Flexible Polymer-based Capacitive Micromachined Ultrasound Transducers (polyCMUTs): Fabrication and Characterization

Omidvar, Amirhossein; Gerardo, Carlos D.; Rohling, Robert; Cretu, Edmond; Hodgson, Antony J.

doi:10.1109/ius52206.2021.9593645

Cited by 9 publications

(6 citation statements)

References 8 publications

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“…This suggests that the bending stresses are highest in the nonfunctional areas (the joints) between the elements due to the lower thickness and lower Young's moduli in these regions. This finding of relatively low curvature across the elements likely explains the minimal variation of resonant behavior of flexible CMUT cells under moderate bending conditions [ 23 ] (min ROC of 3 cm).…”

Section: Resultsmentioning

confidence: 99%

“…Polyimide curing requires stringent temperature control. We found that a rapid temperature ramp (above 10 °C min −1 ) generated microbubbles [ 23 ] (as large as 40 µm in height) which degraded the substrate's smoothness. This roughness propagated to subsequent layers and eventually made the device fabrication fail.…”

Section: Discussionmentioning

confidence: 99%

“…We have previously reported a preliminary version of the proposed fabrication process for a flexible polymer-based CMUT array. [23] Here, we introduce a modified method that improves the functionality and fabrication yield.…”

Section: Fabrication Processmentioning

confidence: 99%

“…We have previously reported a preliminary version of the proposed fabrication process for a flexible polymer‐based CMUT array. [ 23 ] Here, we introduce a modified method that improves the functionality and fabrication yield. Figure outlines the main steps in this revised fabrication process, which uses five lithography masks (refer to the Experimental Section for more details).…”

Section: Device Fabricationmentioning

confidence: 99%

“…[22] A number of attempts have been made to fabricate flexible CMUT-based transducers. [7,[23][24][25] One of the first such attempts involved thinning the silicon substrate postfabrication. [26] A similar approach was used to make curved row-column-addressed CMUT arrays for 3D imaging, [27] and polymer filling of trenches was also proposed.…”

Section: Introductionmentioning

confidence: 99%

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Flexible PolyCMUTs: Fabrication and Characterization of a Flexible Polymer‐Based Capacitive Micromachined Ultrasonic Array for Conformal Ultrasonography

Omidvar

Cretu

Rohling

et al. 2022

Adv Materials Technologies

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field of view [2] and the ability to adapt to deformations in the target object over time (e.g., as a muscle deforms during movement). In addition, if a conformal transducer could substantially surround an anatomical target, it could be used to create tomographic images with high spatial resolution. [3] Such advantages may be useful in a variety of applications, such as inspection of complex-shaped parts in nondestructive evaluation of materials, [4] neuromodulation, [5] ultrasound therapy, [6] touch screens, [7] and medical imaging. [8,9] Musculoskeletal conditions would represent a particularly intriguing field for conformal sonography as tomographic ultrasound could supplement computed tomography (CT) or magnetic resonance (MR) imaging, and its higher temporal resolution and lack of ionizing radiation could generate insights currently unavailable through these other imaging modalities (e.g., visualizing relative movements of adjacent tissues in near-real time). The earliest versions of flexible ultrasound arrays were built using piezoceramic transducers. Since these materials were essentially rigid, flexibility was achieved by connecting the rigid transducers with mechanical joints. [4,10] Flexible arrays for biomedical and healthcare applications were also made by embedding piezoelectric components in or on a soft material, [6,[11][12][13][14] but such devices typically had low array densities. The lack of a stiff backing layer in these designs may result in narrower bandwidths compared to conventional rigid Conventional ultrasound transducers are short and rigid, which limits their applications, especially in the area of musculoskeletal imaging where many of the structures to be imaged lie within long curved anatomical structures, such as limbs. In such cases, conformal ultrasound imaging can be advantageous. This paper presents a process for fabricating 1D and 2D flexible polymer-based capacitive micromachined ultrasound transducers (flexible CMUTs). As a proof of concept, all elements of a 32-element linear flexible array are shown to be functional (100% yield) and uniform in fundamental resonant frequency (SD = 1.8%). One-way and two-way acoustic responses during immersion tests in flat, convex, and concave array configurations (radii of curvature = 3 cm) show an average fractional bandwidth of 83% and 75%, respectively, across these bending conditions. The flexible array shows no signal drop after over 100 bending cycles and only 6% variation in pulse amplitude after over 14 h of continuous operation. Finally, the resulting transducers are shown to operate at up to 15 MHz. The findings demonstrate robust operation of flexible CMUT arrays and justify further development targeted at key imaging applications, particularly in the area of diagnosing musculoskeletal conditions.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Fabrication Processmentioning

confidence: 99%

Section: Device Fabricationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Flexible PolyCMUTs: Fabrication and Characterization of a Flexible Polymer‐Based Capacitive Micromachined Ultrasonic Array for Conformal Ultrasonography

Omidvar

Cretu

Rohling

et al. 2022

Adv Materials Technologies

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PMUT and CMUT Devices for Biomedical Applications: A Review

Moisello,

Novaresi,

Sarkar

et al. 2024

IEEE Access

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Piezoelectric Micromachined Ultrasonic Transducers (PMUT) and Capacitive Micromachined Ultrasonic Transducers (CMUT) have seen great developments in recent years, both in terms of performance and scope of applications within the biomedical ultrasound domain. This paper presents a review of the state-of-the-art of PMUT and CMUT technologies, focusing on their principle of operation, microfabrication techniques and use in different biomedical imaging and therapeutic applications. The advantages and drawbacks of PMUT and CMUT technologies in comparison with conventional bulk transducers are highlighted, the trade-offs among PMUTs and CMUTs are discussed, and their relevance in the current landscape of medical diagnostics and therapeutic uses is outlined, thus providing a clear overview of these promising technologies for the present and the next generation biomedical ultrasound applications.

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A Novel Fabrication Process for Thin, Flexible, Backside-accessible Polymer-based CMUTs for Acoustic Emission Sensing

Welsch,

Gerardo,

Rohling

et al. 2023

2023 IEEE International Ultrasonics Symposium (IUS)

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Flexible Polymer-based Capacitive Micromachined Ultrasound Transducers (polyCMUTs): Fabrication and Characterization

Cited by 9 publications

References 8 publications

Flexible PolyCMUTs: Fabrication and Characterization of a Flexible Polymer‐Based Capacitive Micromachined Ultrasonic Array for Conformal Ultrasonography

Flexible PolyCMUTs: Fabrication and Characterization of a Flexible Polymer‐Based Capacitive Micromachined Ultrasonic Array for Conformal Ultrasonography

PMUT and CMUT Devices for Biomedical Applications: A Review

A Novel Fabrication Process for Thin, Flexible, Backside-accessible Polymer-based CMUTs for Acoustic Emission Sensing

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