Showing papers on "Silicon carbide published in 2006"

Electronic Confinement and Coherence in Patterned Epitaxial Graphene

Abstract: Ultrathin epitaxial graphite was grown on single-crystal silicon carbide by vacuum graphitization. The material can be patterned using standard nanolithography methods. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. All-graphene electronically coherent devices and device architectures are envisaged.

Enhanced thermal conductivity of polymer composites filled with hybrid filler

Abstract: This study aims at investigating package materials based on polymer matrix for microelectronics. The next generation package materials are expected to possess high heat dissipation capability in addition to low coefficient of thermal expansion (CTE) as the accumulated heat from high performance electronic devices should be removed for proper operation. In this study, various inorganic fillers including aluminum nitride (AlN), wollastonite, silicon carbide whisker (SiC) and boron nitride (BN) with different shape and size were used alone or in combination to prepare thermally conductive polymer composites. In case of AlN, titanate coupling agent was used for the surface treatment of fillers. The use of hybrid filler was found to be effective in increasing thermal conductivity of the composite probably due to the enhanced connectivity offered by structuring filler with high aspect ratio in hybrid filler. For given filler loading, the use of larger particle and surface treated filler resulted in composite materials with enhanced thermal conductivity. The surface treatment of filler also allowed producing the composites with lower CTE.

Degradation of hexagonal silicon-carbide-based bipolar devices

Abstract: Only a few years ago, an account of degradation of silicon carbide high-voltage p-i-n diodes was presented at the European Conference on Silicon Carbide and Related Compounds (Kloster Banz, Germany, 2000). This report was followed by the intense effort of multiple groups utilizing varied approaches and subsequent progress in both fundamental understanding of this phenomenon and its elimination. The degradation of SiC p-i-n junctions is now well documented to be due to the expansion of Shockley-type stacking faults in the part of the devices reached by the electron-hole plasma. The faults can gradually cover most of the junction area, impeding current flow and, as a result, increasing the on-state resistance. While in most semiconductors stacking faults are electrically inactive, in hexagonal silicon carbide polytypes (4H- and 6H-SiC) they form quantum-well-like electron states observed in luminescence and confirmed by first-principles calculations. The stacking-fault expansion occurs via motion of 30° sil...

Silicon carbide and diamond for high temperature device applications

Abstract: The physical and chemical properties of wide bandgap semiconductors silicon carbide and diamond make these materials an ideal choice for device fabrication for applications in many different areas, e.g. light emitters, high temperature and high power electronics, high power microwave devices, micro-electromechanical system (MEMS) technology, and substrates. These semiconductors have been recognized for several decades as being suitable for these applications, but until recently the low material quality has not allowed the fabrication of high quality devices. Silicon carbide and diamond based electronics are at different stages of their development. An overview of the status of silicon carbide's and diamond's application for high temperature electronics is presented.

A review of the development of three generations of small diameter silicon carbide fibres

Abstract: Three generations of small diameter ceramic fibres based on polycrystalline silicon carbide have been developed over a period of thirty years. This has been possible due to studies into the relationships between the microstructures and properties of the fibres. A variety of techniques have been employed by research teams on three continents. The fibres are made by the conversion of polymer precursors to ceramic fibres and all three generations are presently produced commercially. The nature of the precursor and the techniques used for cross-linking have been varied in order to optimise both properties and cost of manufacture. It has been possible to improve the characteristics of the fibres as the processes involved in the cross-linking of the precursor fibres have been better understood and the mechanisms governing both room temperature and high temperature behaviour determined. The result is that, although first generation fibres were limited by a low Young's modulus at room temperature and by creep and instability of the structure at temperatures far lower than those limiting the behaviour of bulk silicon carbide, the third generation fibres shows many of the characteristics of stoichiometric silicon carbide. This remarkable improvement in characteristics has been due to a thorough understanding of the materials science governing the behaviour of these fibres which are reinforcements for ceramic matrix composite materials.

Highly Ordered Mesoporous Silicon Carbide Ceramics with Large Surface Areas and High Stability

Abstract: Highly ordered mesoporous silicon carbide ceramics have been successfully synthesized with yields higher than 75 % via a one-step nanocasting process using commercial polycarbosilane (PCS) as a precursor and mesoporous silica as hard templates. Mesoporous SiC nanowires in two-dimensional (2D) hexagonal arrays (p6m) can be easily replicated from a mesoporous silica SBA-15 template. Small-angle X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images show that the SiC nanowires have long-range regularity over large areas because of the interwire pillar connections. A three-dimensional (3D) bicontinuous cubic mesoporous SiC structure (Ia3d) can be fabricated using mesoporous silica KIT-6 as the mother template. The structure shows higher thermal stability than the 2D hexagonal mesoporous SiC, mostly because of the 3D network connections. The major constituent of the products is SiC, with 12 % excess carbon and 14 % oxygen measured by elemental analysis. The obtained mesoporous SiC ceramics are amorphous below 1200 °C and are mainly composed of randomly oriented β-SiC crystallites after treatment at 1400 °C. N2-sorption isotherms reveal that these ordered mesoporous SiC ceramics have high Brunauer–Emmett–Teller (BET) specific surface areas (up to 720 m2 g–1), large pore volumes (∼ 0.8 cm3 g–1), and narrow pore-size distributions (mean values of 2.0–3.7 nm), even upon calcination at temperatures as high as 1400 °C. The rough surface and high order of the nanowire arrays result from the strong interconnections of the SiC products and are the main reasons for such high surface areas. XRD, N2-sorption, and TEM measurements show that the mesoporous SiC ceramics have ultrahigh stability even after re-treatment at 1400 °C under a N2 atmosphere. Compared with 2D hexagonal SiC nanowire arrays, 3D cubic mesoporous SiC shows superior thermal stability, as well as higher surface areas (590 m2 g–1) and larger pore volumes (∼ 0.71 cm3 g–1).

Silicon carbide passive heating elements in microwave-assisted organic synthesis.

Abstract: Microwave-assisted organic synthesis in nonpolar solvents is investigated utilizing cylinders of sintered silicon carbide (SiC)a chemically inert and strongly microwave absorbing materialas passive heating elements (PHEs). These heating inserts absorb microwave energy and subsequently transfer the generated thermal energy via conduction phenomena to the reaction mixture. The use of passive heating elements allows otherwise microwave transparent or poorly absorbing solvents such as hexane, carbon tetrachloride, tetrahydrofuran, dioxane, or toluene to be effectively heated to temperatures far above their boiling points (200−250 °C) under sealed vessel microwave conditions. This opens up the possibility to perform microwave synthesis in unpolar solvent environments as demonstrated successfully for several organic transformations, such as Claisen rearrangements, Diels−Alder reactions, Michael additions, N-alkylations, and Dimroth rearrangements. This noninvasive technique is a particularly valuable tool in ca...

Heterojunctions and superlattices based on silicon carbide

Abstract: In addition to possessing unique electrical properties, silicon carbide (SiC) can crystallize in different modifications (polytypes). Having the same chemical nature, SiC polytypes may significantly differ in their electrical parameters. In recent years, the world's interest in the fabrication and study of heteropolytype structures based on silicon carbide has considerably increased. This review considers studies concerned with polytypism in SiC, fabrication technologies of various types of heterostructures constituted by different SiC polytypes and their electrical parameters. It is shown that heterostructures between SiC polytypes may have a better structural perfection than those constituted by semiconductors that differ in chemical nature. A conclusion is made that SiC-based heterostructures are promising for application in modern electronic devices.

Method for forming silicon carbide film containing oxygen

Abstract: A method for forming a silicon carbide film containing Si, C, O, H, and optionally N on a substrate placed in a reaction space, includes the steps of: introducing into the reaction space a precursor containing Si, C, O, and H and having at least one Si—O bond in its molecule; introducing into the reaction space an inert gas; applying RF power in the reaction space, wherein a ratio of a flow rate (sccm) of the inert gas to the RF power (W/cm2) is controlled at 30-850; and thereby depositing on the substrate a silicon carbide film containing Si, C, O, H, and optionally N.

Growth of planar non-polar {1 -1 0 0} m-plane gallium nitride with metalorganic chemical vapor deposition (MOCVD)

Abstract: A method of growing planar non-polar m-plane Ill-Nitride material, such as an m-plane gallium nitride (GaN) epitaxial layer, wherein the Ill-Nitride material is grown on a suitable substrate, such as an m-plane silicon carbide (m-SiC) substrate, using metalorganic chemical vapor deposition (MOCVD). The method includes performing a solvent clean and acid dip of the substrate to remove oxide from the surface, annealing the substrate, growing a nucleation layer such as an aluminum nitride (AlN) on the annealed substrate, and growing the non-polar m-plane Ill-Nitride epitaxial layer on the nucleation layer using MOCVD.

Oxidation of Zirconium Diboride–Silicon Carbide at 1500°C at a Low Partial Pressure of Oxygen

Abstract: The oxidation behavior of zirconium diboride containing 30 vol% silicon carbide particulates was investigated under reducing conditions. A gas mixture of CO and ∼350 ppm CO2 was used to produce an oxygen partial pressure of ∼10−10 Pa at 1500°C. The kinetics of the growth of the reaction layer were examined for reaction times of up to 8 h. Microstructures and chemistries of reaction layers were characterized using scanning electron microscopy and X-ray diffraction analysis. The kinetic measurements, the microstructure analysis, and a thermodynamic model indicate that oxidation in CO–CO2 produced a non-protective oxide surface scale.

Behavior of disordered boron carbide under stress.

Abstract: In today’s world, the properties of ceramic materials used for body armor determine the safety and survivability of many people. Although the physics governing the performance of such materials has been an active area of research for years, the theoretical assessment of material properties leading to failure under such conditions has not received significant attention. Typically, a key parameter elucidating the nominal potential of a ceramic as an armor grade material is represented by its Hugoniot elastic limit (HEL) which corresponds to the maximum uniaxial dynamic stress that the material can withstand elastically [1]. However, since the highest velocity threats generally lead to stresses which are higher than the HEL of the commonly available materials, it is almost compulsory for the candidate material to also possess a residual plastic behavior above the HEL. Light weight, wide availability, and processability of the material are also important issues in armor applications. Boron carbide possesses the highest HEL of ceramic materials (� 17–20 GPa), surpassing all of its denser competitors such as silicon carbide and alumina by a factor of 2 [1–3]. Such a property would suggest that boron carbide could withstand high pressures. This, however, has not been observed in laboratory experiments or practice. The small amount of plasticity above the HEL is thought to be the primary reason for failure of boron carbide at lower than expected impact pressures. This behavior is peculiar in dynamically elastic materials, being typical at much lower stresses (<1 GPa) of quartz and glasses [1]. This anomalous and poorly understood glasslike behavior in boron carbide has been the subject of research since its discovery over 70 years ago with most experiments geared towards finding a phase transformation [4].

Sequential Lithographic Methods to Reduce Stacking Fault Nucleation Sites

Abstract: An epitaxial silicon carbide layer is fabricated by forming first features in a surface of a silicon carbide substrate having an off-axis orientation toward a crystallographic direction. The first features include at least one sidewall that is orientated nonparallel (i.e., oblique or perpendicular) to the crystallographic direction. A first epitaxial silicon carbide layer is then grown on the surface of the silicon carbide substrate that includes first features therein. Second features are then formed in the first epitaxial layer. The second features include at least one sidewall that is oriented nonparallel to the crystallographic direction. A second epitaxial silicon carbide layer is then grown on the surface of the first epitaxial silicon carbide layer that includes the second features therein.

Ab initio study of nitrogen and boron substitutional impurities in single-wall SiC nanotubes

Abstract: Silicon carbide nanotubes have a great potential for application in chemical sensors in harsh environment or in biological sensors. It is of interest to explore the electronic properties of these nanotubes, and how those are modified in the presence of impurities. It is well known that nitrogen and boron atoms are common contaminations in bulk silicon carbide (SiC). Nitrogen preferentially substitutes the carbon site making $n$-type conductivity in bulk SiC. Boron substitutes both carbon and silicon sites forming a deep and a shallow acceptor in bulk SiC, respectively. In this paper we have studied these defects in armchair and zig-zag SiC nanotubes by ab initio supercell calculations. We found that nitrogen forms relatively shallow or deep donor state depending on the width of the band gap of the SiC nanotube. Boron is a relatively deep or shallow acceptor at carbon and silicon sites, respectively, like in bulk SiC polytypes. The site preference of boron depends on the stoichiometry of the SiC nanotubes. We have found no significant difference in the properties of boron substitutional defect between armchair and zig-zag nanotubes.

Novel abrasive-free planarization of 4H-SiC (0001) using catalyst

Abstract: A new abrasive-free planarization method for silicon carbide (SiC) wafers was proposed using the catalytic nature of platinum (Pt). We named it catalyst-referred etching (CARE). The setup equipped with a polishing pad made of Pt is almost the same as the lapping setup. However, CARE chemically removes SiC with an etching agent activated by a catalyst in contrast to mechanical removal by the lapping process. Hydrofluoric acid which is well known as an etchant of silicon dioxide (SiO2) that cannot etch SiC, was used as the source of the etching agent to SiC. The processed surfaces were observed by Nomarski differential interference contrast (NDIC) microscopy, atomic force microscopy (AFM), and optical interferometry. Those observations presented a marked reduction in surface roughness. Moreover, low-energy electron diffraction (LEED) images showed that a crystallographically well-ordered surface was realized.

Field-effect mobility temperature modeling of 4H-SiC metal-oxide-semiconductor transistors

Abstract: Here a physically based channel mobility model has been developed to investigate the temperature dependence of the field-effect mobility of 4H-SiC metal-oxide-semiconductor (MOS) transistors with thermally oxidized gate insulators. This model has been designed so that it accounts for the high density of traps at the MOS interface. This temperature dependence is a key issue for silicon carbide electronics, as its basic material properties make it the foremost semiconductor for high power/high temperature electronic devices in applications such as spacecraft, aircraft, automobile, and energy distribution. Our modeling suggests that the high density of charged acceptor interface traps, encountered in thermally grown gate oxides, modulates the channel mobility due to the Coulomb scattering of free carriers in the inversion layer. When the temperature increases, the field-effect mobility of these devices also increases, due to an increase in inversion charge and a reduction of the trapped charge. Experimental ...

Improving machining performance of wire electrochemical discharge machining by adding SiC abrasive to electrolyte

Abstract: The use of wire electrochemical discharge machining (WECDM) to slice hard brittle materials has recently been studied because its effectiveness is independent of the mechanical characteristics of the machined materials. Therefore, materials with high hardness, brittleness, strength and electrical insulation, which are difficult-to-cut, can be machined. In ECDM, the electrochemical reaction produces hydrogen bubbles, which accumulate around the cathode. A thin gas layer forms on the surface of the electrode and isolates the electrode from the electrolyte. When a voltage that exceeds the critical voltage is applied, continuous discharge occurs. The material near the electrode is removed by the discharge erosion and chemical etching. The use of WECDM to cut electrically insulating materials has only recently been investigated. However, the breakdown of the gas in the bubbles and the vibration of the wire in WECDM strongly affect the shape accuracy. This work aims to improve the over cut quality by adding SiC abrasive to the electrolyte. A mechanism that combines discharge, chemical etching and abrasive cutting is studied. The effects on expansion, roughness and material removal rate (MRR) are discussed. The experimental results reveal that adding abrasive reduces the slit expansion because it increases the critical voltage. The particles disrupt the bubble accumulation to form an isolating layer around the wire, increasing the critical voltage and reducing the discharge energy. The surface roughness is improved because the abrasive helps to refine the micro-cracks and melted zone that is formed by discharge heat erosion. Meanwhile, smaller grit produces lower roughness. The quality of the slit can be controlled; its expansion and roughness of the slit are 0.024 mm and 0.84 um Ra, respectively.

Athermal crystallization induced by electronic excitations in ion-irradiated silicon carbide

Abstract: Silicon carbide single crystals were irradiated at room temperature with low energy I ions and high energy Pb ions. It is found that the damaged layer formed by the elastic collisions generated during low energy I ion irradiation can readily be removed by the electronic excitations induced by swift Pb ions. This effect occurs at a temperature quite below that at which the conventional ion-beam induced crystallization process is generally achieved by nuclear energy loss. This finding is interesting both from a fundamental point of view for the understanding of the interaction of swift heavy ions with solids and for a large number of technological applications.

Numerical and experimental characterization of 4H-silicon carbide lateral metal-oxide-semiconductor field-effect transistor

Abstract: Combined simulation and experimental analyses are performed to characterize the 4H-silicon carbide (SiC) lateral metal-oxide-semiconductor field-effect transistor (MOSFET). Using a quasi-two-dimensional depth dependent Coulomb mobility model for scattering due to interface and oxide charge, along with existing models for other scattering mechanisms, and an in-house drift diffusion device simulator tailored for SiC MOSFETs, we have extracted values for interface trap density of states for 4H-SiC MOSFETs. Characterization shows that the interface trapped charge in 4H-SiC MOSFETs is responsible for mobility degradation and reduction in mobile inversion charge, and therefore reduced current. Its effect on mobility degradation decreases at higher gate voltages due to increased screening. Our results show that at high gate voltages, surface roughness plays the major role in surface mobility degradation in 4H-SiC MOSFETs. Results indicate that due to high Coulomb scattering near the interface, current density is...

Electroless Ni-P-SiC Composite Coatings with Superfine Particles

Abstract: Superfine silicon carbide particles reinforced nickel-phosphorus(Ni-P)matrix composite coatings were prepared by electroless depositionThe morphology and structure as well as the phase transformation of the composite coatings were studied by SEM,XRD,TEM and DSCIt is shown that SiC particles co-deposited homogeneously,and the structure of Ni-P-SiC composite coatings as deposited was amorphousAfter certain heat treatment,the matrix of composite coatings crystallized into nickel crystal and nickel phosphideAt higher temperature,nickel reacted with SiC and generated nickel silicides accompanied by free carbonFinal products of Ni- P-SiC coating after completely heat treatment were consisted of Ni,Ni_3P,Ni_3Si and carbonThe finer the SiC particles in composite coating,the lower the temperature for the reaction to take place

Protective ceramic multilayer coatings for carbon fibers

Abstract: Uniform, adherent, crack-free and non-bridging HfC and HfC/SiC coatings on carbon fibers have been synthesized by a reactive CVD (RCVD) process at low temperatures. To fabricate SiC coating on HfC-coated carbon fiber, an alternative approach using unsaturated organosilicon polymer solution was also proposed. The schemes describing the formation of carbide coatings on carbon fibers by RCVD and transformation of unsaturated organosilicon polymers into silicon carbide are discussed. The HfC and HfC/SiC coatings were studied by SEM, EDS and XPS techniques. Coatings are composed of hafnium, silicon and carbon as the main constituents and oxygen and fluorine as contaminants. As was proposed, the composition of the coatings is affected by several factors, among them a chemical attack of coated fibers by gaseous oxygen- and fluorine-containing by-products can be considered as dominant ones. The duplex HfC/SiC-coated carbon fibers exhibit more oxidation resistance at elevated temperatures than the initial and HfC-coated carbon fibers.

Formation of Carbide-Derived Carbon on β-Silicon Carbide Whiskers

Abstract: Carbon was synthesized on β-SiC whiskers by extraction of Si atoms from SiC. In this study, three different elevated temperature extraction methods were used to remove Si atoms from SiC: treatments in either Cl2 or HCl and vacuum decomposition. In all chlorination experiments and vacuum treatment at 1700°C, carbon preserved the original shape of SiC whiskers. At higher temperatures (2000°C), vacuum decomposition led to a distortion in the shape of the whiskers. High-resolution transmission electron microscopy and Raman spectroscopy showed that the structure of carbide-derived carbon depends on the Si extraction method and the process parameters. Chlorination of SiC resulted in the formation of mostly amorphous nanoporous carbon. High-temperature treatment of SiC in HCl environment produced fullerene-like structures, while high-temperature vacuum decomposition resulted in the formation of graphite. Transmission electron microscopy studies of the carbon coating thickness produced in Cl2 at various chlorination times revealed linear reaction kinetics at 700°C. Raman studies showed that the carbon structure became more ordered with increasing chlorination temperature. The results obtained demonstrate that by using the silicon extraction technique, one can precisely control the thickness and morphology of the carbon coating.

Densification of liquid phase sintered silicon carbide

Abstract: The densification and phase formation of liquid phase sintered silicon carbide (LPSSiC) with 10 wt.% additives were investigated. The ratio of the Al 2 O 3 /Y 2 O 3 -additives was changed between 4:1 and 1:2. Densification was carried out by hot pressing and gas pressure sintering. The different densification routes result in different major grain boundary phases—aluminates in gas pressure sintered materials and silicates in hot pressed samples. Thermodynamic calculations were carried out to determine the amount of liquid phase during densification and for the interpretation of the results.

In situ synthesis of SiC reinforced MMC surface on AISI 304 stainless steel by TIG surface alloying

Abstract: In this study, an austenitic stainless steel surface was coated with different silicon carbide powder contents. The process parameters were changed in order to determine their influence on the coating microstructure. The results showed that the silicon carbide particles are completely dissolved during the production. At the lower powder contents, the microstructures consisted of dendrites. However, M 7 C 3 primary carbides were generated at the high powder contents. The hardness of the dendritic structure is in the range 550 HV and 750 HV. However, the hardness of the hypereutectic structures is in the range 890 HV and 1210 HV. The lower hardness of dendritic microstructure was related to the presence of primary dendrites and relatively low concentrations of Fe, Cr, Si and C.

Anisotropic etching of SiC whiskers

Abstract: We have demonstrated a method of producing nanoplatelets or complex well-ordered nanostructures from silicon carbide (SiC) whiskers. Preferential etching of SiC whiskers in a mixture of hydrofluoric and nitric acids (3:1 ratio) at 100 °C results in the selective removal of cubic SiC and the formation of complex structures resembling a pagoda architecture. Possible mechanisms governing selective etching are discussed. Reproducible results on SiC whiskers manufactured in different laboratories suggest that the self-patterning phenomena are common in SiC whiskers, and the same electroless etching procedure can be used to synthesize various complex nanostructures from more conventional nano- and microscale objects for use as building blocks in the fabrication of sensors, cellular probes, and electronic, optoelectronic, electromechanical, and other devices.

Preparation of Nanocrystalline Silicon in Amorphous Silicon Carbide Matrix

Abstract: We have successfully prepared silicon quantum dots/amorphous silicon carbide multilayers by the thermal annealing of stoichiometric hydrogenated amorphous silicon carbide (a-SiC:H)/silicon-rich hydrogenated amorphous silicon carbide (a-Si1-xCx) multilayers. Raman scattering spectroscopy and transmission electron microscopy (TEM) revealed that silicon quantum dots were formed in only a-Si1-xCx layers. We also found that the size of silicon quantum dots can be controlled by the thickness of a-Si1-xCx layers.