Aluminum nitride piezoelectric micromachined ultrasound transducers with applications in sonic anemometry

Recent results demonstrate the promise of sonic anemometry for accurate, three dimensional, high update relative wind measurements in high altitude (stratospheric) balloons and for planetary science missions on Mars, Venus, and other environments (Banfield, JASA 2016, White, ASA 2020, White, AIAA 2020). For these applications, low weight and small size is desirable. We propose an aluminum nitride piezoelectric micromachined ultrasound transducer (PMUT) as a candidate for a small (∼1 cm³) low weight (∼10 g) sonic anemometry system. Two PMUT designs were fabricated using Vesper Technologies MEMS microphone process by Vanguard Semiconductor International on 1.4 × 1.4 mm² die. The first device has 270 μm diameter diaphragms and operates at 610 kHz, the second 190 μm diameter diaphragms and operates at 890 kHz. By operating at these high frequencies, the acoustic path length can notionally be reduced to 1 cm, while still retaining sufficient phase resolution to measure wind with 1 to 10 cm/s accuracy. The substantial challenge is producing sufficient signal to overcome acoustic absorption at these elevated frequencies. This design is aggressively exploratory in nature. The PMUT devices have been fabricated and operate, but the sonic anemometry system has not yet been demonstrated. [Work supported by NASA PICASSO NNX16AJ24G, NSF 1934553 and NSF 2110083.]