Academic literature on the topic 'MEMS Pressure Sensors'

Dans certaines recherches précédentes, la fabrication des capteurs de pression se basait sur les puces MEMS à base de SiC (Silicon Carbide). Cependant, des chercheurs de l'Université Concordia ont démontré récemment que SiCN (Silicon Carbide Nitride) avait un avantage plus important par rapport au Si (Silicon) ou SiC à haute température. Il serait donc un matériel potentiel dans un environnement hostile. Dans ce mémoire, un bref historique sur les capteurs MEMS à haute température sera introduit. Certaines questions dont le choix du matériel, la fabrication, l'empaquetage, et l'application des capteurs de température MEMS seront discutées. Une approche pour le conditionnement des capteurs de pression à haute température sera présentée et quelques prototypes seront créés avec succès. En outre, certaines simulations pour ces prototypes seront étudiées et les résultats des simulations seront examinés.

Depuis 1954, où l’effet piézorésistif a été découvert dans Silicium, la démarche pour mesurer la pression a changé et de nouveaux dispositifs avec des performances remarquables sont apparus sur le marché. Grâce au développement des microtechnologies, une nouvelle famille de capteurs de pression piézorésistifs miniatures s’est ainsi progressivement imposée pour de nombreuses applications. Même si le principe de fonctionnement des capteurs de pression piézorésistif en silicium reste le même depuis de nombreuses années, l’optimisation des capteurs pour une application donnée reste toujours une étape couteuse. C’est pourquoi de nombreux travaux ont été effectués pour développer des outils de conception les plus performants possibles afin de limiter les phases de validation expérimentales. Il existe ainsi sur le marché des logiciels de simulation 3D multiphysiques qui permettent de prendre en compte aussi bien les phénomènes thermomécaniques qu’électriques qui sont nécessaires pour ce type de capteurs. Malgré les progrès constants dans la puissance de calcul des ordinateurs, l’optimisation de ces capteurs par des méthodes de simulation élément fini peut s’avérer couteuse en temps si on veut prendre en compte l’ensemble des caractéristiques du capteur. C’est notamment le cas pour les jauges de contraintes en silicium dont le profil de dopage n’est pas constant dans l’épaisseur car les caractéristiques électriques et piézoélectriques dépendent du niveau de dopage. Les travaux de cette thèse portent donc sur le développement d’un outil de simulation analytique qui permet d’une part une optimisation rapide du capteur par une technique multi-objectif semi-automatique et d’autre part une analyse statistique des performances pour estimer le rendement de fabrication potentiel. Le premier chapitre décrit le contexte de ces travaux de thèse. Le second chapitre présente le principe de fonctionnement du capteur ainsi que tous les modèles analytiques mis en oeuvre pour modéliser le capteur. Ces modèles analytiques sont validés par des simulations élément finis. Le troisième chapitre porte sur l’outil d’optimisation et d’analyse statistique développé dans un environnement MATLAB. Le quatrième chapitre décrit la fabrication et la caractérisation des cellules de tests dont le comportement est ensuite comparé aux modèles analytiques. Ces caractérisations ont permis de montrer notamment que les modèles utilisés généralement pour décrire la dérive thermique des piézorésistances présentaient des erreurs notables. Des structures de tests spécifiques ont ainsi été mise en oeuvre pour avoir des données plus fiables. Finalement la dernière partie du manuscrit donne les conclusions générales ainsi que les perspectives de ce travail<br>Since 1954, when the piezoresistive effect in semiconductors was discovered, the approach to the pressure measurement has changed dramatically and new devices with outstanding performances have appeared on the market. Along with the development of microtechnologies for integrated circuits, a new branch of MEMS called devices have stormed our world. One of the biggest branches of today’s microsystems are pressure transducers which use the synergy of the piezoresistivity phenomenon and microfabrication technologies. While the main idea of strain gauge-based pressure measurement has not changed over the last few decades, there has been always a need to develop the design methodology that allows the designer to deliver the optimized product in the shortest possible time at the lowest possible cost. Thus, a lot of work has been done in the field in order to create tools and develop the FTR (first time right) methodology. Obviously, the design of the device that best fulfills the project requirements needs an appropriate simulation that have to be performed at the highest possible details level. Such an approach requires the detailed model of the device and, in case of its high complexity, a lot of computing power. Although over the last decade the most popular approach is the FEM analysis, there are some bottlenecks in such an approach like the difficulty of the implanted layers modeling where the doping profile shape has to be taken into account especially in the coupled electromechanical analysis. In this thesis, we try to present the methodology of the pressure sensor design which uses the analytical model of such a sensor that takes into consideration the nonuniform doping profile of the strain gauge, deals with the basic membrane shapes as well as with thermal and noise issues. The model, despite its limitations in comparison to the FEM one, gives trustworthy results which may be used for the reliable pressure sensor design in an extremely short time. In order to be quantitative, the analysis showing the drawbacks and advantages of the presented method in comparison to the FEM analysis using specialized tools like ANSYS ® and SILVACO-ATHENA® packages is also presented. Then, the model is used in a multi-objective optimization procedure that semi-automatically generates the design of a sensor, taking into account project requirements and constraints. At the end, the statistical analysis that may be helpful to estimate the production yield is performed. All three steps are included in the dedicated design and optimization tool created in a MATLAB ® environment and successfully tested. In the last section, the experimental results of fabricated samples are compared to those obtained by the developed tool

Kraft pulp digesters have been used to convert wood chips into pulp for manufacturing a wide variety of paper products. Inside a kraft digester, chemical reactions remove lignin from their wood matrix in a caustic environment (pH~13.5, 170°C, 2MPa). Data on actual internal operating conditions in a kraft digester is needed to optimize kraft digester operation and obtain maximum production quality. Currently, this information is limited to selected static locations on the periphery of the digester. The objective of this thesis is to develop miniature temperature, pressure, and liquid conductivity sensors for use in autonomous flow-following SmartChips to measure kraft process variables within the digester during their passage through the process. Combined capacitive pressure and temperature sensors were fabricated by bonding silicon and Pyrex chips using a new polymeric gap-controlling layer and a high temperature adhesive. A simple chip bonding technique involving insertion of the adhesive into the gap between two chips was developed. A silicon dioxide layer and a thin layer of Parylene were deposited to passivate the pressure sensor diaphragm against the caustic environment in kraft digesters. The sensors were characterized at both high temperatures and pressures and no signs of corrosion could be identified on the sensors. Integrated piezoresistive pressure and temperature sensors consisting of a square silicon diaphragm and high resistance piezoresistors were developed. A new Parylene and silicone conformal coating process were developed to passivate the pressure sensors against the caustic environment. The sensors were characterized up to 2MPa and 180°C in an environmental chamber. The sensors’ resistances were measured before and after testing in a kraft pulping cycle and showed no change in their values. SEM pictures and topographical surface analyses were also performed before and after pulp liquor exposure and showed no observable changes. Combined liquid conductivity and temperature sensor packages consisting of a platinum resistance temperature detector (RTD) and a four-electrode conductivity sensor formed by stainless steel electrodes and installed on a polyetheretherketone (PEEK) enclosure were developed. The sensors were characterized up to 180°C at NaOH concentrations of 10-100g/l in the presence of wood chips and survived with no signs of corrosion.

Continued demands for better control of the operating conditions of structures and processes have led to the need for better means of measuring temperature (T), pressure (P), and relative humidity (RH). One way to satisfy this need is to use MEMS technology to develop a sensor that will contain, in a single package, capabilities to simultaneously measure T, P, and RH of its environment. Because of the advantages of MEMS technology, which include small size, low power, very high precision, and low cost, it was selected for use in this thesis. Although MEMS sensors that individually measure T, P, and RH exist, there are no sensors that combine all three measurements in a single package. In this thesis, a piezoresistive pressure sensor and capacitive humidity sensor were developed to operate in the range, of 0 to 2 atm and 0% to 100%, respectively. Finally, a polysilicon resistor temperature sensor, which can work in the range of -50ºC to 150ºC, was analyzed. Multimeasurement capability will make this sensor particularly applicable for point-wise mapping of environmental conditions for advanced process control. In this thesis, the development of sensors for such an integrated device is outlined. Selected results, based on the use of analytical, computational, and experimental solutions (ACES) methodology, particularly suited for the development of MEMS sensors, are presented for the pressure, relative humidity, and temperature sensors.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008.<br>Committee Chair: Dr. Mark G. Allen; Committee Co-Chair: Dr. Oliver Brand; Committee Member: Dr. Andrew Peterson; Committee Member: Dr. Elliot Chaikof; Committee Member: Dr. Gregory Durgin; Committee Member: Dr. Robert Butera.

Modern electronic technologies allow for the design and production of Micro Electro-Mechanical Systems, also called MEMS. These microchips are widely used as sensors in many fields of application, also in embedded systems in heavy-duty and agricultural vehicles and in automotive applications. In addition to the classic uses of these sensors, new architectures and sensor topologies exploit electromechanical principles of great interest for the field of hydraulic applications. This paper presents some examples of the application of a new MEMS architecture based on self-oscillating microresonators, which offer interesting capabilities in the measurement of mechanical deformation of mechanical components. MEMS are applied as non-invasive pressure and oil flow sensors, and represent an interesting option for creating smart components. All the applications described are intended to show the sensor potential and have a qualitative and exemplary character, but they can provide a basis for in-depth studies on the potential and applicability of these sensors.