This thesis presents research towards enabling micromachined millimeter and submillimeter wave focal plane arrays (FPAs). The FPAs operate under the following principle: a switch network consisting of microelectromechanical (MEMS) switches, integrated with micromachined waveguides, is used to feed an array of antenna elements, located in the focal plane of a high-gain quasi-optical system. Hence, it is possible to switch between a set of narrow beams in different directions. Such beam steering systems are needed for future millimeter and submillimeter wave imaging and communication systems. The contributions to future MEMS-switchable FPAs presented here are organized in three papers, as described below. Paper I presents a criterion on the spacing between adjacent FPA elements which results in -3 dB overlap between the switched beams, for the special case when an extended hemispherical dielectric lens is used as the optical system. A key step towards this criterion is a closed-form relation between the scan angle and the FPA element's position, which results in an expression for the effective focal length of extended hemispherical lenses. A comparison with full-wave simulations demonstrates an excellent agreement with the presented theoretical results. Finally, it is shown that the maximum feasible FPA spacing when using an extended hemispherical lens is about 0.7 wavelengths. Paper II presents a numerical study of silicon-micromachined planar extended hemispherical lenses, with up to three matching regions used to reduce internal reflections. The effective permittivity of the matching regions is tailor-made by etching periodic holes in the silicon wafer. The optimal thickness and permittivity of the matching regions were determined using TRF optimization, in order to yield the maximum wide-band aperture efficiency and small side-lobes. We introduce a new matching region geometry, referred to as shifted-type matching regions, and it is demonstrated that using three shifted-type matching regions results in twice as large aperture efficiency as compared to using three conventional concentric-type matching regions. Paper III presents a submillimeter-wave single-pole single-throw (SPST) 500-750 GHz MEMS waveguide switch, based on a MEMS-reconfigurable surface inserted between two waveguide flanges. A detailed design parameter study is carried out to select the best combination of the number of horizontal bars and vertical columns of the MEMS-reconfigurable surface, for achieving a low insertion loss in the transmissive state and a high isolation in the blocking state. A method is presented to model the non-ideal electrical contacts between the vertical cantilevers of the MEMS surface, with an excellent agreement between the simulated and measured isolation. It is shown that the isolation can be improved by replacing an ohmic contact by a new, capacitive contact. The measured isolation of the switch prototype is better than 19 dB and the measured insertion loss is between 2.5 and 3 dB. / Denna avhandling presenterar forskning som syftar till att möjliggöra fokalplans-gruppantenner (FPAs) för våglängder i millimeter och submillimeterområdet. Principen för en sådan FPAs funktion är följande: ett nätverk bestående av mikroelektromekaniska (MEMS) switchar, används för att välja mellan de olika antenn-elementen i en gruppantenn, som placerats i fokalplanet av ett optiskt system. Därmed blir det möjligt att välja från en uppsättning av smala lober i olika riktningar. Sådana lob-styrningssystem behövs för framtida radar- och kommunikationssystem i millimeter och submillimeterområdet. Resultaten är uppdelade i tre vetenskapliga artiklar, som beskrivs nedan. I den första artikeln (Paper I) presenteras ett villkor för avståndet mellan närliggande FPA-element som resulterar i -3 dB överlappning mellan de switchade loberna, för specialfallet då en förlängd hemisfärisk lins används som optiskt system. Det viktigaste steget mot att hitta detta villkor är att bestämma en analytisk relation mellan avsökningsvinkeln och FPA-elementens position. Detta resulterar i ett uttryck för den effektiva fokallängden för denna typ av lins. En utmärkt överensstämelse har funnits mellan dessa relationer och simuleringar. Slutligen visas det att de största möjliga FPA-avstånden för en förlängd hemisfärisk lins är ungefär 0.7 våglängder, vilket uppnås för linser med låg permittivitet. I den andra artikeln (Paper II) presenteras en numerisk studie av plana förlängda hemisfäriska linser, som kan produceras från en kiselskiva. Linserna har upp till tre matchningsregioner, som används för att reducera interna reflektioner. Den effektiva permittiviteten av de matchande regionerna skräddarsys genom etsning av periodiska hål i kiselskivan. Den optimala tjockleken och permittiviteten av de matchande regionerna har bestämts med hjälp av TRF-optimering, för att ge maximal bredbandig direktivitet och minimala sidlober. En ny geometri introduceras för matchningsregionerna, som vi kallar matchningsregioner av skiftad typ. Vi visar att användning av tre matchningsregioner av skiftad typ resulterar i en dubbelt så hög apertur-effektivitet, jämfört med att använda tre konventionella matchningsregioner av koncentrisk typ. I den tredje artikeln (Paper III) presenteras en MEMS-switch för rektangulära vågledare, för frekvensområdet 500-750 GHz. Baserat på en designparameterstudie har den bästa kombinationen av antalet horisontella rader och vertikala kolumner hos den MEMS-konfigurerbara ytan valts ut, för att uppnå låga förluster i det öppna tillståndet och hög isolation i det blockerande tillståndet. I artikeln presenteras en metod för att modellera icke-perfekta elektriska kontakter mellan de fixerade och de rörliga delarna i MEMS-ytan. Denna metod uppvisar en utmärkt överensstämmelse mellan den simulerade och den uppmätta isolationen. Vi visara att isolationen kan förbättras med hjälp av en ny typ av kapacitiv kontakt. Den uppmätta isolationen hos den presenterade switch-prototypen är högre än 19 dB, och den uppmätta förlusten är mellan 2.5 och 3 dB. / <p>QC 20161206</p>

The most commonly known macro scale probing devices are simply comprised of metallic leads used for measuring electrical signals. On the other hand, micromachined probing devices are realized using microfabrication techniques and are capable of providing very fine, micro/nano scale interaction with matter; along with a broad range of applications made possible by incorporating MEMS sensing and actuation techniques. Micromachined probes consist of a well-defined tip structure that determines the interaction space, and a transduction mechanism that could be used for sensing a change, imparting external stimuli or manipulating matter. Several micromachined probes intended for biological and nanotechnology applications were fabricated, characterized and tested. Probes were developed under two major categories. The first category consists of Micro Electromagnetic Probes for biological applications such as single cell, particle, droplet manipulation and neuron stimulation applications; whereas the second category targets novel Scanning Probe topologies suitable for direct nanopatterning, variable resolution scanning probe/dip-pen nanolithography, and biomechanics applications. The functionality and versatility of micromachined probes for a broad range of micro and nanotechnology applications is successfully demonstrated throughout the five different probes/applications that were studied. It is believed that, the unique advantages of precise positioning capability, confinement of interaction as determined by the probe tip geometry, and special sensor/actuator mechanisms incorporated through MEMS technologies will render micromachined probes as indispensable tools for microsystems and nanotechnology studies.

Les transducteurs ultrasonores capacitifs micro-usinés (cMUT : capacitive Micromachined Ultrasound Transducers) apparaissent, au vu de leur maturité croissante, comme une alternative de plus en plus viable à la technologie piézoélectrique. Caractérisés par une large bande passante et une large directivité, ces transducteurs sont des solutions intéressantes pour le développement de sondes ultrasonores « exotiques » dont les spécifications sont difficilement atteignables en technologie piézoélectrique. C'est dans ce contexte et fort de l'expérience acquise par notre laboratoire sur cette technologie pendant plus d'une dizaine d'années, que s'est inscrit ce travail de thèse. L'originalité du travail rapporté ici est d'aller de l'analyse du comportement général des barrettes cMUT jusqu'à un exemple précis de conception de sonde cMUT pour l'évaluation du tissu osseux. Des outils de modélisation précis et rapides, basés sur l'introduction de conditions de périodicité, ont été développés. Plusieurs modèles ont ainsi été mis en place afin d'adapter la stratégie de modélisation à la topologie du dispositif cMUT à modéliser : cellule isolée, colonne de cellules, matrice de cellules et élément de barrette. Ces modèles ont permis d'étudier le comportement des éléments de barrette cMUT et d'améliorer notre connaissance sur les mécanismes physiques mis en jeu. De cette façon, l'origine des effets de baffle, problème récurrent du comportement des barrettes cMUT, a clairement été interprété par l'intermédiaire d'une analyse modale. Des solutions ont ainsi été identifiées et proposées afin d'optimiser le comportement des barrettes cMUT, de façon à réduire la présence des effets de baffle et à augmenter leur bande passante. Le développement d'une barrette cMUT dédiée à l'évaluation du tissu osseux est présenté dans sa totalité, afin d'illustrer les différents aspects liés à la conception d'une sonde de cette technologie. Un travail original de caractérisation a été réalisé sur cette barrette, afin d'estimer l'homogénéité inter-cellules à l'échelle de l'élément et l'homogénéité inter-éléments à l'échelle de la barrette. Enfin, une confrontation a été réalisée avec une sonde PZT de même topologie sur plusieurs fantômes osseux. Il a ainsi été démontré que la sonde cMUT permettait la détection d'un plus grand nombre de modes guidés, et par conséquent, une meilleure évaluation du tissu osseux. / Following recent advances, the capacitive Micromachined Ultrasound Transducers (cMUT) technology seems to be a good alternative to the piezoelectric technology. For specific applications, the requirements and specifications of the probe are sometimes difficult to obtain with the traditional PZT technology. The cMUT technology, with both large bandwidth and angular directivity, can be an interesting way to overcome these limitations. This PhD has been carried out in this context, in a laboratory which has nearly 10 years of experience in the field of cMUT technology. The originality of the work sustained in this PhD is that it covers the cMUT technology, from general aspects dealing of modeling and characterization up to a complete example of cMUT-based probe applied to the assessment of cortical bone. Fast and accurate modeling tools, based on periodicity conditions, have been developed. Several models have been proposed to match the modeling strategy to the topology of the cMUT array : isolated cell, columns of cells, 2-D matrix of cells and array element. These models have been used to analyze the cMUT array behavior and to understand how mutual couplings between cMUTs impact the response of one element. Origins of the baffle effect, well-known as a recurrent problem in cMUT probe, have been explained using an original method based on the normal mode decomposition of the radiated pressure field. Thus, solutions have been identified and tested to optimize the cMUT frequency response, i.e. to increase the bandwidth, and to suppress parasitic disturbances linked to baffle effect in the electroacoustic response. The development of a dedicated cMUT array for the assessment of bone tissue is accurately detailed in the manuscript, including description of the design rules, fabrication steps and packaging procedure. An original characterization work has been carried out in order to check the device homogeneity, first from cell to cell and then from element to element. Finally, a comparison with a PZT probe with the same topology has been performed on bone mimicking phantom. Nice results has been obtained, showing that cMUT probe allows detecting higher number of guided modes in the cortical shell, and consequently, improving the cortical bone assessment.