For reducing the CO2 footprint in many industrial fields, the goal is to produce lighter components. The aluminium-silicon (Al-Si) cast alloys are promising candidates to fulfill these goals with a high weight-to-strength ratio, good corrosion properties, excellent castability, and recyclable material. However, the variations within these components need to be understood to produce high-performance components for critical applications. The main reason for the rejection in these applications is defects and microstructural features that reduce the mechanical properties. The addition of copper (Cu) is one way of increasing the mechanical properties in Al-Si alloys and is commonly used in the automotive industry. Casting defects harm the mechanical properties, and these defects can be reduced by improving the melt quality, the correct design of the component, and the gating system. The study aims to investigate the static mechanical properties and the crack initiation and propagation under cyclic loading in an Al-7Si-Mg cast alloy with state-of-the-art experiments. The main focuses were on the effect of the HIP process and the role of Cu addition. In-situ cyclic testing using a scanning electron microscope coupled with electron back-scattered diffraction, digital image correlation, focused ion beam (FIB) slicing, and computed tomography scanning was used to evaluate the complex interaction between the crack path and the microstructural features. The amount of Cu retained in the α-Al matrix in as-cast and heat-treated conditions significantly influenced the static mechanical properties by increasing yield strength and ultimate tensile strength with a decrease in elongation. The three-nearest-neighbor distance of eutectic Si and Cu-rich particles and crack tortuosity were new tools to describe the crack propagation in the alloys, showing that a reduced distance between the Cu-rich phases is detrimental for the mechanical properties. Three dimensional tomography using a FIB revealed that the alloy with 3.2 wt.% Cu had a significantly increased quantity of cracked Si particles and intermetallic phases ahead of the crack tip than the Cu-free alloy. The effect of Cu and HIP process in this work shows the complex interaction between the microstructural features and the mechanical properties, and this needs to be considered to produce high-performance components. / Ett sätt att nå målen med minskade koldioxidutsläpp inom industrin är att producera lättare komponenter. Aluminium-kisel (Al-Si) gjutna legeringar är därför ett bra alternativ då dessa legeringar har ett bra förhållande mellan hållfasthet och vikt, goda korrosionsegenskaper, utmärkt gjutbarhet och är ett återvinningsbart material. En av de största utmaningarna för att producera högpresterande komponenter för kritiska applikationer är variationerna i egenskaper inom dessa komponenter. Orsaken till att inte gjutna Al-Si legeringar andvänds i dessa applikationer är förståelsen av defekter och mikrostruktuella faser påverkar de mekaniska egenskaperna negativt. Koppar (Cu) tillsätts i Al-Si legeringar för att öka de mekaniska egenskaperna vilket ofta nyttjas inom bilindustrin. Hot isostatic pressing (HIP) prosessen är en annan möjlighet att förbättra de mekaniska egenskaperna genom att reducera porositeter i materialet. Studien syftar till att undersöka de mekaniska egenskaperna och sprickinitiering och spricktillväxt i en gjuten legering av Al-7Si-Mg med utmattningstestning i svepelektronmikroskop (SEM) i kombination med electron backscatter diffraction, digital image correlation och focused ion beam (FIB). Mängden Cu i Al-Si legeringen påverkade de statiska mekaniska egenskaperna genom att öka sträckgränsen och brottgränsen. Tillsats av Cu upp till 1.5 vikt.% påverkar inte spricktillväxten märkbart. Däremot förändras beteendet markant vid tillsatser av Cu på mer än 3.0 vikt.% som resulterade i en markant reducering i duktilitet. I det värmebehandlade materialet påverkades de mekaniska egenskaperna av Al-matrisen och mängden intermetalliska faser. Avståndet mellan Cu faserna och Si faserna används för att beskriva spricktillväxten i Al-Si legeringarna. Detta tillsammans med tredimensionell tomografi visade att legeringen med 3.2 vikt.% Cu hade en ökad mängd sprickor i området framför den avancerande sprickan, vilket inte den Cu fria legeringen visade. Al-Si legeringen som utsattes för HIP-processen och värmebehandlingen visade att materialets mikrostruktur i gjutet tillstånd påverkade resultatet. HIP processen slöt porositerena i alla undersökta prover och förbättrade de mekaniska egenskaperna. Dessa resultat kommer kunna användas för att konstruera mer högpresterande komponenter.

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This thesis describes a unique approach of turning on and off transistor cores to reconfigure low-noise amplifiers. A small footprint single-pole, single-throw switch is optimized for low insertion loss and high isolation. A narrowband (non-switchable) LNA is developed as a basis of comparison for reconfigurable designs. The optimized switch is incorporated into different switchable transistor core architectures. These architectures are investigated to determine their ability to reconfigure amplifier performance. One switchable transistor core topology is integrated into a cascode LNA design. An in depth stability analysis employing the S-probe technique is used to help improve the reliability of the cascode design. In addition, a single-pole, double-throw transmit/receive switch, as well as a deserializer are developed to help support the LNA block in a reconfigurable phased-array radar system. This type of flexible radar design is very beneficial in challenging electromagnetic environments.

This work investigates the challenges associated with designing silicon-germanium (SiGe) analog and mixed-signal circuits capable of operating reliably in extreme environment conditions. Three extreme environment operational conditions, namely, operation over an extremely wide temperature range, operation at extremely low temperatures, and operation under radiation exposure, are considered. As a representative for critical analog building blocks, bandgap voltage reference (BGR) circuit is chosen. Several architectures of the BGRs are implemented in two SiGe BiCMOS technology platforms. The effects of wide-temperature operation, deep cryogenic operation, and proton and x-ray irradiation on the performance of BGRs are investigated. The impact of Ge profile shape on BGR's wide-temperature performance is also addressed. Single-event transient response of the BGR circuit is studied through microbeam experiments. In addition, proton radiation response of high-voltage transistors, implemented in a low-voltage SiGe platform, is investigated. A platform consisting of a high-speed comparator, digital-to-analog (DAC) converter, and a high-speed flash analog-to-digital (ADC) converter is designed to facilitate the evaluation of the extreme environment capabilities of SiGe data converters. Room temperature measurement results are presented and predictions on how temperature and radiation will impact their key electrical properties are provided.

This work represents several years' research into the field of radiation hardening by design. The unique characteristics of a SiGe HBT, described in Chapter 1, make it ideally suitable for use in extreme environment applications. Chapter 2 describes the total ionizing dose effects experienced by a SiGe HBT, particularly those experienced on an Earth-orbital or lunar-surface mission. In addition, the effects of total dose are evaluated on passive devices. As opposed to the TID-hardness of SiGe transistors, a clear vulnerability to single-event effects does exist. This field is divided into three chapters. First, the very nature of single-event transients present in SiGe HBTs is explored in Chapter 3 using a heavy-ion microbeam with both bulk and SOI platforms [31]. Then, in Chapter 4, a new device-level SEU-hardening technique is presented along with circuit-design techniques necessarily for its implementation. In Chapter 5, the circuit-level radiation-hardening techniques necessarily to mitigate the effects shown in Chapter 3 are developed and tested [32]. Finally, in Chapter 6, the performance of the SiGe HBT in a cryogenic testing environment is characterized to understand how the widely-varying temperatures of outer space may affect device performance. Ultimately, the built-in performance, TID-tolerance, and now-developing SEU-hardness of the SiGe HBT make a compelling case for extreme environment electronics. The low-cost, high-yield, and maturity of Si manufacturing combine with modern bandgap engineering and modern CMOS to produce a high-quality, high-performance BiCMOS platform suitable for space-borne systems.

Thèse (D.Eng.) -- Université du Québec à Chicoutimi, 2003. / Bibliogr.: f. [325]-340. Document électronique également accessible en format PDF. CaQCU

Made available in DSpace on 2014-10-09T12:51:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:49Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:51:46Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:49Z (GMT). No. of bitstreams: 0 / No presente trabalho quatro ligas Al-Si hipereutéticas, três das quais foram produzidas por conformação por \"spray\" e a outra por fundição, foram caracterizadas quanto a textura, dureza, microestrutura e resistência à corrosão em meio de condensado sintético automotivo (CSA). Duas das ligas conformadas por \"spray\" foram retiradas de camisas de cilindro e a outra de um pré-formado obtido em laboratório. A conformação por \"spray\" envolve a atomização de uma liga e a deposição de gotículas em um substrato, antes mesmo que todas se encontrem no estado sólido. Este processo permite a obtenção de materiais que se caracterizam por uma microestrutura livre de macrossegregações e bastante refinada, implicando melhor trabalhabilidade a quente. A caracterização da microestrutura das quatro ligas hipereutéticas revelou a presença de porosidades na liga obtida em laboratório, e microestrutura com distribuição homogênea de precipitados primários nas três ligas conformadas por \"spray\". A microestrutura de uma das ligas apresentou-se muito diferenciada, com a presença de eutético, sugerindo que esta foi fabricada por fundição. Nas camisas de cilindro foram feitas medidas de rugosidade, e em todas as ligas foram realizados ensaios de microdureza. A liga conformada por \"spray\" e obtida em laboratório foi laminada a quente e a frio. Foram realizados também estudos de textura, para tentar estabelecer uma correlação entre todas as ligas quanto ao processo de fabricação. A avaliação da textura indicou que a presença de fases de silício primário, finamente distribuídas impedem o aparecimento de texturas típicas de deformação de ligas de alumínio, mesmo após severas deformações, como as necessárias para a transformação de pré-formados em tubos que originam as camisas de cilindro. As medidas de rugosidade indicaram características próprias do acabamento superficial usado para a produção das camisas, por brunimento ou por ataque químico. Os ensaios de microdureza apresentaram variações de acordo com as rotas de fabricação sendo que a liga eutética apresentou os maiores valores de microdureza em comparação às ligas conformadas por \"spray\". Todas as ligas foram avaliadas quanto a resistência à corrosão por ensaios de espectroscopia de impedância eletroquímica em dois meios, CSA com pH 3,3 e CSA com pH 11. As quatro ligas hipereutéticas estudadas apresentaram mecanismo de corrosão similar em condensado sintético automotivo (CSA) pH 3,3. Em todas ocorreu o ataque intenso da matriz de alumínio e as partículas de silício primário atuaram como regiões catódicas. A liga 2 apresentou maior resistência à corrosão entre todas as ligas ensaiadas, tanto em CSA pH 3,3 como em pH 11. Neste último meio, uma camada de produtos de corrosão formou-se sobre todas as ligas, e os resultados indicaram mecanismos diferentes para o ataque da matriz de Al e para o crescimento da camada depositada na superfície das ligas estudadas. O ataque da matriz da liga 2 neste meio foi aparentemente mais lento do que sobre as demais ligas, com a formação de uma camada mais compacta de produtos de corrosão, estabelecendo um controle por difusão dos processos interfaciais para maiores períodos de ensaio. A camada formada sobre as demais ligas neste meio apresentou-se mais defeituosa, e nestas ocorreu também menor controle da velocidade das reações interfaciais por processos difusionais. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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