6 research outputs found

    Fabrication of suspended plate MEMS resonator by micro-masonry

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    L'impression par transfert, une technique utilisée pour transférer divers matériaux tels que des molécules d'ADN, de la résine photosensible ou des nanofils semi-conducteurs, s'est dernièrement révélée utile pour la réalisation de structures de silicium statiques sous le nom de micro-maçonnerie. L'étude présentée ici explore le potentiel de la technique de micro-maçonnerie pour la fabrication de résonateurs MEMS. Dans ce but, des microplaques de silicium ont été transférées sur des couches d'oxyde avec cavités intégrées à l'aide de timbres de polymère afin de créer des structures de type plaques suspendues. Le comportement dynamique de ces structures passives a été étudié sous pression atmosphérique et sous vide en utilisant une excitation externe par pastille piézo-électrique mais aussi le bruit thermomécanique. Par la suite, des résonateurs MEMS actifs, à actionnement électrostatique et détection capacitive intégrés, ont été fabriqués en utilisant des étapes supplémentaires de fabrication après impression. Ces dispositifs ont été caractérisés sous pression atmosphérique. Les facteurs de qualité intrinsèques des dispositifs fabriqués ont été évalués à 3000, ce qui est suffisant pour les applications de mesure à pression atmosphérique et en milieu liquide. Nous avons démontré que, puisque l'adhérence entre la plaque et l'oxyde est suffisamment forte pour empêcher une diaphonie mécanique entre les différentes cavités d'une même base, plusieurs résonateurs peuvent être facilement réalisés en une seule étape d'impression. Ce travail de thèse montre que la micro-maçonnerie est une technique simple et efficace pour la réalisation de résonateurs MEMS actifs de type plaque à cavité scellée.Lately, transfer printing, a technique that is used to transfer diverse materials such as DNA molecules, photoresist, or semiconductor nanowires, has been proven useful for the fabrication of various static silicon structures under the name micro-masonry. The present study explores the suitability of the micro-masonry technique to fabricate MEMS resonators. To this aim, silicon microplates were transfer-printed by microtip polymer stamps onto dedicated oxide bases with integrated cavities in order to create suspended plate structures. The dynamic behavior of fabricated passive structures was studied under atmospheric pressure and vacuum using both external piezo-actuation and thermomechanical noise. Then, active MEMS resonators with integrated electrostatic actuation and capacitive sensing were fabricated using additional post-processing steps. These devices were fully characterized under atmospheric pressure. The intrinsic Q factor of fabricated devices is in the range of 3000, which is sufficient for practical sensing applications in atmospheric pressure and liquid. We have demonstrated that since the bonding between the plate and the device is rigid enough to prevent mechanical crosstalk between different cavities in the same base, multiple resonators can be conveniently realized in a single printing step. This thesis work shows that micro-masonry is a powerful technique for the simple fabrication of sealed MEMS plate resonators

    Development of micro and nano resonators for acoustic sensing applications

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    Suspended vibrating structures play a significant role as basic building blocks for mechanical resonators and form the foundation of modern acoustic transducers. The practical use of mechanical resonators is not limited to acoustic technology but also includes a wide range of applications for sensing and actuation purposes. The ultimate goal of this project has been set to realise highly tunable and sensitive resonators that have operating frequencies covering the audible range (20 Hz – 20 kHz). In this thesis, two distinct types of mechanical resonators have been developed, dedicated mainly to hearing assistive devices and acoustic microphones. The overall performance of mechanical resonators is governed by their structural elements design, material properties, and dimensions. Inspired by their unique mechanical properties, a refractory metal of tantalum and a two-dimensional (2D) material of graphene have been utilised as vibrating structural elements for the developed resonators. In the first parts of this project, mechanical resonators of tantalum tunable to audio frequencies have been developed. First, a comprehensive investigation of the influence of fabrication process parameters on the residual stress of tantalum thin-films has been implemented. Based on the residual stress characterisation, an array of suspended microbeams of tantalum has been created and their mechanical static deflection has been investigated. Accordingly, the design and fabrication process of the resonators have been optimised, and hence straight and undeformed free-standing microbeams with lengths of 1 – 3.4 mm have been created and actuated electrostatically. The resonators have achieved a low resonant frequency (1.4 kHz) tuned over the audio range. Unlike the conventional microphones that have their vibrating membranes made of stressed and stiff materials, the graphene-based resonators developed here from ultra-large and thin bilayer membranes have the advantages of possessing enhanced durability and high frequency tuning sensitivity. A simple and reproducible fabrication process has been demonstrated to create millimetric membranes composed of a multilayer graphene and a thin polymeric film. The novelty of the developed resonators lies in the exceptional area to thickness aspect ratios of ~ 10,000, and the implementation of electrothermal actuation to drive the membranes into resonance and tune their resonant frequencies

    Theoretical Approaches in Non-Linear Dynamical Systems

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    From Preface: The 15th International Conference „Dynamical Systems - Theory and Applications” (DSTA 2019, 2-5 December, 2019, Lodz, Poland) gathered a numerous group of outstanding scientists and engineers who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without great effort of the staff of the Department of Automation, Biomechanics and Mechatronics of the Lodz University of Technology. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our event was attended by over 180 researchers from 35 countries all over the world, who decided to share the results of their research and experience in different fields related to dynamical systems. This year, the DSTA Conference Proceedings were split into two volumes entitled „Theoretical Approaches in Non-Linear Dynamical Systems” and „Applicable Solutions in Non-Linear Dynamical Systems”. In addition, DSTA 2019 resulted in three volumes of Springer Proceedings in Mathematics and Statistics entitled „Control and Stability of Dynamical Systems”, „Mathematical and Numerical Approaches in Dynamical Systems” and „Dynamical Systems in Mechatronics and Life Sciences”. Also, many outstanding papers will be recommended to special issues of renowned scientific journals.Cover design: Kaźmierczak, MarekTechnical editor: Kaźmierczak, Mare

    Steady-State, Nonlinear Analysis of Large Arrays of Electrically Actuated Micromembranes Vibrating in a Fluid

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    This paper describes a robust and efficient method to obtain the steady-state, nonlinear behaviour of large arrays of electrically actuated micromembranes vibrating in a fluid. The nonlinear electromechanical behavior and the multiple vibration harmonics it creates are fully taken into account thanks to a multiharmonic finite element formulation, generated automatically using symbolic calculation. A domain decomposition method allows to consider large arrays of micromembranes by efficiently distributing the computational cost on parallel computers. Two- and three- dimensional examples highlight the main properties of the proposed method

    Micro and nanoactuators based on bistable molecular materials

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    Les systèmes microélectromécaniques (MEMS) sont des dispositifs de taille micrométrique capables de transformer un signal mécanique en un signal électrique et vice-versa. Ils sont aujourd'hui largement répandus dans notre vie quotidienne pour la détection, la transformation de l'énergie et l'actionnement de dispositifs grâce à leur faible dissipation énergétique, leur réponse ultra-rapide et leur grande sensibilité. Même si depuis plusieurs décennies, les progrès technologiques ont entraîné la miniaturisation des ces dispositifs, il reste nombreux challenges à surmonter dont l'un des plus importantes est l'intégration à l'échelle nanométrique d'actionneurs à base des matériaux dit " intelligents " (à ces dimensions, les matériaux habituellement utilisés perdent leurs propriétés d'actionnement). Dans ce contexte, ce travail de thèse avait pour objectif d'explorer l'utilisation des matériaux moléculaires à transition de spin pour le développement d'actionneurs électromécaniques. Dans ce but, nous avons conçu des microleviers en silicium que nous avons recouvert par différentes molécules à transition de spin soit par sublimation, soit par " spray-coating ". Les MEMS ont été caractérisés à température et pression variables en modes dynamique et statique à l'aide d'un unique dispositif expérimental. Les résultats obtenus démontrent que les molécules à transition de spin peuvent être intégrées, à l'aide de différents procédés de fabrication, dans des dispositifs MEMS et qu'il est possible de réaliser l'actionnement à l'aide d'une source d'énergie thermique (chauffage et refroidissement) et/ou lumineuse. Simultanément, cette étude a également permis d'évaluer les propriétés mécaniques des matériaux à transition de spin (module de Young, coefficient de Poisson) qui restent mal connues.Microelectromechanical systems (MEMS) are micrometric devices able to transform a mechanical signal into an electrical one and vice-versa. In the past years they have been successfully employed in different fields of our everyday life for sensing, transducing different forms of energy and for actuating purposes thanks to their low energy dissipation, fast response and high sensibility. Even if recent technological progress has allowed a considerable miniaturization of these devices, several challenges remain. In particular the integration of smart actuating materials at the nanometric scale remains arduous because in most cases they lose their actuating properties at reduced sizes. In this context, this thesis work aimed for exploring the possibility of using molecular spin crossover materials for the development of electromechanical actuators. To this aim we have conceived silicon microcantilevers, which have been coated by various spin crossover molecules using either thermal evaporation or spray-coating methods. The MEMS have been characterized at variable temperature and pressure both in dynamical and static modes using a single experimental setup. The results prove that spin crossover molecules can be successfully integrated into silicon MEMS devices using different fabrication processes and their actuation can be achieved using either a thermal energy source or light irradiation. In parallel, this work has allowed us to extract relevant mechanical properties of spin crossover materials (Young's modulus, Poisson's ratio), which have been largely unknown previously
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