Exploration of Graphene-like 2D Materials for Energy Management and Interface Enhancement Applications

Ever since the discovery of graphene in 2004, graphene-like 2D materials and their derivatives have attracted extensive investigations because of their exceptional physical and chemical properties. At present, the study of graphene-like 2D materials is at a stage where most of their outstanding physical and chemical properties have been discovered, but the technology for incorporating them into practical commercial products is rarely revealed. For the potential practical industrial applications of graphene-like 2D materials, energy management and interface enhancement are two of the most promising areas. So far, the behavior of the commercialized graphene-like 2D material products is far from their theoretical performance and expectations as a result of defects and π-π agglomeration, etc. In this regard, there is plenty of research room at the bottom for exploring their practical industrial applications. At present, surface modification is the most widely used strategy to cope with agglomerations. While to be widespread in market, developing low-cost, uniform, and high-quality preparation technology, and encountering the intrinsic agglomeration issues of graphene-like 2D materials are two of the main challenges. To focus on the above two issues, we developed the functionalization method for graphene-like 2D materials, including graphene and hexagonal boron nitride, and explored their potential industrial applications in energy management and interface enhancement. Further, mass production technology and industrial demonstration for graphene and hexagonal boron nitride were explored in some chapters. The main scientific conclusions and innovations of this thesis are listed as below:At first, Chapter 2 presents the experimental research study on using graphene-like 2D materials for energy management, especially in heat dissipation. With the rapid development of microelectronics and 5G communications, efficient heat dissipation is severely demanded for future electronics. To improve heat dissipation efficiency of electronics, based on the ultrahigh thermal conductivity of graphene-like 2D materials, this chapter explored two experimental works, including lightweight and high-performance graphene enhanced heat pipe and hexagonal boron nitride enhanced thermally conductive and electrically insulation heat spreader. (1) Graphene Enhanced Heat PipeIn this work, a unique lightweight and high thermal performance graphene heat pipe were firstly designed and developed. At first, the inner structures of graphene enhanced heat pipe were optimized, including the wicker structures, the filling volume of working fluids and the preparation of high thermal conductivity graphene film. Compared to the conventional copper-based heat pipe, our graphene enhanced heat pipe improves the specific cooling capacity more than 3 times. Further, COMSOL Multiphysics was used to establish the cooling model for graphene enhanced heat pipe. And the equation for quantifying the contribution factor from container and phase change was established. Finally, a graphene/copper composite heat pipe was studied to further improve reliability and mechanical strength. (2) Hexagonal Boron Nitride Enhanced Heat SpreaderIn this work, a hexagonal boron nitride based heat spreader was prepared by electrospinning with polyvinylpyrrolidone. After electrospun, the hexagonal boron nitride nanosheets are aligned along the fiber, and thus increasing the thermal conductivity. At first, the exfoliation technology was investigated. The result shows that a mixture of water and isopropanol (Vwater:VIPA=1:3) shows the highest exfoliation efficiency. With the optimized hexagonal boron nitride particle geometry and loading, the in-plane thermal conductivity of hexagonal boron nitride based heat spreader reaches 22 W m-1 K-1, this value is comparable to most of the reported work. Particularly, such electrospinning process is constant and scalable, showing high potential for mass-production.Chapter 3 still focuses on the application of utilizing graphene-like 2D materials for energy management but specifically in energy storage. Based on the ultrahigh electric mobility, large surface area, flexible, lightweight properties, graphene is an attractive option for energy storage. Therefore, graphene was investigated for electrical double layer capacitors and in-plane micro-supercapacitors in this chapter.(1) Graphene Enhanced Electric Double-layer CapacitorIn this work, a scalable soft template strategy was developed to prepare graphene foam with high electrochemical performance as electrode for supercapacitors. The specific surface areas and wettability of graphene foam is tailored by doping. Further, density functional theory simulation reveals why increasing the polarity of graphene largely improves its wettability. Afterwards, the unique porous structure, low ohm resistance, and high electrical conductivity largely improve the electrochemical performance of graphene foam electrodes and thus achieve ultrahigh specific ca pa city (550 F g-1), cycling sta bility ( 96.1% ca pa city retention after 10 000 cycles at a high current density of 10 A g-1), and outstanding rate capability (308 \ua0\ua0F \ua0\ua0g-1 a \ua0t 100 \ua0\ua0A \ua0\ua0g-1). (2) Graphene Based In-plane Micro-supercapacitorIn this work, graphene assembled film was used to replace the conventional silicon wafer for fabricating flexible and high thermal performance micro-supercapacitors. The result shows that such replacement decreases the surface temperature of micro-supercapacitors by 4 \ub0C, and the graphene based micro-supercapacitor present a similar electrochemical behavior with the referenced silicon based micro-supercapacitor. In addition, the graphene assembled film substrate can work as heat spreader for micro-supercapacitor, thus saving spaces and optimizing the following packaging procedures. This work paves the way for utilizing graphene assembled film in semiconductors.Chapter 4 presents the application of using functional graphene-like 2D materials for interface enhancements due to their high Young’s module, large surface area, anti-friction, etc. Graphene-like 2D materials enhanced composites and bio-application are two of the main categories for the commercialization of interface enhancement. However, the graphene-like 2D materials suffer from π-π agglomeration, which leads to poor dispersibility in solvents and matrix. As a result, graphene-like 2D materials enhanced composites exhibit lower property than their theoretical expectations. At present, surface functionalization is the most effective strategy to encounter the π-π agglomeration. Therefore, this chapter explored the application of using functional graphene-like 2D materials in composites, including graphene enhanced water-borne epoxy coatings and hexagonal boron nitride enhanced cement repair materials.(1) Graphene Enhanced Water-borne Epoxy CoatingGraphene was used to lower the coefficient of friction and extend the lifetime of the water-borne epoxy coating in this work. To improve the dispersibility and the compatibility with epoxy, p-hydroxybenzene diazonium salt was prepared to functional graphene. With the optimized geometry and loading, 30 times less coefficient of friction than graphene-free coatings were achieved. And the wear-out time is more than 2 times longer than the three commercial graphene oxide enhanced coatings. This result is confirmed by Applied Nanosurface AB, Sweden. Besides, mass production technology up to 300 g per batch was developed for the functional graphene. The geometry of graphene was optimized, and the result shows that with the same functional groups, the larger graphene sheets show higher tribological performance than their smaller encounters. Finally, this functionalization strategy was further developed to improve the dispersibility of carbon nanotubes too. (2) Hexagonal Boron Nitride Enhanced Cement Repair MaterialThis work explored the application of using hexagonal boron nitride to enhance cement repair materials. To improve the dispersibility in cement repair materials and the adhesion with substrates, hexagonal boron nitride was functionalized by carboxymethyl cellulose. After functionalization, the surface zeta potential of hexagonal boron nitride decrease from -5.61 mV to -55.07 mV, and thus largely improves its dispersibility. Results show the incorporation of hexagonal boron nitride improve mechanical strength of cement repair materials by contributing to forming alite. Besides, for the repair material containing h-BN, most of the failure happened at the interface repair material/concrete, while the failure is mainly happening in the concrete for the sample containing FBN. Cooperated with a local cement company (Lanark AB), this work has demonstrated the commercial application as repair materials for walls.Besides, we studied the functional graphene quantum dots for mRNA based drug delivery platform. After complexed with mRNA, the transfection efficiency of the graphene quantum dots based drug delivery platform is 25% with a formation concentration as 4000 ng mL-1. A comparable transfection efficiency could be achieved at much lower doses if the ratio between the carrier and the cargo is optimized. This graphene quantum dots based drug delivery platform exhibits excellent processability. This work describes a potentially strategy for prepare stable and effective mRNA delivery systems

Temperature Variation Aware Energy Optimization in Heterogeneous MPSoCs

Thermal effects are rapidly gaining importance in nanometer heterogeneous integrated systems. Increased power density, coupled with spatio-temporal variability of chip workload, cause lateral and vertical temperature non-uniformities (variations) in the chip structure. The assumption of an uniform temperature for a large circuit leads to inaccurate determination of key design parameters. To improve design quality, we need precise estimation of temperature at detailed spatial resolution which is very computationally intensive. Consequently, thermal analysis of the designs needs to be done at multiple levels of granularity. To further investigate the flow of chip/package thermal analysis we exploit the Intel Single Chip Cloud Computer (SCC) and propose a methodology for calibration of SCC on-die temperature sensors. We also develop an infrastructure for online monitoring of SCC temperature sensor readings and SCC power consumption. Having the thermal simulation tool in hand, we propose MiMAPT, an approach for analyzing delay, power and temperature in digital integrated circuits. MiMAPT integrates seamlessly into industrial Front-end and Back-end chip design flows. It accounts for temperature non-uniformities and self-heating while performing analysis. Furthermore, we extend the temperature variation aware analysis of designs to 3D MPSoCs with Wide-I/O DRAM. We improve the DRAM refresh power by considering the lateral and vertical temperature variations in the 3D structure and adapting the per-DRAM-bank refresh period accordingly. We develop an advanced virtual platform which models the performance, power, and thermal behavior of a 3D-integrated MPSoC with Wide-I/O DRAMs in detail. Moving towards real-world multi-core heterogeneous SoC designs, a reconfigurable heterogeneous platform (ZYNQ) is exploited to further study the performance and energy efficiency of various CPU-accelerator data sharing methods in heterogeneous hardware architectures. A complete hardware accelerator featuring clusters of OpenRISC CPUs, with dynamic address remapping capability is built and verified on a real hardware

Amélioration des performances d'un moteur thermique à fluide auto-oscillant par la caractérisation du cycle thermodynamique et du changement de phase

L'objectif de cette thèse est de mieux comprendre les principes de fonctionnement d'un moteur thermique fluidique auto-oscillant (SOFHE) récemment découvert, en caractérisant le cycle thermodynamique (diagramme P-V) et le changement de phase (évaporation-condensation). Le SOFHE est proposé pour la récolte d'énergie thermique, couplé à un transducteur électromécanique, pour alimenter des capteurs sans fil utilisés dans l'Internet des objets (IoT). Le SOFHE est une bulle de vapeur piégée par un bouchon liquide (agissant comme un piston) dans un tube de petit diamètre. Cette bulle de vapeur-bouchon liquide est mise en oscillation par une évaporation-condensation cyclique d'une film liquide mince formée par une fibre de mèche. La première démonstration expérimentale du SOFHE a montré une faible puissance électrique de 1 µW. Cependant, on ne savait toujours pas comment le cycle thermodynamique inconnu de la SOFHE se comporte sous une charge et quelle densité de puissance mécanique la SOFHE peut générer. Pour répondre à cette question, le cycle thermodynamique et la densité de puissance de la SOFHE sont caractérisés expérimentalement pour la première fois sous une charge mécanique variable. La principale contribution de cette caractérisation est de fournir une base de référence pour l'adaptation de l'impédance qui est cruciale pour la conception d'une charge compatible pour la SOFHE. Il est également démontré que la densité de puissance mécanique de la SOFHE est de l'ordre de 0.5 milliwatts/cm3, ce qui en fait une solution prometteuse pour l'alimentation d'une gamme de capteurs sans fil dont la puissance requise est de l'ordre de 10s microwatt. Nous avons également étudié l'effet de la température de fonctionnement de la source de chaleur et de deux paramètres de conception, notamment la longueur de la fibre de mèche et la longueur du bouchon liquide, sur la puissance de la SOFHE. L'augmentation significative de la puissance en augmentant la longueur de la fibre a été la force motrice de la deuxième phase de notre étude dans laquelle nous avons caractérisé le profil de changement de phase complexe et inconnu (évaporation-condensation) de la SOFHE. Un nouveau dispositif a été conçu pour visualiser la variation du film mince autour de la fibre lorsque nous avons joué sur sa longueur à l'intérieur de la zone de vapeur. Les observations ont prouvé notre hypothèse de la formation de coins capillaires entre la fibre et la paroi interne du tube qui pompent le liquide du liquide vers la zone de vapeur. Cela conduit à la formation d'un film mince avec une très faible résistance thermique qui alimente l'évaporation. Le taux de variation de la masse de vapeur, appelé taux de changement de phase, est également mesuré. Il est démontré que pour maximiser l'amplitude de l'oscillation et, par conséquent, la puissance du SOFHE, l'amplitude du taux de changement de phase doit augmenter et être complètement déphasée par rapport à la position. Un nombre sans dimension est également proposé pour évaluer l'efficacité du profil du taux de changement de phase. Enfin, pour mieux contrôler le changement de phase, une nouvelle conception de la SOFHE est proposée et démontrée dans laquelle nous pouvons intégrer des structures de mèche sur mesure pour imiter l'effet de la fibre insérée. Le dispositif est un microcanal à section carrée avec des angles aigus et un chemin capillaire gravé sur la paroi inférieure qui est fabriqué par un procédé standard de microfabrication. Il est démontré que l'amplitude et, par conséquent, la puissance de la SOFHE augmente (multiplication par cinq de 30 à 150 µw/ cm3) avec l'ajout d'un chemin capillaire. Cela ouvre une nouvelle voie vers l'ingénierie du changement de phase de la SOFHE en concevant différentes structures de mèche pour améliorer les performances de la SOFHE.Abstract: The aim of this thesis is to better understand the working principles of a recently discovered self-oscillating fluidic heat engine (SOFHE) by characterizing the thermodynamic cycle (P-V diagram) and phase change (evaporation-condensation). The SOFHE is proposed for thermal energy harvesting, coupled with an electromechanical transducer, for powering wireless sensors used in the Internet of Things (IoT). The SOFHE is a vapor bubble trapped by a liquid plug (acting as a piston) in a small diameter tube. This vapor bubble-liquid plug is set in oscillations by a cyclic evaporation-condensation of a thin liquid film formed by a wicking fiber. The first experimental demonstration of the SOFHE showed a low electrical power of 1 μW. However, it is still unclear how the unknown thermodynamic cycle of the SOFHE behaves under a load and how much mechanical power density the SOFHE can generate. To address this question, the thermodynamic cycle and power density of the SOFHE are experimentally characterized for the first time under a varying mechanical load. The main contribution of this characterization is to provide a baseline for impedance matching that is crucial for designing a compatible load for the SOFHE. It is also shown that the mechanical power density of the SOFHE is in the range of milliwatts/cm3 (maximum 0.5 mW/cm3) which makes it a promising solution to power a range of wireless sensors with a power requirement of tens of microwatt. We also studied the effect of the operating heat source temperature and two design parameters, including the length of the wicking fiber and the length of the liquid plug on the power of SOFHE. The significant increase of the power by increasing the fiber length was the driving force behind the second phase of our study in which we characterized the complex and unknown phase change profile (evaporation-condensation) of the SOFHE. A new setup was designed to visualize the variation of the thin film around the fiber as we played with its length inside the vapor zone. The observations proved our hypothesis of forming capillary corners between the fiber and the inner wall of the tube that pumps liquid from the liquid plug toward the vapor zone. This leads to the formation of a thin film with a very small thermal resistance that feeds evaporation. The rate of change of mass of vapor, the so-called phase change rate, is also measured. It is shown that to maximize the amplitude of the oscillation and consequently the power of the SOFHE, the amplitude of the phase change rate should increase and be completely out of phase with the position. A dimensionless number is also proposed to evaluate the effectiveness of the phase change rate profile. Finally, to better control the phase change, a new design of the SOFHE is proposed in which we can integrate tailored wicking structures to mimic the effect of the inserted fiber. The device is a square cross-section microchannel with sharp corners as well as an etched capillary path on the bottom wall that is fabricated by a standard microfabrication process. It is shown that the amplitude and consequently the power of SOFHE increase (a fivefold increase from 30 to 150 μw/ cm3) as we add a capillary path. This opens a new path towards engineering the phase change of the SOFHE by designing different wicking structures to improve its performance

Reliability Analysis of Power Electronic Devices

The thesis deals with the reliability of Power Electronic Devices to the purpose of evaluating the phenomena which mainly dictate the limiting conditions where a power device can safely operate. Reliability analyses are conducted by means of either simulations and experimental measurements

Methods and Results of Power Cycling Tests for Semiconductor Power Devices

This work intends to enhance the state of the research in power cycling tests with statements on achievable measurement accuracy, proposed test bench topologies and recommendations on improved test strategies for various types of semiconductor power devices. Chapters 1 and 2 describe the current state of the power cycling tests in the context of design for reliability comprising applicable standards and lifetime models. Measurement methods in power cycling tests for the essential physical parameters are explained in chapter 3. The dynamic and static measurement accuracy of voltage, current and temperature are discussed. The feasibly achievable measurement delay tmd of the maximal junction temperature Tjmax, its consequences on accuracy and methods to extrapolate to the time point of the turn-off event are explained. A method to characterize the thermal path of devices to the heatsink via measurements of the thermal impedance Zth is explained. Test bench topologies starting from standard setups, single to multi leg DC benches are discussed in chapter 4. Three application-closer setups implemented by the author are explained. For tests on thyristors a test concept with truncated sinusoidal current waveforms and online temperature measurement is introduced. An inverter-like topology with actively switching IGBTs is presented. In contrast to standard setups, there the devices under test prove switching capability until reaching the end-of-life criteria. Finally, a high frequency switching topology with low DC-link voltage and switching losses contributing significantly to the overall power losses is presented providing new degrees of freedom for setting test conditions. The particularities of semiconductor power devices in power cycling tests are thematized in chapter 5. The first part describes standard packages and addressed failure mechanisms in power cycling. For all relevant power electronic devices in silicon and silicon carbide, the devices’ characteristics, methods for power cycling and their consequences for test results are explained. The work is concluded and suggestions for future work are given in chapter 6.:Abstract 1 Kurzfassung 3 Acknowledgements 5 Nomenclature 10 Abbreviations 10 Symbols 12 1 Introduction 19 2 Applicable Standards and Lifetime Models 25 3 Measurement parameters in power cycling tests 53 4 Test Bench Topologies 121 5 Semiconductor Power Devices in Power Cycling 158 6 Conclusion and Outlook 229 References 235 List of Publications 253 Theses 257Diese Arbeit bereichert den Stand der Wissenschaft auf dem Gebiet von Lastwechseltests mit Beiträgen zu verbesserter Messgenauigkeit, vorgeschlagenen Teststandstopologien und verbesserten Teststrategien für verschiedene Arten von leistungselektronischen Bauelementen. Kurzgefasst der Methodik von Lastwechseltests. Das erste Themengebiet in Kapitel 1 und Kapitel 2 beschreibt den aktuellen Stand zu Lastwechseltests im Kontext von Design für Zuverlässigkeit, welcher in anzuwendenden Standards und publizierten Lebensdauermodellen dokumentiert ist. Messmethoden für relevante physikalische Parameter in Lastwechseltests sind in Kapitel 3. erläutert. Zunächst werden dynamische und statische Messgenauigkeit für Spannung, Strom und Temperaturen diskutiert. Die tatsächlich erreichbare Messverzögerung tMD der maximalen Sperrschichttemperatur Tjmax und deren Auswirkung auf die Messgenauigkeit der Lastwechselfestigkeit wird dargelegt. Danach werden Methoden zur Rückextrapolation zum Zeitpunkt des Abschaltvorgangs des Laststroms diskutiert. Schließlich wird die Charakterisierung des Wärmepfads vom Bauelement zur Wärmesenke mittels Messung der thermischen Impedanz Zth behandelt. In Kapitel 4 werden Teststandstopologien beginnend mit standardmäßig genutzten ein- und mehrsträngigen DC-Testständen vorgestellt. Drei vom Autor umgesetzte anwendungsnahe Topologien werden erklärt. Für Tests mit Thyristoren wird ein Testkonzept mit angeschnittenem sinusförmigem Strom und in situ Messung der Sperrschichttemperatur eingeführt. Eine umrichterähnliche Topologie mit aktiv schaltenden IGBTs wird vorgestellt. Zuletzt wird eine Topologie mit hoch frequent schaltenden Prüflingen an niedriger Gleichspannung bei der Schaltverluste signifikant zur Erwärmung der Prüflinge beitragen vorgestellt. Dies ermöglicht neue Freiheitsgrade um Testbedingungen zu wählen. Die Besonderheiten von leistungselektronischen Bauelementen werden in Kapitel 5 thematisiert. Der erste Teil beschreibt Gehäusetypen und adressierte Fehlermechanismen in Lastwechseltests. Für alle untersuchten Bauelementtypen in Silizium und Siliziumkarbid werden Charakteristiken, empfohlene Methoden für Lastwechseltests und Einflüsse auf Testergebnisse erklärt. Die Arbeit wird in Kapitel 6 zusammengefasst und Vorschläge zu künftigen Arbeiten werden unterbreitet.:Abstract 1 Kurzfassung 3 Acknowledgements 5 Nomenclature 10 Abbreviations 10 Symbols 12 1 Introduction 19 2 Applicable Standards and Lifetime Models 25 3 Measurement parameters in power cycling tests 53 4 Test Bench Topologies 121 5 Semiconductor Power Devices in Power Cycling 158 6 Conclusion and Outlook 229 References 235 List of Publications 253 Theses 25

Degradation in FPGAs: Monitoring, Modeling and Mitigation

This dissertation targets the transistor aging degradation as well as the associated thermal challenges in FPGAs (since there is an exponential relation between aging and chip temperature). The main objectives are to perform experimentation, analysis and device-level model abstraction for modeling the degradation in FPGAs, then to monitor the FPGA to keep track of aging rates and ultimately to propose an aging-aware FPGA design flow to mitigate the aging

Physical parameter-aware Networks-on-Chip design

PhD ThesisNetworks-on-Chip (NoCs) have been proposed as a scalable, reliable and power-efficient communication fabric for chip multiprocessors (CMPs) and multiprocessor systems-on-chip (MPSoCs). NoCs determine both the performance and the reliability of such systems, with a significant power demand that is expected to increase due to developments in both technology and architecture. In terms of architecture, an important trend in many-core systems architecture is to increase the number of cores on a chip while reducing their individual complexity. This trend increases communication power relative to computation power. Moreover, technology-wise, power-hungry wires are dominating logic as power consumers as technology scales down. For these reasons, the design of future very large scale integration (VLSI) systems is moving from being computation-centric to communication-centric. On the other hand, chip’s physical parameters integrity, especially power and thermal integrity, is crucial for reliable VLSI systems. However, guaranteeing this integrity is becoming increasingly difficult with the higher scale of integration due to increased power density and operating frequencies that result in continuously increasing temperature and voltage drops in the chip. This is a challenge that may prevent further shrinking of devices. Thus, tackling the challenge of power and thermal integrity of future many-core systems at only one level of abstraction, the chip and package design for example, is no longer sufficient to ensure the integrity of physical parameters. New designtime and run-time strategies may need to work together at different levels of abstraction, such as package, application, network, to provide the required physical parameter integrity for these large systems. This necessitates strategies that work at the level of the on-chip network with its rising power budget. This thesis proposes models, techniques and architectures to improve power and thermal integrity of Network-on-Chip (NoC)-based many-core systems. The thesis is composed of two major parts: i) minimization and modelling of power supply variations to improve power integrity; and ii) dynamic thermal adaptation to improve thermal integrity. This thesis makes four major contributions. The first is a computational model of on-chip power supply variations in NoCs. The proposed model embeds a power delivery model, an NoC activity simulator and a power model. The model is verified with SPICE simulation and employed to analyse power supply variations in synthetic and real NoC workloads. Novel observations regarding power supply noise correlation with different traffic patterns and routing algorithms are found. The second is a new application mapping strategy aiming vii to minimize power supply noise in NoCs. This is achieved by defining a new metric, switching activity density, and employing a force-based objective function that results in minimizing switching density. Significant reductions in power supply noise (PSN) are achieved with a low energy penalty. This reduction in PSN also results in a better link timing accuracy. The third contribution is a new dynamic thermal-adaptive routing strategy to effectively diffuse heat from the NoC-based threedimensional (3D) CMPs, using a dynamic programming (DP)-based distributed control architecture. Moreover, a new approach for efficient extension of two-dimensional (2D) partially-adaptive routing algorithms to 3D is presented. This approach improves three-dimensional networkon- chip (3D NoC) routing adaptivity while ensuring deadlock-freeness. Finally, the proposed thermal-adaptive routing is implemented in field-programmable gate array (FPGA), and implementation challenges, for both thermal sensing and the dynamic control architecture are addressed. The proposed routing implementation is evaluated in terms of both functionality and performance. The methodologies and architectures proposed in this thesis open a new direction for improving the power and thermal integrity of future NoC-based 2D and 3D many-core architectures