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The increased power consumption and power density demands of modern technologies have increased the technical requirements of DC/DC and AC/DC power supplies. In this regard, the primary objective of the power supply researcher/engineer is to build energy efficient, high power density converters by reducing the losses and increasing the switching frequency of converters respectively. Operating the converter circuits at higher switching frequencies reduces the size of the passive components such as transformers, inductors, and capacitors, which results in a compact size, weight, and increased power density of the converter. Therefore, the thesis work is focussed on the design, analysis and evaluation of isolated converters operating in the 1 - 5MHz frequency region with the assistance of the latest semi conductor devices, both coreless and core based planar power transformers designed in Mid Sweden University and which are suitable for consumer applications of varying power levels ranging from 1 – 60W. In high frequency converter circuits, since the MOSFET gate driver plays a prominent role, different commercially available MOSFET gate drivers were evaluated in the frequency range of 1 - 5MHz in terms of gate drive power consumption, rise/fall times and electromagnetic interference (EMI) and a suitable driver was proposed. Initially, the research was focused on the design and evaluation of a quasi resonant flyback converter using a multilayered coreless PCB step down transformer in the frequency range of 2.7 – 4MHz up to the power level of 10W. The energy efficiency of this converter is found to be 72 - 84% under zero voltage switching conditions (ZVS). In order to further improve the energy efficiency of the converter in the MHz frequency region, the new material device GaN HEMT was considered. The comparisons were made on a quasi resonant flyback DC-DC converter using both the Si and GaN technology and it was found that an energy efficiency improvement of 8 – 10% was obtained with the GaN device in the frequency range of 3.2 – 5MHz. In order to minimize the gate drive power consumption, switching losses and to increase the frequency of the converter in some applications such as laptop adapters, set top box (STB) etc., a cascode flyback converter using a low voltage GaN HEMT and a high voltage Si MOSFET was designed and evaluated using a multi-layered coreless PCB transformer in the MHz frequency region. Both the simulation and experimental results have shown that, with the assistance of the cascode flyback converter, the switching speeds of the converter can be increased with the benefit of obtaining a significant improvement in the energy efficiency as compared to that for the single switch flyback converter. In order to further maximize the utilization of the transformer, to reduce the voltage stress on MOSFETs and to obtain the maximum power density from the converter circuit, double ended topologies were considered. Due to the lack of high voltage high side gate drivers in the MHz frequency region, a gate drive circuitry utilizing the multi-layered coreless PCB signal transformer was designed and evaluated in both a half-bridge and series resonant converter (SRC). It was found that the gate drive power consumption using this transformer was around 0.66W for the frequency range of 1.5 - v 3.75 MHz. In addition, by using this gate drive circuitry, the maximum energy efficiency of the SRC using multilayered coreless PCB power transformer was found to be 86.5% with an output power of 36.5W in the switching frequency range of 2 – 3MHz. In order to further enhance the energy efficiency of the converter to more than 90%, investigations were carried out by using the multiresonant converter topology (LCC and LLC), novel hybrid core high frequency planar power transformer and the GaN HEMTs. The simulated and experimental results of the designed LCC resonant converter show that it is feasible to obtain higher energy efficiency isolated DC/DC converters in the MHz frequency region. The peak energy efficiency of the LCC converter at 3.5MHz is reported to be 92% using synchronous rectification. Different modulation techniques were implemented to regulate the converter for both line and load variations using a digital controller. In order to realize an AC/DC converter suitable for a laptop adapter application, consideration was given to the low line of the universal input voltage range due to the GaN switch limitation. The energy efficiency of the regulated converter operating in the frequency range of 2.8 – 3.5MHz is reported to be more than 90% with a load power of 45W and an output voltage of 22V dc. In order to determine an efficient power processing method on the secondary side of the converter, a comparison was made between diode rectification and synchronous rectification and optimal rectification was proposed for the converters operating in the MHz frequency range for a given power transfer application. In order to maintain high energy efficiency for a wide load range and to maintain the narrow switching frequency range for the given input voltage specifications, the LLC resonant converter has been designed and evaluated for the adapter application. From the observed results, the energy efficiency of the LLC resonant converter is maintained at a high level for a wide load range as compared to that for the LCC resonant converter. Investigations were also carried out on isolated class E resonant DC-DC converter with the assistance of GaN HEMT and a high performance planar power transformer at the switching frequency of 5MHz. The simulated energy efficiency of the converter for the output power level of 16W is obtained as 88.5% which makes it feasible to utilize the designed isolated converter for various applications that require light weight and low profile converters. In conclusion, the research in this dissertation has addressed various issues related to high frequency isolated converters and has proposed solution by designing highly energy efficient converters to meet the current industrial trends by using coreless and core based planar transformer technologies along with the assistance of GaN HEMTs. With the provided solution, in the near future, it is feasible to realize low profile, high power density DC/DC and AC/DC converters operating in MHz frequency region suitable for various applications. / High Frequency Switch Mode Power Supplies

Les composants HEMTs (High Electron Mobility Transistors) à base d’AlGaN/GaN sont à ce jour les candidats les plus prometteurs pour des applications hyperfréquences de puissance, dû essentiellement à leur forte densité de porteurs et des mobilités électroniques élevées. Cependant, la température générée en condition réelle est un paramètre capital à mesurer, afin d’estimer précisément la fiabilité des composants et leur durée de vie. Pour ces raisons, nous avons comparé les méthodes de caractérisation thermique par thermoréflectance et par spectroscopie Raman car elles sont non destructives et avec une résolution spatiale submicronique. Ces techniques ont déjà prouvé leur faisabilité pour la caractérisation thermique des transistors, en modes de fonctionnement continu et pulsé. Nous comparons dans cette étude leurs adaptabilité et performance dans le cadre de la réalisation d’un banc d’essai thermique dédié. Ces méthodes sont reconnues pour ne caractériser que certaines catégories de matériaux : les métaux pour la thermoréflectance et les semiconducteurs pour la spectroscopie Raman, ce qui nous a conduit à l’éventualité de les combiner. Nous avons confronté des résultats obtenus par thermoréflectance à partir des équipements de deux fabricants commercialisant cette méthode, nous permettant ainsi de mettre en évidence des résultats originaux sur des aspects et inconvénients qui ne sont pas relayés dans la littérature. Avec la spectroscopie Raman, nous avons identifié les paramètres de métrologie qui permettent de réaliser un protocole de mesure thermique le plus répétable possible, et nous présentons également une technique innovante pour sonder les matériaux en surface, à l'aide du même équipement, et notamment les métaux. / At the moment, AlGaN/GaN HEMTs (High Electron Mobility Transistors) are the most promising for high-power hyperfrequency applications, essentially due to their large carrier density and a high electronic mobility. However, the temperature generating during operational conditions is a crucial parameter to measure, in order to estimate the reliability and durability of components. For these reasons, we compared thermoreflectance and Raman spectroscopy, that are non-destructive and possessing a submicronic spatial resolution. These techniques have already proven their feasibility as thermal characterization methods in both continuous wave and pulsed operational modes. We compare here their adaptability and performance to the conception of a thermal test bench. These methods are known for characterizing specific types of material: metals for thermoreflectance and semiconductors for Raman spectroscopy, leading us to the eventuality to combine them. We compared several results measured by thermoreflectance method with equipment from two different manufacturers that commercialize this technology, so we could highlight some aspects and drawbacks that are note relayed in the literature. With Raman spectroscopy, we identified metrology parameters allowing to realize a thermal measurement setup as reproducible as possible, and we also present an innovative method to probe surface material, especially metals.

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Yes / Much attention has been paid to making 5G developments more en-ergy efficient, especially in view of the need for using high data rates with more complex modulation schemes within a limited bandwidth. The concept of the Doherty power amplifier for improving amplifier efficiency is explained in addi-tion to a case study of a 70W asymmetrical Doherty power Amplifier using two GaN HEMTs transistors with peak power ratings of 45W and 25W. The rationale for this choice of power ratio is discussed. The designed circuit works in the 3.4GHz frequency band with 200 MHz bandwidth. Rogers RO4350B substrate with dielectric constant εr=4.66 and thickness 0.035 mm is used. The perfor-mance analysis of the Doherty power amplifier is simulated using AWR MWO software. The simulated results showed that 54-64% drain efficiency has been achieved at 8 dB back-off within the specified bandwidth with an average gain of 10.7 dB.

<p>Management of incoming solar radiation and use of the sky as an ultimate heat sink are technological imperatives as climate change shifts our reliance from fossil fuels to sustainable sources.  Selective solar absorbers are a possible route for solar harvesting as they collect the incoming radiation for process heat or space heating.  Here, improvement in the performance of selective solar absorbers via photon recycling is investigated using a stepped index rugate filter.  The final proposed filter when integrated with a high vacuum selective solar absorber could see an improvment in solar-thermal conversion efficiency from 13% to 30.6%. Then, a frequency selective optical filter is fabricated with uses including improvement of radiative coolers.  The measured optical characteristics are compared with simulation data and found to match well.</p> <p><br></p> <p>The shift to sustainable sources of electricity will require an expansion of the electrical grid.  The backbone of the grid for converting high voltage AC to DC, and vice versa, is power electronics.  The current state-of-the-art technology is GaN HEMTs, but GaN MISHEMTs are poised to replace them since MISHEMTs reduce the gate leakage current; a deficiency of the GaN HEMT architecture.  First, time dependent dielectric breakdown in GaN MISHEMTs is investigated using concurrent electrical and thermoreflectance methods.  A susceptibility in the MISHEMT architecture is found and possible solutions are proposed.  Then, liquid cooling of GaN HEMT PAs is explored by demonstrating integration of an X-band front end module, printed circuit board, and fluid manifold.  The integration shows great promise as two-phase cooling performance improved with increasing power dissipated, while single-phase cooling performance degraded.</p>

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La microscopie à émission de photons spectrale (SPEM) est une technique non destructive utilisée comme outil de localisation des défauts et comme indicateur des mécanismes de défaillance. Cette thèse présente un nouveau système de SPEM développé pour étudier la fiabilité des dispositifs de puissance à large bande interdite, notamment les MOSFET SiC et les MEMTs AlGaN/GaN. Un aperçu des différents aspects fondamentaux de l'émission de lumière dans les dispositifs à semi-conducteurs est présenté. L'analyse spectrale en électroluminescence des MOSFET SiC à haute puissance et des HEMTs AlGaN/GaN est rapportée et corrélée avec des analyses électriques et micro-structurales pour localiser les défaillances et identifier l'origine physique de la dérive des performances de ces composants. / Spectroscopic photon emission microscopy (SPEM) is a non-destructive technique used as a defect localizing tool and as an indicator of the failure mechanisms. This thesis presents a new system of SPEM developed to study the reliability of wide band Gap power devices notably SiC MOSFETs and AlGaN/GaN HEMTs. An overview of different fundamental aspects of the light emission defects on semiconductors devices is presented. The electroluminescence spectral analysis of high power stressed SiC MOSFETs and AlGaN/GaN HEMTs is reported and correlated with electrical and micro-structural analysis to localize the failures and identify the physical origin of the performance drift of these components.