Development of MEMS Piezoelectric Vibration Energy Harvesters with Wafer-Level Integrated Tungsten Proof-Mass for Ultra Low Power Autonomous Wireless Sensors

La génération d’énergie localisée et à petite échelle, par transformation de l’énergie vibratoire disponible dans l’environnement, est une solution attrayante pour améliorer l’autonomie de certains noeuds de capteurs sans-fil pour l’Internet des objets (IoT). Grâce à des microdispositifs inertiels résonants piézoélectriques, il est possible de transformer l’énergie mécanique en électricité. Cette thèse présente une étude exhaustive de cette technologie et propose un procédé pour fabriquer des microgénérateurs MEMS offrant des performances surpassant l’état de l’art. On présente d’abord une revue complète des limites physiques et technologiques pour identifier le meilleur chemin d’amélioration. En évaluant les approches proposées dans la littérature (géométrie, architecture, matériaux, circuits, etc.), nous suggérons des métriques pour comparer l’état de l’art. Ces analyses démontrent que la limite fondamentale est l’énergie absorbée par le dispositif, car plusieurs des solutions existantes répondent déjà aux autres limites. Pour un générateur linéaire résonant, l’absorption d’énergie dépend donc des vibrations disponibles, mais aussi de la masse du dispositif et de son facteur de qualité. Pour orienter la conception de prototypes, nous avons réalisé une étude sur le potentiel des capteurs autonomes dans une automobile. Nous avons évalué une liste des capteurs présents sur un véhicule pour leur compatibilité avec cette technologie. Nos mesures de vibrations sur un véhicule en marche aux emplacements retenus révèlent que l’énergie disponible pour un dispositif linéaire résonant MEMS se situe entre 30 à 150 Hz. Celui-ci pourrait produire autour de 1 à 10 μW par gramme. Pour limiter la taille d’un générateur MEMS pouvant produire 10 μW, il faut une densité supérieure à celle du silicium, ce qui motive l’intégration du tungstène. L’effet du tungstène sur la sensibilité du dispositif est évident, mais nous démontrons également que l’usage de ce matériau permet de réduire l’impact de l’amortissement fluidique sur le facteur de qualité mécanique Qm. En fait, lorsque l’amortissement fluidique domine, ce changement peut améliorer Qm d’un ordre de grandeur, passant de 103 à 104 dans l’air ambiant. Par conséquent, le rendement du dispositif est amélioré sans utiliser un boîtier sous vide. Nous proposons ensuite un procédé de fabrication qui intègre au niveau de la tranche des masses de tungstène de 500 μm d’épais. Ce procédé utilise des approches de collage de tranches et de gravure humide du métal en deux étapes. Nous présentons chaque bloc de fabrication réalisé pour démontrer la faisabilité du procédé, lequel a permis de fabriquer plusieurs prototypes. Ces dispositifs ont été testés en laboratoire, certains démontrant des performances records en terme de densité de puissance normalisée. Notre meilleur design se démarque par une métrique de 2.5 mW-s-1/(mm3(m/s2)2), soit le meilleur résultat répertorié dans l’état de l’art. Avec un volume de 3.5 mm3, il opère à 552.7 Hz et produit 2.7 μW à 1.6 V RMS à partir d’une accélération de 1 m/s2. Ces résultats démontrent que l’intégration du tungstène dans les microgénérateurs MEMS est très avantageuse et permet de s’approcher davantage des requis des applications réelles.Small scale and localized power generation, using vibration energy harvesting, is considered as an attractive solution to enhance the autonomy of some wireless sensor nodes used in the Internet of Things (IoT). Conversion of the ambient mechanical energy into electricity is most often done through inertial resonant piezoelectric microdevices. This thesis presents an extensive study of this technology and proposes a process to fabricate MEMS microgenerators with record performances compared to the state of the art. We first present a complete review of the physical and technological limits of this technology to asses the best path of improvement. Reported approaches (geometries, architectures, materials, circuits) are evaluated and figures of merit are proposed to compare the state of the art. These analyses show that the fundamental limit is the absorbed energy, as most proposals to date partially address the other limits. The absorbed energy depends on the level of vibrations available, but also on the mass of the device and its quality factor for a linear resonant generator. To guide design of prototypes, we conducted a study on the potential of autonomous sensors in vehicles. A survey of sensors present on a car was realized to estimate their compatibility with energy harvesting technologies. Vibration measurements done on a running vehicle at relevant locations showed that the energy available for MEMS devices is mostly located in a frequency range of 30 to 150 Hz and could generate power in the range of 1-10 μW per gram from a linear resonator. To limit the size of a MEMS generator capable of producing 10 μW, a higher mass density compared to silicon is needed, which motivates the development of a process that incorporates tungsten. Although the effect of tungsten on the device sensitivity is well known, we also demonstrate that it reduces the impact of the fluidic damping on the mechanical quality factor Qm. If fluidic damping is dominant, switching to tungsten can improve Qm by an order of magnitude, going from 103 to 104 in ambient air. As a result, the device efficiency is improved despite the lack of a vacuum package. We then propose a fabrication process flow to integrate 500 μm thick tungsten masses at the wafer level. This process combines wafer bonding with a 2-step wet metal etching approach. We present each of the fabrication nodes realized to demonstrate the feasibility of the process, which led to the fabrication of several prototypes. These devices are tested in the lab, with some designs demonstrating record breaking performances in term of normalized power density. Our best design is noteworthy for its figure of merit that is around 2.5 mW-s-1/(mm3(m/s2)2), which is the best reported in the state of the art. With a volume of 3.5 mm3, it operates at 552.7 Hz and produces 2.7 μW at 1.6 V RMS from an acceleration of 1 m/s2. These results therefore show that tungsten integration in MEMS microgenerators is very advantageous, allowing to reduce the gap with needs of current applications

Controls on Mass and Thermal Loading to an Oil Sands End Pit Lake from Underlying Fluid Fine Tailings

End pit lakes (EPLs) are a relatively new strategy proposed for reclaiming oil sands surface mines. An EPL is formed within a depleted mine pit, with fluid fine tailings (FFT) stored below a water cover. Fluid fine tailings are a by-product of the oil sands bitumen extraction process with high water contents, low bearing capacities, and elevated concentrations of various constituents. This thesis considers mass and heat transfer between the FFT and overlying water cover at the first EPL, Base Mine Lake (BML). The study objectives were: (1) characterize the FFT thermal properties and the thermal regime in BML; (2) assess FFT settlement rates and characteristics; and (3) evaluate a range of potential mechanisms for mass and heat movement, including diffusion or conduction, and mixing of the FFT due to unstable density profiles or fluid movement within the water cover. These objectives were achieved through a combination of field investigations, laboratory testing, and numerical modelling, and the results were published in three manuscripts comprising the main body of the thesis. Overall, FFT is the largest (Cl) mass source to the BML water cover. The dominant transport mechanism was advective mass transport or convective heat transport due to tailings settlement; however, tailings disturbance near the FFT-water interface may also contribute to mass release. The predicted pore water fluxes based on the advective or convective regimes were similar to previously estimated FFT settlement rates and decreased throughout the studied period from approximately 1.46 m/a in 2013 to 2014, to 0.73 m/a in 2014 to 2015. Declining advection rates indicate that diffusive mass transport and conductive heat transfer will likely become more significant in the future. The results also confirmed that EPL design should consider the size of the water cover, volume and characteristics of the FFT, and operational controls, as these factors will likely influence EPL success as a sustainable reclamation landscape

Controls on Mass and Thermal Loading to an Oil Sands End Pit Lake from Underlying Fluid Fine Tailings

End pit lakes (EPLs) are a relatively new strategy proposed for reclaiming oil sands surface mines. An EPL is formed within a depleted mine pit, with fluid fine tailings (FFT) stored below a water cover. Fluid fine tailings are a by-product of the oil sands bitumen extraction process with high water contents, low bearing capacities, and elevated concentrations of various constituents. This thesis considers mass and heat transfer between the FFT and overlying water cover at the first EPL, Base Mine Lake (BML). The study objectives were: (1) characterize the FFT thermal properties and the thermal regime in BML; (2) assess FFT settlement rates and characteristics; and (3) evaluate a range of potential mechanisms for mass and heat movement, including diffusion or conduction, and mixing of the FFT due to unstable density profiles or fluid movement within the water cover. These objectives were achieved through a combination of field investigations, laboratory testing, and numerical modelling, and the results were published in three manuscripts comprising the main body of the thesis. Overall, FFT is the largest (Cl) mass source to the BML water cover. The dominant transport mechanism was advective mass transport or convective heat transport due to tailings settlement; however, tailings disturbance near the FFT-water interface may also contribute to mass release. The predicted pore water fluxes based on the advective or convective regimes were similar to previously estimated FFT settlement rates and decreased throughout the studied period from approximately 1.46 m/a in 2013 to 2014, to 0.73 m/a in 2014 to 2015. Declining advection rates indicate that diffusive mass transport and conductive heat transfer will likely become more significant in the future. The results also confirmed that EPL design should consider the size of the water cover, volume and characteristics of the FFT, and operational controls, as these factors will likely influence EPL success as a sustainable reclamation landscape

Musique et séduction

Il est ardu d’expliquer de manière précise l’émotion que peut procurer une œuvre musicale. Afin de comprendre les mécanismes de la séduction en musique, l’auteur identifie quelques stratégies et rouages utilisés par les compositeurs au fil des siècles et partage quelques-unes de ses expériences personnelles en tant que compositeur.It is difficult to precisely explain the emotion a musical work can procure. To understand the mechanisms of musical seduction, the author identifies some strategies and cogs used by composers for centuries and shares some of his personal experiences as a composer