@inproceedings{KupnikHoVaithilingametal., author = {Kupnik, Mario and Ho, Min-Chieh and Vaithilingam, Srikant and Khuri-Yakub, Butrus T.}, title = {CMUTs for air coupled ultrasound with improved bandwidth}, series = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, booktitle = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4577-1252-4}, pages = {592 -- 595}, language = {en} } @inproceedings{ApteVaithilingamSariogluetal., author = {Apte, Nikhil and Vaithilingam, Srikant and Sarioglu, Ali Fatih and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Large area 1D CMUT phased arrays for multi-modality ultrasound imaging}, series = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, booktitle = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4577-1252-4}, pages = {612 -- 615}, language = {en} } @inproceedings{HoHoffmannUngeretal., author = {Ho, Min-Chieh and Hoffmann, Maik and Unger, Alexander and Park, Kwan Kyu and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {CMUTs in Permanent Contact Operation for High Output Pressure}, series = {Proceedings, ASME 2015 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems and ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels}, booktitle = {Proceedings, ASME 2015 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems and ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5690-1}, doi = {10.1115/IPACK2015-48733}, pages = {6}, language = {en} } @inproceedings{UngerHoffmannHoetal., author = {Unger, Alexander and Hoffmann, Maik and Ho, Min-Chieh and Park, Kwan Kyu and Khuri-Yakub, Butrus T. and Kupnik, Mario}, title = {Finite element analysis of mechanically amplified CMUTs}, series = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, booktitle = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, publisher = {IEEE}, doi = {10.1109/ULTSYM.2013.0074}, pages = {287 -- 290}, abstract = {We introduce the possibility of improving a single-cell capacitive micromachined ultrasonic transducer (CMUT) for air-coupled ultrasound by simply adding a hollow conical-shaped structure (horn) on top of the CMUT plate. The main objective is to improve both transmit and receive sensitivity by lowering the center-to-average displacement ratio, which for bending plate operated devices inherently is limited. In addition, for receive mode the force generated from the impinging sound pressure wave is concentrated to the center of the plate, resulting in larger signals and, in contrast to piston-shaped plates, the horn has the advantage of only moderately increasing the modal mass of the structure. By using finite element analysis and first sound pressure measurements of our modified CMUT, we demonstrate that this idea is feasible and promising for air-coupled CMUTs operating at frequencies below 150kHz, as it has been been proven to be successful for commercially available piezoelectric - driven bending plate devices as well.}, language = {en} } @inproceedings{HoffmannUngerHoetal., author = {Hoffmann, Maik and Unger, Alexander and Ho, Min-Chieh and Park, Kwan Kyu and Khuri-Yakub, Butrus T. and Kupnik, Mario}, title = {Volumetric characterization of ultrasonic transducers for gas flow metering}, series = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, booktitle = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, publisher = {IEEE}, doi = {10.1109/ULTSYM.2013.0336}, pages = {1315 -- 1318}, abstract = {The design of ultrasonic gas flowmeters requires a thorough three dimensional characterization of the acoustic sound field. For large pipe flowmeters, such as used for flare gas metering, the transducers are operated at frequencies ranging from 20 kHz up to 150 kHz. Thus, in this work we use a commercially available calibrated 1/8-inch microphone, mounted on a 3D positioning system for performing volumetric measurements in a volume of up to 1x1x1 m. By using proper corrections in terms of angular and free-field response of the microphone, the measurement system is efficient and delivers around 30000 measurements in about only eight hours. The data then is visualized in form of 3D figures or various slices to extract all relevant information. The system has been used to identify non-uniform velocity profiles in capacitive micromachined ultrasonic transducers (CMUTs), operating in permanent contact mode. Further, the system can be used to investigate the effect of various acoustic boundary conditions the transducers are facing when mounted inside transducer port cavities and it can be used for general model validation purpose.}, language = {en} } @inproceedings{HoParkEckhoffetal., author = {Ho, Min-Chieh and Park, Kwan Kyu and Eckhoff, Kristian and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Air-coupled CMUTs operating at ambient pressures ranging from 1 to 20 atm}, series = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, booktitle = {Proceedings, 2013 IEEE International Ultrasonics Symposium}, publisher = {IEEE}, doi = {10.1109/ULTSYM.2013.0358}, pages = {1412 -- 1415}, abstract = {We present impedance and pitch-catch measurements of capacitive micromachined ultrasonic transducers (CMUTs) in permanent contact mode with improved mechanical strength that demonstrate functionality up to 20 atm ambient pressure. Changes in device design and fabrication are made to improve the mechanical strength of the CMUT plates, including using smaller deflection to thickness ratio (9 - 33\%), choosing better quality SOI wafers (bowing < 20 μm), and designing a much larger bonding area (300 - 700 μm overlap in radial direction) for each cell. As a result, all designs with 2000 μm radius, 65-μm-thick plates, 7.74 μm gap heights and with 300, 500, and 700 μm wide bonding area overlap for the plate, performed from 1 - 20 atm without a single failure. Despite larger bonding area, pitch-catch measurements with these CMUTs (700 μm bonding width biased at 250 Vdc still give received signal with good SNR even at 20 atm. Our results support that such CMUTs are reliable and efficient over a wide pressure range.}, language = {en} } @misc{SariogluKupnikVaithilingametal., author = {Sarioglu, Ali Fatih and Kupnik, Mario and Vaithilingam, Srikant and Khuri-Yakub, Butrus T.}, title = {Nanoscale topography of thermally-grown oxide films at right-angled convex corners of silicon}, series = {Journal of The Electrochemical Society}, volume = {159}, journal = {Journal of The Electrochemical Society}, number = {2}, issn = {0013-4651}, doi = {10.1149/2.005202jes}, pages = {79 -- 84}, language = {en} } @misc{KupnikKhuriYakub, author = {Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Monolithic integrated CMUTs fabricated by low temperature wafer bonding}, abstract = {Low temperature wafer bonding (temperature of 450°C. or less) is employed to fabricate CMUTs on a wafer that already includes active electrical devices. The resulting structures are CMUT arrays integrated with active electronics by a low-temperature wafer bonding process.The use of a low-temperature process preserves the electronics during CMUT fabrication. With this approach, it is not necessary to make compromises in the CMUT or electronics designs, as is typical of the sacrificial release, such as low process control, poor design flexibility, low reproducibility, and reduced performance are avoided with the present approach. With this approach, a CMUT array can be provided with per-cell electrodes connected to the substrate integrated circuitry. This enables complete flexibility in electronically assigning the CMUT cells to CMUT array elements.}, language = {en} } @misc{LeeParkKupniketal., author = {Lee, Hyunjoo J. and Park, Kwan Kyu and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Functionalization layers for CO2 sensing using capacitive micromachined ultrasonic transducers}, series = {Sensors and Actuators B: Chemical}, journal = {Sensors and Actuators B: Chemical}, number = {174}, issn = {0925-4005}, pages = {87 -- 93}, abstract = {Sensing of carbon dioxide(CO2)using inexpensive, miniaturized,and highly sensitive sensors is of great interest for environmental and consumer applications. In this paper, we present four functionalization layers that are suitable for resonant sensors based on mass-loading for CO2 detection. We compare the volume sensitivities of these layers to CO2 and relative humidity (RH) by using a highly sensitive 50-MHz capacitive micromachined ultrasonic transducer (CMUT) as a resonant sensor. Among the four function-alization layers, the layer based on a guanidine polymer exhibits the highest volume sensitivity to CO2 of 1.0 ppm/Hz in N2 and 3.8 ppm/Hz in air (∼45\%RH). Furthermore, we report on other important characteristics of the guanidine polymer for sensing applications, including polymer saturation, regeneration, and repeatability.}, language = {en} } @misc{LeeParkKupniketal., author = {Lee, Hyunjoo J. and Park, Kwan Kyu and Kupnik, Mario and Melosh, Nicholas A. and Khuri-Yakub, Butrus T.}, title = {Mesoporous thin-film on highly sensitive resonant chemical sensors for relative humidity and CO2 detection}, series = {Analytical Chemistry}, volume = {84}, journal = {Analytical Chemistry}, number = {7}, issn = {1520-6882}, doi = {10.1021/ac300225c}, pages = {3063 -- 3066}, abstract = {Distributed sensing of gas-phase chemicals is a promising application for mesoporous materials when combined with highly sensitive miniaturized gas sensors. We present a direct application of a mesoporous silica thin film on a highly sensitive miniaturized resonant chemical sensor with a mass sensitivity at the zeptogram scale for relative humidity and CO2 detection. Using mesoporous silica thin-film, we report one of the lowest volume resolutions and a sensitive detection of 5.1 × 10-4\% RH/Hz to water vapor in N2, which is 70 times higher than a device with a nontemplated silica layer. In addition, a mesoporous thin-film that is functionalized with an amino-group is directly applied on the resonant sensor, which exhibits a volume sensitivity of 1.6 × 10-4\%/Hz and a volume resolution of 1.82 × 10-4\% to CO2 in N2.}, language = {en} } @misc{KupnikKhuriYakub, author = {Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Sensor for measuring properties of liquids and gases}, abstract = {The present invention provides a device that measures at least one property of the liquid or gas, where the invention is a CMUT sensor that includes a substrate, a first layer disposed on the substrate, where the first layer includes a cavity, and a compound plate, where the compound plated includes a bottom plate, an intermediate plate and a top plate. According to the invention, the intermediate plate has at least one sample inlet, a sample cavity and at least one sample outlet, where the bottom plate is disposed on the first layer, and the cavity in the first layer is sealed by the compound plate. The cavity in the first layer can be a vacuum or contain a gas. The CMUT sensor can be disposed in an array of two or more sensors and connected electrically in parallel.}, language = {en} } @inproceedings{HoKupnikParketal., author = {Ho, Min-Chieh and Kupnik, Mario and Park, Kwan Kyu and Eckhoff, Kristian and Khuri-Yakub, Butrus T.}, title = {Wide pressure range operation of air-coupled CMUTs}, series = {IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012}, booktitle = {IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4673-4561-3}, doi = {10.1109/ULTSYM.2012.0023}, pages = {93 -- 96}, abstract = {We present measurement results of capacitive micromachined ultrasonic transducers (CMUTs)in permanent contact mode over a wide pressure range(1 - 8 atm). The CMUT plates are in contact with the bottom of the cavities due to atmospheric pressure, even without any dc bias voltage. The electrical input impedance at various dc bias voltages are measured at elevated pressure to characterize individual devices. The open and short circuit resonant frequencies are extracted from the impedance data, and the acoustic performance of pairs of devices is evaluated by performing pitch-catch measurements. A frequency matching method is proposed and used to determine the optimal dc bias voltages for the transmitting and receiving CMUTs individually. Our electrical impedance results show good agreement with the finite element model results (modal and harmonic analysis performed with ANSYS) over the entire pressure range. Moreover, the pitch-catch measurement results validate the proposed frequency matching method for an optimal biasing scheme, and a received signal with good signal-to-noise ratio of 45 dB was observed at a pressure of 7 atm. In conclusion, the behavior of CMUTs in permanent contact mode can be predicted well with our FEA, and they are indeed a promising solution in providing ultrasonic transducers that can operate over a wide pressure range.}, language = {en} } @inproceedings{HoKupnikParketal., author = {Ho, Min-Chieh and Kupnik, Mario and Park, Kwan Kyu and Khuri-Yakub, Butrus T.}, title = {Long-term measurement results of pre-charged CMUTs with zero external bias operation}, series = {IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012}, booktitle = {IEEE International Ultrasonics Symposium, Dresden, Germany, 7 - 10 October 2012}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4673-4561-3}, doi = {10.1109/ULTSYM.2012.0022}, pages = {89 -- 92}, abstract = {We present long-term measurement results (<1.5 years) of CMUTs, which have been pre-charged for zero external bias operation. The fabrication is based on a direct wafer bonding process with a thick-buried-oxide-layer, which allows the realization of only partially connected, donut-shaped bottom electrodes. The only partially connected bottom electrode has a central portion that is completely encapsulated by 3-μm-thick thermally-grown silicon dioxide, and, thus, electrically floating. The devices are pre-charged by applying a dc voltage higher than the pull-in voltage, which injects charges into the electrically floating portion and creates a sufficiently strong intrinsic electric field in the gap. Measurements of resonant frequency at various bias voltages show that the charges have completely remained in the floating portion for the last 19 months. We prove the zero-external-bias operations with the pre-charged CMUTs by measuring the electrical input impedance, the ac signal displacement, and pitch-catch measurements under zero external dc bias voltage. Our results show that pre-charging CMUTs is feasible, and that the devices are capable of long-term, zero external bias voltage operation.}, language = {en} } @misc{ParkLeeKupniketal., author = {Park, Kwan Kyu and Lee, Hyunjoo J. and Kupnik, Mario and Oralkan, {\"O}mer and Ramseyer, Jean-Pierre and Lang, Hans Peter and Hegner, Martin and Gerber, Christoph and Khuri-Yakub, Butrus T.}, title = {Capacitive micromachined ultrasonic transducer (CMUT) as a chemical sensor for DMMP detection}, series = {Sensors and Actuators B: Chemical}, volume = {160}, journal = {Sensors and Actuators B: Chemical}, number = {1}, issn = {0925-4005}, doi = {10.1016/j.snb.2011.09.036}, pages = {1120 -- 1127}, language = {en} } @misc{ParkLeeKupniketal., author = {Park, Kwan Kyu and Lee, Hyunjoo J. and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Fabrication of capacitive micromachined ultrasonic transducers via local oxidation and direct wafer bonding}, series = {Journal of Microelectromechanical Systems}, volume = {20}, journal = {Journal of Microelectromechanical Systems}, number = {1}, issn = {1941-0158}, doi = {10.1109/JMEMS.2010.2093567}, pages = {95 -- 103}, language = {en} } @misc{LeeParkKupniketal., author = {Lee, Hyunjoo J. and Park, Kwan Kyu and Kupnik, Mario and Oralkan, {\"O}mer and Khuri-Yakub, Butrus T.}, title = {Chemical vapor detection using a capacitive micromachined ultrasonic transducer}, series = {Analytical chemistry}, volume = {83}, journal = {Analytical chemistry}, number = {24}, issn = {1520-6882}, doi = {10.1021/ac201626b}, pages = {9314 -- 9320}, language = {en} } @misc{KupnikKhuriYakub, author = {Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {Monolithic integrated CMUTs fabricated by low temperature wafer bonding}, language = {en} } @misc{KupnikKhuriYakub, author = {Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {High-temperature electrostatic transducers and fabrication method}, language = {en} } @inproceedings{HoKupnikVaithilingametal., author = {Ho, Min-Chieh and Kupnik, Mario and Vaithilingam, Srikant and Khuri-Yakub, Butrus T.}, title = {Fabrication and model validation for CMUTs operated in permanent contact mode}, series = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, booktitle = {IEEE International Ultrasonics Symposium 2011, Orlando, Florida, USA, October 18-21, 2011}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {978-1-4577-1252-4}, pages = {1016 -- 1019}, language = {en} } @inproceedings{HoKupnikKhuriYakub, author = {Ho, Min-Chieh and Kupnik, Mario and Khuri-Yakub, Butrus T.}, title = {FEA of CMUTs suitable for wide gas pressure range applications}, series = {2010 IEEE International Ultrasonics Symposium (IUS 2010), San Diego, California, USA, 11 - 14 October 2010, vol. 2}, booktitle = {2010 IEEE International Ultrasonics Symposium (IUS 2010), San Diego, California, USA, 11 - 14 October 2010, vol. 2}, publisher = {IEEE}, address = {Piscataway, NJ}, pages = {1234 -- 1237}, language = {en} }