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Showing papers on "Silicon carbide published in 2000"


Journal ArticleDOI
TL;DR: In this paper, capacitance and voltage measurements for metal-oxide-semiconductor capacitors fabricated using the 4H polytype of silicon carbide doped with either nitrogen (n) or aluminum (p).
Abstract: Results of capacitance–voltage measurements are reported for metal–oxide–semiconductor capacitors fabricated using the 4H polytype of silicon carbide doped with either nitrogen (n) or aluminum (p). Annealing in nitric oxide after a standard oxidation/reoxidation process results in a slight increase in the defect state density in the lower portion of the band gap for p-SiC and a significant decrease in the density of states in the upper half of the gap for n-SiC. Theoretical calculations provide an explanation for these results in terms of N passivating C and C clusters at the oxide–semiconductor interface.

453 citations



Journal ArticleDOI
TL;DR: Silicon carbide (SiC) is a material with very attractive properties for microsystems applications as discussed by the authors, its mechanical strength, high thermal conductivity, ability to operate at high temperatures and extreme chemical inertness in several liquid electrolytes, make SiC an attractive candidate for MEMS applications, both as structural material and as coating layer.
Abstract: Silicon carbide (SiC) is a material with very attractive properties for microsystems applications Its mechanical strength, high thermal conductivity, ability to operate at high temperatures and extreme chemical inertness in several liquid electrolytes, make SiC an attractive candidate for MEMS applications, both as structural material and as coating layer The recently reported progress in material growth and processing techniques has strengthened the potential of this material for MEMS, especially for applications requiring operation at high temperature or in severe environments Examples of SiC microsensors and microstructures are given and interesting development in both material characteristics and micromachining processes are discussed

414 citations


Journal ArticleDOI
TL;DR: In this article, high carbon concentrations at distinct regions at thermally-grown SiO2/6H-SiC(0001) interfaces have been detected by electron energy loss spectroscopy (EELS).
Abstract: High carbon concentrations at distinct regions at thermally-grown SiO2/6H-SiC(0001) interfaces have been detected by electron energy loss spectroscopy (EELS). The thickness of these C-rich regions is estimated to be 10-15 Angstrom. The oxides were grown on n-type 6H-SiC at 1100 degrees C in a wet O-2 ambient for 4 h immediately after cleaning the substrates with the complete RCA process. In contrast, C-rich regions were not detected from EELS analyses of thermally grown SiO2/Si interfaces nor of chemical vapor deposition deposited SiO2/SiC interfaces. Silicon-rich layers within the SiC substrate adjacent to the thermally grown SiO2/SiC interface were also evident. The interface state density D-it in metal-oxide-SiC diodes (with thermally grown SiO2) was approximately 9x10(11) cm(-2) eV(-1) at E- E-v=2.0 eV, which compares well with reported values for SiC metal-oxide-semiconductor (MOS) diodes that have not received a postoxidation anneal. The C-rich regions and the change in SiC stoichiometry may be associated with the higher than desirable D-it's and the low channel mobilities in SiC-based MOS field effect transistors. (C) 2000 American Institute of Physics. [S0003-6951(00)01940-9].

205 citations


Journal ArticleDOI
TL;DR: In this article, the growth morphology, microstructure, and defects in SiC nanowires were characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscope (HRTEM).
Abstract: Silicon carbide (SiC) nanowires were synthesized at 900°C by the laser ablation technique. The growth morphology, microstructure, and defects in SiC nanowires were characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The Raman scattering study indicated that the Raman peaks corresponding to the TO and LO phonon modes of the SiC nanowires had larger red shifts compared to those of bulk SiC material. The red shift, broadening peak, and the asymmetry of the Raman peak could be explained by the size confinement effect in the radial and growth directions. The growth mechanism of SiC nano-wires was discussed based on the vapor–liquid–solid reaction.

194 citations


Journal ArticleDOI
TL;DR: In this paper, the material properties, deposition techniques, micromachining processes, and other issues regarding the fabrication of SiC-based sensors and actuators are reviewed, and special emphasis is placed on the properties that make SiC attractive for MEMS, and the Si-based processing techniques that have been adapted to realize SiC MEMS structures and devices.
Abstract: Silicon carbide (SiC) has recently attracted attention as a wide bandgap semiconductor with great potential for microelectromechanical systems (MEMS). SiC exhibits excellent electrical, mechanical, and chemical properties, making it well suited for harsh environment applications where traditional MEMS are constrained by the physical limitations of silicon (Si). This paper reviews the material properties, deposition techniques, micromachining processes, and other issues regarding the fabrication of SiC-based sensors and actuators. Special emphasis is placed on the properties that make SiC attractive for MEMS, and the Si-based processing techniques that have been adapted to realise SiC MEMS structures and devices. An introduction to micromachining is provided for readers not familiar with MEMS fabrication techniques.

132 citations


Journal ArticleDOI
TL;DR: The conduction-band structure of these interfaces has been determined by angle-resolved inverse photoemission spectroscopy (KRIPES) as discussed by the authors, which reveals that the first graphite layer is strongly bound to the C face.

130 citations


Journal ArticleDOI
TL;DR: In this paper, the drift velocity of electrons parallel to the basal plane in 6H and 4H silicon carbide (SiC) as a function of applied electric field was measured and the dependence of low field mobility and saturated drift velocity on temperature were also reported.
Abstract: We report recent measurements of the drift velocity of electrons parallel to the basal plane in 6H and 4H silicon carbide (SiC) as a function of applied electric field. The dependence of the low field mobility and saturated drift velocity on temperature are also reported. The saturated drift velocities at room temperature are approximately 1.9/spl times/10/sup 7/ cm/s in 6H-SiC and 2.2/spl times/10/sup 7/ cm/s in 4H-SiC.

128 citations


Journal ArticleDOI
TL;DR: In this article, the effect of the addition of an amount of ultrafine SiC to commercial silicon carbide powder was evaluated, and the results showed that flexural strength and microstructure of SiC ceramics varied with type and amount of liquid phase as densification proceeded via a classical solution-reprecipitation mechanism.
Abstract: Dense SiC ceramics were obtained by hot pressing of β-SiC powders using Al2O3-Y2O3 and La2O3-Y2O3 additive systems. The effect of the addition of an amount of ultrafine SiC to commercial silicon carbide powder was evaluated. Sintering behaviour and microstructure depended on type and amount of liquid phase, as densification proceeded via a classical solution-reprecipitation mechanism. A core/rim structure of SiC grains indicated that reprecipitation of a solid solution of SiC containing Al and O occurred on pure SiC nuclei. Grain boundary phase was constituted of crystalline YAG and amorphous silicates. Values of flexural strength up to ∼750 MPa at RT and up to ∼550 MPa at 1000 °C were measured. At 1300 °C a strong degradation of strength was attributed to softening of the amorphous portion of grain boundary phase. In highly dense materials toughness ranged from 2.95 to 3.17 MPa·m1/2 and hardness from 21 to 23 GPa.

123 citations


Journal ArticleDOI
TL;DR: In this article, the low-cost production and performance of 6061-aluminium alloy matrices reinforced with coated and non-coated particulate silicon carbide has been studied.

119 citations


Journal ArticleDOI
TL;DR: In this paper, a numerically controlled plasma chemical vaporization machining (CVM) machine for x-ray mirror fabrication is described. And the defect density of a silicon wafer surface polished by various machining method was evaluated by the surface photo voltage spectroscopy.
Abstract: Conventional machining processes, such as turning, grinding, or lapping are still applied for many materials including functional ones. But those processes are accompanied with the formation of a deformed layer, so that machined surfaces cannot perform their original functions. In order to avoid such points, plasma chemical vaporization machining (CVM) has been developed. Plasma CVM is a chemical machining method using neutral radicals, which are generated by the atmospheric pressure plasma. By using a rotary electrode for generation of plasma, a high density of neutral radicals was formed, and we succeeded in obtaining high removal rate of several microns to several hundred microns per minute for various functional materials such as fused silica, single crystal silicon, molybdenum, tungsten, silicon carbide, and diamond. Especially, a high removal rate equal to lapping in the mechanical machining of fused silica and silicon was realized. 1.4 nm (p–v) was obtained as a surface roughness in the case of machining a silicon wafer. The defect density of a silicon wafer surface polished by various machining method was evaluated by the surface photo voltage spectroscopy. As a result, the defect density of the surface machined by plasma CVM was under 1/100 in comparison with the surface machined by mechanical polishing and argon ion sputtering, and very low defect density which was equivalent to the chemical etched surface was realized. A numerically controlled CVM machine for x-ray mirror fabrication is detailed in the accompanying article in this issue.


Journal ArticleDOI
TL;DR: In this article, the effects of various parameters of ultrasonic drilling, including abrasives, volume ratio, electric current and downforce, on the material removal rate, hole clearance, edge quality and tool wear are discussed and discussed.
Abstract: Ultrasonic drilling of two-dimensional carbon fiber-reinforced silicon carbide(C/SiC) composites was investigated in this study. The composites were made through a polymer pyrolysis route. X-ray diffraction was adopted to examine the formation of crystalline structure in the matrix of the fabricated composites. Density and porosity, and flexural strength were measured to study the densification efficiency and the mechanical properties, respectively, of the C/SiC composites fabricated under various conditions. The fracture morphologies were also examined by scanning electron microscopy to investigate the fracture behavior of the composites under flexural test. The effects of various parameters of ultrasonic drilling, including abrasives, volume ratio, electric current and down-force, on the material removal rate, hole clearance, edge quality and tool wear are presented and discussed. Optimal operating conditions are identified. In comparison with other feasible machining processes, ultrasonic drilling for this composite material possesses advantages concerning machinability and cost.

Journal ArticleDOI
TL;DR: In this article, the porosity, pore size distribution, and transport characteristics of the resulting SiC-sintered bodies depend on the nature of the original powder, the particle size in the green SiC samples, and the type and molar ratio of the sintering aid utilized.
Abstract: Silicon carbide (SiC) porous substrates are prepared by pressureless sintering of SiC powders under an inert atmosphere of argon. The porous SiC substrates were characterized by measuring their porosity, pore size distribution, surface characteristics, and structure. Their transport characteristics were investigated using N2 and He as the test gases. Three different starting powders and four different sintering aids, Al2O3, B4C, carbon black, and phenolic resin, either by themselves or in combination, were investigated in terms of their ability to prepare good quality substrates. It was found that the porosity, pore size distribution, and transport characteristics of the resulting SiC-sintered bodies depend on the nature of the original powder, the particle size in the green SiC samples, and the type and molar ratio of the sintering aid utilized. Depending on the preparation technique, both mesoporous and macroporous materials could be prepared. These supports are currently utilized for the preparation of...

Journal ArticleDOI
TL;DR: The present status of the silicon carbide and gallium nitride bipolar power semiconductor devices is reviewed in this paper, where several conventional as well as novel device structures have been examined, some of which have already been demonstrated and others are in their early stages of development.
Abstract: The present status of the silicon carbide and gallium nitride bipolar power semiconductor devices is reviewed. Several unipolar and bipolar figures of merit have been examined to demonstrate the potential performance gain to be obtained from silicon carbide and gallium nitride based power devices. Several conventional as well as novel device structures have been examined, some of which have already been demonstrated and others are in their early stages of development. Conventional silicon theory has often been found to be inadequate to explain the characteristics of silicon carbide. Appropriate modifications have been applied to investigate more complicated characteristics of silicon carbide devices.

Journal ArticleDOI
TL;DR: In this article, the effect of magnesium and silicon additions to aluminum, free silicon on the SiC substrate, nitrogen gas in the atmosphere, and process temperature on the wetting characteristics of SiC by aluminum alloys were investigated using the sessile drop technique.
Abstract: The effect of magnesium and silicon additions to aluminum, free silicon on the SiC substrate, nitrogen gas in the atmosphere, and process temperature on the wetting characteristics of SiC by aluminum alloys are investigated using the sessile drop technique The contribution of each of these parameters and their interactions to the contact angle, surface tension, and driving force for wetting are determined In addition, an optimized process for enhanced wetting is suggested and validated Results show that the presence of free silicon on the surface of SiC significantly reduces the contact angle between the molten alloy and the substrate The positive effect of silicon on the contact angle is attributed to a chemical reaction in which both SiC and aluminum are active participants The results also indicate that nitrogen gas in the atmosphere positively influences the liquid/vapor surface tension, and the presence of magnesium in the aluminum alloy favorably affects the overall driving force for wetting A mechanism is proposed to explain the beneficial role that the interaction of nitrogen with magnesium plays in enhancing wetting Magnesium significantly reduces the surface tension of aluminum melts but has a low vapor pressure Consequently, it readily volatilizes during holding at the processing temperature and is lost from the alloy It is proposed that a series of chemical reactions in the system Al-Mg-N are responsible for reintroducing magnesium into the melt, thus, maintaining a low melt surface tension Interactions between the aluminum alloy and the silicon carbide substrate that may lead to the dissolution of the substrate and the formation of undesirable reaction products, particularly Al4C3, are examined, and means for mitigating their formation are outlined

Journal ArticleDOI
TL;DR: In this paper, thin films of silicon carbide nitride (SiCN) have been prepared by reactive radioactive frequency (r.f.) sputtering using SiC target and nitrogen as the reactant gas.

Journal ArticleDOI
TL;DR: In this paper, the infrared (IR) absorption spectra and the transmission electron microscopy observations reveal an onset of crystallization at Ts as low as 300 °C and the crystalline fraction increases with Ts and reaches a value of about 60%.
Abstract: Silicon carbide thin films have been deposited by reactive magnetron sputtering in a pure hydrogen plasma at substrate temperatures, Ts, ranging between 100 and 600 °C. The infrared (IR) absorption spectra and the transmission electron microscopy observations reveal an onset of crystallization at Ts as low as 300 °C. The crystalline fraction increases with Ts and reaches a value of about 60% for Ts=600 °C. Both refractive index n and room temperature dark conductivity σd(RT) show quite consistent behaviors with the structural evolution of the layers. Thus n increases from 1.9 to 2.4 and σd(RT) improves by six orders of magnitude when Ts is raised from 100 to 600 °C.

Journal ArticleDOI
TL;DR: Field effect chemical sensors, utilising silicon carbide as semiconductor, can be operated at high temperature and in rough environments as mentioned in this paper, and Gas sensitive field effect transistors, MISiCFET, are now d...
Abstract: Field effect chemical sensors, utilising silicon carbide as semiconductor, can be operated at high temperature and in rough environments. Gas sensitive field effect transistors, MISiCFET, are now d ...

Journal ArticleDOI
TL;DR: Two generations of multilayered interphases, composed of carbon and silicon carbide, have been developed to act as a mechanical fuse in SiC/SiC composites with improved oxidation resistance as discussed by the authors.
Abstract: Two generations of multilayered interphases, composed of carbon and silicon carbide, have been developed to act as a mechanical fuse in SiC/SiC composites with improved oxidation resistance. Pyrocarbon is an ideal interfacial material, from the mechanical point of view, whereas SiC has a good oxidation resistance. In the multilayered interphase, the carbon mechanical fuse is split into thin sublayers, each being protected against oxidation by the neighbouring SiC-based glass former layers. A first generation of multilayers as synthesised by means of isobaric-CVI with sublayers with micrometric thickness. Then, in order to push forward the concept, pressure pulsed-CVI was involved to deposit nanometric scale sublayers. In this work, transmission electron microscopy was developed to characterise the two generations of materials. The microstructure of the layers and the influence of the fibrous preforms on the structure of the layers were studied. Examinations were then performed on the loaded samples and damaging mode characterised at nanometric scale.

Journal ArticleDOI
TL;DR: In this article, amorphous silicon carbide (SiC) thin films have been deposited by RF magnetron sputtering on hat surfaces and into micromachined cavities of Si (100).
Abstract: There is a need for chemically resistant coatings that protect the exposed surface of microfluidics components. Pinhole free films with low stress and a good uniformity on flat and inclined surfaces are required. In this study, amorphous silicon carbide (SiC) thin films have been deposited by RF magnetron sputtering on hat surfaces and into micromachined cavities of Si (100). The variation of RF power, deposition pressure and substrate bias voltage have been studied. Depending on the deposition conditions, the film stress can be adjusted from - 1400 MPa to + 100 MPa. Modifications of the deposition rate and the morphology between normal and inclined (54.7 degrees) planes have been observed. Optimal chemical stability was found with slightly compressive (-100 MPa) SiC thin films. No degradation of the protective layer has been observed after 3 h in KOH at 80 degrees C. (C) 2000 Elsevier Science S.A. All rights reserved.

Patent
10 May 2000
TL;DR: SiSiC MESFETs with a selectively doped p-type buffer layer are also provided in this article, which reduce output conductance by a factor of 3 and produce a 3 db increase in power gain over SiC MESSFET with conventional p- type buffer layers.
Abstract: SiC MESFETs are disclosed which utilize a semi-insulating SiC substrate which substantially free of deep-level dopants. Utilization of the semi-insulating substrate may reduce back-gating effects in the MESFETs. Also provided are SiC MESFETs with a two recess gate structure. MESFETS with a selectively doped p-type buffer layer are also provided. Utilization of such a buffer layer may reduce output conductance by a factor of 3 and produce a 3 db increase in power gain over SiC MESFETs with conventional p-type buffer layers. A ground contact may also be provided to the p-type buffer layer and the p-type buffer layer may be made of two p-type layers with the layer formed on the substrate having a higher dopant concentration. SiC MESFETs according to embodiments of the present invention may also utilize chromium as a Schottky gate material. Furthermore, an oxide-nitride-oxide (ONO) passivation layer may be utilized to reduce surface effects in SiC MESFETs. Also, source and drain ohmic contacts may be formed directly on the n-type channel layer, thus, the n + regions need not be fabricated and the steps associated with such fabrication may be eliminated from the fabrication process. Methods of fabricating such SiC MESFETs and gate structures for SiC FETs as well as passivation layers are also disclosed.

Journal ArticleDOI
TL;DR: Gelcasting of high concentrated aqueous silicon carbide suspension with 50 vol.% solids loading is discussed in this article, where it is found that SiC powder is suitable for being suspended in basic solution, provided that a proper pH value is chosen for it.
Abstract: Gelcasting of high concentrated aqueous silicon carbide suspension with 50 vol.% solids loading is discussed in this paper. It is found that SiC powder is suitable for being suspended in basic solution, provided that a proper pH value is chosen for it. The rheological property of SiC suspension is also affected by solids loading. When SiC slurry is cast at 70°C, reaction between free Si on the surface of SiC powder and an organic base used as dispersant gives out H 2 gas, which produces pores in green bodies. However, by vacuum pumping and controlling pH value of the suspensions, complicated shapes of uniform SiC green bodies without pores are prepared.

Journal ArticleDOI
TL;DR: In this article, a simple method was developed to produce silicon carbide foams using polysilane polymeric precursors, which showed well-defined open-cell structures and the struts in the foams were free of voids.
Abstract: A simple method was developed to produce silicon carbide foams using polysilane polymeric precursors Polyurethane foams were immersed in polysilane precursor solutions to prepare pre-foams Subsequently, these were heated in nitrogen at different temperatures in the range of 900°C to 1300°C The silicon carbide foams produced in this manner showed well-defined open-cell structures and the struts in the foams were free of voids The shrinkage which accompanies pyrolysis of the pre-foams was reduced with increasing the concentration of the polymeric precursor solutions

Journal ArticleDOI
TL;DR: In this paper, the effects of neutron irradiation on SiC-based fiber preforms were investigated and two parallel studies were conducted for two parallel systems: the Hi-Nicalon™ system and the Ceramic Grade Nicalon system.

Patent
07 Mar 2000
TL;DR: In this paper, the static charge dissipative layer is made of a material selected from the group consisting of diamond-like carbon, silicon carbide, silicon dioxide, boron trifluoride, and silicon dioxide.
Abstract: Circuit and circuit carries include a dielectric substrate having a conductive layer mounted thereon. The conductive layer is patterned to define a plurality of spaced apart conductive elements. A static charge dissipative layer is in contact with and extending between at least two of the conductive elements. The static charge dissipative layer has a surface resistivity of between about 1×105 and about 1×1010 ohms/□. The static charge dissipative layer is made of a material selected from the group consisting of diamond-like carbon, silicon nitride, boron nitride, boron trifluoride, silicon carbide and silicon dioxide. Circuits and circuit carriers according to the present invention allow static charges to be controllably and reliably dissipated from a surface of the circuit or circuit carrier such that the potential for damage from static discharge to electrical components connected to the circuit is reduced.

Journal ArticleDOI
TL;DR: In this paper, the influence of substrate temperature (150 −500°C) and polarization (0−100 V), Ar pressure (0.05 −4 Pa) and RF power (50 −400 W) on the mechanical properties (hardness and stress) of the resulting films was studied.

Journal ArticleDOI
TL;DR: In this paper, a new method of forming silicon carbide-silicon nitride composite foams is presented by immersing a polyurethane foam in a polysilane precursor solution mixed with Si3N4 powder to form a pre-foam followed by heating it in nitrogen at >900°C.
Abstract: A new method of forming silicon carbide–silicon nitride composite foams is presented. These are prepared by immersing a polyurethane foam in a polysilane precursor solution mixed with Si3N4 powder to form a pre-foam followed by heating it in nitrogen at >900°C. X-ray diffraction patterns indicate that a SiC–Si3N4 composite was formed after sintering the ceramic foam at >1500°C. Micrographs show that most of these foams have well-defined open-cell structures and macro-defect free struts. The shrinkage is reduced considerably due to the addition of Si3N4 particles.

Journal ArticleDOI
TL;DR: In this article, the temperature dependent thermal conductivity of silicon carbide has been calculated taking into account the various phonon scattering mechanisms, and the results compared very well with available experimental data.
Abstract: The temperature dependent thermal conductivity of silicon carbide has been calculated taking into account the various phonon scattering mechanisms. The results compared very well with available experimental data. The inclusion of four-phonon processes is shown to be necessary for obtaining a good match. Several important phonon scattering parameters have been extracted in this study. Dislocations are shown to have a strong effect at 300 K, but not as much at the higher temperatures.

Journal ArticleDOI
TL;DR: In this paper, mechanical properties at room temperature and at high temperature of liquid phase sintered silicon carbide (LPSSC) was determined by means of four-point bend tests in the range RT-1400°C.