Global interconnect reliability is becoming a bigger issue as we scale down further into the submicron regime. As transistor dimensions get smaller, variations in the manufacturing process, and temperature variations may cause undesired behavior, and as a result, compromise performance. This work makes an effort to characterize the effects of such variations, to provide designers with a guideline for making designs tolerant to these variations while benefiting from tighter design margins. Since interconnects contribute to most of the delay and power on a chip, interconnect performance becomes a primary issue in design. One of the main concerns when considering physical transistor dimension variations is the effect on delay. Due to smaller transistor dimensions, the photolithographic process may produce transistors with significant variations from the ideal physical dimensions. Such variations cause delay uncertainty which can lead to over or underestimation in the design phase. This work examines interconnects to establish a guideline of the effect that process variations have on delay. A repeated interconnect is analyzed and the effects of physical device variations on delay are observed. Given the delay distribution in the presence of Leff variation, a supply voltage assignment technique is proposed to correct the observed deviation from the nominal delay on a long, repeated interconnect. This technique results in a significant reduction of the delay distribution, with a negligible power overhead. After looking at static variation effects on interconnect performance, this thesis addresses thermal variations on global signals, which cause delay degradation and may lead to timing failures. Given the presence of a large thermal gradient along a clock signal in a data path clocked by two leaves of an H-tree, several thermal scenarios which can compromise timing are discussed. A buffer-based skew compensation technique is proposed to correct the effect of thermal and manufacturing variations on this system. Having characterized repeated interconnect performance under process variations, the bandwidth of the line can be more effectively utilized by using a technique called phase coding. Phase coded interconnects are introduced in the context of using them once an interconnect has been adequately modeled in the presence of variations. With guidelines quantifying the effects of process variations on interconnect techniques and careful characterization, designers can factor these considerations into their design process, reducing the variation from the nominal expected behavior and allowing for smaller design margins. This will lead to more reliable products as we advance into future technologies and transistor dimensions get smaller.

Le travail présenté dans ce mémoire a porté sur l’auscultation d’un versant rocheux potentiellement instable, les Rochers de Valabres, soumis aux variations naturelles de température de surface. En effet, les variations thermiques sont supposées agir comme facteur préparatoire aux éboulements. Leur action est continu, lente et quasi-imperceptible mais le phénomène est peu exploré et rarement quantifié. Préalablement à l’auscultation, une phase de caractérisation du versant, basée sur des relevés topographiques par scannérisation laser, des mesures de contraintes et des essais en laboratoire, a été menée. Ces investigations ont permis d’appréhender les paramètres intrinsèques du versant et de mettre en évidence, dans la zone superficielle, un état de contraintes élevées, marqué par une forte rotation des axes principaux et influencé par la topographie et la présence d’hétérogénéités. L’auscultation des phénomènes thermomécaniques a été réalisée par un réseau de mesures de déformations et de températures en forage. Les mesures de température ont permis d'évaluer les apports de chaleur, en fonction du temps et de l’espace. Les mesures de déformations, bien qu’affectées par de nombreux artefacts instrumentaux, ont permis de quantifier le phénomène, à l’échelle quotidienne et annuelle, en terme de déformations, de contraintes équivalentes et de profondeurs d’influence. Afin d’explorer l’hypothèse de propagation de fissures sous contraintes d’origine thermique, une approche analytique, basée sur la mécanique de la rupture, a été mise en œuvre. Cette démarche a permis de révéler que les niveaux de contraintes / déformations mesurés sur le site étaient suffisants, sous certaines conditions et hypothèses, pour induire la propagation de fissures préexistantes. Par conséquent, les travaux menés dans cette thèse permettent de confirmer que les phénomènes thermomécaniques constituent un facteur préparatoire non négligeable aux éboulements et peuvent contribuer à la dégradation de la matrice rocheuse et/ou des ponts rocheux par propagation de fissures préexistantes / The present work focuses on the monitoring of a rockslope, prone to instability, named “Rochers de Valabres”, subjected to natural thermal fluctuation at the rock surface. Thermal variations are supposed to be a preparatory factor for rockfalls. Their action is continuous, slow and imperceptible. This phenomenum is not widly studied and seldom quantified. As a first step, investigations, based on topographic survey using Lidar, stress measurements and laboratory testing, have been performed. They reveals parameters of the rockslope, as well as the stress field at shallow depths, characterized by high magnitudes, high turnover of the principal orientations and affected by topography and geological heterogeneities. Thermomechanical monitoring was performed by a network composed of strain cells and thermal sensors, deployed in boreholes. Thermal data give us information about thermal transfer, as a function of time or space. Strain variation data, although affected by thermal artefacts, give quantitative information on strains, equivalent stresses and depth of influence, on daily and seasonal basis. In order to evaluate the assumption of fracture propagation on thermal loading, an analytical model, based on fracture mechanic, is suggested. Using specific conditions and assumptions, this model reveals that measured stress and strains are sufficient to lead to propagation of pre-existing discontinuities. Consequently, this study confirms that thermomechanical variations can be considered as a non negligible preparatory factor for rockfall and can contribute to mechanical degradation of the rock masse and discontinuities

La photonique au silicium est une technologie émergente considérée comme l'une des solutions clés pour les interconnexions sur puce de génération future, offrant plusieurs avantages potentiels tels qu'une faible latence de transmission et une bande passante élevée. Cependant, elle reste confrontée à des défis en matière d'efficacité énergétique. Différentes topologies, layout et architectures offrent diverses options d'interconnexion. Ceci conduit à une grande variation des pertes optiques, qui est l'un des facteurs prédominants dans la consommation d'énergie. De plus, les composants photoniques au silicium sont très sensibles aux variations de température. Sous une activité de puces donnée, ceci conduit à une réduction de l’efficacité des lasers et à une dérive des longueurs d'onde des composants optiques, ce qui entraîne un «Bit Error Ratio (BER)» plus élevé et réduit par conséquent l'efficacité énergétique des interconnexions optiques. Dans cette thèse, nous travaillons sur des méthodologies de conception pour les interconnexions photoniques sur silicium économes-en-énergie et prenant en compte la topologie / le layout, la variation thermique et l'architecture. / Silicon photonics is an emerging technology considered as one of the key solutions for future generation on-chip interconnects, providing several prospective advantages such as low transmission latency and high bandwidth. However, it still encounters challenges in energy efficiency. Different topologies, physical layouts, and architectures provide various interconnect options for on-chip communication. This leads to a large variation in optical losses, which is one of the predominant factors in power consumption. In addition, silicon photonic devices are highly sensitive to temperature variation. Under a given chip activity, this leads to a lower laser efficiency and a drift of wavelengths of optical devices (on-chip lasers and microring resonators (MRs)), which in turn results in a higher Bit Error Ratio (BER) and consequently reduces the energy efficiency of optical interconnects. In this thesis, we work on design methodologies for energy-efficient silicon photonic interconnects on chip related to topology/layout, thermal variation, and architecture.

Concrete slabs used in thepulp and paper industries are often situated outdoors, which means that theslabs are exposed to temperature variations due to different weatherconditions. These temperature variations together with operational temperaturesassociated with the manufacturing process, may introduce high temperaturegradients in the concrete. It is believed that the combination of these thermalloads have resulted in cracking in a slender concrete slab.The aim of this degree project has been to determine if the combination ofseasonal temperature and operational temperature is sufficient to introduce thetype of cracking seen in-situ in the concrete slab of a factory in Sundsvall,400 km north of Stockholm. This was achieved by simulating the development ofcracks in a slender concrete slab exposed to thermal loads using finite elementanalysis (FEA). In order to determine the accuracy of the model, the resultswere compared and evaluated against a crack mapping produced by Sweco. Furthersimulations were also carried out, in order to investigate if continuedcracking would occur beyond the time span of the Sweco investigation.The material model Concrete damage plasticity (CDP) in BRIGADE/Plus and Abaquswas used to predict the crack pattern and crack width in the concrete slab.Linear-elastic and non-linear material properties were used in the modelling ofthe concrete slab. The linear-elastic model indicated that thermal variationshowed significant risk of cracking. Thereafter, non-linear material propertieswere used in the modelling process. The cracking was simulated using ambienttemperature data and operational temperatures from the production plant.The results showed that cracking started when thermal loads were introduced tothe model. The ambient seasonal temperature alone was not enough to introducethe type of cracking seen in-situ on the slab. The combination of seasonalambient temperature and operational temperature was needed, in order for cracksto develop in the concrete slab. The results also indicated that the crackswill propagate further, but this can only be confirmed by performing additionalcrack mapping on site. / Betonggrunder som används för utrustning inom massa- och pappersindustrin befinner sig ofta utomhus vilket betyder att dessa är utsatta för vädrets förändringar. Temperaturvariationer i omgivningen och temperaturer som kommer från tillverkningsprocesserna kan medföra att höga temperaturgradienter skapas i betongen. Det är troligt att kombinationen av dessa termiska belastningar har gett upphov till sprick-bildning i en betonggrund.Målet för detta examensarbete har varit att bestämma, om huruvida kombinationen av års- temperaturer och temperaturer från industriprocessen är tillräckligt för att skapa den typ av sprickbildning i betonggrunden som iaktagits på plats hos en fabrik i Sundsvall. Det gjordes genom simulering av sprickbildning på betonggrunden, där grunden utsattes för termiska belastningar genom att använda finita element analys (FEA). För att bestämma tillförlitligheten hos metoden jämfördes och utvärderades resultatet mot en sprickkartering utförd av Sweco baserad på observationer ute på fabriken. Vidare gjordes ytterligare simuleringar utöver det tidsspann som Swecoundersökningarna visade, detta för att undersöka om huruvida sprickningen skulle fortgå.Materialmodellen Concrete damage plasticity (CDP) som finns i programmen BRIGADE/Plus och Abaqus användes för att förutse sprickbildning och sprickbredd i betonggrunden. Linjärelastiska och icke-linjära materialparametrar användes i modelleringen av betonggrunden. Utetemperatursdata tillsammans med temperaturer från industriprocessen användes för att undersöka anledningen till sprickbildningen.Resultaten av analyserna visade att sprickbildning uppkom när betonggrunden ut-sattes för termiska laster. Temperaturer från omgivningen var inte tillräckligt för att initiera sprickbildning. Kombinationen av temperaturer från omgivningen och industriprocessen behövdes för att sprickbildning skulle ske. Resultaten visade även att sprickbildningen kan fortsätta, med fler och bredare sprickor som följd.För att förhindra att sprickor uppstår i framtiden är det väsentligt att betona vikten av att minska uppkomsten av stora temperaturgradienter i betonggrunden.