"Microelectromechanical systems (MEMS) technology has been evolving for about two decades and, now it is integrated in many designs, including radio frequency (RF) switches characterized by µm dimensions. Today, designers are attempting o develop the ideal RF MEMS switch, yet electro-thermo-mechanical (ETM) effects still limit the design possibilities and adversely affect reliability of these microswitches. The ETM effects are a result of Joule heat generated at the microswitch contact areas. This heat is due to the current passing through the microswitch, characteristics of the contact interfaces, and other parameters characterizing a particular design. It significantly raises temperature of the microswitch, thus affecting the mechanical and electrical properties of the contacts, which may lead to welding, causing a major reliability issue. Advanced research was performed, in this thesis, to minimize the Joule heat effects on the contact areas, thus improving performance of the microswitch. Thermal analyses done computationally on a cantilever-type RF MEMS switch indicate heat-effected zones and the influences that various design parameters have on these zones. Uncertainty analyses were also performed to ensure accuracy of the computational results, which indicate contact temperatures on the order of 700˚C, for the cases considered in this thesis. Although these temperatures are well below the melting temperatures of the materials used, new designs of the microswitches will have to be developed, in order to lower their maximum operating temperatures and reduce temporal effects they cause, to increase reliability of the RF MEMS switches."

Compte tenu de la multiplication des standards dans le domaine des télécommunications,l’accordabilité au sein des systèmes est devenue une priorité en termes d’intégration et de coût.Un seul circuit accordable doit ainsi permettre d’adresser plusieurs normes. Dans la gamme deshyperfréquences, en technologie planaire, la fonction accordable (filtre ou antenne) estactuellement un dispositif passif distribué sur lequel sont reportés un ou plusieurs élémentsd’accords. Il est ainsi possible de faire varier au moins une des caractéristiques du dispositif(fréquence centrale et/ou bande passante pour les filtres et fréquence de résonance, diagrammede rayonnement ou mode de polarisation pour les antennes). Le circuit passif étant distribué, pourassurer la propagation de l’onde, un matériau diélectrique faible pertes est généralement utilisé.Cependant, l’ajout d’éléments d’accord engendre des pertes et des perturbations liées au report ducomposant (éléments parasites au niveau de l’interconnexion et des discontinuités composantd’accord-dispositif passif, et de la mise en boitier du composant reporté). Enfin, cette manière deréaliser des fonctions accordables rend peu flexible la conception (dimensions et localisation ducomposant d’accord) et la fabrication (perçage et métallisation pour les vias).Dans ce contexte, nous proposons de co-concevoir des fonctions hyperfréquences accordablessur un substrat semi-conducteur sur lequel il est à la fois possible de réaliser le composantd’accord et le dispositif passif distribué. Cette co-conception du circuit passif et de son élémentd’accord permet d’éliminer toutes les contraintes liées au report de composant, au perçage de viamétallique et apporte une grande flexibilité au niveau du dimensionnement de la zone dopée. Eneffet, elles peuvent être soit localisées soit distribuées. Toutefois, ce concept nécessite que lesupport semi-conducteur soit à la fois compatible à la propagation de l’onde et à la réalisation del’élément d’accord. Ces travaux de thèse ont permis de lever ce verrou en proposant descompromis permettant la réalisation de composants accordables validés par des démonstrateurssur technologie silicium.Au cours de ces travaux, une ligne de transmission micro-ruban et un composant d’accord de typeswitch ont été co-conçus. De très bonnes performances, validées par la mesure, ont été obtenues.De plus, une démarche de co-simulation a été proposée pour prendre en compte les effets semiconducteursdans la simulation électromagnétique.Le concept ayant été validé, il a été ensuite appliqué à des dispositifs accordables relativementsimples afin de montrer le potentiel de cette démarche (en termes de performances et de flexibilitéde conception), tels que des filtres accordables, des guides d’ondes de type SIW (SubstrateIntegrated Waveguide) reconfigurables ou encore des antennes accordables en fréquence. Cestravaux font également apparaître de nombreuses perspectives pour la réalisation de nouvellestopologies de filtres accordables (filtres SIW, interdigités…), d’antennes accordables (enfréquence, en diagramme de rayonnement…) ou de déphaseurs. Enfin, un potentiel a été identifiépour de nouvelles topologies de fonctions accordables en continu à base de jonction de typediodes varactors (composants à capacités variables). / Given the proliferation of standards in telecommunication systems, tunability is becoming a priorityboth in terms of integration and cost. A single tunable circuit needs to be able to work according toseveral different standards. Nowadays, a tunable function (filter or antenna) in planar technology isa passive distributed device to which some active tuning elements are soldered. At least onecharacteristic of the device can therefore be varied (the central frequency and/or the bandwidth inthe case of a filter; or the resonant frequency, radiating pattern or polarization mode in the case ofan antenna). Because passive devices are distributed in order to propagate the electromagneticwave, they are often designed on a dielectric substrate to minimize losses. However, the additionof tuning elements causes some additional losses and disturbances (some parasitic effects canarise due to the packaging or the interconnection and discontinuities between active and passiveparts). Finally, these tunable functions reduce the flexibility of the design (due to the size andlocalization of the active tuning elements) and manufacturing (due to drilling and via metallization).In this context, we propose to co-design tunable microwave functions on a semiconductorsubstrate on which it is possible to build both the tunable element and the passive distributedcomponent. This co-design between the passive and active parts removes the constraints relatedto the tuning elements and drilling of via holes. The concept offers a greater flexibility with regard tothe size of doped areas, allowing them to be either localized or distributed. However, this approachrequires the substrate to be compatible with the propagation of the electromagnetic field and withthe design of the tunable element. The work of this thesis makes it possible to overcome suchobstacles by proposing some tradeoffs allowing the design and the manufacture of tunablemicrowave components in silicon technology, which have been validated by demonstrator circuits.During this work, a microstrip transmission line and a switch were co-designed. Goodperformances were obtained both in simulations and measurements. Moreover, a co-simulationapproach is proposed to take into account the semiconductor effects in electromagneticsimulations.Once validated, this concept was applied to other relatively simple tunable devices to show thepotential of this approach (in terms of performances and design flexibility). Applications includedtunable filters, reconfigurable waveguides (such as SIW: Substrate Integrated Waveguides) andfrequency-tunable antennas. This study showed promising results for the design of new tunablefilter topologies (SIW filters, coupled-line filters), tunable antennas (in resonant frequency orradiation pattern) and phase shifters. Finally, the approach shows potential for continuous tunablefunctions based on varactor diodes (with capacitance variation).

The first objective of this dissertation is to present hybrid numerical-analytical approaches and reduced-order models to simulate microelectromechanical systems (MEMS) in multi-physics fields. These include electric actuation (AC and DC), squeeze-film damping, thermoelastic damping, and structural forces. The second objective is to investigate MEMS phenomena, such as squeeze-film damping and dynamic pull-in, and use the latter to design a novel RF-MEMS switch. In the first part of the dissertation, we introduce a new approach to the modeling and simulation of flexible microstructures under the coupled effects of squeeze-film damping, electrostatic actuation, and mechanical forces. The new approach utilizes the compressible Reynolds equation coupled with the equation governing the plate deflection. The model accounts for the slip condition of the flow at very low pressures. Perturbation methods are used to derive an analytical expression for the pressure distribution in terms of the structural mode shapes. This expression is substituted into the plate equation, which is solved in turn using a finite-element method for the structural mode shapes, the pressure distributions, the natural frequencies, and the quality factors. We apply the new approach to a variety of rectangular and circular plates and present the final expressions for the pressure distributions and quality factors. We extend the approach to microplates actuated by large electrostatic forces. For this case, we present a low-order model, which reduces significantly the cost of simulation. The model utilizes the nonlinear Euler-Bernoulli beam equation, the von K´arm´an plate equations, and the compressible Reynolds equation. The second topic of the dissertation is thermoelastic damping. We present a model and analytical expressions for thermoelastic damping in microplates. We solve the heat equation for the thermal flux across the microplate, in terms of the structural mode shapes, and hence decouple the thermal equation from the plate equation. We utilize a perturbation method to derive an analytical expression for the quality factor of a microplate with general boundary conditions under electrostatic loading and residual stresses in terms of its structural mode shapes. We present results for microplates with various boundary conditions. In the final part of the dissertation, we present a dynamic analysis and simulation of MEMS resonators and novel RF MEMS switches employing resonant microbeams. We first study microbeams excited near their fundamental natural frequencies (primary-resonance excitation). We investigate the dynamic pull-in instability and formulate safety criteria for the design of MEMS sensors and RF filters. We also utilize this phenomenon to design a low-voltage RF MEMS switch actuated with a combined DC and AC loading. Then, we simulate the dynamics of microbeams excited near half their fundamental natural frequencies (superharmonic excitation) and twice their fundamental natural frequencies (subharmonic excitation). For the superharmonic case, we present results showing the effect of varying the DC bias, the damping, and the AC excitation amplitude on the frequency-response curves. For the subharmonic case, we show that if the magnitude of the AC forcing exceeds the threshold activating the subharmonic resonance, all frequency-response curves will reach pull-in. / Ph. D.

Ces travaux de recherche portent sur la conception et la réalisation de commutateurs RF basées sur l’intégration de matériaux innovants fonctionnels tels que le dioxyde de vanadium (VO2) et les alliages de chalcogénures de types Ge2Sb2Te5 (GST) et GeTe. Le principe de fonctionnement de ces composants repose sur le changement de résistivité que présentent ces matériaux. Le VO2 possède une transition Isolant-Métal (MIT) autour de 68°C à travers laquelle le matériau passe d’un état isolant (forte résistivité) à un état métallique (faible résistivité). La transition MIT présente l’intérêt de pouvoir être initiée sous l’effet de plusieurs types de stimuli externes (thermique, électrique et optique) avec de faibles temps de commutation. Les alliages de types GST et GeTe ont la particularité de commuter réversiblement entre un état amorphe à forte résistivité à un état cristallin à faible résistivité suite à un traitement thermique spécifique. Les commutateurs à base de GST ou de GeTe présentent l'avantage de pouvoir opérer en mode bistable car le changement de résistivité présenté par ces matériaux est de type non volatile. Les composants réalisés ont de bonnes performances électriques (isolation et pertes d’insertion) sur une large bande. Nos travaux de recherche visent à proposer une solution alternative aux solutions classiques (semi-conducteurs et MEMS-RF) pour réaliser des commutateurs RF qui peuvent être par la suite utilisés dans la conception des dispositifs reconfigurables (filtres, Antennes). / This research work focuses on the design and realization of RF switches based on the integration of new materials such as vanadium dioxide (VO2), Ge2Sb2Te5 (GST) and GeTe chalcogenides alloys. The operating principle of these devices is based on the resistivity change presented by these materials. VO2 exhibits a Metal-Insulator transition (MIT) around 68°C for which the material changes from an insulating state (high resistivity) to a metallic one (low resistivity). The MIT transition can be triggered in different ways (thermally, electrically and optically) with low switching time. GST and GeTe alloys have the particularity to be reversibly switched between a high resistive-amorphous state to low resistive-crystalline state, under a specific heat treatment. Thanks to the non-volatile resistivity change presented by these materials, GST/GeTe-based switches are able to operate in bistable mode. The fabricated devices exhibit good electrical performances (insertion loss and isolation) over a broadband. The aim of our work is to propose an alternative solution to conventional technologies (semiconductors and RF-MEMS), to design RF switches that can be used afterward in the design of reconfigurable devices (filters, antennas).

State-of-the-art SiGe BiCMOS technologies leverage the maturity of deep-submicron silicon CMOS processing with bandgap-engineered SiGe HBTs in a single platform that is suitable for a wide variety of high performance and highly-integrated applications (e.g., system-on-chip (SOC), system-in-package (SiP)). Due to their bandgap-engineered base, SiGe HBTs are also naturally suited for cryogenic electronics and have the potential to replace the costly de facto technologies of choice (e.g., Gallium-Arsenide (GaAs) and Indium-Phosphide (InP)) in many cryogenic applications such as radio astronomy. This work investigates the response of mixed-signal circuits (both RF and analog circuits) when operating in extreme environments, in particular, at cryogenic temperatures and in radiation-rich environments. The ultimate goal of this work is to attempt to fill the existing gap in knowledge on the cryogenic and radiation response (both single event transients (SETs) and total ionization dose (TID)) of specific RF and analog circuit blocks (i.e., RF switches and voltage references). The design approach for different RF switch topologies and voltage references circuits are presented. Standalone Field Effect Transistors (FET) and SiGe HBTs test structures were also characterized and the results are provided to aid in the analysis and understanding of the underlying mechanisms that impact the circuits' response. Radiation mitigation strategies to counterbalance the damaging effects are investigated. A comprehensive study on the impact of cryogenic temperatures on the RF linearity of SiGe HBTs fabricated in a new 4th-generation, 90 nm SiGe BiCMOS technology is also presented.