Au cours des dernières années le silicium est apparu comme un matériau hôte prometteur pour les qubits de spin. Grâce à la microélectronique moderne, la technologie du silicium a connu un formidable développement. Réaliser des qubits utilisant la technologie bien établie de fabrication CMOS de semi-conducteurs favoriserait clairement leur intégration à grande échelle.Dans cette thèse nous présentons les travaux effectués dans une perspective des qubits CMOS. En particulier, nous avons abordé les problèmes de confinement des charges et des spins dans les boîtes quantiques, la manipulation des spins et la lecture des charges et des spins.Nous avons exploré les différentes propriétés de confinement de charge et de spin dans des échantillons de tailles et de géométries différentes. Les MOSFETs de taille extrêmement réduites montrent du blocage de Coulomb jusqu'à température ambiante, avec des énergies de charges jusqu'à 200meV. Les dispositifs multi-grilles avec des dimensions géométriques plus grandes ont été utilisés pour confiner les spins et lire leur état par blocage de spin, en réalisant ainsi une conversion spin / charge.La manipulation des spins est réalisée au moyen d'un dipôle électronique induisant la résonance de spin (EDSR). Les deux plus basses vallées de la bande de conduction du silicium sont visibles sous forme de transitions de spin intra et inter-vallées. Nous observons une levée de dégénérescence de vallée d'amplitude 36μeV. La résonance de spin que l'on observe résulte de la géométrie spécifique de l'échantillon, de la physique des vallées et de l'interaction spin-orbite de type Rashba. Des signatures de manipulation cohérente, sous forme d'oscillations de Rabi, ont été mesurées, avec une fréquence de Rabi de 6MHz. Nous discutons également de la lecture rapide des charges et des spins effectuée par réflectométrie dispersive couplée à la grille. Nous montrons comment l'utiliser pour reconstruire le diagramme de stabilité de charge du dispositif et le signal attendu pour un système à double boîte isolé. La tension de polarisation finie modifie la réponse du système et nous l'avons utilisée pour sonder les états excités et leur dynamique. / In the recent years, silicon has emerged as a promising host material for spin qubits. Thanks to its widespread use in modern microelectronics, silicon technology has seen a tremendous development. Realizing qubit devices using well-established complementary metal-oxide-semiconductor (CMOS) fabrication technology would clearly favor their large scale integration.In this thesis we present a detailed study on CMOS devices in a perspective of qubit operability.In particular we tackled the problems of charge and spin confinement in quantum dots, spin manipulation and charge and spin readout.We explored the different charge and spin confinement capabilities of samples with different sizes and geometries. Ultrascaled MOSFETs show Coulomb blockade up to room temperature with charging energies up to 200meV. Multigate devices with larger geometrical dimensions have been used to confine spins and read their states through spin-blockade as a way to perform spin to charge conversion.Spin manipulation is achieved by means of Electron Dipole induced Spin Resonance (EDSR). The two lowest valleys of silicon's conduction band originate as intra and inter-valley spin transitions; we probe a valley splitting of 36μeV. The origin of this spin resonance is explained as an effect of the specific geometry of the sample combined with valley physics and Rashba spin-orbit interaction. Signatures of coherent Rabi oscillations have been measured, with a Rabi frequency of 6MHz. We also discuss fast charge and spin readout performed by dispersive gate-coupled reflectometry. We show how to use it to recover the complete charge stability diagram of the device and the expected signal for an isolated double dot system. Finite bias changes the response of the system and we used it to probe excited states and their dynamics.

Investigations performed in order to understand the electronic and optoelectronic properties of field effect transistors based on few layers of 2D Copper Indium Selenide (CuIn7Se11) are reported. In general, field effect transistors (FETs), electric double layer field effect transistors (EDL-FETs), and photodetectors are crucial part of several electronics based applications such as tele-communication, bio-sensing, and opto-electronic industry. After the discovery of graphene, several 2D semiconductor materials like TMDs (MoS2, WS2, and MoSe2 etc.), group III-VI materials (InSe, GaSe, and SnS2 etc.) are being studied rigorously in order to develop them as components in next generation FETs. Traditionally, thin films of ternary system of Copper Indium Selenide have been extensively studied and used in optoelectronics industry as photoactive component in solar cells. Thus, it is expected that atomically thin 2D layered structure of Copper Indium Selenide can have optical properties that could potentially be more advantageous than its thin film counterpart and could find use for developing next generation nano devices with utility in opto/nano electronics. Field effect transistors were fabricated using few-layers of CuIn7Se11 flakes, which were mechanically exfoliated from bulk crystals grown using chemical vapor transport technique. Our FET transport characterization measurements indicate n-type behavior with electron field effect mobility µFE ≈ 36 cm^2 V^-1 s^-1 at room temperature when Silicon dioxide (SiO2) is used as a back gate. We found that in such back gated field effect transistor an on/off ratio of ~ 10^4 and a subthreshold swing ≈ 1 V/dec can be obtained. Our investigations further indicate that Electronic performance of these materials can be increased significantly when gated from top using an ionic liquid electrolyte [1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6)]. We found that electron field effect mobility µFE can be increased from ~ 3 cm^2 V^-1 s^-1 in SiO2 back gated device to ~ 18 cm^2 V^-1 s^-1 in top gated electrolyte devices. Similarly, subthreshold swing can be improved from ~ 30 V/dec to 0.2 V/dec and on/off ratio can be increased from 10^2 to 10^3 by using an electrolyte as a top gate. These FETs were also tested as phototransistors. Our photo-response characterization indicate photo-responsivity ~ 32 A/W with external quantum efficiency exceeding 10^3 % when excited with a 658 nm wavelength laser at room temperature. Our phototransistor also exhibit response times ~ tens of µs with specific detectivity (D*) values reaching ~ 10^12 Jones. The CuIn7Se11 phototransistor properties can be further tuned & enhanced by applying a back gate voltage along with increased source drain bias. For example, photo-responsivity can gain substantial improvement up to ~ 320 A/W upon application of a gate voltage (Vg = 30 V) and/or increased source-drain bias. The photo-responsivity exhibited by these photo detectors are at least an order of magnitude better than commercially available conventional Si based photo detectors coupled with response times that are orders of magnitude better than several other family of layered materials investigated so far. Further photocurrent generation mechanisms, effect of traps is discussed in detail.

O transistor de efeito de campo de porta estendida e separada (SEGFET) é um dispositivo alternativo ao tradicional transistor de efeito de campo seletivo a íons (ISFET). A grande vantagem desse dispositivo se refere ao seu fácil processamento, ou seja, se restringe somente a manipulação do eletrodo de porta, evitando processos convencionais de microeletrônica. Neste sentido, sensores iônicos e biossensores podem ser facilmente implementados combinando materiais de reconhecimento químico e/ou biológico. Por sua vez, a técnica de fabricação de filmes finos camada por camada (layer-by-layer, LbL) se mostra versátil para manipulação de diversos tipos de materiais em nível molecular. Materiais orgânicos e inorgânicos podem ser automontados em substratos sólidos por meio da simples adsorção eletrostática formando compósitos com propriedades únicas com o objetivo de serem aplicados em sensores ou biossensores. Neste trabalho, o conceito de dispositivo SEGFET foi combinado com a técnica LbL por meio da manipulação de materiais orgânicos (polieletrólitos, dendrímeros e polianilina) e inorgânicos (TiO2 e V2O5) nanoparticulados a fim de se obter novos sensores de pH e biossensores para a detecção de glicose e uréia, dois importantes analitos de interesse clínico. Numa primeira etapa, diferentes filmes LbL foram produzidos, caracterizados e testados como camada sensível (porta estendida) em dispositivos SEGFETs. Todos os sistemas estudados se mostraram promissores como sensores de pH, ou seja, com uma sensibilidade próxima do valor teórico sugerido pela equação de Nernst (59,15 mV.pH-1). Esses resultados podem ser atribuídos à natureza anfotérica do material da última camada no filme LbL. Numa segunda etapa, as enzima glicose oxidase (GOx) e urease foram convenientemente imobilizadas nos filmes LbL. Pelo fato dessas enzimas gerarem ou consumirem prótons durante a catálise da reação, os filmes LbL modificados enzimaticamente foram utilizados em biossensores de glicose e uréia, apresentando eficiente detecção. Assim, a união de dispositivos SEGFET com a técnica de automontagem se mostrou promissora para construção de sensores e biossensores eficientes e de baixo custo. / Separative extended gate field-effect transistor (SEGFET) device is an alternative to the conventional ion-sensitive field-effect transistor (ISFET). The great advantage of SEGFET refers to its easy processing, i.e., it is limited under only manipulation of the gate electrode, avoiding the conventional microelectronic processes. In this way, ion sensors and biosensors can be easily implemented combining chemical and/or biological recognition materials. In turn, the layer-by-layer (LbL) technique shows be versatile for handling various types of materials at molecular level. In this thesis, the concept of SEGFET device was combined with the LbL technique through the manipulation of organic (polyelectrolytes, dendrimers and poly (aniline)) and inorganic materials (TiO2 and V2O5 nanoparticles) in order to get new pH sensors and biosensors for the detection of glucose and urea, two important analytes of clinical interest. In a first step, different LbL films were produced, characterized and tested as the sensitive layer (extended gate) in SEGFETs devices. All studied systems were promissing as pH sensors, i.e., with a sensitivity close to the theoretical value suggested by Nernst equation (59.15 mV.pH-1). These results can be attributed to the amphoteric nature of the material in the last layer of the LbL films. In a second step, glucose oxidase (GOx) and urease enzymes were conveniently immobilized onto LbL films. Because these enzymes generate or consume protons during catalysis of the reaction, the enzymatically modified LbL films were used in biosensors for glucose and urea, with efficient detection. Thus, the union of SEGFET devices with the LbL technique is promising to building up efficient and low-cost sensors and biosensors.

Orientadores: Peter Jurgen Tatsch, Jose Alexandre Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-13T19:29:46Z (GMT). No. of bitstreams: 1 Souza_JairFernandesde_M.pdf: 4396662 bytes, checksum: cf77f050e25403e0bd758bdb52214aa2 (MD5) Previous issue date: 2009 / Resumo: Esta dissertação consiste de duas etapas. Inicialmente são estudados filmes de nitreto de silício depositados por LPCVD, Low Pressure Chemical Vapor Deposition, utilizando-se diferentes relações de concentração de gases reagentes, [SiH2Cl2]/[NH3], e utilizando-se como substrato lâminas de silício tipo p, com e sem camada almofada de oxinitreto de silício; estruturas SiNx/Si e SiNx/SiOxNy/Si, respectivamente. Os filmes foram caracterizados física e eletricamente, bem como do ponto de vista da capacidade de adsorção de monocamadas biologicamente ativas. As características dos filmes foram comparadas, buscando-se identificar um filme cujas propriedades fossem adequadas para utilização como material dielétrico a ser empregado na porta de Transistores de Efeito de Campo química e bioquimicamente sensíveis. Os resultados da elipsometria realizada apontaram filmes com índices de refração variando de 1,875 a 1,990, indicando filmes ricos em nitrogênio, e com espessura diretamente proporcional à relação de concentração dos gases reagentes, ou seja, o aumento na relação de concentração de gases produz aumento na taxa de deposição dos filmes. A espectroscopia de absorção de infra-vermelho permitiu analisar as ligações químicas presentes nos filmes e nas monocamadas automontadas formadas pela imobilização de biomoléculas. Os espectros dos filmes apresentam picos de absorção em 827/837 cm-1 e 451/484 cm-1 que correspondem a ligações Si-N, confirmando a indicação da elipsometria referente à presença de nitrogênio. Após a formação das camadas automontadas, compostas de proteínas do tipo Imunoglobulina, IgG 2,5 e 5%, os espectros mostraram bandas de absorção de IR em torno de 3300 cm-1 e nas faixas de 1700 a 1600 cm-1 e 1600 a 1500 cm-1. Este espectro caracteriza a formação de grupos amida A, I e II, respectivamente, ou seja, a formação das monocamadas biologicamente ativas. Através de espectroscopia micro-Raman foram detectados deslocamentos nos picos principais do substrato de silício. Tais deslocamentos foram relacionados com o stress provocado pelos filmes depositados. Foram fabricados capacitores Metal/Isolante/Semicondutor, MIS, utilizando-se as estruturas dielétrico/semicondutor obtidas. Os capacitores possibilitaram realizar a caracterização elétrica dos filmes através de medidas C-V, capacitância-voltagem, de alta frequência de 1MHz, obtendo-se a densidade de cargas existente na interface dielétrico/semicondutor, em torno de 1011cm-2, e permitiram observar o comportamento da interface com a realização de etapas térmicas e a degradação em suas propriedades de recombinação. Após a fabricação e a caracterização das camadas dielétricas, foi iniciada a segunda etapa do trabalho com a fabricação de matrizes de Transistores de Efeito de Campo, FETs. Foi usado como dielétrico de porta os filmes da etapa anterior que apresentaram melhor desempenho do ponto de vista físico, elétrico, químico e biológico. A caracterização elétrica dos FETs foi realizada utilizando-se dispositivos de controle dispostos isoladamente nas pastilhas. Foram obtidas as características elétricas dos dispositivos e observado seu comportamento nas etapas térmicas. A sensibilidade química foi verificada aplicando-se analitos com diferentes concentrações de íons H+ , correspondente a diferentes valores de pH, na região de porta dos FETs. Foi demonstrada a viabilidade da utilização dos FETs fabricados na detecção química/bioquímica, com possibilidade de emprego em atividades de diagnóstico médico, controle ambiental, controle da produção de fármacos e cosméticos, e aplicações agropecuárias / Abstract: This dissertation consists of two stages. Initially are studied Silicon Nitride films deposited by LPCVD (Low Pressure Chemical Vapor Deposition) using different relationship of reagent gases concentration ([SiH2Cl2] / [NH3]) and using as substratum Silicon wafers p-type with and without pad layer of Silicon Oxinitride - SiNx/Si and SiNx/SiOxNy /Si structures. The films were characterized physically and electrically as well as the point of view of adsorption capacity of biologically active monolayer. The films characteristics were compared, seeking to identify a film whose characteristics are adequate to be used as dielectric material applied at the project and fabrication of chemically and biochemically sensitive Field Effect Transistors - FETs. Ellipsometry results pointed films with refraction indexes ranging from 1,875 to 1,990, it indicating films rich in Nitrogen, and with thickness directly proportional to the relationship of reagent gases concentration. In the other words, the increase of the relationship of gases concentration produces an increase of the films deposition rates. The infra-red absorption spectroscopy allowed us to analyze the chemical bonds present in the dielectric films and in the self assembled monolayers formed by the immobilization of biological molecules. The films spectrum have absorption spike in 827/837 cm-I and 451/484 cm-I that correspond to Si-N bonds, confirming the indication of the ellipsometry regarding as nitrogen presence. After self assembled monolayers formation composed by proteins of the type Immunoglobulin - IgG 2.5 and 5%, the spectra showed absorption bands of IR, around 3300 cm-1 and in the ranges of 1700 to 1600 cm-1 and 1600 to 1500 cm-1, spectrum that characterizes the formation of amida groups A, I and II, respectively, in other words, the formation of biologically active monolayers. Through micro-Raman spectrometry were detected displacements in the main spikes of the Silicon substratum. This displacement has been related with the stress induced by the deposited films. It was manufactured Metal Insulating Semiconductor (MIS) capacitors, using the structures dielectric/semiconductor obtained. The capacitors made possible to accomplish the electric characterization of the films through high frequency (1 MHz) capacitance-voltage (C-V) measurements, obtained the density of charges existent on the interface dielectric/semiconductor - around 1011 cm-2; and to observe the behavior of the interface with the accomplishment of thermal stages and the degradation in its recombination properties. After production and characterization of the dielectric layers, has been accomplished the second stage of the work with the production of FETs, being used as dielectric gate the films that presented better performance of the point of view physical, electric, chemical and biological. The electric characterization of the FETs that compose the arrays, has been accomplished being used the control devices disposed separately in the dies allowing to raise the characteristics of the devices construction, as well as, the behavior of the same ones when submitted to thermal stages. The chemical sensibility was verified being applied analytes with different H+ ions concentrations - different pH values - in the gate area of the FETs that compose the arrays. The viability of use of the modified FETs for chemistry/biochemistry detection was demonstrated, with employment possibility in activities of medical diagnosis, environmental control, control of the production of drugs and cosmetics and agricultural applications. / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

No description available.

V této práci byl demonstrován grafenový polem řízený transistor (GFET) jako platforma pro detekci glukózy. Sukcinimidyl ester pyrenbutanové kyseliny (PSE) sloužící jako nosič a enzym glukóza oxidáza (GOx) byly úspěšně použity k funkcionalizaci grafenového kanálu ve FE transistoru. Enzym GOx byl imobilizován na kanálu pro glukózovou detekci, jelikož indukuje selektivní katalytickou reakci glukózy. Proces funkcionalizace byl charakterizován pomocí Ramanovy spektroskopie a Atomární silové mikroskopie (AFM). Vyrobený biosenzor na bázi grafenu umožnil elektrickou detekci glukózy ve dvou různých uspořádáních. V uspořádní FET prostřednictvím posunu Diracova bodu ve voltampérové charakteristice, jakož i v nastavení pro kotinuální monitorování v reálném čase prostřednictvím změny odporu grafenového kanálu. Tato studie naznačuje, že grafen je slibným materiálem pro vývoj nanoelektronických biosenzorů včetně aplikací pro monitorování hladiny glukózy.

<p>The enhancement of the emission from nitrogen vacancy color centers will help facilitate advancements in quantum information technology. To this end, the reduction of the excited state lifetimes of NVs as well as the design of devices which support electroluminescence of nitrogen vacancies, as well as the broadband enhancement of the emission from these centers is of great importance.</p> <p> </p> <p>In this study, we create diamond thin films containing nitrogen vacancy color centers using salt-assisted ultrasonic disaggregation techniques and electrophoretic deposition. These films are implanted with xenon atoms and the resulting structures are characterized optically. We report a reduction in the bulk emission lifetime of nitrogen vacancy color centers of two orders of magnitude. A coupled-mode theory approach is used to analyze the emission from the xenon-doped nanodiamond species. It is determined that the lifetime reduction occurs due to coupling between nitrogen vacancy color centers and xenon color centers within the diamond lattice.</p> <p> </p> <p>A diamond field effect transistor is investigated via simulations utilizing Sentaurus TCAD software. The device is scaled by three orders of magnitude from previous experiments involving the same structure. Transport characteristics are obtained from simulation results. We confirm the existence of a decreasing saturation voltage with a decrease in gate length in the diamond field effect transistor. Further investigation into the device’s viability as a quantum emitter is conducted. </p> <p> </p> <p>The design of a single photon source utilizing plasmonic structures to enhance emission from nitrogen vacancy color centers is proposed. The plasmonic structure is investigated to extract operating parameters and to quantify the optical coupling and propagation characteristics for various physical dimensions</p> <p> </p> The design of a plasmonic device which features both electroluminescence via nitrogen vacancy color centers and their enhancement via plasmonic effects is numerically simulated. The device features large Purcell enhancement factor and good photon emission rate. In summary, this work paves the way towards the advancement of the nitrogen vacancy color center as a stable source of room temperature photons for quantum information applications.

Le principal objectif de cette thèse est de montrer le potentiel pour l’électronique organique de films moléculaires minces liés de façon covalente au substrat et déposés par greffage électro- chimique. Ces couches organiques de 5 à 100 nm d’épaisseur visent à proposer une alternative aux films minces organiques d’épaisseur supérieure à 100 nm et aux couches mono-moléculaires autoassemblées d’épaisseur comprise entre 1 et 5 nm.Ce travail a d’abord permis d’établir les conditions optimales de greffage de trois différents sels de diazonium : un dérivé de la tris-bipyridine fer (II), un sel de diazonium comportant une longue chaîne fluorée et un autre comportant une fonction thiol. En particulier, un contrôle fin de l’épaisseur des films est démontré sur des électrodes patternées micrométriques adaptées à la réalisation de dispositifs.L’électrogreffage de doubles couches est ensuite étudié. Il consiste à utiliser une électrode electrogreffée par des molécule électroactives, ici le dérivé de la tris-bipyridine fer (II), comme électrode de travail pour l’électrogreffage d’un second sel de diazonium. Cette technique permet de former des couches organiques d’épaisseur contrôlée par la première couche et présentant des fonctions terminales contrôlées par le choix du second composé (ici, fonctions thiols ou chaînes fluorées). L’intérêt de ces couches fonctionnelles est ensuite évalué dans des jonctions verticales métal-molécules-métal utilisant différents types d’électrodes supérieures : des électrodes imprimées à partir d’une solution de nanoparticules d’or, suivant un procédé élaboré dans cette thèse, et des électrodes fabriquées à partir de métaux évaporés sous vide. Enfin, des transistors à base de MoS2 utilisant 30 nm de ces couches greffées comme diélectrique de grille sont fabriqués et étudiés. Leurs performances (mobilité électronique de 46 cm2.(V.s)-1, rapport ION/IOFF de 9.107, etc.) confirment la qualité de ces isolants organiques électrogreffés. La méthode s’avère ainsi efficace et versatile pour la préparation de couches organiques robustes d’épaisseur contrôlée et aux propriétés de surface ajustables. / The main objective of this PhD thesis is to show the potential for organic electronics of molecular thin films covalently bounded and formed by electrochemical grafting. These 5 to 100 nm thick layers aim to propose an alternative to organic thin films of thickness above 100 nm and to self-assembled monolayers of thickness between 1 and 5 nm.This work first establishes the optimal electrografting conditions of three diazonium salts : a derivative from the tris-bipyridine iron (II), a diazonium salt with a long fluorinated chain and another with a thiol function). In particular, a fine tuning of the thickness of the resulting layers is demonstrated on micrometric patterned electrodes.Double layer electrografting is then studied. It consists in using an electrode electrografted with electroactive molecules, here the tris-bipyridine iron (II) derivative, as a working electrode for the electrografting of a second diazonium salt. This technique allows the formation of organic double-layers of thickness controlled by the first layer and presenting terminal functions controlled by the choice of the second compound (here, thiol functions or fluorinated chains).The potential of these layers is then evaluated in vertical metal-molecules-metal junctions using various top electrodes : electrodes printed from an aqueous gold nanoparticle ink through a method developed in this thesis, and electrodes made by metal evaporation in vacuum. To conclude, field-effect transistors based on MoS2 using these electrografted thin layers as gate-dielectric are fabricated and studied. Their performances (electronic mobility of 46 cm2.(V.s)-1, ION/IOFF ratio of 9.107,etc.) confirm the quality of these organic electrografted insulators. The method is thus efficient and versatile for the preparation of robust organic layers with adjustable surface properties and thickness.

Les capteurs biologiques basés sur l’électronique nanométrique ont la propriété intéressante d’être à l’échelle des molécules étudiées. Plus spécifiquement, grâce à leurs propriétés électroniques exceptionnelles, les transistors à effet de champ à base de graphène (TECG) permettent des mesures électriques locales à grandes vitesses d’acquisition et sur de longues durées, offrant un cadre idéal pour la biodétection et l’étude de la cinétique moléculaire. Le présent mémoire traite de l’analyse, la mesure et la fonctionnalisation des TECG dans l’optique d’en faire des biocapteurs performants. En introduction, nous décrirons les propriétés électroniques du graphène ainsi que les principaux concepts reliés aux transistors de graphène et à la détection biologique. Puis, nous établirons les trois objectifs qui seront élaborés en autant de chapitres. Dans le premier chapitre, nous présenterons une revue de littérature critique qui cible l’analyse statistique et l’assemblage de l’interface de détection comme facteurs déterminants de la performance à l’aide d’analyses originales et d’une description approfondie de l’état du domaine. Dans le deuxième chapitre, nous présenterons des ajustements concrets aux sysèmes expérimentaux basés sur les recommandations émises dans la revue. D’abord, nous améliorons la productivité de la fabrication des transistors, puis développons une instrumentation permettant de mesurer plusieurs capteurs en parallèle. Dans le troisième chapitre, nous prendrons avantage de ces modifications pour présenter dans le deuxième article une méthode permettant une fonctionnalisation du graphène à la fois contrôlée et solide. En utilisant le voltage de grille, nous initions et suspendons la fonctionnalisation covalente du graphène aux sels de diazonium afin d’obtenir le taux de greffage désiré, tout en observant la réaction en temps-réel. Ainsi, par nos avancées méthodologiques et d’instrumentation, nous résolvons un enjeu critique du développement de la chimie de surface, centrale à la performance de biodétection. / Nanoscale electronics are a promising tool for biosensing as they fit their target’s size and allow for local, fast-paced measurements over long time scales. Because of their exceptional electronic properties, graphene field-effect transistors (GFETs) are excellent candidates for biosensing and studying molecular kinetics. This work discusses the analysis, measurement, and functionalization of GFETs as optimized biosensors. In the introduction, we describe the electronic properties of graphene and the main concepts related to GFETs and biodetection. We also establish the three aims of the project, elaborated in three chapters. The first chapter contains a critical literature review that uses original analyses and a thorough state-of-the-field to target statistical analysis and the biorecognition interface assembly as determining factors in sensing performance. In the second chapter, we present the practical adjustments to the experimental systems based on the review’s recommendations. First, we increase the productivity of device fabrication, then we develop a multiplexed electrical measurement setup. In the third chapter, we take advantage of these modifications to present in the second article a method for stable and controlled functionalization. Using the gate voltage, we start and stop the covalent functionalization of graphene with aryldiazonium salts to get the desired grafting level, while observing the reaction in real-time. Thus, with our advances in methodology and instrumentation, we solve a critical aspect of surface chemistry, central for biodetection performance

Power device robustness refers to the device capability of withstanding abnormal events in power electronics applications, which is one of the key device capabilities that are desired in numerous applications. While the current robustness test methods and qualification standards are developed across the 70 years of Silicon (Si) device history, their applicability to the recent wide bandgap (WBG) power devices is questionable. While the market of WBG power devices has exceeded $1 billion and is fast growing, there are many knowledge gaps regarding their robustness, including the failure or degradation physics, testing methods, and lifetime extraction. This dissertation work studies the robustness of Gallium Nitride (GaN) power device. The structures of many GaN power devices are fundamentally different from Si or Silicon Carbide (SiC) power devices, leading to numerous open questions on GaN power device robustness. Based on the device structure, this dissertation is divided into two parts: The first half discusses the robustness of lateral GaN high electron mobility transistor (HEMT), which recently sees rapid adoption among wide range of applications such as the power adapter and chargers, data center, and photovoltaic panels. The absence of p-n junction between the source and drain of GaN HEMT results in the lack of avalanche mechanism. This raises a concern on the device capability of withstanding surge-energy or overvoltage stress, which hinders the penetration of GaN HEMTs in broader applications. To address this concern, the study begins with conducting the single-event unclamped inductive switching (UIS) test on two mainstream commercial p-gate GaN HEMTs with the Ohmic- and Schottky-type gate contacts, where the GaN HEMT is found to withstand surge energy through a resonant energy transfer between the device capacitance and the loop inductance. The failure mechanism is identified to be a pure electrical breakdown determined by device transient breakdown voltage (BV). The BV of GaN HEMT is further found to be "dynamic" from the switching tests with various pulse widths and frequencies, which is further explained by the time-dependent buffer trapping. This dynamic BV (BVDYN) phenomenon indicates that the static or single-pulse test may not reveal the true BV of GaN HEMT in high frequency switching applications. To address this gap, a novel testbed based on a zero-voltage-switching converter with an active clamping circuit is developed to enable the stable switching with kilovolt overvoltage and megahertz frequency. The overvoltage failure boundaries and failure mechanisms of four commercial p-gate GaN HEMTs from multiple vendors are explored. In addition to the frequency-dependent BVDYN, two new failure mechanisms are observed in some devices, which are attributable to the serious carrier trapping in GaN HEMTs under the high-frequency overvoltage switching. At last, based on the findings in the high frequency overvoltage test (HFOT), a physics-based lifetime model for commercial GaN HEMTs utilizing the device on resistance (RON) shift is established and validated by experimental results. Overall, the switching-based test methodology and experimental results provide critical references for the overvoltage protection and qualification of GaN power HEMTs. The second half of the dissertation discusses the robustness of the vertical GaN fin-channel junction field effect transistor (Fin-JFET), a promising pre-commercialized GaN power device with the p-n junction embedded between the gate and drain which enables the avalanche breakdown. The robustness study on GaN JFET follows similar test approaches as Si metal-oxide-semiconductor field-effect transistor (MOSFET) with two key interests: the avalanche and short circuit capabilities. The avalanche breakdown is first explored via the single-event and repetitive UIS tests and under various gate drivers, from which an interesting "avalanche-through-fin-channel" mechanism is discovered. By leveraging this avalanche path, the electro-thermal stress migrates from the main blocking p-n junction to the n-GaN fin channel, resulting in a very favorable failure-to-open-circuit signature. The single-pulse critical avalanche energy density (EAVA) of vertical GaN Fin-JFET is measured to be as high as 10 J/cm2, which is much higher than the Si MOSFET and comparable to the SiC MOSFET. The short circuit capability is explored utilizing the hard-switching fault on the 650-V rated GaN Fin-JFET, with a gate driving circuit identical to the switching application to best mimic device operation in converters. The short circuit withstanding time is measured to be 30.5 µs at an input voltage of 400 V, 17.0 µs at 600 V, and 11.6 µs at 800 V, all among the longest reported for 600-700 V normally-off transistors. In addition, the failure-to-open-circuit signature is also shown in the single-event and repetitive short circuit tests; all devices retain the avalanche breakdown after failure, which is highly desirable for system applications. These results suggest that, while GaN HEMT is already available in market, vertical GaN Fin-JFET shows superior avalanche and short-circuit robustness and thereby can unlock great potential of GaN devices for applications like automotive powertrains, motor drives, and grids. / Doctor of Philosophy / In recent years, many power electronics applications such as data centers and electric vehicles have witnessed a rapid increase in the adoption of wide bandgap (WBG) power devices. The Gallium Nitride (GaN) device is one of the most attractive candidates in WBG devices, owing to its good tradeoff between breakdown voltage and on resistance, as well as the small gate charge that enables high frequency switching. For power devices, their robustness against overvoltage and overcurrent stresses is as important as their performance under normal operations. However, the new material, new device structure, and new device physics in GaN power devices brought up many open knowledge gaps in their robustness study, particularly under the dynamic operation in switching circuits. This dissertation presents the work in exploring the robustness of GaN power devices. Based on the device structure, the discussion is divided in two parts: The first half of the dissertation focuses on the overvoltage robustness of the lateral GaN High Electron Mobility Transistor (HEMT), the commercially available device covering 30 to 900 V voltage classes. A key feature of this device is the lack of p-n junction between source and drain, leading to an absence of avalanche capability. The study is conducted on mainstream, commercial p-gate GaN HEMTs, with a combination of circuit testing, microscale failure analysis, and physics-based device simulation. The main contribution is on three aspects: identifying the single-event and high-frequency repetitive overvoltage boundaries of GaN HEMT, unveiling the failure and degradation mechanisms under transient overvoltage conditions, and providing guidelines to GaN HEMT device users with proper robustness test methodology for device qualification and screening. The second half of the dissertation focuses on the robustness of vertical GaN fin-channel junction field effect transistor (Fin-JFET), a promising pre-commercial GaN power device with the p-n junction implemented between the source and drain. The robustness tests follow the classic approaches deployed for Silicon power devices, where both the avalanche and short circuit capabilities are investigated. From the single-event and repetitive test results, the GaN JFET shows excellent avalanche robustness with a desirable failure-to-open-circuit behavior, as well as a critical avalanche energy (EAVA) of 10 J/cm2 that is higher than the Silicon metal-oxide-semiconductor field-effect transistor (MOSFET) and comparable to the Silicon Carbide MOSFET. For a 650-V rated GaN Fin-JFET, a record high 30.5 μs short circuit time is demonstrated under the hard-switching fault condition at 400 V input voltage. Overall, the results show great potential of GaN power devices for the power electronics applications that involve more stressful operation conditions for devices.