Advances in Capacitive Micromachined Ultrasonic Transducers

Brenner, Kevin; Ergun, A.S.; Firouzi, Kamyar; Rasmussen, Morten Fischer; Stedman, Quintin; Khuri‐Yakub, Butrus T.

doi:10.3390/mi10020152

Cited by 125 publications

(114 citation statements)

References 73 publications

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“…The two most common CMUT fabrication techniques are the sacrificial release process [19], and the wafer bonding process [4], both of which are investigated and discussed in this paper. Utilizing advanced microfabrication technology, individual CMUT cells can be fabricated to form an array of sensors with various arrangements including circular, square, O-ring, as well as hexagonal shapes [20][21][22]. This ability to form an array of sensors on the same chip is beneficial when a CMUT is designed to detect a target gas in a complex environment.…”

Section: Cmut Sensor Microfabrication Techniquesmentioning

confidence: 99%

Mass Sensors Based on Capacitive and Piezoelectric Micromachined Ultrasonic Transducers—CMUT and PMUT

Nazemi

Balasingam

Swaminathan

et al. 2020

Sensors

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Microelectromechanical system (MEMS)-based mass sensors are proposed as potential candidates for highly sensitive chemical and gas detection applications owing to their miniaturized structure, low power consumption, and ease of integration with readout circuits. This paper presents a new approach in developing micromachined mass sensors based on capacitive and piezoelectric transducer configurations for use in low concentration level gas detection in a complex environment. These micromachined sensors operate based on a shift in their center resonant frequencies. This shift is caused by a change in the sensor’s effective mass when exposed to the target gas molecules, which is then correlated to the gas concentration level. In this work, capacitive and piezoelectric-based micromachined sensors are investigated and their principle of operation, device structures and configurations, critical design parameters and their candidate fabrication techniques are discussed in detail.

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Section: Cmut Sensor Microfabrication Techniquesmentioning

confidence: 99%

Mass Sensors Based on Capacitive and Piezoelectric Micromachined Ultrasonic Transducers—CMUT and PMUT

Nazemi

Balasingam

Swaminathan

et al. 2020

Sensors

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“…By using the lumped element method, a cMUT can be simplified as a parallel plate capacitor and modeled as a mass–spring–damper system, with a spring constant

, a mass

, and a damping constant

(usually negligible). The acoustic impedance from the medium can be modeled by a damper

and a mass

[ 159 ]. With the lumped modeling, the resonance frequency of a cMUT is [ 159 ]:

where

represents the spring softening effect generated by the DC bias, implying that the resonance frequency shifts as the DC bias voltage changes.…”

Section: Cmutsmentioning

confidence: 99%

“…The acoustic impedance from the medium can be modeled by a damper

and a mass

[ 159 ]. With the lumped modeling, the resonance frequency of a cMUT is [ 159 ]:

where

represents the spring softening effect generated by the DC bias, implying that the resonance frequency shifts as the DC bias voltage changes.…”

Section: Cmutsmentioning

confidence: 99%

“…The maximum receive sensitivity at its resonance frequency and the fractional bandwidth of a cMUT can be expressed as [ 159 ]:

where

is the input pressure,

is the output current,

is the electric field,

is the clamped capacitance of the cMUT at the bias voltage

, A is the top electrode area of the cMUT, and

and

are the effective gap height under zero bias and gap change under the bias voltage

, respectively.…”

Section: Cmutsmentioning

confidence: 99%

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MEMS Ultrasound Transducers for Endoscopic Photoacoustic Imaging Applications

Wang

Yang

et al. 2020

Micromachines

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Photoacoustic imaging (PAI) is drawing extensive attention and gaining rapid development as an emerging biomedical imaging technology because of its high spatial resolution, large imaging depth, and rich optical contrast. PAI has great potential applications in endoscopy, but the progress of endoscopic PAI was hindered by the challenges of manufacturing and assembling miniature imaging components. Over the last decade, microelectromechanical systems (MEMS) technology has greatly facilitated the development of photoacoustic endoscopes and extended the realm of applicability of the PAI. As the key component of photoacoustic endoscopes, micromachined ultrasound transducers (MUTs), including piezoelectric MUTs (pMUTs) and capacitive MUTs (cMUTs), have been developed and explored for endoscopic PAI applications. In this article, the recent progress of pMUTs (thickness extension mode and flexural vibration mode) and cMUTs are reviewed and discussed with their applications in endoscopic PAI. Current PAI endoscopes based on pMUTs and cMUTs are also introduced and compared. Finally, the remaining challenges and future directions of MEMS ultrasound transducers for endoscopic PAI applications are given.

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“…However, the low output pressure is still one major limitation of CMUT that restricts its further development in areas dominated by the piezoelectric ultrasonic transducer. As for a CMUT with a uniform membrane, the clamped membrane and the arising spring force from the bending of a uniform membrane restricts the amplitude in vibrating that results in a limited output pressure [7]. In recent years, several solutions have been proposed to alter CMUT structure or the working mode for achieving higher output pressures.…”

Section: Introductionmentioning

confidence: 99%

Experimental Characterization of an Embossed Capacitive Micromachined Ultrasonic Transducer Cell

Wang

Liu

et al. 2020

Micromachines

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Capacitive Micromachined Ultrasonic Transducer (CMUT) is a promising ultrasonic transducer in medical diagnosis and therapeutic applications that demand a high output pressure. The concept of a CMUT with an annular embossed pattern on a membrane working in collapse mode is proposed to further improve the output pressure. To evaluate the performance of an embossed CMUT cell, both the embossed and uniform membrane CMUT cells were fabricated in the same die with a customized six-mask sacrificial release process. An annular nickel pattern with the dimension of 3 μ m × 2 μ m (width × height) was formed on a full top electrode CMUT to realize an embossed CMUT cell. Experimental characterization was carried out with optical, electrical, and acoustic instruments on the embossed and uniform CMUT cells. The embossed CMUT cell achieved 27.1% improvement of output pressure in comparison to the uniform CMUT cell biased at 170 V voltage. The fractional bandwidths of the embossed and uniform CMUT cells were 52.5% and 41.8%, respectively. It substantiated that the embossed pattern should be placed at the vibrating center of the membrane for achieving a higher output pressure. The experimental characterization indicated that the embossed CMUT cell has better operational performance than the uniform CMUT cell in collapse region.

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Advances in Capacitive Micromachined Ultrasonic Transducers

Cited by 125 publications

References 73 publications

Mass Sensors Based on Capacitive and Piezoelectric Micromachined Ultrasonic Transducers—CMUT and PMUT

Mass Sensors Based on Capacitive and Piezoelectric Micromachined Ultrasonic Transducers—CMUT and PMUT

MEMS Ultrasound Transducers for Endoscopic Photoacoustic Imaging Applications

Experimental Characterization of an Embossed Capacitive Micromachined Ultrasonic Transducer Cell

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