CMUT characterization by interferometric and electric measurements

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 56; no. 12; pp. 2711 - 2721
• Main Authors: Martinussen, H., Aksnes, A., Leirset, E., Engan, H.E.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.12.2009; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustics; Arrays; Carbon; Electric Capacitance; Electric Impedance; Electric variables measurement; Equipment Failure Analysis - methods; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Higher harmonics; Interferometers; Interferometry - methods; Mathematical models; Measurement methods; Micro-Electrical-Mechanical Systems - instrumentation; Optical interferometry; Optical mixing; Performance evaluation; Physics; Resonance; Resonant frequency; Spreads; Temperature; Transducers; Transduction; acoustical devices for the generation and reproduction of sound; Ultrasonic transducers; Ultrasonic variables measurement; Ultrasonography - instrumentation; Vibration mode; Wafer bonding; Optical interferometry; Vibration; Q factor; Capacitive transducer; Wafer bonding; Temperature measurement; Optical measurement; Electrical measurement; Heterodyne detection; Resonance frequency; Voltage; Membrane; Acoustic antenna; Vibrational mode; Ultrasonic transducer; Temperature fluctuation; Higher harmonic; Room temperature
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2009.1362

Capacitive micromachined ultrasonic transducers (CMUTs) with 5.7 ¿m radius, realized by wafer bonding, have been characterized by both optical and electrical measurements. These measurements are performed by our heterodyne interferometer and a network analyzer, respectively. The results from this article will be used to improve the fabrication of next-generation CMUTs. We have investigated the spread in resonance frequency of different CMUT membranes along the array. Q-factors have been obtained using both measurement methods, and the results from the 2 methods have been numerically compared. The relation between applied dc voltage and resonance frequency has been studied. Temperature measurements show that increasing temperature leads to a small decrease in the resonance frequency of the CMUTs; however, the decrease is small enough to ensure stable operation with small variations in room temperature. The heterodyne interferometer is used to inspect the vibration pattern of the CMUTs' higher harmonic modes. These modes are located at approximately 60 MHz in air. To the authors' knowledge, vibration modes at frequencies >40 MHz have not been previously studied.