A point-of-load converter was designed for a distributed power architecture using a normally off silicon carbide (SiC) junction field effect transistor (JFET) as the enabling technology. The power supply accepts a 208-V single phase input and generates a +26 V and +10 V output for pulsed loads as well as a +5 V and -5 V auxiliary supplies for digital/control circuitry. This work focuses on the integration of the first normally off SiC JFET to allow for an efficient (≥ 93%), high power density (≥ 100 W/in3) power converter demonstrating higher switching frequency. A switching frequency of 500 kHz was achieved which more than doubles the operating frequency of a reference design with silicon MOSFETs. The power supply design described in this thesis integrates a power factor correction pre-regulator with multiple output Weinberg and flyback converters each utilizing normally off SiC JFETs. Experimental results are presented to validate the design.

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Silicon-on-insulator formed by high dose oxygen ion implantation and subsequent epitaxially grown silicon layers were studied and compared with silicon on sapphire materials. Czochralski grown, (100) silicon wafers were implanted with molecular oxygen ions, 0+2, to a total dose of 2.12 x 10^18 0+/cm^2 at an energy of 150 keV/atom.

We have completed mechanism of action studies on a new class of anticancer nucleosides typified by a novel nucleoside discovered in our lab, MAP-870. In order to study the mechanism of MAP-870, several experiments were completed on a colorectal adenocarcinoma cell line, HT-29, including trypan blue cell count, sulforhodamine B assays, flow cytometry of cell cycle, propidium iodide incorporation, and phosphatidylserine externalization, Caspase-Glo3/7 assays, DNA fragmentation gel, cyclophilin A release gel, PAMPA, and confocal imaging. Sulforhodamine B assays show that MAP-870 does indeed cause growth inhibition and cell death in the model tested. PAMPA assays show that MAP-870 does not appear to enter the cell via passive diffusion. Flow cytometry showed that MAP-870 doe not appear to cause cell cycle arrest or externalization of phosphatidylserine. Caspase-Glo3/7 assays demonstrated that MAP-870 does not appear to cause caspase activation. From confocal microscopy, it appears preliminarily that MAP-870 is taken up by cells, often through pseudopodia. The mechanism of MAP-870 on cancer cells must be further studied to elucidate its mechanism of action. However, preliminarily our data could point to TGFβ as a potential target pathway involving a unique, heretofore never described, cell death mechanism.

付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第23431号 / 工博第4886号 / 新制||工||1764(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 白石 誠司, 教授 木本 恒暢, 教授 引原 隆士 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Silicon photonics (SiP) has evolved into a mature platform for cost-effective low power compact integrated photonic microsystems for many applications. There is a looming capacity crunch for telecommunications infrastructure to overcome the data-hungry future, driven by streaming and the exponential increase in data traffic from consumer-driven products. To increase data capacity, researchers are now looking at the wavelength window of the thulium-doped fiber amplifier (TDFA), centered near 2 µm as an attractive new transmission window for optical communications, motivated by the demonstrations of low loss, low nonlinearity, and high bandwidth transmission. Large-scale implementation of SiP telecommunication infrastructure will require light sources (lasers) and amplifiers to generate signals and boost transmitted and/or received signals, respectively. Silicon (Si) and silicon nitride (Si3N4) have become the leading photonic integrated circuit (PIC) material platforms, due to their low-cost and wafer-scale production of high-performance circuits. Silicon does however have a number of limitations as a photonic material, including that it is not an ideal light-emitting/amplifying material. This proposed research pertains to the fabrication of on-chip silicon and silicon nitride lasers and amplifiers to be used in a newly accessible optical communications window of the TDFA band, which is a significant step towards compact PICs for the telecommunication networks. Tellurium oxide (TeO2) is an interesting host material due to its large linear and non-linear refractive indices, low material losses and large rare-earth dopant solubility showing good performance for compact low-loss waveguides and on-chip light sources and amplifiers. Chapter 1 provides an overview of silicon photonics in the context of particularly rare earth lasers and amplifiers, operating at extended wavelengths enabled by the Thulium doped fiber amplifier. Chapter 2 presents a theoretical performance of waveguides and microresonators as the efficient structure for laser and amplifiers applications designed for optimized use in Erbium and Thulium doped fiber amplifier wavelength bands. Then spectroscopic study thulium (Tm3+) has been studied as the rare earth element for Thulium doped fiber amplifier wavelength bands. Chapter 3 presents an experimental study of TeO2:Tm3+ coated Si3N4 waveguide amplifiers with internal net gains of up to 15 dB total in a 5-cm long spiral waveguide. Chapter 4 provides a study of TeO2:Tm3+ -coated Si3N4 waveguide lasers with up to 16 mW double-sided on-chip output power. Chapter 5 presents an experimental study of low loss and high-quality factor silicon microring resonators coated with TeO2 for active, passive, and nonlinear applications. Chapter 6 represents the first demonstration of an integrated rare-earth silicon laser, with high performance, including single-mode emission, a lasing threshold of 4 mW, and bidirectional on-chip output powers of around 1 mW. Further results with a different design are presented showing lasers with more than 2 mW of double-sided on-chip output power, threshold pump powers of < 1 mW and lasing at wavelengths over a range of > 100 nm. Importantly, a simple, low-cost design was used which is compatible with silicon photonics foundry processes and enables wafer scale integration of such lasers in SiP PICs using robust materials. Chapter 7 summarizes the thesis and provides paths for future work. / Dissertation / Doctor of Engineering (DEng)

Doping control is the most important technology for any semiconductor system. In spite of significant progress in the doping of SiC, advancements are needed in the growth techniques and dopant incorporation. During processes such as Chemical Vapor Deposition (CVD), hydrogen is known to be trapped at defects or impurities and to alter the electrical properties of the material. This effect is known as ?hydrogen passivation?. In addition to the observed hydrogen passivation of shallow impurities in SiC crystals, it is important to know whether, and how, hydrogen present in the epi ? reactor can passivate doping impurities during growth of the material. Variations in hydrogen incorporation can affect the net doping density and make process control difficult. This makes it essential for technologists to understand the process of hydrogen passivation and its effects on the doping concentration in the crystal. To understand this phenomenon, a process has been developed to intentionally hydrogenate SiC crystals by striking a hydrogen plasma using the Reactive Ion Etching (RIE) System in the Emerging Materials Research Laboratory at MSU. Photoluminescence (PL) and Capacitance ? Voltage (CV) were used to determine the effect of hydrogen incorporation on dopants in the SiC crystal lattice. Crystal annealing was performed at 1000 oC using the Thermco Oxidation Furnace to drive hydrogen out of the lattice (a process referred to as ?de-hydrogenation?). PL and CV measurements were taken to look for changes in the hydrogen concentration as well as free carrier concentration, respectively. Experiments conducted during this thesis research were successful in incorporating hydrogen and then driving it out of the lattice. CV profiling did not indicate a considerable change in free carrier concentration, probably because of the shallow diffusion depth of hydrogen in the SiC lattice. More reliable characterization techniques such as Secondary Ion Mass Spectrometry (SIMS) are required to get a clear picture of the doping densities of all chemical species present in the lattice at the end of each processing stage. However, resources did not permit this to be conducted during this preliminary work. As a result of this research, a process for hydrogenating and de-hydrogenating the SiC lattice has been developed to permit more extensive future studies.

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