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A. Nikoozadeh,
I.O. Wygant,
Der-Song Lin, O. Oralkan,
A.S. Ergun,
D.N. Stephens,
K.E. Thomenius,
A.M. Dentinger,
D. Wildes,
G. Akopyan,
K. Shivkumar,
A. Mahajan,
D.J. Sahn,
B.T. Khuri-Yakub
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ABSTRACT: Minimally invasive catheter-based electrophysiological (EP) interventions are becoming a standard procedure in diagnosis and treatment of cardiac arrhythmias. As a result of technological advances that enable small feature sizes and a high level of integration, nonfluoroscopic intracardiac echocardiography (ICE) imaging catheters are attracting increasing attention. ICE catheters improve EP procedural guidance while reducing the undesirable use of fluoroscopy, which is currently the common catheter guidance method. Phased-array ICE catheters have been in use for several years now, although only for side-looking imaging. We are developing a forwardlooking ICE catheter for improved visualization. In this effort, we fabricate a 24-element, fine-pitch 1-D array of capacitive micromachined ultrasonic transducers (CMUT), with a total footprint of 1.73 mm x 1.27 mm. We also design a custom integrated circuit (IC) composed of 24 identical blocks of transmit/ receive circuitry, measuring 2.1 mm x 2.1 mm. The transmit circuitry is capable of delivering 25-V unipolar pulses, and the receive circuitry includes a transimpedance preamplifier followed by an output buffer. The CMUT array and the custom IC are designed to be mounted at the tip of a 10-Fr catheter for high-frame-rate forward-looking intracardiac imaging. Through-wafer vias incorporated in the CMUT array provide access to individual array elements from the back side of the array. We successfully flip-chip bond a CMUT array to the custom IC with 100% yield. We coat the device with a layer of polydimethylsiloxane (PDMS) to electrically isolate the device for imaging in water and tissue. The pulse-echo in water from a total plane reflector has a center frequency of 9.2 MHz with a 96% fractional bandwidth. Finally, we demonstrate the imaging capability of the integrated device on commercial phantoms and on a beating ex vivo rabbit heart (Langendorff model) using a commercial ultrasound imaging system.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 01/2009; · 1.69 Impact Factor
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S. Vaithilingam,
T.-J. Ma,
Y. Furukawa, O. Oralkan,
A. Kamaya,
K. Torashima,
M. Kupnik,
I.O. Wygant,
X. Zhuang,
R.B. Jeffrey,
B.T. Khuri-Yakub
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ABSTRACT: In this paper, we investigate using a large aperture (64 times 64 element array) to perform photoacoustic and acoustic imaging by mechanically scanning a smaller array (16 times 16 elements) of capacitive micromachined ultrasonic transducers (CMUTs). We show results from the imaging of: 1) A fishing-line phantom. 2) Tubes embedded in chicken breast tissue containing the contrast agent indocyanine green (ICG), pig blood and a mixture of the two. The tubes were embedded at a depth of 0.8 cm inside the tissue and were at an overall distance of 1.9 cm from the CMUT array. Three-dimensional volume rendered images of traditional pulse-echo data as well as photoacoustic data are shown.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: This paper presents optimum design of circular membrane for high quality factor. A quality factor of CMUT, we designed for resonant chemical sensor, is dominated by Q<sub>air</sub> and Q<sub>support</sub>. We investigated these two factors independently. We calculate Q<sub>air</sub> of circular silicon membrane analytically, and numerically. Calculated Q<sub>air</sub> is compared to measured value. In order to find Q<sub>support</sub> empirically, we measured quality factor of CMUT in vacuum chamber. Q<sub>air</sub> is proportional to (radius/thickness)<sup>-2</sup> and Q<sub>support</sub> is proportional to (radius/thickness)<sup>3</sup>. Thus the optimum aspect ratio of membrane exists for maximum quality factor.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: We investigated the effects of electrically connecting multiple microresonators on the frequency noise with a goal to improve the resolution of a chemical sensor based on the capacitive micromachined ultrasonic transducer (CMUT) technology. We fabricated twenty-two 50-MHz CMUTs with varying number of cells and measured the input impedance characteristics. The impedance measurement results show a linear increase in quality factor as the number of cells increases. Further, a phase noise simulation of Colpitts oscillators employing these CMUTs verifies that the phase noise of the oscillator in the 1/f<sup>2</sup> regime are influenced by the quality factor while the phase noise in the white noise regime are primarily affected by the motional impedance. The oscillator based on the CMUT with 1027 cells has 8.8 dB and 11.4 dB lower phase noise than that based on the CMUT with 397 cells at offset frequencies of 1 kHz and 5 MHz, respectively. Therefore, we demonstrated that electrically connecting multiple microresonators is an effective technique to improve the sensor resolution.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: We present a resonant chemical sensor based on a capacitive micromachined ultrasonic transducer (CMUT) technology. Depending on the frequency of the devices (18 to 32 MHz), the mass sensitivity per unit area ranges from 73 to 130 zg/Hz/mum<sup>2</sup>. We functionalized the 18-MHz device with polyisobutylene (PIB) to detect dimethyl methylphosphonate (DMMP), a common simulant for the sarin nerve agent. Even with only a 50-nm thick coating layer, our sensor has a high volume sensitivity of 37 ppbv/Hz to DMMP in air. Taking advantage of multiple CMUT cells (100 to 2240), all resonating in parallel, the sensor achieves an equivalent volume resolution of 21 ppbv (parts per 10<sup>9</sup> by volume) to DMMP. In addition, 200 test cycles with DMMP applied over 26 hours revealed a zero false alarm rate and a 4.7% (3-sigma) variation of volume sensitivity to DMMP. By using principal component analysis (PCA), we successfully classified all analytes in 21 experiments, and we present the results of pattern recognition. This work demonstrates that CMUT has a great potential for the sensitive, reliable, and yet portable chemical sensing systems.
Sensors, 2008 IEEE; 11/2008
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D N Stephens,
J Cannata,
Ruibin Liu,
Jian Zhong Zhao,
K K Shung,
Hien Nguyen,
R Chia,
A Dentinger,
D Wildes,
K E Thomenius,
A Mahajan,
K Shivkumar,
Kang Kim,
M O'Donnell,
A Nikoozadeh, O Oralkan,
P T Khuri-Yakub,
D J Sahn
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ABSTRACT: A family of 3 multifunctional intracardiac imaging and electrophysiology (EP) mapping catheters has been in development to help guide diagnostic and therapeutic intracardiac EP procedures. The catheter tip on the first device includes a 7.5 MHz, 64-element, side-looking phased array for high resolution sector scanning. The second device is a forward-looking catheter with a 24-element 14 MHz phased array. Both of these catheters operate on a commercial imaging system with standard software. Multiple EP mapping sensors were mounted as ring electrodes near the arrays for electrocardiographic synchronization of ultrasound images and used for unique integration with EP mapping technologies. To help establish the catheters' ability for integration with EP interventional procedures, tests were performed in vivo in a porcine animal model to demonstrate both useful intracardiac echocardiographic (ICE) visualization and simultaneous 3-D positional information using integrated electroanatomical mapping techniques. The catheters also performed well in high frame rate imaging, color flow imaging, and strain rate imaging of atrial and ventricular structures. The companion paper of this work discusses the catheter design of the side-looking catheter with special attention to acoustic lens design. The third device in development is a 10 MHz forward-looking ring array that is to be mounted at the distal tip of a 9F catheter to permit use of the available catheter lumen for adjunctive therapy tools.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control 08/2008; 55(7):1570-81. · 1.80 Impact Factor
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ABSTRACT: Flexible transducer arrays are desired to wrap around catheter tips for side-looking intravascular ultrasound imaging. We present a technique for constructing flexible capacitive micromachined ultrasonic transducer (CMUT) arrays by forming polymer-filled deep trenches in a silicon substrate. First, we etch deep trenches between the bottom electrodes of CMUT elements on a prime silicon wafer using deep reactive ion etching. Second, we fusion-bond a silicon-on-insulator (SOI) wafer to the prime silicon wafer. Once the silicon handle and buried oxide layers are removed from the back side of the SOI wafer, the remaining thin silicon device layer acts as a movable membrane and top electrode. Third, we fill the deep trenches with polydimethylsiloxane, and thin the wafer down from the back side. The 16 by 16 flexible 2-D arrays presented in this paper have a trench width that varies between 6 and 20 ; the trench depth is 150 ; the membrane thickness is 1.83 ; and the final substrate thickness is 150 . We demonstrate the flexibility of the substrate by wrapping it around a needle tip with a radius of 450 (less than catheter size of 3 French). Measurements in air validate the functionality of the arrays. The 250- by 250- transducer elements have a capacitance of 2.29 to 2.67 pF, and a resonant frequency of 5.0 to 4.3 MHz, for dc bias voltages ranging from 70 to 100 V.
Journal of Microelectromechanical Systems 05/2008; · 2.10 Impact Factor
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ABSTRACT: For three-dimensional (3D) ultrasound imaging, connecting elements of a two-dimensional (2D) transducer array to the imaging system's front-end electronics is a challenge because of the large number of array elements and the small element size. To compactly connect the transducer array with electronics, we flip-chip bond a 2D 16 times 16-element capacitive micromachined ultrasonic transducer (CMUT) array to a custom-designed integrated circuit (IC). Through-wafer interconnects are used to connect the CMUT elements on the top side of the array with flip-chip bond pads on the back side. The IC provides a 25-V pulser and a transimpedance preamplifier to each element of the array. For each of three characterized devices, the element yield is excellent (99 to 100% of the elements are functional). Center frequencies range from 2.6 MHz to 5.1 MHz. For pulse-echo operation, the average -6-dB fractional bandwidth is as high as 125%. Transmit pressures normalized to the face of the transducer are as high as 339 kPa and input-referred receiver noise is typically 1.2 to 2.1 rnPa/ radicHz. The flip-chip bonded devices were used to acquire 3D synthetic aperture images of a wire-target phantom. Combining the transducer array and IC, as shown in this paper, allows for better utilization of large arrays, improves receive sensitivity, and may lead to new imaging techniques that depend on transducer arrays that are closely coupled to IC electronics.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2008; · 1.69 Impact Factor
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ABSTRACT: We present an improved fabrication method for capacitive micromachined ultrasonic transducers (CMUTs). Recently, a process was developed to fabricate CMUTs using direct wafer-bonding instead of the traditional sacrificial release method. This paper presents a method based on local oxidation of silicon (LOCOS) and direct wafer-bonding to improve the controllability of gap heights and the parasitic capacitance. Critical vertical dimensions are determined by a thermal oxidation process, which allows tight vertical tolerances (< 10 nm) with unmatched uniformity over the entire wafer. Using this process we successfully fabricated CMUTs with gap heights as small as 40 nm with a uniformity of plusmn 2 nm over the entire wafer.
Micro Electro Mechanical Systems, 2008. MEMS 2008. IEEE 21st International Conference on; 02/2008
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01/2008
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ABSTRACT: A scanning acoustic and photoacoustic microscope is demonstrated. The laser illumination and ultrasound detection in the system are co-axial. Pulsed light from a tunable optical parametric oscillator (OPO) laser is delivered to the scan tank via optical fiber. Multiple acoustic transducers with center frequencies varying from 5 MHz to 25 MHz are utilized. Images of a pig kidney (ex vivo) and a microcalcification phantom (eggshells embedded in agarose) are shown.
Ultrasonics Symposium, 2007. IEEE; 12/2007
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A. Nikoozadeh,
I.O. Wygant,
Der-Song Lin, O. Oralkan,
A.S. Ergun,
K. Thomenius,
A. Dentinger,
D. Wildes,
G. Akopyan,
K. Shivkumar,
A. Mahajan,
D.N. Stephens,
D. Sahn,
P.T. Khuri-Yakub
[show abstract]
[hide abstract]
ABSTRACT: Minimally invasive percutaneous electrophysiological mapping of the heart chambers is becoming a standard procedure to diagnose and treat cardiac arrhythmias. Due to advances in technology that enable small feature sizes and a high level of integration, non-fluoroscopic intracardiac imaging is attracting more attention to better guide electrophysiologal (EP) interventions. In this effort, we are developing a forward-looking intracardiac ultrasound imaging catheter, which is also equipped with several EP electrode sensor bands and a metal RF ablation tip enclosure. A 24-element fine-pitch (63 mum) 1-D array, based on capacitive micromachined ultrasonic transducer (CMUT) technology, has been fabricated for high-frame-rate imaging. Through-wafer vias are incorporated in the device to connect the signal and ground electrodes to the flip-chip bond pads on the backside of the array. The total footprint of the array measures 1.73 mm x 1.27 mm. Also a custom-designed integrated circuit (IC) has been fabricated to be closely integrated with the CMUT array for improved SNR. This IC comprises some of the important front- end electronics of an ultrasound imaging system. It measures 2 mm x 2 mm and is composed of 24 individual transmit/receive blocks. The transmit circuitry is capable of delivering 25 -V unipolar pulses. The receive circuitry includes a transimpedance preamplifier followed by a line driver buffer. A CMUT array was flip-chip bonded directly on to the IC for initial testing. All of the 24 elements of the array and the IC are functional. Array uniformity was tested by measuring the resonant frequency in air. A standard deviation of 0.37 percent was measured around the mean value of 17.9 MHz. The same array operates at 9.2 MHz in immersion with a 104 percent fractional bandwidth. Imaging performance of the described front-end was tested on a commercial phantom and also in ex- vivo environment on an isolated perfused rabbit heart (Langendorfl). The final goal is to i-
ntegrate the CMUT array and the front-end electronics at the tip of a 10 -F catheter. A flexible printed circuit board (PCB) has been designed and the first sub-assembly is ready for cable attachment and final catheter integration.
Ultrasonics Symposium, 2007. IEEE; 12/2007
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ABSTRACT: The cost and complexity of medical ultrasound imaging systems can be reduced by integrating the transducer array with an integrated circuit (IC). By incorporating some of the system's front-end electronics into an IC, bulky cables and costly system electronics can be eliminated. Here we present an IC for 3D intracavital imaging that requires few electrical connections but uses a large fraction of a 16times16-element 2D transducer array to transmit focused ultrasound. To simplify the receive and data acquisition electronics, only the 32 elements along the array diagonals are used as receivers. The IC provides a preamplifier for each receiving element. Each of the 224 transmitting elements is provided an 8-bit shift register, a comparator, and a 25-V pulser. To transmit, a global counter is incremented from 1 to 224; each pulser fires when its stored register value is equal to the global count value. Electrical testing of the fabricated IC shows that it works as designed. The IC was flip-chip bonded to a two-dimensional capacitive micromachined ultrasonic transducer (CMUT) array. A two-dimensional image of a wire target phantom was acquired.
Ultrasonics Symposium, 2007. IEEE; 11/2007
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ABSTRACT: We report on the characterization and imaging results of trench-isolated CMUT arrays with a supporting frame. The CMUT arrays are built on a silicon-on-insulator (SOI) wafer using direct wafer-to-wafer fusion bonding technique. Electrical contacts to individual elements are brought to the back side of the wafer by highly conductive silicon pillars. Mechanical support for array elements is provided by a silicon frame structure. 1D and 2D arrays with 250-mum element pitch were fabricated and tested in air and in immersion. Rectangular membranes are used, which feature two distinctive pull-in (collapse) points in both air and immersion tests. The double collapsing membranes enable an operating frequency ranging from 1.9 MHz in conventional mode to 58 MHz in second collapse mode on the same device. After flip-chip bonding the 2D arrays to custom-designed integrated circuits (IC), volumetric imaging was demonstrated.
Ultrasonics Symposium, 2007. IEEE; 11/2007
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B.T. Khuri-Yakub,
K.K. Park,
H.J. Lee,
G.G. Yaralioglu,
S. Ergun, O. Oralkan,
M. Kupnik,
C.F. Quate,
T. Braun,
H.P. Lang,
M. Hegner,
J.-P. Ramseyer,
C. Gerber,
J. Gimzewski
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ABSTRACT: Airborne chem/bio sensors increase in importance every day for applications in homeland security for the detection of bio-hazardous materials and improvised explosive devices (IED); in the spoilage of food; in the health care industry for detecting cancer, diabetes, and other conditions; and in many other industries. A number of ultrasonic sensors have been developed and used in the chem/bio sensing arena: quartz crystal micro balance (QCM), surface acoustic wave (SAW) resonators, and more recently resonant and simply deflected cantilevers. The capacitive micromachined ultrasonic transducer (CMUT) is a "platform" device that has been investigated in many airborne and immersion ultrasound applications. In this work, we explore the use of the CMUT as a Chem/bio sensor. Because the membrane of a CMUT can be a fraction of a micron thick, and the frequency of operation in the MHz range, it is possible to obtain sensitivity in the order of 1 femto-gram mass loading per cell with proper design. Another important attribute of the CMUT as a chem/bio sensor is that many cells are used to make a sensor which helps improve its false alarm rate over existing sensors where only one resonant element is used. Finally, a high mechanical quality factors (Q) realized in CMUTs which results in very low noise floor, which is necessary to make a very sensitive sensor. An array of CMUTs was made resonant in air at 6 MHz with a Q of 160 and a noise floor of 0.4 Hz in a 1 Hz bandwidth, and where each element consisted of 750 cells. Each cell had a diameter of 30 microns and a silicon nitride thickness of 0.85 microns. Six elements of the array were functionalized with different polymers (PAAM, PEG, PSS, PVA) and the sensitivity of the sensors was measured by flowing different analytes (water, ethanol, isopropyl alcohol, toluene) at different concentrations over the sensors. The frequency shift of each resonator was measured using a frequency counter. The sensor had a volume detection sensit-
ivity of 20 ppb, and a calculated mass loading sensitivity of 1 femto-gram. We will also present results from a new generation of sensors operating in the 25 MHz frequency range and with an expected sensitivity improvement of one to two orders of magnitude over the earlier design.
Ultrasonics Symposium, 2007. IEEE; 11/2007
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ABSTRACT: Ultrasound is an imaging tool with a broad range of applications such as medical diagnostics, underwater exploration and nondestructive
evaluation of materials. As early as the first half of the 19th century, sound waves had been used for underwater navigation
and ranging. However, the history of modern acoustics began with the establishment of the theory of sound by Lord Rayleigh,
and the discovery of piezoelectric effect by the Curie brothers, both in the late 1800s. Acoustical devices have been used
for practical underwater imaging applications since World War I. Use of ultrasound in medicine started in the 1930s, and initially
was confined to therapy, particularly in tissue heating. The first use of ultrasound as a medical diagnostic tool was for
transmission imaging of brain tumors in the early 1940s. In the following years, sonic energy reflection from within soft
tissue histological elements was reported, pioneering pulse-echo ultrasound imaging. Linear transducer arrays with electronic
scanning started replacing fixed-focus mechanical sector scanners in the 1970s, providing greatly improved resolution and
faster image formation. The details of the history of ultrasound imaging and transducer technologies can be found in several
books [1, 2] and papers [3]–[6].
10/2007: pages 553-615;
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K. K. Park,
H. J. Lee,
G. G. Yaralioglu,
A. S. Ergun, O. Oralkan,
M. Kupnik,
C. F. Quate,
B. T. Khuri-Yakub,
T. Braun,
J.-P. Ramseyer,
H. P. Lang,
M. Hegner,
Ch. Gerber,
J. K. Gimzewski
[show abstract]
[hide abstract]
ABSTRACT: The authors present the prototype of a chemical sensor using a capacitive micromachined ultrasonic transducer array. Each element in the array consists of a large number of resonating membranes connected in parallel. A five-channel oscillator circuit operates at the resonant frequency around 6 MHz in this prototype. The surface of the elements in the array is coated by polymers such as polyallylamine hydrochloride, polyethylene glycol, and polyvinyl alcohol to detect different chemicals. By measuring shift in oscillation frequencies due to the mass-loading effect, analytes, e.g., water and isopropanol, with concentrations around 20 ppbv (parts per 10<sup>9</sup> by volume) range can be detected.
Applied Physics Letters 09/2007; · 3.84 Impact Factor
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ABSTRACT: Crosstalk is the coupling of energy between the elements of an ultrasonic transducer array. This coupling degrades the performance of transducers in applications such as medical imaging and therapeutics. In this paper, we present an experimental demonstration of guided interface waves in capacitive micromachined ultrasonic transducers (CMUTs). We compare the experimental results to finite element calculations using a commercial package (LS-DYNA) for a 1-D CMUT array operating in the conventional and collapsed modes. An element in the middle of the array was excited with a unipolar voltage pulse, and the displacements were measured using a laser interferometer along the center line of the array elements immersed in soybean oil. We repeated the measurements for an identical CMUT array covered with a 4.5-mum polydimethyl-siloxane (PDMS) layer. The main crosstalk mechanism is the dispersive guided modes propagating in the fluid-solid interface. Although the transmitter element had a center frequency of 5.8 MHz with a 130% fractional bandwidth in the conventional operation, the dispersive guided mode was observed with the maximum amplitude at a frequency of 2.1 MHz, and had a cut-off frequency of 4 MHz. In the collapsed operation, the dispersive guided mode was observed with the maximum amplitude at a frequency of 4.0 MHz, and had a cut-off frequency of 10 MHz. Crosstalk level was lower in the collapsed operation (-39 dB) than in the conventional operation (-24.4 dB). The coverage of the PDMS did not significantly affect the crosstalk level, but reduced the phase velocity for both operation modes. Lamb wave modes, A<sub>0</sub> and S<sub>0</sub>, were also observed with crosstalk levels of -40 dB and -65 dB, respectively. We observed excellent agreement between the finite element and the experimental results
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 03/2007; · 1.69 Impact Factor
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ABSTRACT: This paper reports on a method to fabricate flexible one-dimensional (1D) and two-dimensional (2D) micromachined transducer arrays that are electrically connected to flip-chip bond pads on the back side of the array. In our case, the transducers are capacitive micromachined ultrasonic transducers (CMUT) intended for medical ultrasound imaging. For ultrasound imaging, flexible arrays conform to the body part being imaged. Flexible arrays are also desired for certain catheter and fixed-focus array geometries. Electrical connection to bond pads on the back side of the array is provided for flip-chip bonding to an integrated circuit or flexible PCB. The arrays are made flexible by etching through-wafer trenches and filling the trenches with polydimethylsiloxane (PDMS). The flexibility of the substrate is demonstrated by wrapping it around a needle tip with a radius of 650 mum (French catheter size of 4).
Micro Electro Mechanical Systems, 2007. MEMS. IEEE 20th International Conference on; 02/2007
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ABSTRACT: We present a trench-isolated CMUT process with a supporting mesh frame for a fully populated 2D array. In this process, the CMUT array is built on a silicon-on-insulator (SOI) wafer. Electrical interconnections to array elements are provided through the highly conductive silicon substrate. Neighboring array elements are separated from one another by trenches on both the device layer and the bulk silicon. A mechanically supporting frame is designed as a mesh structure between the silicon pillars providing electrical connections to the individual elements. Like the frameless trench isolation process, the framed trench isolation is compatible with both wafer-bonded and surface-micromachined CMUTs. In addition, this process eliminates the need for attaching the device wafer to a carrier wafer for the required mechanical support during the deep trench etching and flip-chip bonding steps, which presents difficulties during the release of the carrier wafer
Ultrasonics Symposium, 2006. IEEE; 11/2006
