89
• Main Authors: Luo, Guo-Lun, Kusano, Yuri, Horsley, David A.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustic absorption; Acoustics; airborne; Aluminum nitride; Arrays; Fabrication; III-V semiconductor materials; Lead zirconate titanates; MEMS; Micromachining; Permittivity; piezoelectric; Piezoelectricity; PMUT; PZT; range detection; Sensitivity; Silicon; Single crystals; Sound pressure; Transducers; Ultrasonic testing; Ultrasonic transducers; ultrasound
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2020.3037298

This paper presents an airborne piezoelectric micromachined ultrasonic transducers (PMUTs) operated at low frequency (40-50 kHz) for long-range detection, where the acoustic absorption loss in air is relatively low (0.8-1 dB/m). The PMUTs made with single-crystal Lead Zirconate Titanate (PZT) enables a high piezoelectric coefficient (<inline-formula> <tex-math notation="LaTeX">{e} _{31, f} \approx ~16 </tex-math></inline-formula>- 24 C/<inline-formula> <tex-math notation="LaTeX">\text{m}^{{2}} </tex-math></inline-formula>), and a low dielectric constant (<inline-formula> <tex-math notation="LaTeX">\varepsilon _{\mathrm {r}}~\approx ~308 </tex-math></inline-formula>), achieving high PMUT transceiver efficiency. The <inline-formula> <tex-math notation="LaTeX">2\times 2 </tex-math></inline-formula> PMUT array achieves a very high sound pressure level (SPL) output of 109.4 dB at 26 cm distance. Different from conventional PZT PMUTs, this study utilized single-crystal PZT with a low permittivity to achieve a good acoustic reception, demonstrating the sensitivity of 2 mV/Pa. This work reports the PMUT design, modeling, fabrication, characterization, enabling a long-range detection of 4.8 meters in a pulse-echo experiment, which was conducted by a pair of <inline-formula> <tex-math notation="LaTeX">2\times 2 </tex-math></inline-formula> PMUT arrays with the matched resonances. [2020-0270]