Dual-Backplate CMUTs with Wide Bandwidth and Low Driving Voltage for Airborne Applications

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 70; no. 10; p. 1
• Main Authors: Anzinger, Sebastian, Bretthauer, Christian, Wasisto, Hutomo Suryo, Dehe, Alfons
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-10-2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustics; Actuation; Air-coupling; Bandwidth; Bandwidths; CMUT; Damping; distance-sensing; dual-backplate; Electrodes; MEMS; Metal plates; Micromachining; Micromechanical devices; Sensitivity; Silicon; Transducers; ultrasound transducers; Voltage measurement
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2023.3309997

In this work, novel airborne capacitive micromachined ultrasonic transducers (CMUTs) based on a dual-backplate (DBP) technology are presented. In contrast to conventional CMUTs, these transducers use a three-electrode-based capacitive system, where the membrane is placed between two highly-perforated counter electrodes, enabling enlarged displacement amplitudes in electrostatic actuation and wide and tunable bandwidth due to a ventilated air cavity. Fabricated DBP-CMUT prototypes therefore show exceptionally high receive and transmit sensitivities of -34.5 dB(V/Pa) and 259 nm/V, respectively, in their 84 kHz resonance. The viscous dissipation introduced by ventilating the cavity results in a wide factional bandwidth (FBW) of 29%. An applicability of the developed CMUT for airborne ranging is demonstrated in pulse-echo based ranging measurements, where the distance of a sound reflecting metal plate can be clearly detected by a single CMUT operated in a transceiver mode.