Natural resources are always collected from harsh environments, such as mines and deep wells. Currently, depleted oil wells force the gas and oil industry to drill deeper. As the industry drills deeper, temperatures of these wells can exceed 210 °C. Contemporary downhole systems have reached their depth and temperature limitations in deep basins and are no longer meet the high requirements in harsh environment industries. Therefore, robust electronic systems that can operate reliably in harsh environments are in high demand. This thesis presents a high temperature reference voltage generator that can operate reliably up to 250 °C for a downhole communication system. The proposed reference voltage generator is designed and prototyped using 4H-SiC bipolar transistors. Silicon carbide (SiC) is a semiconductor material that exhibits wide bandgap, high dielectric breakdown field strength, and high thermal conductivity. Due to these properties, it is suitable for high-frequency, high-power, and high-temperature applications. For bypassing the lack of high temperature p-type SiC transistors (pnp BJT, PMOS) and OpAmp inconvenience, an all npn voltage reference architecture has been developed based on Widlar bandgap reference concept. The proposed reference voltage generator demonstrates for the first time a functional high temperature discrete reference voltage generator that uses only five 4H-SiC transistors to achieve both temperature and supply independent. Measurement results show that the proposed voltage reference generator provides an almost constant negative reference voltage around -3.23 V from 25 °C to 250 °C regardless of any change in power supply with a low temperature coefficient (TC) of 42 ppm/°C. / Master of Science

With GaN and SiC switching devices becoming more commercially available, higher switching frequency is being applied to achieve higher efficiency and power density in power converters. However, electro-magnetic interference (EMI) becomes a more severe problem as a result. In this thesis, the switching frequency effect on conducted EMI noise is assessed. As EMI noise increases, the EMI filter plays a more important role in a power converter. As a result, an effective EMI modeling technique of the power converter system is required in order to find an optimized size and effective EMI filter. The frequency-domain model is verified to be an efficient and easy model to explore the EMI noise generation and propagation in the system. Of the various models, the unterminated behavioral model can simultaneously predict CM input and output noise of an inverter, and the prediction falls in line with the measurement around 10 MHz or higher. The DM terminated behavioral model can predict the DM input or output noise of the motor drive higher than 20 MHz. These two models are easy to extract and have high prediction capabilities; this is verified on a 10 kHz-switching-frequency Si motor drive. It is worthwhile to explore the prediction capability of the two models when they are applied to a SiC-based power inverter with switching frequency ranges from 20 kHz to 70 kHz. In this thesis, the CM unterminated behavioral model is first applied to the SiC power inverter, and results show that the model prediction capability is limited by the noise floor of the oscilloscope measurement. The proposed segmented-frequency-range measurement is developed and verified to be a good solution to the noise floor. With the improved impedance fixtures, the prediction from CM model matches the measurement to 30 MHz. To predict the DM input and output noise of the SiC inverter, the DM terminated behavioral model can be used under the condition that the CM and DM noise are decoupled. With the system noise analysis, the DM output side is verified to be independent of the CM noise and input side. The DM terminated behavioral model is extracted at the inverter output and predicts the DM output noise up to 30 MHz after solving the noise floor and DM choke saturation problem. At the DM input side, the CM and DM are seen to be coupled with each other. It is found experimentally that the mixture of the CM and DM noise results from the asymmetric impedance of the system. The mixed mode terminated behavioral model is proposed to predict the DM noise when a mixed CM effect exists. The model can capture the DM noise up to to 30 MHz when the impedance between the inverter to CM ground is not balanced. The issue often happens in extraction of the model impedance and is solved by the curving-fitting optimization described in the thesis. This thesis ends with a summary of contributions, limitations, and some future research directions. / Master of Science

Nanostructured ferritic alloy and silicon carbide composite materials (NFA-SiC) were sintered with spark plasma sintering (SPS) method and systematically investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as density and Vickers hardness tests. Pure NFA, pure SiC, and their composites NFA-SiC with different compositions (2.5 vol% NFA-97.5 vol% SiC, 5 vol% NFA-95 vol% SiC, 97.5 vol% NFA-2.5 vol% SiC, and 95 vol% NFA-5 vol% SiC) were successfully sintered through SPS. In the high-NFA samples, pure NFA and NFA-SiC, minor gamma-Fe phase formation from the main alfa-Fe matrix occurred in pure NFA 950 degree C and 1000 degree C. The densities of the pure NFA and NFA-SiC composites increased with sintering temperature but decreased with SiC content. The Vickers hardness of the pure NFA and NFA-SiC composites was related to density and phase composition. In the high-SiC samples, NFA addition of 2.5 vol% can achieve full densification for the NFA-SiC samples at relative low temperatures. With the increase in sintering temperature, the Vickers hardness of the pure SiC and NFA-SiC composite samples were enhanced. However, the NFA-SiC composites had relative lower hardness than the pure SiC samples. A carbon layer was introduced in the NFA particles to prevent the reaction between NFA and SiC. Results indicated that the carbon layer was effective up to 1050 degree C sintering temperature. Green samples of gradient-structured NFA-SiC composites were successfully fabricated through slip casting of an NFA-SiC co-suspension. / Master of Science

This thesis provides insight into state-of-the-art 1.2 kV silicon carbide (SiC) power semiconductor transistors, including the MOSFET, BJT, SJT, and normally-on and normally-off JFETs. Both commercial and sample devices from the semiconductor industry's well-known manufacturers were evaluated in this study. These manufacturers include: Cree Inc., ROHM Semiconductor, General Electric, Fairchild Semiconductor, GeneSiC Semiconductor, Infineon Technologies, and SemiSouth Laboratories. To carry out this work, static characterization of each device was performed from 25 ºC to 200 ºC. Dynamic characterization was also conducted through double-pulse tests. Accordingly, this thesis describes the experimental setup used and the different measurements conducted, which comprise: threshold voltage, transconductance, current gain, specific on-resistance, parasitic capacitances, internal gate resistance, and the turn on and turn off switching times and energies. For the latter, the driving method used for each device is described in detail. Furthermore, for the devices that require on-state dc currents, driving losses are taken into consideration. While all of the SiC transistors characterized in this thesis demonstrated low specific on-resistances, the SiC BJT showed the lowest, with Fairchild's FSICBH057A120 SiC BJT having 3.6 mΩ•cm2 (using die area) at 25 ºC. However, the on-resistance of GE's SiC MOSFET proved to have the smallest temperature dependency, increasing by only 59 % from 25 ºC to 200 ºC. From the dynamic characterization, it was shown that Cree's C2M0080120D second generation SiC MOSFET achieved dv/dt rates of 57 V/ns. The SiC MOSFETs also featured low turn off switching energy losses, which were typically less than 70 µJ at 600 V bus voltage and 20 A load current. / Master of Science

Silicon carbide and silicon nitride turbine engine components are susceptible to hot corrosion by molten sodium sulfate salts which are formed from impurities in the engine's fuel and air intake. Several oxide materials were identified which may be able to protect these components from corrosion and preserve their structural properties. Ta20, coatings were identified as one of the most promising candidates. Thermochemical calculations showed that the chemical vapor deposition(CVD) of tantalum oxide from O2 and TaCI5 precursors is thermodynamically feasible over a range of pressures, temperatures, and reactant concentrations. The deposition of Ta205, as a single phase is predicted in regions of excess oxygen, where the reaction is predicted to yield nearly 100% efficiency. CVD experiments were carried out to deposit tantalum oxide films onto SiC substrates. Depending on the deposition conditions, a variety of coating morphologies have been produced, and conditions have been identified which produce dense, continuous Ta205 deposits. Preliminary corrosion tests on these coatings showed no apparent degradation of the CVD deposited tantalum oxide coatings. The feasibility of depositing ZrTi04 as a coating material was also investigated based on thermochemical considerations. Since no data were available for this material, thermodynamic values were estimated. Thermochemical calculations indicated the chemical vapor deposition of zirconium titanate from O2, ZrCl4, and TiCl4 occurs over a range of temperatures in a very narrow region of the phase diagram. Deviations from the single phase region predicted the codeposition of either Zr02 or Ti02 with ZrTi04. These results suggested that the chemical vapor deposition of ZrTi04 may be difficult from a process handling perspective. Additionally, the process is predicted to be very inefficient, leaving substantial amounts of unreacted chlorides in the reactor exhaust. / Master of Science

As wide-bandgap devices continue to experience deeper penetration in commercial applications, there are still a number of factors which make the adoption of such technologies difficult. One of the most notable issues with the application of wide-bandgap technologies is meeting existing noise requirements and regulations. Due to the faster dv/dt and di/dt of SiC devices, more noise is generated in comparison to Si IGBTs. Therefore, in order to fully experience the benefits offered by this new technology, the noise must either be filtered or mitigated by other means. A survey of various DC/DC topologies was conducted in order to find a candidate for a battery interface in a UPS system. A three-level NPC topology was explored for its potential benefit in terms of noise, efficiency, and additional features. This converter topology was modeled, simulated, and a hardware prototype constructed for evaluation within a UPS system, although its uses are not limited to such applications. A UPS system is a good example of an application with strict noise requirements which must be fulfilled according to IEC standards. Based on a newly devised mode of operation, this converter was verified to produce no common-mode voltage under ideal conditions, and was able to provide a 6 dB reduction in common-mode voltage emissions in the UPS prototype. This was done while achieving a peak efficiency in excess of 99% with the ability to provide bidirectional power flow between the UPS and battery backup. The converter was verified to operate at the rated UPS conditions of 20 kW while converting between a total DC bus voltage of 800 V and a nominal battery voltage of 540 V. / Master of Science / As material advancements allow for the creation of devices with superior electrical characteristics compared to their predecessors, there are still a number of factors which cause these devices to see limited usage in commercial applications. These devices, typically referred to as wide-bandgap devices, include silicon carbide (SiC) transistors. These SiC devices allow for much faster switching speeds, greater efficiencies, and lower system volume compared to their silicon counterparts. However, due to the faster switching of these devices, there is more electromagnetic noise generated. In many applications, this noise must be filtered or otherwise mitigated in order to meet international standards for commercial use. Consequently, new converter topologies and configurations are necessary to provide the most benefit of the new wide-bandgap devices while still meeting the strict noise requirements. A survey of topologies was conducted and the modeling, design, and testing of one topology was performed for use in an uninterruptible power supply (UPS). This converter was able to provide a noticeable reduction in noise compared to standard topologies while still achieving very high efficiency at rated conditions. This converter was also verified to provide power bidirectionally—both when the UPS is charging the battery backup, and when the battery is supplying power to the load.

The corrosion resistance of two commercially available SiC filter materials coated with Mg-doped Al₂ TiO₅ and (Ca _0.6.6' Mg_0.52) Zr₄P₆O₂₄ (CMZP) was investigated in high-temperature high pressure (HTHP) alkali-steam environments. Coated specimen properties, including cold and hot compressive strengths, bulk density, apparent porosity, permeability, and weight change, detected after exposure to 92% air-S% steam 10 ppm Na at 8OO°C and 1.8 MPs for 500 h were compared with those of uncoated specimens. Procedures for applying homogeneous coatings of Mg-doped Al₂ TiO₅ and CMZP to porous SiC filters were established and coating of the materials was successfully accomplished. Efforts to stabilize the Al₂ TiO₅ coating composition at elevated temperature were successful. Coatings show promise for providing improved corrosion resistance of the materials in pressurized fluidized bed combustion (PFBC) environments as evidenced by higher compressive strengths exhibited by coated SiC specimens than by uncoated SiC specimens following HTHP alkali-steam exposure. / Master of Science

Silicon carbide and nanostructured ferritic alloy (SiC-NFA) composites have the potential to maintain the outstanding high temperature corrosion and irradiation resistance and enhance the mechanical integrity for nuclear cladding. However, the formation of detrimental silicide phases due to reaction between SiC and NFA remains a major challenge. By introducing a carbon interfacial barrier on NFA (C@NFA), SiC-C@NFA composites are investigated to reduce the reaction between SiC and NFA. In a similar way, the effect of chromium carbide (Cr3C2) interfacial barrier on SiC (Cr3C2@SiC) is also presented for Cr3C2@SiC-NFA composites. Both the coatings were successful in suppressing silicide formation. However, despite the presence of coatings, SiC was fully consumed during spark plasma sintering process. TEM and EBSD investigations revealed that spark plasma sintered SiC-C@NFA and Cr3C2@SiC-NFA formed varying amounts of different carbides such as (Fe,Cr)7C3, (Ti,W)C and graphite phases in their microstructure. Detailed microstructural examinations after long term thermal treatment at 1000oC on the microstructure of Cr3C2@SiC-NFA showed precipitation of new (Fe,Cr)7C3, (Ti,W)C carbides and also the growth of existing and new carbides. The results were successfully explained using ThermoCalc precipitation and coarsening simulations respectively. The oxidation resistance of 5, 15 and 25 vol% SiC@NFA and Cr3C2@SiC-NFA composites at 500-1000oC temperature under air+45%water vapor containing atmosphere is investigated. Oxidation temperature effects on surface morphologies, scale characteristics, and cross-sectional microstructures were investigated and analyzed using XRD and SEM. SiC-C@NFA showed reduced weight gain but also showed considerable internal oxidation. Cr3C2@SiC-NFA composites showed a reduction in weight gain with the increasing volume fraction of Cr3C2@SiC (5, 15 and 25) without any indication of internal oxidation in the microstructure. 25 vol% SiC-C@NFA and 25 vol% Cr3C2@SiC-NFA showed over 90% and 97% increase in oxidation resistance (in terms of weight gain) as compared to NFA. The results were explained using the fundamental understanding of the oxidation process and ThermoCalc/DICTRA simulations. Finally, the irradiation performance of SiC-C@NFA and Cr3C2@SiC-NFA composites was assessed in comparison with NFA using state-of-the-art TEM equipped with in-situ ion irradiation capability. Kr++ ions with 1 MeV energy was used for irradiation experiments. The effect of ion irradiation was recorded after particular dose levels (0-10 dpa) at 300oC and 450oC temperatures. NFA sample showed heavy dislocation damage at both 300oC and 450oC increasing gradually with dose levels (0-10 dpa). Cr3C2@SiC-NFA showed similar behavior as NFA at 300oC. However, at 450oC, Cr3C2@SiC-NFA showed remarkably low dislocation loop density and loop size as compared to NFA. At 300oC, microstructures of NFA and Cr3C2@SiC-NFA show predominantly 1/2<111> type dislocation loops. At 450oC, NFA showed predominantly <100> type loops, however, Cr3C2@SiC-NFA composite was still predominant in ½<111> loops. The possible reasons for this interesting behavior were discussed based on the large surface sink effects and enhanced interstitial-vacancy recombination at higher temperatures. The molecular dynamics simulations did not show considerable difference in formation energies of ½<111> and <100> loops for NFA and Cr3C2@SiC-NFA composites. The additional Si element in the SiC-NFA sample could have been an important factor in determining the dominant loop types. SiC-C@NFA composites showed heavy dislocation damage during irradiation at 300oC. At 450oC, SiC-C@NFA showed high dislocation damage in thicker regions. Thinner regions near the edge of TEM samples were largely free from dislocation loops. The precipitation and growth of new (Ti,W)C carbides were observed at 450oC with increasing irradiation dose. (Fe,Cr)7C3 precipitates were largely free from any dislocation damage. Some Kr bubbles were observed inside (Fe,Cr)7C3 precipitates and at the interface between α-ferrite matrix and carbides ((Fe,Cr)7C3, (Ti,W)C). The results were discussed using the fundamental understanding of irradiation and ThermoCalc simulations. / Doctor of Philosophy / With the United Nations describing climate change as 'the most systematic threat to humankind', there is a serious need to control the world's carbon emissions. The ever increasing global energy needs can be fulfilled by the development of clean energy technologies. Nuclear power is an attractive option as it can produce low cost electricity on a large scale with greenhouse gas emissions per kilowatt-hour equivalent to wind, hydropower and solar. The problem with nuclear power is its vulnerability to potentially disastrous accidents. Traditionally, fuel claddings, rods which encase nuclear fuel (e.g. UO2), are made using zirconium based alloys. Under 'loss of coolant accident (LOCA) scenarios' zirconium reacts with high temperature steam to produce large amounts of hydrogen which can explode. The risks associated with accidents can be greatly reduced by the development of new accident tolerant materials. Nanostructured ferritic alloys (NFA) and silicon carbide (SiC) are long considered are leading candidates for replacing zirconium alloys for fuel cladding applications. In this dissertation, a novel composite of SiC and NFA was fabricated using spark plasma sintering (SPS) technology. Chromium carbide (Cr3C2) and carbon (C) coatings were employed on SiC and NFA powder particles respectively to act as reaction barrier between SiC and NFA. Microstructural evolution after spark plasma sintering was studied using advanced characterization tools such as scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) techniques. The results revealed that the Cr3C2 and C coatings successfully suppressed the formation of detrimental reaction products such as iron silicide. However, some reaction products such as (Fe,Cr)7C3 and (Ti,W)C carbides and graphite retained in the microstructure. This novel composite material was subjected to high temperature oxidation under a water vapor environment to study its performance under the simulated reactor environment. The degradation of the material due to high temperature irradiation was studied using state-of-the-art TEM equipped with in-situ ion irradiation capabilities. The results revealed excellent oxidation and irradiation resistance in SiC-NFA composites as compared to NFA. The results were discussed based on fundamental theories and thermodynamic simulations using ThermoCalc software. The findings of this dissertation imply a great potential for SiC-NFA based composites for future reactor material designs.

As the boundaries of Moore's Law rapidly approach, research is increasingly turning to exotic materials and metamaterials to advance the capabilities of electronic and micromechanical systems. This thesis presents systems, models, and simulation techniques for novel microfabrication in the realms of silicon carbide (SiC) and metal mesh filters. Through the unification of femtosecond laser pulses, high numerical aperture (NA) objective lenses, and system power and motion control, a system capable of achieving arbitrary 3D features without line-of-sight with aspect ratios up to 109:1 in SiC is developed. Additionally, a model of a direct-write femtosecond-laser-ablation fabricated metal mesh filter (MMF) is simulated in ANSYS High Frequency Structure Simulator (HFSS) and validates the novel fabrication technique. Finally, a transmission-line-theory based MMF model is presented as an alternative to modelling multilayer filters in HFSS. This model produces comparable results to an HFSS simulation with dramatically reduced computational intensity.

Modern data center power architecture developing trend is analyzed, efficiency improvement method is also discussed. Literature survey of high frequency isolated power conversion system which is also called solid state transformer is given including application, topology, device and magnetic transformer. Then developing trend of this research area is clearly shown following by research target. State of art wide band gap device including silicon carbide (SiC) and gallium nitride (GaN) devices are characterized and compared, final selection is made based on comparison result. Mostly used high frequency high power DC/DC converter topology dual active bridge (DAB) is introduced and compared with novel CLLC resonant converter in terms of switching loss and conduction loss point of view. CLLC holds ZVS capability over all load range and smaller turn off current value. This is beneficial for high frequency operation and taken as our candidate. Device loss breakdown of CLLC converter is also given in the end. Medium voltage high frequency transformer is the key element in terms of insulation safety, power density and efficiency. Firstly, two mostly used transformer structures are compared. Then transformer insulation requirement is referred for 4160 V application according to IEEE standard. Solid insulation material are also compared and selected. Material thickness and insulation distance are also determined. Insulation capability is preliminary verified in FEA electric field simulation. Thirdly two transformer magnetic loss model are introduced including core loss model and litz wire winding loss model. Transformer turn number is determined based on core loss and winding loss trade-off. Different core loss density and working frequency impact is carefully analyzed. Different materials show their best performance among different frequency range. Transformer prototype is developed following designed parameter. We test the developed 15 kW 500 kHz transformer under 4160 V dry type transformer IEEE Std. C57.12.01 standard, including basic lightning test, applied voltage test, partial discharge test. 500 kHz 15 kW CLLC converter gate drive is our design challenge in terms of symmetry propagation delay, cross talk phenomenon elimination and shoot through protection. Gate drive IC is carefully selected to achieve symmetrical propagation delay and high common mode dv/dt immunity. Zero turn off resistor is achieved with minimized gate loop inductance to prevent cross talk phenomenon. Desaturation protection is also employed to provide shoot through protection. Finally 15 kW 500 kHz CLLC resonant converter is developed based on 4160V 500 kHz transformer and tested up to full power level with 98% peak efficiency. / Master of Science / Modern data center power architecture developing trend is analyzed, efficiency improvement method is also discussed. At the same time high frequency operation is preferred to reduce reactive component size like transformer and capacitor. To achieve better trade-off between high efficiency and high frequency in our research. Literature survey of high frequency isolated DC/DC power converter is given including application, circuit topology, power electronics device and magnetic transformer. Then developing trend of this research area is clearly shown following by research target. State of art advance material based power electronics devices are characterized and compared, final selection is made based on comparison result. Mostly used high frequency high power DC/DC converter topology dual active bridge (DAB) is introduced and compared with novel CLLC resonant converter in terms of converter loss. CLLC holds smaller converter loss. This is beneficial for high frequency operation and taken as our candidate. Medium voltage high frequency transformer is the key element in terms of insulation safety, power density and efficiency. Firstly, two mostly used transformer structures are compared. Then transformer insulation requirement is referred for 4160 V application according to IEEE standard. Solid insulation material are also compared and selected. Material thickness and insulation distance are also determined. Thirdly transformer loss model are introduced including core loss model and winding loss model. Transformer turn number is determined based on transformer loss and volume trade-off. Transformer prototype is developed following designed parameter. We test the developed transformer under IEEE standard requirement and pass all the test. Converter gate drive is one of our design challenge. We need to achieve symmetrical propagation delay between command signal and final drive circuit output, suppress interference from other high frequency switching devices, and protect device under short circuit condition. Gate drive IC is carefully selected to achieve symmetrical propagation delay and suppress other’s interference. Device conduction voltage is employed to compare with threshold value to determine whether it is under short circuit condition. Finally 15 kW 500 kHz CLLC resonant converter is developed based on 4160V 500 kHz transformer and tested up to full power level with 98% peak efficiency.