The focus of this work involves optical and RF (radio frequency) applications of novel microactuation and self-assembly techniques in MEMS (Microelectromechanical systems). The scaling of physical forces into the micro domain is favorably used to design several types of actuators that can provide large forces and large static displacements at low operation voltages. A self-assembly method based on thermally induced localized plastic deformation of microstructures has been developed to obtain truly three-dimensional structures from a planar fabrication process. RF applications include variable discrete components such as capacitors and inductors as well as tunable coupling circuits. Optical applications include scanning micromirrors with large scan angles (>90 degrees), low operation voltages (<10 Volts), and multiple degrees of freedom. One and two-dimensional periodic structures with variable periods and orientations (with respect to an incident wave) are investigated as well, and analyzed using optical phased array concepts. Throughout the research, permanent tuning via plastic deformation and power-off latching techniques are used in order to demonstrate that the optical and RF devices can exhibit zero quiescent power consumption once their geometry is set.

The focus of this work involves optical and RF (radio frequency) applications of novel microactuation and self-assembly techniques in MEMS (Microelectromechanical systems). The scaling of physical forces into the micro domain is favorably used to design several types of actuators that can provide large forces and large static displacements at low operation voltages. A self-assembly method based on thermally induced localized plastic deformation of microstructures has been developed to obtain truly three-dimensional structures from a planar fabrication process. RF applications include variable discrete components such as capacitors and inductors as well as tunable coupling circuits. Optical applications include scanning micromirrors with large scan angles (>90 degrees), low operation voltages (<10 Volts), and multiple degrees of freedom. One and two-dimensional periodic structures with variable periods and orientations (with respect to an incident wave) are investigated as well, and analyzed using optical phased array concepts. Throughout the research, permanent tuning via plastic deformation and power-off latching techniques are used in order to demonstrate that the optical and RF devices can exhibit zero quiescent power consumption once their geometry is set.

Ce travail de recherche a été mené afin d'introduire une nouvelle classe de résonateurs Fabry-Pérot (FP) : les cavités FP incurvées basées sur des miroirs de Bragg sans revêtement, de forme cylindrique sont obtenues par micro-usinage du silicium. Une autre spécificité est la longueur de la cavité relativement grande (L> 200 µm) combinée à un haut facteur de qualité Q (jusqu'à 10^4 ), pour répondre aux applications de type spectroscopie d'absorption améliorée par résonance optique, dans lesquelles le produit Q.L est une figure de mérite. Dans ce contexte, l'architecture de base a été modélisée analytiquement pour déterminer les modes transverses d'ordre élevé supportés par de telles cavités. Par conséquent, les conditions expérimentales qui conduisent à une excitation préférentielle (ou rejet) de ces modes ont été testées menant à la validation de notre modèle théorique et à une meilleure compréhension du comportement de la cavité. Une seconde architecture,basée sur la cavité FP incurvée avec une lentille cylindrique a été développée dans le but de fournir une architecture plus stable. Cette dernière a été également modélisée, fabriquée et caractérisée, menant à l'amélioration attendue en termes de performances. D'un autre côté, un point surlignant l'une des applications potentielles que nous avons identifiées pour les cavités incurvées est présentée en insérant la cavité dans un système électromécanique. Ceci consiste à exciter et mesurer les vibrations d'amplitude nanométrique par couplage opto-mécanique dans un résonateur mécanique MEMS intégrant une cavité optique FP. Enfin, comme complément à notre étude sur les résonateurs, nous avons commencé à explorer les applications des interféromètres optiques à base de miroirs de Bragg en silicium. À cette fin, un microsystème de mesure optique a été conçu, fabriqué et caractérisé, il consiste en une sonde optique pour la profilométrie de surface dans des milieux confinés, basé sur un interféromètre de Michelson monolithique en silicium / This research work has been conducted to introduce a novel class of Fabry-Perot (FP) resonators : curved FP cavity based on coating-free Bragg mirrors of cylindrical shape, obtained by silicon micromachining. Another specificity is the rather large cavity lengths (L>200 µm) combined with high quality factor Q (up to 104), for the purpose of applications requiring cavity enhanced absorption spectroscopy, in which the product Q.L is a figure of merit. In this contest, the basic architecture has been modeled analytically to know the high order transverse modes supported by such cavities. Hence, the experimental conditions which lead to preferential excitation (or rejection) of these modes have been tested experimentally leading to the validation of our theoretical model and to a better understanding of the cavity behaviour. A second architecture, based on the curved FP together with a fiber rod lens has been developed for the purpose of providing stable designs. It was also modeled, fabricated and characterized leading to the expected performance improvements. On another side, a highlight on one of the potential applications that we identified for the curved cavities is presented by inserting the cavity into an electro-mechanical system. It consists of exciting and measuring tiny vibration through opto-mechanical coupling in a MEMS mechanical resonator embedding an FP cavity.Finally, as a complement to our study on resonators, we started exploring applications of optical interferometers based on similar micromachined silicon Bragg mirrors. For this purpose, an optical measurement microsystem was designed, fabricated and characterized ; it consists of an optical probe for surface profilometry in confined environments, based on an all-silicon Michelson interferometer

This research work has been conducted to introduce a novel class of Fabry-Perot (FP) resonators : curved FP cavity based on coating-free Bragg mirrors of cylindrical shape, obtained by silicon micromachining. Another specificity is the rather large cavity lengths (L>200 µm) combined with high quality factor Q (up to 104), for the purpose of applications requiring cavity enhanced absorption spectroscopy, in which the product Q.L is a figure of merit. In this contest, the basic architecture has been modeled analytically to know the high order transverse modes supported by such cavities. Hence, the experimental conditions which lead to preferential excitation (or rejection) of these modes have been tested experimentally leading to the validation of our theoretical model and to a better understanding of the cavity behaviour. A second architecture, based on the curved FP together with a fiber rod lens has been developed for the purpose of providing stable designs. It was also modeled, fabricated and characterized leading to the expected performance improvements. On another side, a highlight on one of the potential applications that we identified for the curved cavities is presented by inserting the cavity into an electro-mechanical system. It consists of exciting and measuring tiny vibration through opto-mechanical coupling in a MEMS mechanical resonator embedding an FP cavity.Finally, as a complement to our study on resonators, we started exploring applications of optical interferometers based on similar micromachined silicon Bragg mirrors. For this purpose, an optical measurement microsystem was designed, fabricated and characterized ; it consists of an optical probe for surface profilometry in confined environments, based on an all-silicon Michelson interferometer

Ces travaux de thèse portent sur la conception, la réalisation et d'une nouvelle génération de MOEMS (Micro-Optical-Electrical-Mechanical System) pour le contrôle actif du faisceau laser émis par des matrices de VCSELs (Vertical-Cavity Surface-Emitting Lasers). Le microsystème à base de polymères que nous avons conçu est compatible avec une intégration monolithique en post-processing. Il est composé d'une membrane suspendue associée à une microlentille réfractive. Le plan de focalisation est contrôlé dynamiquement grâce au déplacement vertical de la membrane grâce à un actionnement électrothermique. La géométrie du MOEMS a été optimisée à l'aide notamment de simulations électro-thermo-mécaniques pour minimiser l'énergie de commande et fiabiliser les dispositifs. Nous avons ensuite développé l'ensemble des briques technologiques pour la fabrication collective de ce dispositif sur des matrices de VCSELs. En particulier, une technique originale de transfert thermique doux de films secs photosensibles épais a été mise au point au moyen d'un équipement de nano-impression, pour permettre un dépôt uniforme et précis sur des substrats fragiles ou de faible taille. En outre, nous avons développé un procédé simple et totalement planaire pour la fabrication du MOEMS et optimisé un procédé de dépôt par jets d'encre pour l'intégration finale des microlentilles, avec la possibilité de choisir la distance focale la plus adaptée à la fin du process. La caractérisation des microsystèmes que nous avons réalisés a conduit à l'obtention de déplacements mécaniques de 8µm pour seulement 12.5mW appliqués, ce qui constitue une validation de nos résultats de modélisation. Enfin, des premiers résultats de focalisation dynamique du faisceau VCSELs sont présentés. / This thesis deals with the study and the fabrication of a novel type of polymer MOEMS (Micro Optical Electrical Mechanical Systems) to achieve passive or active beam shaping of Vertical-Cavity Surface-Emitting Lasers (VCSELs). To improve the photonic integration of these compact laser sources in optical communication and detection systems (sensors, biomedical analysis), we designed a polymer-based optical microsystem that is suitable with a post-processing integration on VCSELs. Its operation principle is based on the out-of-plane displacement of a suspended SU-8 membrane including a polymer refractive microlens at its surface. Thanks to electro-thermal actuation, the vertical displacement of the membrane allows to dynamically modify the microlens-source distance and leads to a vertical shift of the laser beam waist position. MOEMS actuation power and reliability were optimized owing to a comprehensive tri-dimensional thermo-electro-mechanical model that takes into account SU-8 material properties and precise geometry of the device. Technological steps necessary for the collective fabrication of such MOEMS on VCSELs arrays were also developed. In particular, we report on a new photoresist film transfer method we developed to achieve a highly uniform fabrication of high aspect ratio MOEMS on small-sized or fragile samples such as GaAs-based VCSELs wafers. This method that we call "soft thermal printing" is based on the use of a thermal nano-imprint set-up. Moreover, a simple and planar process for MOEMS fabrication was successfully tested. A dedicated inkjet printing process for drop-on-demand deposition of the microlens on the membrane center was also developed. Finally, the fabricated MOEMS were characterized. A vertical displacement as high as 8µm was observed for only 12.5mW applied, in good agreement with our 3D modeling results and first results on 850nm VCSEL dynamic beam focusing were obtained, demonstrating the interest of our approach.