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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23900号 / 工博第4987号 / 新制||工||1779(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 邑瀬 邦明, 教授 宇田 哲也, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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Silicon carbide (SiC) is a wide bandgap material capable of higher voltage and higher temperature operation compared to its silicon (Si) counterparts due to its higher critical electric field (E-field) and higher thermal conductivity. Using SiC, MOSFETs with a theoretical high temperature operation and reliability is achievable. However, current bottlenecks in high temperature SiC MOSFETs lie within the limitations of standard packaging. Additionally, there are reliability issues relating to the gate oxide region of the MOSFET, which is exacerbated through high temperature conditions. In this thesis, high temperature effects on current-generation SiC MOSFETs are studied and analyzed. To achieve this, a high temperature package is created to achieve reliable operation of a SiC MOSFET at junction temperatures of 300 °C. The custom, high temperature package feasibility is verified through studying trends in SiC MOSFET behavior with increasing temperature up to 300 °C by static characterization. Additionally, the reliability of SiC MOSFETs at 300 °C is tested with accelerated lifetime bias tests. / M.S. / Electrical devices that are rated for high temperature applications demand a use of a material that is stable and reliable at the elevated temperatures. Silicon carbide (SiC) is such a material. Devices made from SiC are able to switch faster, have a superior efficiency, and are capable of operating at extreme temperatures much better than the currently widely used silicon (Si) devices. There are limitations on SiC certain structures of SiC devices, such as the metal oxide semiconductor field effect transistor (MOSFET), have inherent reliability issues related to the fabrication of the device. These reliability issues can get worse over higher temperature ranges. Therefore, studies must be made to determine the feasibility of SiC MOSFETs in high temperature applications. To do so, industry standard tests are conducted on newer generation SiC MOSFETs to ascertain their use for said conditions.

Aluminium is one of the metals playing a prominent role in automobile industry after cast iron. Because of its light weight property and good mechanical properties. When aluminium reinforced with silicon carbide showing good tribological properties and improved strength. Aluminium silicon carbide needs some good wear and frictional properties to use it as break disc. Aluminium reinforced with 15% and 20% silicon carbide and casted in two different ways, liquid casting and stir casting. Four different composites are compared in this paper. Hardness test was carried out on the samples. Increase in the Vickers hardness with increase in silicon carbide reinforcement for both the castings is observed. Rockwell C hardness is showing decreasing trend with increase in SiC reinforcement. The scratch resistance of the surface under micro level was analysed with the help of nano scratch test. The SiC particles in the aluminium matrix are resisting the indenter from deep deformation of the surface. Frictional forces are dropped whenever the indenter met the SiC particles. In other cases, SiC particles are deforming the aluminium matrix in the form of broken particles. The plastic deformation of aluminium is observed, and material is piled up on sideways of groove at high load.Sliding wear behaviour of the composites are investigated by means of reciprocating pin on plate wear rig. The test was carried out at load of 20N for five different sliding duration. Aluminium with 20% silicon carbide of liquid casting is used as a base metal. The worn-out surface of the samples is analysed in SEM. The metallography of the worn-out samples is showing some deep grooves and abrasion of the material. Wear debris from both the surfaces are forming into a cluster of layers. These layers are protecting the surface from wear in some areas were observed. Composition of tribo layer formed during the test was investigated with the help of EDS analysis. The tribo layer are rich in aluminium and silicon elements because both the samples are made of aluminium silicon carbide.

Silicon Carbide has been a semiconductor material of interest as a high power and temperature replacement for Silicon (Si) in harsh environments due to the higher thermal conductivity and chemical stability of SiC. The cost, however, to produce this material is quite high. There are also defects in the substrate material (SiC) that penetrate into the active devices layers which are known device killers. Silicon is a material that provides a low cost substrate material for epitaxial growth and does not contain the defects that SiC substrates have. However, the large (~22%) lattice mismatch between Si and SiC creates dislocations at the SiC/Si interface and defects in the SiC epitaxial layer. These defects result in high leakage currents in 3C-SiC/Si devices. The main focus of the this research was to reduce or eliminate these defects using novel Si substrates. First a 3C-SiC on Si baseline process was developed under atmospheric pressure conditions consisting of 3 steps - an in-situ hydrogen etch to remove the native oxide, a carbonization step to convert the Si surface to SiC, and finally a growth step to thicken the SiC layer to the desired value. This process was then modified to establish a high-quality, low-pressure 3C-SiC CVD growth process. This LPCVD process was then used to grow 3C-SiC on numerous novel Si substrates, including porous Si, porous 3C-SiC "free-standing" substrates and SOI substrates which consisted on thin Si films bonded to poly-crystalline SiC plates. The results of these experiments are presented along with suggestions for future work so that device-grade films of 3C-SiC can be developed for various applications.

Title from PDF of title page. / Document formatted into pages; contains 70 pages. / Thesis (M.Ch.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: SiC is a hard man-made material and has emerged as an excellent material for a wide range of applications which are exposed to extreme conditions such as high temperatures and harsh chemical environments. These applications range from SiC being used as an abrasive, to a refractory material, to a semiconductor material for high power and high frequency electronic devices. The properties of the material for each application is different, with the semiconductor grade material for electronic devices being the most refined. SiC, with its excellent thermal properties and high resistance to harsh chemical environments, lends itself to being an ideal support for catalyst systems. / ABSTRACT: Various characterisation & analysis techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography (GC) are used in this thesis to investigate the suitability of single crystal SiC for high temperature catalytic systems. Low temperature oxidation of methane was used to investigate the catalytic activity of: - Porous and standard 4H-SiC with and without Pd - Porous and Standard 6H-SiC with and without Pd. - Nanocrystalline Beta-SiC powder with and without Pd. Part of the samples were impregnated with Pd using Palladium Nitrate (Pd (NO3)2) which is a common precursor for Pd. Activation treatments which were investigated were oxidation and reduction. Oxidation was generally better in activating the catalyst, as was expected, since the PdO phase is known to be more active in oxidising methane. / ABSTRACT: A mixed set of Pd and PdO were observed by SEM and EDS which were the main characterisation techniques used to analyze the structure of the catalysts before and after the reaction. The Beta-SiC showed by far the best activity which could be attributed to the micro-crystalline powder format in which it was used, where as all other catalysts studied here were derived from crushed wafer pieces. Type II porous 4H-SiC was another of the samples which registered impressive results, vis-à-vis catalytic activity. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

The growth of bulk cubic silicon carbide has for a long time seemed to be something for the future. However, in this thesis the initial steps towards bulk cubic silicon carbide have been taken. The achievement of producing bulk cubic silicon carbide will have a great impact in various fields of science and industry such as for example the fields of semiconductor technology within electronic- and optoelectronic devices and bio-medical applications. The process that has been used to grow the bulk cubic silicon carbide is a modification of the seeded sublimation growth, and the seeds have been grown by sublimation epitaxy. Selected samples have been characterized with a variety of different methods. The surface morphology of the samples has been examined using optical microscope, atomic force microscope and scanning electron microscope. The crystal structure has been investigated by the methods X-ray diffraction and transmission electron microscopy. The electrical resistance of the grown seeds was evaluated by four probe measurements. High crystal quality seeds have been grown with semiconductor properties and bulk silicon carbide was demonstrated using the seeds.

>Magister Scientiae - MSc / The growth of hydrogenated amorphous silicon carbide (a-SiC:H) thin films deposited by Hot- Wire Chemical Vapour Deposition (HWCVD) for solar cell applications has been studied. The films were characterized for structural properties using Fourier Transform Infrared Spectroscopy FTIR, Elastic Recoil Detection Analysis (ERDA), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Raman Spectroscopy (RS). A low temperature of the substrate heater maintained at 280 °C was used in this thesis due to the demand of low-cost solar cells based on cheap substrate that require deposition at such low temperatures. In this thesis, we showed that the structural properties of a-SiC:H films are dependent on the filament temperature and also on the CH4 gas flow rate. It was shown that in non-stoichiometric a-SiC:H, hydrogen content throughout the deposited films varies with depth. An attempt is done in this study to determine, for the first time the absorption strength of the C-Hn bonds in the 950 -1050 cm-1 band of the FTIR spectrum. Real-time ERDA was used to determine the hydrogen kinetics parameters in a single temperature ramp; a model based on the solution of the diffusion equation is used for this effect.