Download or read book Capacitive Micromachined Ultrasonic Transducer CMUT Chemical Sensor and Its Interface Circuits written by Hyunjoo Jenny Lee and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Miniaturized chemical sensors based on microelectromechanical-systems (MEMS) offer competitive advantages over existing bench-top chemical analyzers, such as small size, low power consumption, low cost due to batch fabrication, and CMOS compatibility. The potential for system integration of these chemical sensors with on-chip CMOS circuitry expands the spectrum of use, including consumer, industrial, and homeland security applications. This thesis introduces a miniaturized resonant chemical sensor based on a 50-MHz capacitive micromachined ultrasonic transducer (CMUT). With a high mass sensitivity of 4.3 ag/Hz, this CMUT-based chemical sensor achieves excellent volume sensitivity of 21.2 ppt/Hz to dimethyl methylphosphonate (DMMP), a common simulant for Sarin gas. In addition, a direct application of a mesoporous silica thin-film on a CMUT for relative humidity and carbon dioxide detection is presented. Using a mesoporous silica thin-film with a pore size of ~11 nm, this sensor achieves one of the lowest volume resolutions and a sensitive detection of 5.1 × 10-4%RH/Hz to water vapor in nitrogen. 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 carbon dioxide in nitrogen. Lastly, this thesis describes the sensor interface circuitry for CMUT and discusses the frequency noise analysis of CMUT-based oscillators. Specifically, a multi-channel interface integrated circuit (IC) implemented using 0.18-um CMOS technology, which results in reduced area and power consumption for each channel is presented. Two-channel detection of relative humidity is demonstrated using this circuit.

Download or read book Capacitive Micromachined Ultrasonic Transducer CMUT for Chemical Detection in Air written by Kwan Kyu Park and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Demand for a highly sensitive, accurate, and portable chemical sensor system has been increasing over the recent years for a wide range of applications. For these applications; resonant chemical sensors based on the mass-loading effect (i.e., gravimetric sensors) with chemical functionalization layers are promising candidates. Among them, a capacitive micromachined ultrasonic transducer (CMUT) is a strong candidate with key advantages: 1) it utilizes a thin resonator backed by a vacuum cavity which results in a high quality factor, 2) it has the ability to apply massive parallelism, thereby, increasing its reliability and lowering the motional impedance, and 3) consistent repeatability and reliability in the fabrication process. The development of a CMUT-based chemical sensor encompasses device selection and characterization, oscillation circuit design and implementation, chemical functionalization, and a chemical test. CMUTs with a resonant frequency ranging from 6 MHz to 50 MHz are selected. An oscillation circuit is designed to track the parallel resonant frequency of the CMUT. The CMUT is chemically activated by thin polymer layers (e.g., Polyisobutylene or synthesized polymer) to absorb an analyte of interest. Chemical experimentation reveals that the CMUT-based chemical sensor has a high sensitivity, the capability of analyte identification, and a reliable operation. In order to improve the performance of the CMUT as a mass-loading sensor, the device should have the following elements: a thin plate with a high frequency, low parasitic capacitance, low operating voltage, and a high breakdown voltage. The local oxidation of silicon/wafer-bonding (LOCOS/wafer-bonding) process meets this criteria. The process realizes a CMUT with a quality factor of 400 in air, a resonant frequency up to 50 MHz, and an unprecedented small gap of 40-nm. This thesis presents a highly sensitive chemical sensor based on the CMUT technology with theoretical mass sensitivities of 54.4 zg/Hz/um^2 for the devices operating at 50 MHz. The multi-resonator configuration is more reliable in operation and makes the oscillator circuit easier to design. Since the oscillator circuit was designed with low-frequency (0.2 Hz) noise and an equivalent volume resolution of 21 ppt of Dimethyl methylphosphonate (DMMP); a simulant of Sarin (GB) was achieved. This work thus demonstrates that CMUT technology has great potential for the implementation of chemical sensing systems that are sensitive; yet reliable and portable.

Download or read book Interface Engineering of Capacitive Micromachined Ultrasonic Transducers for Medical Applications written by Der-Song Lin and published by Stanford University. This book was released on 2011 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: Capacitive micromachined ultrasonic transducers (CMUTs), have been widely studied in academia and industry over the last decade. CMUTs provide many benefits over traditional piezoelectric transducers including improvement in performance through wide bandwidth, and ease of electronics integration, with the potential to batch fabricate very large 2D arrays with low-cost and high-yield. Though many aspects of CMUT technology have been studied over the years, packaging the CMUT into a fully practical system has not been thoroughly explored. Two important interfaces of packaging that this thesis explores are device encapsulation (the interface between CMUTs and patients) and full electronic integration of large scale 2D arrays (the interface between CMUTs and electronics). In the first part of the work, I investigate the requirements for the CMUT encapsulation. For medical usage, encapsulation is needed to electrically insulate the device, mechanically protect the device, and maintain transducer performance, especially the access of the ultrasound energy. While hermetic sealing can protect many other MEMS devices, CMUTs require mechanical interaction to a fluid, which makes fulfilling the previous criterion very challenging. The proposed solution is to use a viscoelastic material with the glass-transition-temperature lower than room temperature, such as Polydimethylsiloxane (PDMS), to preserve the CMUT static and dynamic performance. Experimental implementation of the encapsulated imaging CMUT arrays shows the device performance was maintained; 95 % of efficiency, 85% of the maximum output pressure, and 91% of the fractional bandwidth (FBW) can be preserved. A viscoelastic finite element model was also developed and shows the performance effects of the coating can be accurately predicted. Four designs, providing acoustic crosstalk suppression, flexible substrate, lens focusing, and blood flow monitoring using PDMS layer were also demonstrated. The second part of the work, presents contributions towards the electronic integration and packaging of large-area 2-D arrays. A very large 2D array is appealing for it can enable advanced novel imaging applications, such as a reconfigurable array, and a compression plate for breast cancer screening. With these goals in mind, I developed the first large-scale fully populated and integrated 2D CMUTs array with 32 by 192 elements. In this study, I demonstrate a flexible and reliable integration approach by successfully combining a simple UBM preparation technique and a CMUTs-interposer-ASICs sandwich design. The results show high shear strength of the UBM (26.5 g), 100% yield of the interconnections, and excellent CMUT resonance uniformity ([lowercase Sigma] = 0.02 MHz). As demonstrated, this allows for a large-scale assembly of a tile-able array by using an interposer. Interface engineering is crucial towards the development of CMUTs into a practical ultrasound system. With the advances in encapsulation technique with a viscoelastic polymer and the combination of the UBM technique to the TSV fabrication for electronics integration, a fully integrated CMUT system can be realized.

Download or read book Capacitive Micromachined Ultrasonic Transducers CMUTs for Humidity Sensing written by Zhou Zheng and published by . This book was released on 2019 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the last two decades, capacitive micromachined ultrasonic transducers (CMUTs) have proven themselves to be promising for various ultrasound imaging and chemical sensing applications. Although holding many benefits for ultrasound imaging, CMUTs have certain weaknesses such as the relatively low output pressure at transmission, which hinder their development in the diagnostic imaging application. In the sensing area, CMUTs have shown attractive features such as high mass sensitivity, miniaturized array configuration, and ease of functionalization. However, their potential for humidity sensing is less explored. The objectives of this thesis lie in two aspects. One is to offer a solution to overcome the limitation of low output pressure, and the other is to develop CMUTs as resonant gravimetric humidity sensors. The major efforts are made on the second task. For the first objective, a novel dual-element ultrasonic transducer is proposed. It incorporates two transducer technologies by using a circular piezoelectric element for ultrasound transmission and an annular CMUT element for reception. The hybrid transducer combines the broad bandwidth and high receive sensitivity of the CMUT and the high output power of the piezoelectric transducer to improve the overall sensitivity and axial resolution. The annular CMUT is designed, fabricated, and concentrically aligned with the piezoelectric probe via a custom housing. Immersion measurements show that the hybrid dual-element transducer improves the axial resolution by 25.58% and the signal-to-noise ratio by 8.55 dB over the commercial piezoelectric probe. For the second objective, a CMUT-based resonant humidity sensor is first developed with the direct wafer bonding technique. Graphene oxide (GO) is employed as the sensing material. Due to combination of the mass-sensitive CMUT and the moisture-sensitive GO, the sensor exhibits rapid response/recovery, good repeatability, and higher sensitivity than most of its competitors. The second generation of CMUT-based humidity sensors aims to further improve the relative humidity (RH) sensing performance by adopting the nitride-to-oxide wafer bonding technology for CMUT fabrication. In contrast to conventional wafer bonding CMUT processes that use expensive silicon-on-insulator (SOI) wafers to produce resonating membranes, the new process employs low-pressure chemical vapor deposition (LPCVD) silicon nitride as the membrane material. It provides thinner and lighter membranes, and thus more sensitive CMUT resonators. Additional benefits of the nitride-to-oxide wafer bonding technique are the reduced fabrication complexity and more controllable membrane thickness. Finally, a dual-frequency (10/14 MHz) CMUT is developed using this fabrication technique. It generates two RH response curves and can provide more accurate RH sensing. Due to the independence of the two resonance frequencies, the dual-frequency CMUT also shows great potential for identification of different chemicals. This thesis demonstrates that CMUT sensors can be strong candidates for miniaturized, highly sensitive, and reliable humidity sensors.

Download or read book A Feasibility Study of Micromachined Ultrasonic Transducers Functionalized for Ethanol Dectection written by Yaning Cui and published by . This book was released on 2017 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: The chemical sensing system plays an important role in medical and environmental monitoring. Gases exhaled by humans include nitrogen, oxygen, water vapor, carbon dioxide and volatile organic compounds (VOCs). The VOCs are important and provide valuable information for non- invasive diagnosis. For instance, ethanol detection is beneficial for checking blood alcohol. In time blood alcohol level checking before checking can prevent a person from unsafe driving. Due to the extremely low concentration of the target gases, a gas sensor with high sensitivity, selectivity and low detection limit is required. There is a high demand for low cost, fast, accurate and easy-to-use self-check diagnosis devices. With low cost and high portability, micro-electromechanical systems (MEMS) sensors have been extensively studied for chemical sensing, which provide a cheap self-diagnosis solution. Capacitive Micromachined Ultrasonic Transducers (CMUTs) and Piezoelectric Micromachined Ultrasonic Transducer (PMUTs), which both work based on the mass-loading effect, are considered as the promising types of MEMS sensors for gas sensing. Since they are fabricated in a batch manner with the similar process of silicon-based integrated circuits, CMUTs and PMUTs are able to provide massive parallelism, easy integration with microelectronic circuits, and a higher quality factor. In this research, studied the feasibility of using PMUTs and CMUTs fabricated by our lab for ethanol detection through simulation and experiments. Models for are built via COMSOL for PMUT and CMUT respectively. The simulation results of a single sensing element demonstrated that both CMUTs and PMUTs show great potential for gas sensors. The chemical experiments through frequency response measurement exhibit that both the PMUTs and CMUTs are effective for ethanol detection based on the mass-loading effect. When the gas analyte is attached to the sensing layer, a higher resonance frequency of the transducer induces a higher frequency shift, which means the higher resonance frequency of transducer, the higher sensitivity of a gas sensor is and the lower concentration of ethanol can be detected. Additionally, a CMUT array is also applied to ethanol detection. It provides a good preliminary study of the CMUTs functionalized with more sensing materials for chemical detection in future.

Download or read book On the Design of High voltage Analog Front end Circuits for Capacitive Micromachined Ultrasonic Transducers CMUT written by Parisa Behnamfar and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Integrated Circuits Compatible Membrane based Micro Electro mechanical Sensors and Actuators written by Tariq Alsaiary and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "The work described in the current thesis can be divided into two (2) main topics - both target the fabrication of CMOS compatible, membrane-based, micro electro-mechanical sensors and actuators (MEMS). The results of the two studies are reported. In both cases, the maximum temperature allowed during designing was set at 300oC, in order to facilitate above-CMOS monolithic integration.The first part of this thesis describes a process flow design to build an amorphous silicon carbide (a-SiC)-and-polysilicon-based capacitive absolute pressure sensor for medium to high-pressure readings. Previous work by our research team at McGill University attempted to manufacture a membrane for wafer level packaging and pressure sensing, using a-SiC thin film. However, the prototype did not successfully seal the reference cavity of the sensor, due to the porous nature of the amorphous structure. The contribution in this thesis consists of proposing a design that mitigates the sealing problem, while also being suitable for above-CMOS monolithic integration. The process involves back-etching and bonding to a silicon wafer to form the reference cavity of the pressure sensor. The methodology and design were filed with the US patent office in 2016.The second part of the thesis aimed at the design and fabrication of a silicon nitride (SiN) air-coupled capacitive micromachined ultrasonic transducer (CMUT). The PolyMUMPs commercial process was used for proof of concept. According to the electrical and acoustical characterization of the PolyMUMPs CMUT, the 2.8x1.4 mm array of a 120 μm-diameter membrane radiated at 1.38 MHz for 38 mm. The Q-factor was 12.29 and the bandwidth was approximately 0.11 MHz. These results provide an initial estimate for the SiN CMUT response. Because of the thinner membrane and the receiver thin air gap in the SiN design, we expected that the sound wave radiation of the SiN CMUT would be stronger than that of the PolyMUMPs CMUT. However, we could not verify the performance of the transducer, owing to an inadequate polyimide sacrificial layer releasing recipe which did not etch as desired. We did not have access to a powerful asher system which may have provided a solution to this problem. Therefore, we considered and studied an aluminum sacrificial layer, and demonstrated that the 110 μm-diameter-perforated membrane can be released in less than 320 min. We also validated the compatibility of the aluminum sacrificial layer with the SiN CMUT process." --

Download or read book Micromachined Ultrasonic Transducers written by and published by . This book was released on 1997 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microfabricated ultrasonic transducers have been generated which operate in both liquids and gases. Air coupled through transmission of aluminum was observed for the first time using a pair of 2.3 MHz transducers. The dynamic range of the transducers was 110 dB, and the received signal had an SNR of 30 dB. Air coupled through transmission of steel and glass has also been observed. A theoretical model for the transducers has been refined and agrees well with experimental results. A robust microfabrication process has been developed and was used to generate air transducers which resonate from 2 to 12 MHz, as well as immersion transducers that operate in water from 1 to 20 MHz with a 60 dB dynamic range. Optimized immersion and air transducers have been designed and a dynamic range above 110 dB is anticipated. This development effort finds applications in hydrophones, medical ultrasound, nondestructive evaluation, ranging, flow metering, and scanning tip force sensing and lithography.

Download or read book Interface Engineering of Capacitive Micromachined Ultrasonic Transducers for Medical Applications written by Der-Song Lin and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Capacitive micromachined ultrasonic transducers (CMUTs), have been widely studied in academia and industry over the last decade. CMUTs provide many benefits over traditional piezoelectric transducers including improvement in performance through wide bandwidth, and ease of electronics integration, with the potential to batch fabricate very large 2D arrays with low-cost and high-yield. Though many aspects of CMUT technology have been studied over the years, packaging the CMUT into a fully practical system has not been thoroughly explored. Two important interfaces of packaging that this thesis explores are device encapsulation (the interface between CMUTs and patients) and full electronic integration of large scale 2D arrays (the interface between CMUTs and electronics). In the first part of the work, I investigate the requirements for the CMUT encapsulation. For medical usage, encapsulation is needed to electrically insulate the device, mechanically protect the device, and maintain transducer performance, especially the access of the ultrasound energy. While hermetic sealing can protect many other MEMS devices, CMUTs require mechanical interaction to a fluid, which makes fulfilling the previous criterion very challenging. The proposed solution is to use a viscoelastic material with the glass-transition-temperature lower than room temperature, such as Polydimethylsiloxane (PDMS), to preserve the CMUT static and dynamic performance. Experimental implementation of the encapsulated imaging CMUT arrays shows the device performance was maintained; 95 % of efficiency, 85% of the maximum output pressure, and 91% of the fractional bandwidth (FBW) can be preserved. A viscoelastic finite element model was also developed and shows the performance effects of the coating can be accurately predicted. Four designs, providing acoustic crosstalk suppression, flexible substrate, lens focusing, and blood flow monitoring using PDMS layer were also demonstrated. The second part of the work, presents contributions towards the electronic integration and packaging of large-area 2-D arrays. A very large 2D array is appealing for it can enable advanced novel imaging applications, such as a reconfigurable array, and a compression plate for breast cancer screening. With these goals in mind, I developed the first large-scale fully populated and integrated 2D CMUTs array with 32 by 192 elements. In this study, I demonstrate a flexible and reliable integration approach by successfully combining a simple UBM preparation technique and a CMUTs-interposer-ASICs sandwich design. The results show high shear strength of the UBM (26.5 g), 100% yield of the interconnections, and excellent CMUT resonance uniformity ([lowercase Sigma] = 0.02 MHz). As demonstrated, this allows for a large-scale assembly of a tile-able array by using an interposer. Interface engineering is crucial towards the development of CMUTs into a practical ultrasound system. With the advances in encapsulation technique with a viscoelastic polymer and the combination of the UBM technique to the TSV fabrication for electronics integration, a fully integrated CMUT system can be realized.

Download or read book Smart Sensors and MEMS written by S Nihtianov and published by Woodhead Publishing. This book was released on 2014-03-24 with total page 563 pages. Available in PDF, EPUB and Kindle. Book excerpt: Smart sensors and MEMS can include a variety of devices and systems that have a high level of functionality. They do this either by integrating multiple sensing and actuating modes into one device, or else by integrating sensing and actuating with information processing, analog-to-digital conversion and memory functions. Part one outlines the industrial applications for smart sensors, covering direct interface circuits for sensors, capacitive sensors for displacement measurement in the sub-nanometer range, integrated inductive displacement sensors for harsh industrial environments, advanced silicon radiation detectors in the vacuum ultraviolet (VUV) and extreme ultraviolet (EUV) spectral range, and advanced optical incremental sensors (encoders and interferometers), among other topics. The second part of the book describes the industrial applications of smart micro-electro-mechanical systems (MEMS). Some of the topics covered in this section include microfabrication technologies used for creating smart devices for industrial applications, microactuators, dynamic behaviour of smart MEMS in industrial applications, MEMS integrating motion and displacement sensors, MEMS print heads for industrial printing, Photovoltaic and fuel cells in power MEMS for smart energy management, and radio frequency (RF)-MEMS for smart communication microsystems. Smart sensors and MEMS is invaluable reference for academics, materials scientists and electrical engineers working in the microelectronics, sensors and micromechanics industry, and engineers looking for industrial sensing, monitoring and automation solutions. Outlines industrial applications for smart sensors and smart MEMS Covers smart sensors including capacitive, inductive, resistive and magnetic sensors and sensors to detect radiation and measure temperature Covers smart MEMS including power MEMS, radio frequency MEMS, optical MEMS, inertial MEMS, and microreaction chambers

Download or read book Capacitive Micromachined Ultrasonic Transducers with Substrate embedded Springs written by Byung Chul Lee and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: After the first capacitive micromachined ultrasonic transducer (CMUT) was invented in 1994, it became one of the candidate technologies to advance the state-of-the-art of medical ultrasound imaging. Benefiting from its fabrication technique based on the semiconductor industry, CMUT technology has broadened the medical and therapeutic applications such as real-time volumetric ultrasound imaging, catheter-based forward-looking intravascular ultrasound (IVUS), photoacoustic imaging, high-intensity focused ultrasound (HIFU) and so on. In spite of many advantages, however, CMUT technology has been criticized with its relatively low transmit sensitivity (~10 kPa/V) or low average volume displacement efficiency (0.1 nm/V) as well as large drive and bias voltage requirements (in a range of a few hundreds of volts). In order to resolve these issues and open up new potential of clinical applications, this dissertation describes the design, fabrication, and system implementation of CMUTs with substrate-embedded springs, so-called post-CMUT (PCMUT). Since PCMUT structure resembles an ideal piston transducer, the improvements in performance mainly stem from the higher average displacement of the top plate for a given gap height. The overview of the first generation PCMUT is introduced and two main issues in simulation and fabrication aspects of the first generation PCMUT is discussed. To further improve the PCMUT device, a 3D finite element analysis (FEA) model of the PCMUT is demonstrated to predict the performance of the first generation PCMUT. In addition, the design guideline of the second generation PCMUT is proposed for achieving the maximum fractional bandwidth (100 %) as well as with the highest transmit sensitivity (~28 kPa/V). The second generation PCMUT is fabricated by using three combination MEMS processes: usage of two silicon-on-insulator (SOI) wafers, wafer bonding process, and wafer polishing process. The second generation PCMUT achieves high transmit sensitivity (~21 kPa/V) or large average volume displacement efficiency (1.1 nm/V) with a low bias voltage (55 V). Compared to a commercial piezoelectric transducer, the second generation PCMUT improves 2.75 times of the maximum output pressure and 5.25 times of the average volume displacement efficiency with respect to the same voltage. After fabrication and performance characterization of the second generation PCMUT, this dissertation demonstrates the feasibility of PCMUT to use it in medical imaging system by integrating PCMUT with a custom-built integrated circuit (IC). Photoacoustic imaging is also presented for one of its application examples.

Download or read book CMOS Integrated Lab on a chip System for Personalized Biomedical Diagnosis written by Hao Yu and published by John Wiley & Sons. This book was released on 2018-04-04 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: A thorough examination of lab-on-a-chip circuit-level operations to improve system performance A rapidly aging population demands rapid, cost-effective, flexible, personalized diagnostics. Existing systems tend to fall short in one or more capacities, making the development of alternatives a priority. CMOS Integrated Lab-on-a-Chip System for Personalized Biomedical Diagnosis provides insight toward the solution, with a comprehensive, multidisciplinary reference to the next wave of personalized medicine technology. A standard complementary metal oxide semiconductor (CMOS) fabrication technology allows mass-production of large-array, miniaturized CMOS-integrated sensors from multi-modal domains with smart on-chip processing capability. This book provides an in-depth examination of the design and mechanics considerations that make this technology a promising platform for microfluidics, micro-electro-mechanical systems, electronics, and electromagnetics. From CMOS fundamentals to end-user applications, all aspects of CMOS sensors are covered, with frequent diagrams and illustrations that clarify complex structures and processes. Detailed yet concise, and designed to help students and engineers develop smaller, cheaper, smarter lab-on-a-chip systems, this invaluable reference: Provides clarity and insight on the design of lab-on-a-chip personalized biomedical sensors and systems Features concise analyses of the integration of microfluidics and micro-electro-mechanical systems Highlights the use of compressive sensing, super-resolution, and machine learning through the use of smart SoC processing Discusses recent advances in complementary metal oxide semiconductor-integrated lab-on-a-chip systems Includes guidance on DNA sequencing and cell counting applications using dual-mode chemical/optical and energy harvesting sensors The conventional reliance on the microscope, flow cytometry, and DNA sequencing leaves diagnosticians tied to bulky, expensive equipment with a central problem of scale. Lab-on-a-chip technology eliminates these constraints while improving accuracy and flexibility, ushering in a new era of medicine. This book is an essential reference for students, researchers, and engineers working in diagnostic circuitry and microsystems.

Download or read book Fabrication of Capacitive Micromachined Ultrasonic Transducers Based on Adhesive Wafer Bonding written by Zhenhao Li and published by . This book was released on 2017 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt: Capacitive micromachined ultrasonic transducers (CMUTs) can be used for medical imaging, non-destructive testing or medical treatment applications. It can also be used as gravimetric sensors for gas sensing or immersion bio-sensing. Although various CMUT fabrication methods have been reported, there are still many challenges to address. Conventional fabrication methods can be categorized as either surface micromachining or the wafer bonding method. These methods have design trade-offs and limitations associated with process complexity, structural parameter optimization and wafer materials selection. For example, surface micromachining approaches can suffer from complicated fabrication processes. In addition, structural parameters cannot be fully optimized due to feasibility concerns during fabrication. In contrast, the development of wafer bonding techniques enabled CMUTs to be fabricated in a straightforward way and structural parameters can be easily optimized when compared with a surface micromachining approach. However, the yield of the traditional wafer bonded CMUTs is very sensitive to contaminations and the surface quality at the bonding interface. Although the difficulties of the wafer bonding process are not always reported, they definitely exist for every researcher who wants to fabricate their own CMUTs. As a result, this dissertation work aims to develop a CMUT fabrication process with fewer fabrication constraints, low-cost and low process temperature for CMOS integration. The developed CMUT fabrication processes reported in the thesis applied photosensitive polymer adhesive for wafer bonding in order to make a process with good tolerance to contaminations and defects on the wafer surface, present a wide range of material selection at the bonding interface and require low process temperature (less than 250°C). These features can benefit CMUT fabrication with increased yield better design flexibility and lower cost. Having maximum process temperature of 250°C, the developed processes can also be CMOS compatible. Furthermore, a novel CMUT structure, which can only be achieved by the reported technique, was developed showing more than doubled ultrasound receive sensitivity when compared with conventional CMUT structures. The fabrication processes were developed systematically and the details of process development will be presented in this thesis.

Download or read book Polysilicon Surface Micromachined Capacitive Sensors and Interface Circuits written by Xiaofeng Yang (M.S.) and published by . This book was released on 1997 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Capacitive Micromachined Ultrasonic Transducer CMUT Technologies written by James Stuart McIntosh and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Interconnection Interface and Instrumentation for Micromachined Chemical Sensors written by Naveenkumar Palsandram and published by . This book was released on 2005 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: In realizing a portable chemical analysis system, adequate partitioning of a reusable component and a disposable is required. For successful implementation of micromachined sensors in an instrument, reliable methods for interconnection and interface are in great demand between these two major parts. This thesis work investigates interconnection methods of micromachined chip devices, a hybrid fluidic interface system, and measurement circuitry for completing instrumentation. The interconnection method based on micromachining and injection molding techniques was developed and an interconnecting microfluidic package was designed, fabricated and tested. Alternatively, a plug-in type design for a large amount of sample flow was designed and demonstrated. For the hybrid interface, sequencing of the chemical analysis was examined and accordingly, syringe containers, a peristaltic pump and pinch valves were assembled to compose a reliable meso-scale fluidic control unit. A potentiostat circuit was modeled using a simulation tool. The simulated output showed its usability toward three-electrode electrochemical microsensors. Using separately fabricated microsensors, the final instrument with two different designs--flow-through and plug-in type was tested for chlorine detection in water samples. The chemical concentration of chlorine ions could be determined from linearly dependent current signals from the instrument.

Download or read book Simulation of a Capacitive Micromachined Ultrasonic Transducer with a Parylene Membrane and Graphene Electrodes written by David Sadat and published by . This book was released on 2012 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt: Medical ultrasound technology accounts for over half of all imaging tests performed worldwide. In comparison to other methods, ultrasonic imaging is more portable and lower cost, and is becoming more accessible to remote regions where traditionally no medical imaging can be done. However, conventional ultrasonic imaging systems still rely on expensive PZT-based ultrasound probes that limit broader applications. In addition, the resolution of PZT based transducers is low due to the limitation in hand-fabrication methods of the piezoelectric ceramics. Capacitive Micromachined Ultrasonic Transducers (CMUTs) appears as an alternative to the piezoelectric (PZT) ceramic based transducer for ultrasound medical imaging. CMUTs show better ultrasound transducer design for batch fabrication, higher axial resolution of images, lower fabrication costs of the elements, ease of fabricating large arrays of cells using MEMS fabrication, and the extremely important potential to monolithically integrate the 2D transducer arrays directly with IC circuits for real-time 3D imaging. Currently most efforts on CMUTs are silicon based. Problems with current silicon-based CMUT designs include low pressure transmission and high-temperature fabrication processes. The pressure output from the silicon based CMUTs cells during transmission are too low when compared to commercially available PZT transducers, resulting in relatively blurry ultrasound images. The fabrication of the silicon-based cells, although easier than PZT transducers, still suffers from inevitable high temperature process and require specialized and expensive equipment. Manufacturing at an elevated temperature hinders the capability of fabricating front end analog processing IC circuits, thus it is difficult to achieve true 3D/4D imaging. Therefore novel low temperature fabrication with a low cost nature is needed. A polymer (Parylene) based CMUTs transducer has been investigated recently at UCF and aims to overcome limitations posted from the silicon based counterparts. This thesis describes the numerical simulation work and proposed fabrication steps of the Parylene based CMUT. The issue of transducer cost and pressure transmission is addressed by proposing the use of low cost and low temperature Chemical Vapor Deposition (CVD) fabrication of Parylene-C as the structural membrane plus graphene for the membrane electrodes. This study focuses mainly on comparing traditional silicon-based CMUT designs against the Parylene-C/Graphene CMUT based transducer, by using MEMS modules in COMSOL. For a fair comparison, single CMUT cells are modeled and held at a constant diameter and the similar operational frequency at the structural center. The numerical CMUT model is characterized for: collapse voltage, membrane deflection profile, center frequency, peak output pressure transmission over the membrane surface, and the sensitivity to the change in electrode surface charge. This study took the unique approaches in defining sensitivity of the CMUT by calculating the membrane response and the change in the electrode surface charge due to an incoming pressure wave. Optimal design has been achieved based on the simulation results. In comparison to silicon based CMUTs, the Parylene/Graphene based CMUT transducer produces 55% more in volume displacement and more than 35% in pressure output. The thesis has also laid out the detailed fabrication processes of the Parylene/Graphene based CMUT transducers. Parylene/Graphene based ultrasonic transducers can find wide applications in both medical imaging and Non destructive evaluation (NDE).