title: Capacitive micromachined ultrasonic transducers based on annular cell geometry for air-coupled applications.
abstract: A novel design of an air-coupled capacitive micromachined ultrasonic transducer (CMUT) with annular cell geometry (annular CMUT) is proposed. Finite element analysis shows that an annular cell has a ratio of average-to-maximum displacement (RAMD) of 0.52-0.58 which is 58-76% higher than that of a conventional circular cell. The increased RAMD leads to a larger volume displacement which results in a 48.4% improved transmit sensitivity and 127.3% improved power intensity. Single-cell annular CMUTs were fabricated with 20-μm silicon plates on 13.7-μm deep and 1.35-mm wide annular cavities using the wafer bonding technique. The measured RAMD of the fabricated CMUTs is 0.54. The resonance frequency was measured to be 94.5kHz at 170-V DC bias. The transmit sensitivity was measured to be 33.83Pa/V and 25.85Pa/V when the CMUT was excited by a continuous wave and a 20-cycle burst, respectively. The receive sensitivity at 170-V DC bias was measured to be 7.7mV/Pa for a 20-cycle burst, and 15.0mV/Pa for a continuous incident wave. The proposed annular CMUT design demonstrates a significant improvement in transmit efficiency, which is an important parameter for air-coupled ultrasonic transducers.
authors.affiliation: Advanced Micro-/Nano-Devices Lab, Department of Systems Design Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada.
authors.forename: Shuai
authors.initials: S
authors.lastname: Na
authors.affiliation: Advanced Micro-/Nano-Devices Lab, Department of Systems Design Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada.
authors.forename: Albert I H
authors.initials: AIH
authors.lastname: Chen
authors.affiliation: Advanced Micro-/Nano-Devices Lab, Department of Systems Design Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada.
authors.forename: Lawrence L P
authors.initials: LLP
authors.lastname: Wong
authors.affiliation: Advanced Micro-/Nano-Devices Lab, Department of Systems Design Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada.
authors.forename: Zhenhao
authors.initials: Z
authors.lastname: Li
authors.affiliation: Techno Scientific Inc, 259 Edgeley Blvd, Concord, ON L4K 3Y5, Canada.
authors.forename: Mirek
authors.initials: M
authors.lastname: Macecek
authors.affiliation: Advanced Micro-/Nano-Devices Lab, Department of Systems Design Engineering, Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada. Electronic address: jyeow@uwaterloo.ca.
authors.forename: John T W
authors.initials: JTW
authors.lastname: Yeow
keywords: Air-coupled ultrasound; Annular cells; Capacitive micromachined ultrasonic transducers (CMUTs)