Made available in DSpace on 2016-03-15T19:38:51Z (GMT). No. of bitstreams: 1 Rafael Euzebio Pereira de Oliveira.pdf: 2811606 bytes, checksum: 24b62fb14019ae86cc9e69acbf481604 (MD5) Previous issue date: 2014-08-18 / Nonlinear effects are essential for the construction of photonic devices such as modulators, optical switches and frequency converters. Aiming at the development of devices for optical frequency conversion and the generation of nonclassical states of light in photonic chips, this thesis presents the design and simulation of a frequency converter based on second harmonic generation controlled by static electric field in a silicon nitride ring resonator. The developed simulation appraises conversion efficiencies up to -8.25 dB with the advantage to provide an electrical interface to control the conversion. Optical fiber based devices are also within the scope of the thesis and a new technique is presented for manufacturing optical fibers with enhanced nonlinear response by the presence of metallic gold nanoparticles. The manufactured fibers are based on silica that is doped with aluminum and gold in the core, offering full compatibility and integration with conventional optical fibers. The nanoparticles were created by annealing in an oven or by heating with a CO2 laser beam, which offers unprecedented control over particle size and density in optical fibers. Compared to previously reported fibers with gold nanoparticles, higher concentration of nanoparticles were obtained which was estimated by the plasmonic absorption peak exceeding 800 dB/m and by a consequent increasing in the nonlinear refractive index of at least 50x under continuous wave excitation, achieving values of n2=(6,75±0,55)×10-15 m²/W. The development of these fibers and the design of the on chip frequency converter provide platforms for the development of efficient and integrated devices in fiber based optical systems and in photonic chips. / Efeitos não lineares são essenciais para construção de dispositivos fotônicos como moduladores, chaves ópticas e conversores de frequências. Esta tese apresenta o projeto e a simulação de um conversor de frequências baseado na geração de segundo harmônico controlado por campo elétrico estático em um ressonador em anel de nitreto de silício, visando o desenvolvimento de dispositivos para conversão de frequências ópticas e geração de estados não clássicos da luz em chips fotônicos. A simulação desenvolvida prevê eficiência de conversão de até -8,25 dB com o diferencial de oferecer uma interface elétrica no controle de conversão. Dispositivos baseados em fibras ópticas também são visados nesta tese e uma nova técnica para fabricação de fibras ópticas com resposta não linear aumentada pela presença de nanopartículas metálicas de ouro é apresentada. As fibras fabricadas são baseadas em sílica com dopagem de alumínio e ouro no núcleo, possuindo total compatibilidade de integração com fibras ópticas convencionais. As nanopartículas foram sintetizadas através de tratamentos térmicos em forno ou aquecimento com feixe laser de CO2, obtendo-se um controle sem precedentes das dimensões e densidade de nanopartículas em fibras ópticas. Comparadas às fibras previamente reportadas na literatura, foram obtidas maiores concentrações de nanopartículas estimadas por picos de absorções plasmônicas maiores que 800 dB/m e por um consequente aumento no índice de refração não linear de pelo menos 50x no regime de onda contínua, obtendo-se valores de n2=(6,75±0,55)×10-15 m²/W. O desenvolvimento dessas fibras e o projeto do ressonador em anel para conversão de frequências oferecem plataformas para o desenvolvimento de dispositivos eficientes e integrados para sistemas ópticos baseados em fibras ópticas e em chips fotônicos.

The increasing demand for high performance and miniature high frequency electronics has motivated the development of Micro-electro Mechanical Systems (MEMS) resonators, some of which have already become a commercial success for the making of filters, duplexers and oscillators used in radio frequency (RF) front-end systems for portable electronic devices. These MEMS components not only enable size, power and cost reduction with respect to their existing counterparts, but also open exciting opportunities for implementing new functionalities when used in large arrays. Almost all MEMS resonators require interfacing with one or more Complementary Metal Oxide Semiconductor (CMOS) integrated circuit components or modules in processing raw signals from individual MEMS devices. Hence, these devices should be integrated with CMOS circuits in an efficient and robust way in order to facilitate their deployment in large arrays with minimal parasitics, delay and power losses due to signal routing and CMOS-MEMS interconnects. Among the MEMS resonators developed to date, Aluminum Nitride (AlN) MEMS Contour-Mode Resonators (CMRs) offer high electro-mechanical coupling coefficient (𝑘𝑡2) and quality factor (Q), and a center frequency (f0) that can be set lithographically by varying the device in-plane dimensions. Also, AlN MEMS CMRs can be fabricated using state-of-the-art CMOS processes and micromachining techniques. These properties allow the synthesis of multi-frequency band-pass filters (BPFs) on a single chip with a low insertion loss and the capability of direct matching to 50 Ω systems. All these advantages, along with a sufficiently mature fabrication process, make AlN CMRs one of the ideal candidates for pursuing their integration with CMOS technology and implement high performance filters with programming capability. In this work we develop for the first time a three-dimensional (3D) heterogeneously integrated AlN MEMS-CMOS platform that enables the realization of such systems as self- healing filters for RF front-ends and programmable filter arrays for cognitive radios. We collaborated with the A*STAR, Institute of Microelectronics (IME), Singapore in the development of AlN MEMS platform on an 8" silicon (Si) wafer; on the other hand, CMOS chips were fabricated in 65 nm International Business Machines Corporation (IBM) and 28 nm Samsung processes. Solder bumps were placed on CMOS chips by Tag and Label Manufacturers Institute (TLMI) under the supervision of Metal Oxide Semiconductor Implementation Service (MOSIS). We demonstrated 3D integrated chip stacks with primary RF signal routing on MEMS and on CMOS for self-healing filters, and showcased the other system via wire-bonding to off-the-shelf CMOS components on a printed circuit board (PCB) because of the inability to continue to have access to the CMOS wafers and bumping processes over the last two years of the project.

Silicon photonics as a one of the most promising photonic integration technologies has attracted many attentions in recent years. The major feature of this technology is its compatibility with complementary metal-oxide semiconductor (CMOS) processes which makes it possible to integrate optical and electronic devices in a same chip and reduce the cost significantly. Another reason of using silicon photonics is the high index contrast between the silicon core and silicon dioxide cladding which ensures the high density integration of photonic devices on a single chip. Monolithic integration with electronic and optical circuits makes silicon photonics technology suitable for numerous applications. One example is microwave photonics (MWP). MWP is an area that studies the interaction between microwave and optical signal for the generation, processing, control and distribution of microwave signals by means of photonics. Silicon photonics offers a reduction in footprint, losses, packaging cost and power dissipation in MWP systems. This research in this thesis is focused on the design and fabrication of the silicon photonic devices for MWP signal processing and generation. Four MWP systems based on silicon photonic devices are proposed and experimentally demonstrated. 1) A single pass-band frequency-tunable MWP filter based on phase-modulation to intensity-modulation conversion in an optically pumped silicon-on-insulator (SOI) microring resonator (MRR) is designed and experimentally demonstrated. In the proposed filter, a phase-modulated optical signal is filtered by the SOI MRR, to have one first-order sideband suppressed by the MRR notch. The phase-modulated optical signal is converted to an intensity-modulated single-sideband (SSB) signal and detected at a photodetector (PD). The entire operation is equivalent to a single pass-band filter. The frequency tunability is achieved by tuning the resonance wavelength of the MRR, which is realized by optically pumping the MRR. A single pass-band MWP filter with a tunable center frequency from 16 to 23 GHz is experimentally demonstrated. 2) A broadband optically tunable MWP phase shifter with a tunable phase shift using three cascaded SOI MRRs that are optically pumped is designed and experimentally demonstrated. A microwave signal to be phase shifted is applied to an optical single-sideband (OSSB) modulator to generate an optical carrier and an optical sideband. The phase shift is introduced to the optical carrier by placing the optical carrier within the bandwidth of one resonance of the three cascaded MRRs. The experimental results show that by optically pumping the cascaded MRRs, a broadband MWP phase shifter with a bandwidth of 7 GHz with a tunable phase shift covering the entire 360o phase shift range is achieved. 3) A multi tap MWP filter with positive and negative coefficients using a silicon ring resonator modulator (RRM) is proposed and experimentally demonstrated. The RRM is designed and fabricated to operate based on the carrier depletion effect. The positive and negative coefficients are obtained by using opposite slopes of the modulation transmission response of the RRM. Two filter responses with two and three taps are experimentally demonstrated, showing the proof-of-principle for frequencies up to 18 GHz. 4) An approach to generate microwave signal based on enhanced four wave mixing (FWM) in an active silicon waveguide (SiWG) is studied. This SiWG is designed and fabricated, and the use of the active SiWG for MWP frequency multiplication to generate a frequency-sextupled millimeter-wave signal is experimentally demonstrated. Thanks to a reverse-biased p-n junction across the SiWG, the conversion efficiency of the FWM is improved, which leads to the improvement of the microwave frequency multiplication efficiency.

Ce travail porte sur l'étude de propriétés optiques des fluides à échelle micrométrique. A cet effet, nous avons conçu, réalisé et étudié différents types de micro-résonateurs optofluidiques, sous forme de laboratoires sur puce. Notre analyse est fondée sur la modélisation analytique et numérique, ainsi que sur des mesures expérimentales menées sur des micro-cavités optiques; nous utilisons l'une d'entre elles pour des applications de réfractométrie de fluides homogènes et de fluides complexes ainsi que pour la localisation par piégeage optique de microparticules solides. Nous nous sommes d'abord concentrés sur l'étude d'une nouvelle forme de micro-cavité Fabry-Pérot basée sur des miroirs courbes entre lesquels est inséré un tube capillaire permettant la circulation d'une solution liquide. Les résultats expérimentaux ont démontré la capacité de ce dispositif à être utilisé comme réfractomètre avec un seuil de détection de 1,9 × 10-4 RIU pour des liquides homogènes. De plus, pour un liquide contenant des particules solides, la capacité de contrôler la position des microparticules, par des effets de piégeage optique ou de liaison optique, a été démontrée avec succès. Dans un second temps, un résonateur optique est formé simplement à partir d'une goutte de liquide disposée sur une surface super-hydrophobe. La forme quasi-sphérique résultante est propice à des modes de galerie. Il est démontré que, jusqu'à des tailles de gouttelettes millimétriques, la technique de couplage en espace libre est toujours en mesure d'accéder à ces modes à très faible queue évanescente d'interaction, contrairement à ce qu'indiquait jusqu'ici la littérature. De tels résonateurs optofluidiques à gouttelette devraient trouver leur application notamment comme capteur d'environnement de l'air ambiant ou encore comme incubateur de micro-organismes vivants pouvant être suivis par voie optique / This work focuses on the study of optical properties of fluids at the micrometer scale. To this end, we designed, implemented and studied different types of optofluidic micro- resonators in the Lab-on-Chip format. Our analysis is based on analytical and numerical modeling, as well as experimental measurements conducted on optical microcavities; we use one of them for refractometry applications on homogeneous fluids and on complex fluids, as well as for the localization of solid microparticles by optical trapping. We first focused on the study of a new form of Fabry-Perot micro-cavity based on curved mirrors between which a capillary tube is inserted for injecting a fluidic solution. Experimental results demonstrated the ability of this device to be used as a refractometer with a detection limit of 1.9 × 10-4 RIU for homogeneous liquids. Furthermore, for liquid containing solid particles, the ability to control the microparticles position either by optical trapping or optical binding effects has been successfully demonstrated. In a second step, an optical resonator is simply formed from a liquid droplet placed on top of a superhydrophobe surface. The resulting quasi-spherical shape supports resonant whispering gallery modes. It is shown that, up to millimeter size droplets, the proposed technique of free-space coupling of light is still able to access these modes with very low evanescent tail interaction, contrary to what was indicated in the literature so far. Such optofluidic droplet resonators are expected to find their applications for environmental air quality monitoring, as well as for incubator of living micro-organisms that can be monitored optically

This master's thesis describes ways of signal processing via digital devices. Major field of interest is an analysis of Doppler radar response and then mining of informations about detected object (e.g. speed, movement direction, length, ...). There was realized too little research, that's why borrowing some procedures from different branches not too much related to the IT is necessary. In case of using very complex methods that are easy to parallel, hardware implementation on the FPGA is supposed. With transceiver there is created a very powerful on-line system able to process most of tasks real-time. Then processed and transformed data are sent to the output so visualization and display can be made.

Depuis plusieurs années, le département Temps-Fréquence de l’institut FEMTO-ST mène une étude sur le comportement des résonateurs à ondes acoustiques de volume à énergie piégée dans des cristaux à quartz à température cryogénique, typiquement proche de 4 K. Les performances en termes de coefficient de qualité mécanique relevé à ces températures, plusieurs milliards à quelques dizaines de MHz, font des cavités acoustiques en quartz de bons candidats pour des sources de fréquences cryogéniques ultrastables.Les travaux présentés dans ce manuscrit s’inscrivent dans la continuité de ce programme d’étude. Ils visent à consolider l’intérêt du quartz mais aussi à envisager des solutions alternatives à base de matériaux à très faibles pertes acoustiques mais non piézoélectriques pour lesquels l’excitation optique est une alternative crédible. Les présents travaux peuvent être résumés en trois parties majeures :- La première partie a été réalisée dans le but de déterminer une coupe de quartz possédant un point d’inversion sur sa caractéristique fréquence-température aux températures cryogéniques. La seule régulation de température du résonateur d’une source de fréquence ultrastable est en effet insuffisante sans l’existence d’un tel point qui doit servir de point de fonctionnement à la régulation thermique. La recherche d’une coupe compensée a nécessité une campagne préliminaire de mesure des coefficients de température des coefficients élastiques du matériau, inconnus à basses températures. Il a alors été possible, à partir de la connaissance de ces coefficients, d’identifier par le calcul puis de réaliser une coupe remplissant les conditions recherchées.- La seconde partie a pour objectif de faire la preuve de concept consistant à utiliser une cavité acoustique en quartz en cavité optique. Dans sa version de base, le résonateur à quartz à onde de volume piégée est plan-convexe (pour assurer le piégeage) et à électrodes (métalliques pour assurer l’excitation électrique !) déposées sur chacune de ses faces. Il est démontré, théoriquement et expérimentalement, qu’une telle géométrie fonctionne en cavité optique, avec son avantage de simplicité mais avec ses limites. Cette structure de base doit être mise à profit pour le couplage optomécanique abordé en troisième partie et constitue le socle de conception de dispositifs optomécaniques plus performants.- La troisième partie est consacrée à l’évaluation de la pertinence du couplage optomécanique de tels dispositifs fonctionnant à température cryogénique. Une étude portant sur la quantification théorique du couplage optomécanique que peut atteindre une telle cavité a été réalisée. / For a few years, the Time and Frequency department in FEMTO-ST Insitute has been leading research about the behavior of Bulk Acoustic Wave (BAW) trapped in quartz crystal at cryogenic temperatures (near 4K).The measured quality factor are around a few billions at few tens of MHz for such temperatures. Acoustical quartz cavities are therefore good candidates for ultrastable cryogenic frequency sources. The work presented here is in the natural continuation of the research cited above. They aim at strenghtening the interest for quartz crystal, but also to consider alternative solutions with non-piezoelectric material with very-low acoustical losses, for which optical excitation is an option. The following work can be summed up in three main parts:- The first part is about the determination of a quartz crystal cut for which a turnover point exists in the frequency-temperature curve in the cryogenic region. Indeed, it is not enough to barely control the temperature in an ultrastable frequency source. Such a turnover point needs to be the operation point for thermal regulation. Searching a compensated cut arose the need for a preliminary measurements campaign of thermal coefficients of elastics coefficients of the material, which were unknown at low temperature. It was then possible, based on these coefficients, to calculate and even realize a cut fulfilling the required condition.- The second part had the objective to demonstrate conceptually that using a quartz acoustical cavity as an optical cavity was feasible. In its basic scheme, a BAW quartz resonator is plano-convex (to ensure the trapping of the acoustic wave) and has electrodes (metal-made to ensure electrical excitation) deposited on each face. It has been demonstrated, both theoretically and experimentally, that such a geometry works fine as an optical cavity, with its corresponding advantages and limitations. This scheme is used for the optomechanical coupling discussed in the third part and constitutes the very base for more efficient optomechanical devices.- The third part is dedicated to the evaluation of how efficient will such devices be while functioning at cryogenic temperature. A theoretical quantification of the optomechanical coupling that these cavities might reach is also presented.

Industrial innovation is mostly driven by miniaturization. As a result of remarkable technological advancements in the fields of equipment, materials and production processes, transistor, the fundamental active component in conventional electronics, has shrunk in size. Semiconductor technology is unique in that all performance metrics are enhanced, while at the same time unit prices are reduced. Moore’s Law, which predicts that the number of components per chip will double every two years, was established in 1965, and the industry has been able to keep up with this prophetic prognosis since. Thermal management, on the other hand, has become a key limiting factor for current electronic circuits and is set to put a stop to Moore’s Law. Given the fact that complementary metal oxide semiconductor (CMOS) scaling is reaching fundamental limits, there are several new alternative processing devices and architectures that have been investigated for both traditional integrated circuit (IC) technologies and novel technologies, including new technologies aimed at contributing to advances in scaling progress and cost reductions in manufacturing operations in the coming decades. These factors will encourage the development of new information processing and memory systems, new technologies for integrating numerous features heterogeneously and new system architectural design layouts, among other things. Energy efficiency is advantageous from a sustainability perspective and for consumer electronics, for which fewer power-hungry components mean longer times between charges and smaller batteries. The creation of novel chip-scale tools that can aid in the transfer of information across optical frequencies and microscale photonics between nanoscale electronic devices is now a possibility. Bridging this technological gap may be achieved by plasmonics. The incorporation of plasmonic, photonic and electrical components on a single chip may lead to a number of innovative breakthroughs. Photonic integrated circuits (PICs) enable the realization of ultra-small, high-efficiency, ultra-responsive and CMOS-compatible devices that can be used in applications ranging from optical wireless communication systems (6G and beyond) and supercomputers to health and energy.   This thesis provides a platform from which to design nanoplasmonic devices while facilitating high-transmission and/or absorption efficiency, miniaturized size and the use of near-infrared (NIR) wavelengths for telecom applications. With a significant amount of Internet traffic transmitted optically, communication systems are further tightening the requirements for the development of new optical devices. Several new device structures based on the metal-insulator-metal (MIM) plasmonic waveguide are proposed and investigated using performance metrics. The transmission line theory (TLM) from microwave circuit theory and coupled mode theory (CMT) is studied and employed in the design process of the nanostructures, in particular to address the losses in plasmonic-based devices, which has been the major factor hampering their widespread usage in communication systems. By taking advantage of well-established microwave circuit theory (through new design that paves the way for mitigating these losses and enabling efficient transmission of power flow in the optical devices), we have suggested a number of high-transmission efficiency nanodevices that offer highly competitive performance compared with other platforms. As a result, a promising future for plasmonic technology, which would enable design and fabrication of multipurpose and multifunctional optical devices that are efficient in terms of losses, footprint and capability of integrating active devices, is anticipated. / Branschinnovation drivs främst av miniatyrisering. Som ett resultat av anmärkningsvärda tekniska framsteg inom områdena utrustning, material och produktionsprocesser kunde transistoren, den grundläggande aktiva komponenten i samtida elektronik, krympa i storlek. Halvledarteknik är unik genom att alla prestandamått förbättras, samtidigt som enhetspriserna sänks. Moores Lag, som förutspår att antalet komponenter per chip skulle fördubblas vartannat år, inrättades 1965, och branschen har kunnat hålla jämna steg med den profetiska prognosen sedan dess. Termisk hantering, å andra sidan, har blivit en viktig begränsande faktor för nuvarande elektroniska kretsar, och är inställd på att sätta stopp för Moores Lag. Med tanke på att CMOS-skalningen (Complementary Metal Oxide Semiconductor) når grundläggande gränser finns det flera nya alternativa bearbetningsanordningar och arkitekturer som har undersökts för både traditionell integrerad kretsteknik och ny teknik. Ny teknik som syftar till att bidra till framsteg i skalningen av framsteg och kostnadsminskningar i tillverkningsverksamheten under de kommande årtiondena. Dessa faktorer uppmuntrar utvecklingen av nya informationsbehandlings- och minnessystem, ny teknik för att integrera många funktioner heterogent och nya systemarkitekturdesignlayouter, bland annat. Energieffektivitet är fördelaktigt ur ett hållbarhetsperspektiv och för hemelektronik, där färre krafthungriga elektroniker innebär längre tid mellan laddningar och stimulerar för ett mindre energilagringssystem ombord. Skapandet av nya chip-scale verktyg som kan bidra till överföring av information över optiska frekvenser och mikroskala fotonik mellan elektroniska enheter i nanoskala är nu en möjlighet. Överbrygga denna tekniska klyfta kan uppnås av plasmonics. Införlivandet av plasmoniska, fotoniska och elektriska komponenter på ett enda chip kan leda till ett antal innovativa genombrott. Fotoniska integrerade kretsar (PIC-enheter) möjliggör förverkligande av ultrasmå, högeffektiva, ultraresponsiva och CMOS-kompatibla enheter som kan användas i applikationer som sträcker sig från optiska trådlösa kommunikationssystem (6G och därefter), superdatorer till hälso- och energiändamål. Denna avhandling ger en plattform för att designa nanoplasmoniska enheter samtidigt som den innehåller hög överförings- och eller absorptionseffektivitet, miniatyriserad storlek och vid önskade våglängder av nära infraröd (NIR) för telekomapplikationer. Med den betydande mängden Internettrafik som överförs optiskt skärper kommunikationssystemen ytterligare kraven för utveckling av nya optiska enheter. Flera nya enhetsstrukturer baserade på metall-isolator-metall (MIM) plasmonisk vågledare föreslås och numeriskt undersöks. Överföringslinjeteorin (TLM) från mikrovågskretsteori och kombinationslägesteori (CMT) studeras och används i nanostrukturerna. För att ta itu med de förluster i plasmonbaserade enheter som har varit den viktigaste parametern som hindrade deras utbredda användning i kommunikationssystem, genom att dra nytta av den väletablerade mikrovågskretsteorin (genom ny design som banar väg för att mildra förlusterna och möjliggöra effektiv överföring av kraftflödet i den optiska enheten).  Vi har framgångsrikt föreslagit ett antal nanodevices med hög överföringseffektivitet som erbjuder en mycket konkurrenskraftig prestanda jämfört med andra plattformar. Som ett resultat förväntar vi oss en lovande framtid för plasmonisk teknik som skulle möjliggöra design och tillverkning av mångsidiga och multifunktionella optiska enheter som är effektiva när det gäller förluster, fotavtryck och förmåga att integrera aktiva enheter. / <p>Vid tidpunkten för framläggandet av avhandlingen var följande delarbeten opublicerade: delarbete II inskickat, III, IV, V manuskript.</p><p>At the time of the licentiate defence the following papers were unpublished: paper II submitted, III, IV, V manuscript.</p>

<p dir="ltr">Rapid evolution in wireless technology and the increasing demand for high bandwidth communication for 5G/6G and the Internet of Things (IoT) have necessitated a growing number of components in radio front-end modules in an increasingly overcrowded radio frequency (RF) spectrum. Low-cost ad-hoc radios have drawn consumer interest, enabling new devices like microelectromechanical (MEMS) resonators for on-chip clocking, frequency-selective filters, RF signal processing, and spectral sensing for their small footprint and low power consumption. Gallium nitride (GaN) is an attractive electromechanical material due to its high coupling coefficient, acoustic velocity, and low viscoelastic losses. These benefits enable high-Q MEMS resonators in GaN monolithic microwave integrated circuits (MMICs) with scaling capability up to mm-wave frequencies, making this technology platform a contender for high-performance programmable radios in RF/mm-wave, sensors for harsh environments, and information processing in quantum systems.</p><p dir="ltr">The bias-dependent control mechanism of the 2D electron gas (2DEG) in GaN heterostructures can be exploited to design different switchable and tunable devices for reconfigurable MEMS components. This work presents, for the first time, a comprehensive study of the electromechanical performances of different transduction mechanisms in switchable GaN MEMS resonators. A unique OFF-state shunt design, where the 2DEG in an AlN/GaN heterostructure is utilized to control electromechanical transduction in Lamb mode resonators, is also experimentally demonstrated in this work. To make a valid comparison among switchable transducers, equivalent circuit models are developed to extract key parameters from the measurements by fitting them in both ON and OFF states. The switchable transducer with Ohmic interdigitated transducers (IDTs) and Schottky control gate shows superior performance among the designs under consideration with complete suppression of the mechanical mode in the OFF state and a maximum frequency-quality factor product of 5x10¹²s^-1 and a figure-of-merit of 5.18 at 1GHz in the ON state.</p><p dir="ltr">Over the past few years, there have been numerous efforts to scale the frequencies of MEMS devices in the GaN platform towards mm-wave frequencies. However, challenges remain due to the multi-layer thick buffer, typical in the growth of GaN epilayer on a substrate. This work presents the investigation of SweGaN QuanFINEbuffer-free and ultrathin GaN-on-SiC for the performance of surface acoustic wave (SAW) devices beyond 10GHz. Finite element analysis (FEA) is performed to find the range of frequencies for the Sezawa mode in the structure. Transmission lines and resonators are designed, fabricated, and characterized. Modified Mason circuit models are developed for each class of devices to extract critical performance metrics and benchmark with the state-of-the-art and theoretical limits for GaN. Sezawa modes are observed at frequencies up to 14.3GHz, achieving a record high in GaN MEMS to the best of our knowledge. A maximum piezoelectric coupling of 0.61% and frequency-quality factor product of 6x10¹²s^-1 are achieved for Sezawa resonators at 11GHz, with a minimum propagation loss of 0.26dB/λ for the two-port devices. The devices also exhibit high linearity with input third-order intercept points (IIP3) of 65dBm at 9GHz.</p><p dir="ltr">This work also investigates tunable acoustoelectric (AE) devices in the QuanFINE platform, leveraging its inherent 2DEG in the AlGaN/GaN heterostructure. Using 9.7GHz Sezawa mode acoustic delay lines, we report the highest frequency of AE in GaN to date. Active and passive AE devices are designed for voltage-dependent non-reciprocity and propagation loss without modification to the standard process for the High Electron Mobility Transistors (HEMTs) in MMICs. Drain/source Ohmic contacts control the drift velocity of the 2DEG, and the Schottky gate modulates 2DEG carrier concentration, resulting in a 30dB/cm separation between forward and reverse acoustic waves for a 2.56kV/cm lateral DC electric field and a maximum change in propagation loss of 50dB/cm for -5V DC at the control gate, respectively. The QuanFINEtechnology with AlGaN/GaN heterostructure enables a platform for switchable MEMS resonators and tunable acoustoelectric devices in MMICs for reconfigurable front end approaching mm-wave frequencies.</p>

Metamaterials are typically described as materials with ’unusual’ wave propagation properties. Originally developed for electromagnetic waves, these materials have also spread into the field of acoustic wave guiding and cloaking, with the most relevant of these ’unusual’ properties, being the so called band-gap phenomenon. A band-gap signifies a frequency region where elastic waves cannot propagate through the material, which in principle, could be used to protect buildings from earthquakes. Based on this, two relevant concepts have been proposed in the field of seismic engineering, namely: metabarriers, and metamaterial-based foundations. This thesis deals with the development of the Metafoundation, a metamaterial-based foundation system for the seismic protection of fuel storage tanks against excessive base shear and pipeline rupture. Note that storage tanks have proven to be highly sensitive to earthquakes, can trigger sever economic and environmental consequences in case of failure and were therefore chosen as a superstructure for this study. Furthermore, when tanks are protected with traditional base isolation systems, the resulting horizontal displacements, during seismic action, may become excessively large and subsequently damage connected pipelines. A novel system to protect both, tank and pipeline, could significantly augment the overall safety of industrial plants. With the tank as the primary structure of interest in mind, the Metafoundation was conceived as a locally resonant metamaterial with a band gap encompassing the tanks critical eigenfrequency. The initial design comprised a continuous concrete matrix with embedded resonators and rubber inclusions, which was later reinvented to be a column based structure with steel springs for resonator suspension. After investigating the band-gap phenomenon, a parametric study of the system specifications showed that the horizontal stiffness of the overall foundation is crucial to its functionality, while the superstructure turned out to be non-negligible when tuning the resonators. Furthermore, storage tanks are commonly connected to pipeline system, which can be damaged by the interaction between tank and pipeline during seismic events. Due to the complex and nonlinear response of pipeline systems, the coupled tank-pipeline behaviour becomes increasingly difficult to represent through numerical models, which lead to the experimental study of a foundation-tank-pipeline setup. Under the aid of a hybrid simulation, only the pipeline needed to be represented via a physical substructure, while both tank and Metafoundation were modelled as numerical substrucutres and coupled to the pipeline. The results showed that the foundation can effectively reduce the stresses in the tank and, at the same time, limit the displacements imposed on the pipeline. Leading up on this, an optimization algorithm was developed in the frequency domain, under the consideration of superstructure and ground motion spectrum. The advantages of optimizing in the frequency domain were on the one hand the reduction of computational effort, and on the other hand the consideration of the stochastic nature of the earthquake. Based on this, two different performance indices, investigating interstory drifts and energy dissipation, revealed that neither superstructure nor ground motion can be disregarded when designing a metamaterial-based foundation. Moreover, a 4 m tall optimized foundation, designed to remain elastic when verified with a response spectrum analysis at a return period of 2475 years (according to NTC 2018), reduced the tanks base shear on average by 30%. These results indicated that the foundation was feasible and functional in terms of construction practices and dynamic response, yet unpractical from an economic point of view. In order to tackle the issue of reducing the uneconomic system size, a negative stiffness mechanism was invented and implemented into the foundation as a periodic structure. This mechanism, based on a local instability, amplified the metamaterial like properties and thereby enhanced the overall system performance. Note that due to the considered instability, the device exerted a nonlinear force-displacement relationship, which had the interesting effect of reducing the band-gap instead of increasing it. Furthermore, time history analyses demonstrated that with 50% of the maximum admissible negative stiffness, the foundation could be reduced to 1/3 of its original size, while maintaining its performance. Last but not least, a study on wire ropes as resonator suspension was conducted. Their nonlinear behaviour was approximated with the Bouc Wen model, subsequently linearized by means of stochastic techniques and finally optimized with the algorithm developed earlier. The conclusion was that wire ropes could be used as a more realistic suspension mechanism, while maintaining the high damping values required by the optimized foundation layouts. In sum, a metamaterial-based foundation system is developed and studied herein, with the main findings being: (i) a structure of this type is feasible under common construction practices; (ii) the shear stiffness of the system has a fundamental impact on its functionality; (iii) the superstructure cannot be neglected when studying metamaterial-based foundations; (iv) the complete coupled system can be tuned with an optimization algorithm based on calculations in the frequency domain; (v) an experimental study suggests that the system could be advantageous to connected pipelines; (vi) wire ropes may serve as resonator suspension; and (vii) a novel negative stiffness mechanism can effectively improve the system performance.

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