Microcapteurs de hautes fréquences pour des mesures en aéroacoustique

L aéroacoustique est une filière de l'acoustique qui étudie la génération de bruit par un mouvement fluidique turbulent ou par les forces aérodynamiques qui interagissent avec les surfaces. Ce secteur en pleine croissance a attiré des intérêts récents en raison de l évolution de la transportation aérienne, terrestre et spatiale. Les microphones avec une bande passante de plusieurs centaines de kHz et une plage dynamique couvrant de 40Pa à 4 kPa sont nécessaires pour les mesures aéroacoustiques. Dans cette thèse, deux microphones MEMS de type piézorésistif à base de silicium polycristallin (poly-Si) latéralement cristallisé par l induction métallique (MILC) sont conçus et fabriqués en utilisant respectivement les techniques de microfabrication de surface et de volume. Ces microphones sont calibrés à l'aide d'une source d onde de choc (N-wave) générée par une étincelle électrique. Pour l'échantillon fabriqué par le micro-usinage de surface, la sensibilité statique mesurée est 0.4 V/V/Pa, la sensibilité dynamique est 0.033 V/V/Pa et la plage fréquentielle couvre à partir de 100 kHz avec une fréquence du premier mode de résonance à 400kHz. Pour l'échantillon fabriqué par le micro-usinage de volume, la sensibilité statique mesurée est 0.28 V/V/Pa, la sensibilité dynamique est 0.33 V/V/Pa et la plage fréquentielle couvre à partir de 6 kHz avec une fréquence du premier mode de résonance à 715kHz.Aero-acoustics, a branch of acoustics which studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces, is a growing area and has received fresh emphasis due to advances in air, ground and space transportation. Microphones with a bandwidth of several hundreds of kHz and a dynamic range covering 40Pa to 4kPa are needed for aero-acoustic measurements. In this thesis, two metal-induced-lateral-crystallized (MILC) polycrystalline silicon (poly-Si) based piezoresistive type MEMS microphones are designed and fabricated using surface micromachining and bulk micromachining techniques, respectively. These microphones are calibrated using an electrical spark generated shockwave (N-wave) source. For the surface micromachined sample, the measured static sensitivity is 0.4 V/V/Pa, dynamic sensitivity is 0.033 V/V/Pa and the frequency range starts from 100kHz with a first mode resonant frequency of 400kHz. For the bulk micromachined sample, the measured static sensitivity is 0.28 V/V/Pa, dynamic sensitivity is 0.33 V/V/Pa and the frequency range starts from 6kHz with a first mode resonant frequency of 715kHz.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Optimization of piezoresistive cantilevers for static and dynamic sensing applications

The presented work aims to optimize the performance of piezoresistive cantilevers in cases where the output signal originates either from a static deflection of the cantilever or from the dynamic (resonance) characteristic of the beam. Based on a new stress concentration technique, which utilizes silicon beams and wires embedded in the cantilever, the force sensitivity of the cantilever is increased up to 8 fold with only about a 15% decrease in the cantilever stiffness. Moreover, the developed stress-concentrating cantilevers show almost the same resonance characteristic as conventional cantilevers. The focus of the second part of the present work is to provide guidelines for designing rectangular silicon cantilever beams to achieve maximum quality factors for the fundamental and higher flexural resonance at atmospheric pressure. The applied methodology is based on experimental data acquisition of resonance characteristics of silicon cantilevers, combined with modification of analytical damping models to match the measurement data. To this end, rectangular silicon cantilever beams with thicknesses of 5, 7, 8, 11 and 17 um and lengths and widths ranging from 70 to 1050 um and 80 to 230 um, respectively, have been fabricated and tested. To better describe the experimental data, modified models for air damping have been developed. Moreover, to better understand the damping mechanisms in a resonant cantilever system, analytical models have been developed to describe the cantilever effective mass in any flexural resonance mode. To be able to extract reliable Q-factor data for low signal-to-noise ratios, a new iterative curve fitting technique is developed and implemented. To address the challenge of frequency drift in (mass-sensitive) resonant sensors, and especially cantilever-based devices, the last part of the research deals with a novel compensation technique to cancel the unwanted environmental effects (e.g., temperature and humidity). This technique is based on exploring the resonance frequency difference of two flexural modes. Experimental data show improvements in temperature and humidity coefficients of frequency from -19.5 to 0.2 ppm/˚C and from 0.7 to -0.03 ppm/%RH, respectively. The last part of the work also aims on techniques to enhance or suppress the flexural vibration amplitude in desired overtones.Ph.D.Committee Chair: Brand, Oliver; Committee Member: Adibi, Ali; Committee Member: Allen, Mark G.; Committee Member: Bottomley, Lawrence A.; Committee Member: Degertekin, F. Leven

Single-Chip Scanning Probe Microscopes

Scanning probe microscopes (SPMs) are the highest resolution imaging instruments available today and are among the most important tools in nanoscience. Conventional SPMs suffer from several drawbacks owing to their large and bulky construction and to the use of piezoelectric materials. Large scanners have low resonant frequencies that limit their achievable imaging bandwidth and render them susceptible to disturbance from ambient vibrations. Array approaches have been used to alleviate the bandwidth bottleneck; however as arrays are scaled upwards, the scanning speed must decline to accommodate larger payloads. In addition, the long mechanical path from the tip to the sample contributes thermal drift. Furthermore, intrinsic properties of piezoelectric materials result in creep and hysteresis, which contribute to image distortion. The tip-sample interaction signals are often measured with optical configurations that require large free-space paths, are cumbersome to align, and add to the high cost of state-of-the-art SPM systems. These shortcomings have stifled the widespread adoption of SPMs by the nanometrology community. Tiny, inexpensive, fast, stable and independent SPMs that do not incur bandwidth penalties upon array scaling would therefore be most welcome. The present research demonstrates, for the first time, that all of the mechanical and electrical components that are required for the SPM to capture an image can be scaled and integrated onto a single CMOS chip. Principles of microsystem design are applied to produce single-chip instruments that acquire images of underlying samples on their own, without the need for off-chip scanners or sensors. Furthermore, it is shown that the instruments enjoy a multitude of performance benefits that stem from CMOS-MEMS integration and volumetric scaling of scanners by a factor of 1 million. This dissertation details the design, fabrication and imaging results of the first single-chip contact-mode AFMs, with integrated piezoresistive strain sensing cantilevers and scanning in three degrees-of-freedom (DOFs). Static AFMs and quasi-static AFMs are both reported. This work also includes the development, fabrication and imaging results of the first single-chip dynamic AFMs, with integrated flexural resonant cantilevers and 3 DOF scanning. Single-chip Amplitude Modulation AFMs (AM-AFMs) and Frequency Modulation AFMs (FM-AFMs) are both shown to be capable of imaging samples without the need for any off-chip sensors or actuators. A method to increase the quality factor (Q-factor) of flexural resonators is introduced. The method relies on an internal energy pumping mechanism that is based on the interplay between electrical, mechanical, and thermal effects. To the best of the author’s knowledge, the devices that are designed to harness these effects possess the highest electromechanical Qs reported for flexural resonators operating in air; electrically measured Q is enhanced from ~50 to ~50,000 in one exemplary device. A physical explanation for the underlying mechanism is proposed. The design, fabrication, imaging, and tip-based lithographic patterning with the first single-chip Scanning Thermal Microscopes (SThMs) are also presented. In addition to 3 DOF scanning, these devices possess integrated, thermally isolated temperature sensors to detect heat transfer in the tip-sample region. Imaging is reported with thermocouple-based devices and patterning is reported with resistive heater/sensors. An “isothermal electrothermal scanner” is designed and fabricated, and a method to operate it is detailed. The mechanism, based on electrothermal actuation, maintains a constant temperature in a central location while positioning a payload over a range of >35μm, thereby suppressing the deleterious thermal crosstalk effects that have thus far plagued thermally actuated devices with integrated sensors. In the thesis, models are developed to guide the design of single-chip SPMs and to provide an interpretation of experimental results. The modelling efforts include lumped element model development for each component of single-chip SPMs in the electrical, thermal and mechanical domains. In addition, noise models are developed for various components of the instruments, including temperature-based position sensors, piezoresistive cantilevers, and digitally controlled positioning devices

Design and fabrication of precision carbon nanotube-based flexural transducers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 179-197).As mechanical devices move towards the nanoscale, smaller and more sensitive force and displacement sensors need to be developed. Currently, many biological, materials science, and nanomanufacturing applications could benefit from multi-axis micro- and nanoscale sensors with fine force and displacement resolutions. Unfortunately, such systems do not yet exist due to the limitations of traditional sensing techniques and fabrication procedures. Carbon nanotube-based (CNT) piezoresistive transducers offer the potential to overcome many of these limitations. Previous research has shown the potential for the use of CNTs in high resolution micro- and nanoscale sensing devices due to the high gauge factor and inherent size of CNTs. However, a better understanding of CNT-based piezoresistive sensors is needed in order to be able to design and engineer CNT-based sensor systems to take advantage of this potential. The purpose of this thesis is to take CNT-based strain sensors from the single element test structures that have been fabricated and turn them into precision sensor systems that can be used in micro- and nanoscale force and displacement transducers. In order to achieve this purpose and engineer high resolution CNT-based sensor systems, the design and manufacturing methods used to create CNT-based piezoresistive sensors were investigated. At the system level, a noise model was developed in order to be able to optimize the design of the sensor system. At the element level, a link was established between the structure of the CNT and its gauge factor using a theoretical model developed from quantum mechanics. This model was confirmed experimentally using CNT-based piezoresistive sensors integrated into a microfabricated test structure. At the device level, noise mitigation techniques including annealing and the use of a protective ceramic coating were investigated in order to reduce the noise in the sensor. From these investigations, best practices for the design and manufacturing of CNT-based piezoresistive sensors were established. Using these best practices, it is possible to increase the performance of CNT-based piezoresistive sensor systems by more than three orders of magnitude. These best practices were implemented in the design and fabrication of a multi-axis force sensor used to measure the adhesion force of an array of cells to the different material's surfaces for the development of biomedical implants. This force sensor is capable of measuring forces in the z-axis as well as torques in the [theta]x and [theta]y axis. The range and resolution of the force sensor were determined to be 84 [mu]N and 5.6 nN, respectively. This corresponds to a dynamic range of 83 dB, which closely matches the dynamic range predicted by the system noise model used to design the sensor. The accuracy of the force sensor is better than 1% over the device's full range.by Michael A. Cullinan.Ph.D

Solid State Circuits Technologies

The evolution of solid-state circuit technology has a long history within a relatively short period of time. This technology has lead to the modern information society that connects us and tools, a large market, and many types of products and applications. The solid-state circuit technology continuously evolves via breakthroughs and improvements every year. This book is devoted to review and present novel approaches for some of the main issues involved in this exciting and vigorous technology. The book is composed of 22 chapters, written by authors coming from 30 different institutions located in 12 different countries throughout the Americas, Asia and Europe. Thus, reflecting the wide international contribution to the book. The broad range of subjects presented in the book offers a general overview of the main issues in modern solid-state circuit technology. Furthermore, the book offers an in depth analysis on specific subjects for specialists. We believe the book is of great scientific and educational value for many readers. I am profoundly indebted to the support provided by all of those involved in the work. First and foremost I would like to acknowledge and thank the authors who worked hard and generously agreed to share their results and knowledge. Second I would like to express my gratitude to the Intech team that invited me to edit the book and give me their full support and a fruitful experience while working together to combine this book

Instrumentation development for wall shear-stress applications in 3D complex flows

In the turbomachines field, friction losses are intensively studied due to their important influence in the overall efficiency of the machine. The parameter helping in quantifying these friction losses is the wall shear-stress. Its role is essential for the qualification of the boundary layer separation tendency and the losses prediction. Thus, the first aim of this PhD is to characterize the boundary layer development, in the cone of the Francis turbine. Afterwards, in the second part of this study, a new multidirectional wall shear-stress sensor is designed, manufactured and tested for the turbomachines applications. To develop this knowledge and the tools for flows prediction in the draft tube, EPFL joined major manufacturers in the context of the European initiative EUREKA project n° 1625. In the first part of the thesis, an experimental campaign is leaded in the cone of the nq 92 Francis turbine, to characterize the wall stress, using the hot-film technique. 6 operating points were investigated, covering a large operating range – from 70% to 110% from best efficiency point flow rate. For this specific draft tube, the efficiency characteristic has a sever drop, close to the best efficiency point, and the wall shear stress evolution in this region is pointed out. The calibration and measurement procedures are exposed and the accuracy study is performed. The evolution of the wall shear-stress steady values related to the spatial position of sensor – 16 positions were explored – and to the corresponding operating point is analyzed. A boundary layer separation tendency for the part load operating points is pointed out, as well as the bend influence on the spatial evolution of the wall shear-stress. These results were used to validate numerical calculation in the draft tube. Additional LDV measurements combined with the wall shear-stress results allowed to reconstruct the boundary layer. The best fit for representing the boundary layer is obtained with a composite power law. However the 3D boundary layer is complex and a profound knowledge is needed. From the unsteady point of view, in the runner outlet section, the amplitude of the wall shear-stress fluctuations obtained synchronous with the runner's rotating frequency is predominant. For the partial load operating points, the main fluctuations magnitude is obtained for the rope passage frequency and its amplitude depends on 2 parameters: the σ value and the proximity of the rope to the wall. To increase the knowledge for the boundary layers in turbomachines, it is necessary to explore fully 3D unsteady boundary layers, both in the fixed and rotating parts of the machine. Thus a multidirectional sensor with specific requirements is needed for the turbomachines application: a miniature hot film probe, which can be implemented in the complex geometry of the turbines, a multidirectional one, to take into account the complex character of the flow, mainly the strongly 3D flow, a sensor with a sensitivity and dynamic, allowing to obtain the main flow unsteady characteristics (guide vanes wake, runner blades wake, rope frequency, turbine-circuit interaction frequency, etc.), a good electrical isolation between the surface of the probe, which comes in contact with the water, and with the hot-film support. In this way, the second aim of this PhD becomes the design and development of a new multidirectional wall shear-stress sensor for turbulent boundary layer research for turbomachines applications. The development of the new multidirectional sensor implies technological developments using microtechnology, as MEMS offers opportunities for developing and manufacturing sensors with regard to complex applications, allowing, in the same time, a high accuracy at low cost. The new sensor represents a bridge between 2 different disciplines: micromechanical technology and fluid mechanics. Its concept is based on the heat transfer generated by a hot film with a general top-area of 1.12 × 0.1 mm and a thickness of 110 nm. The film, in platinum, is maintained at a constant temperature, of 65°C, by a feed-back electronic. Key process steps in fabrication of the new device are lithography, bulk micromachining, thin film deposition, surface micromachining, lift-off and chemical mechanical polishing. The manufacturing of new miniature wall shear-stress sensor is based on a combination of these techniques. A specific development is performed for the achievement of an insulating surface to reduce the heat conduction between the hot film and the sensor body, on which the hot film is deposed. This surface is obtained by manufacturing silicon dioxide layers, of 4 µm, by DRIE technique, in order to create high-aspect-ratio silicon pillars, which are then oxidized and/or refilled with LPCVD oxide or nitride. One of the major criteria for the trenches filling was the surface planarity at the end of the refill. 2 parameters are optimized: the thickness and the silicon pillars arrangement. Thermal numerical computations were carried out using Ansys and they allowed the achievement of the optimum thermal isolation thickness between the heated structures and the surrounding structures. During the development of the new wall shear-stress probe, the main topics, achievements and contributions can be categorized into: design of a new wall shear-stress sensor, fabrication steps development, validation and optimization of the design, numerical simulations of the thermal behavior of the heated-films, manufacturing of the new device. The new sensor is characterized in terms of time response, electrical insulation between the surface of the probe, which comes in contact with the water, and the hot-film, and reliability. The sensor is robust, with a good sensitivity for water measurements. The main improvements, which make the current device distinct, are its design for a directional response for 3D turbulent boundary layer study and the insulating surface for substantially reduction of the heat losses by conduction between the film and the surrounding substrate