Showing papers on "Silicon carbide published in 1998"

Coaxial Nanocable: Silicon Carbide and Silicon Oxide Sheathed with Boron Nitride and Carbon

Abstract: Multielement nanotubes comprising multiple phases, with diameters of a few tens of nanometers and lengths up to 50 micrometers, were successfully synthesized by means of reactive laser ablation. The experimentally determined structure consists of a β-phase silicon carbide core, an amorphous silicon oxide intermediate layer, and graphitic outer shells made of boron nitride and carbon layers separated in the radial direction. The structure resembles a coaxial nanocable with a semiconductor-insulator-metal (or semiconductor-insulator-semiconductor) geometry and suggests applications in nanoscale electronic devices that take advantage of this self-organization mechanism for multielement nanotube formation.

Group III nitride photonic devices on silicon carbide substrates with conductive buffer interlayer structure

Abstract: An optoelectronic device with a Group III Nitride active layer is disclosed that comprises a silicon carbide substrate; an optoelectronic diode with a Group III nitride active layer; a buffer structure selected from the group consisting of gallium nitride and indium gallium nitride between the silicon carbide substrate and the optoelectronic diode; and a stress-absorbing structure comprising a plurality of predetermined stress-relieving areas within the crystal structure of the buffer structure, so that stress-induced cracking that occurs in the buffer structure occurs at predetermined areas rather than elsewhere in the buffer structure.

Silicon carbide MEMS for harsh environments

Abstract: Silicon carbide (SiC) is a promising material for the development of high-temperature solid-state electronics and transducers, owing to its excellent electrical, mechanical, and chemical properties. This paper is a review of silicon carbide for microelectromechanical systems (SiC MEMS). Current efforts in developing SiC MEMS to extend the silicon-based MEMS technology to applications in harsh environments are discussed. A summary is presented of the material properties that make SiC an attractive material for use in such environments. Challenges faced in the development of processing techniques are also outlined. Last, a review of the current stare of SiC MEMS devices and issues facing future progress are presented.

High-strength alkali-resistant sintered SiC fibre stable to 2,200 °C

Abstract: The high-temperature stability of SiC-based ceramics has led to their use in high-temperature structural materials and composites1,2,3 In particular, silicon carbide fibres are used in tough fibre-reinforced composites Here we describe a type of silicon carbide fibre obtained by sintering an amorphous Si–Al–C–O fibre precursor at 1,800 °C The fibres, which have a very small aluminium content, have a high tensile strength and modulus, and show no degradation in strength or change in composition on heating to 1,900 °C in an inert atmosphere and 1,000 °C in air — a performance markedly superior to that of existing commercial SiC-based fibres such as Hi-Nicalon Moreover, our fibres show better high-temperature creep resistance than commercial counterparts We also find that the mechanical properties of the fibres are retained on heating in air after exposure to a salt solution, whereas both a representative commercial SiC fibre and a SiC-based fibre containing a small amount of boron were severely degraded under these conditions4 This suggests that our material is well suited to use in environments exposed to salts — for example, in structures in a marine setting or in the presence of combustion gases containing alkali elements

Biomorphic cellular silicon carbide ceramics from wood : II. Mechanical properties

Abstract: Silicon carbide ceramics with anisotropic pore microstructures pseudomorphous to wood were obtained by liquid Si infiltration of porous carbonized wood templates. Depending on the initial cellular microstructure of the various kinds of wood (ebony, beech, oak, maple, pine, balsa) ceramic materials of different density, pore structure and degree of anisotropy were obtained. Strength and elastic modulus of the pyrolyzed carbon preform and of the final silicon carbide ceramic were measured in different loading directions with respect to the initial cell orientation, e.g. axial, radial and tangential. Generally, the mechanical properties increase with fractional density. Strength and strain-to-failure in axial direction exhibit significantly higher values compared to loading in radial and tangential directions. The orientation dependence of microstructure-property relations may become important for the development of advanced anisotropic light weight structural materials.

Ion-beam induced damage and annealing behaviour in SiC

Abstract: The paper presents the damage accumulation in silicon carbide (SiC) as a function of the ion mass, the ion energy and the implantation temperature. A defect-interaction and amorphization model is used to analyse the dose dependence of defect production, as obtained by the various methods. The temperature dependence of the amorphization dose can be represented assuming a thermally enhanced annealing within the primary collision cascades. On the basis of such a model, a critical implantation temperature is obtained, which was found to vary with the ion mass and the implantation energy. The concurrent influence of implantation temperature and ion fluence on the resulting damage distribution in SiC is demonstrated. The damage annealing of ion implanted SiC is investigated for low, medium and high damage concentrations. The effect of the implantation temperature and the concentration of implanted atoms, both influencing the kind of defects obtained after implantation, on the annealing behaviour is analysed.

Method for manufacturing silicon carbide semiconductor device

Abstract: In a method for manufacturing a silicon carbide semiconductor device, preliminary heat treatment is conducted after implanting impurity ions into a silicon carbide substrate, such that the silicon carbide substrate is heated at a temperature in a range of, for example, 800 to 1200° C, in a hydrogen atmosphere or a mixed gas ambient comprising hydrogen and inert gas After the preliminary heat treatment, the silicon carbide substrate may be annealed at a high temperature

Oxidation Protection Coatings for C/SiC based on Yttrium Silicate

Abstract: The factor which currently precludes the use of carbon fibre reinforced silicon carbide (C/SiC) in high temperature structural applications such as gas turbine engines is the oxidation of carbon fibres at temperatures greater than 400°C. It is, therefore, necessary to develop coatings capable of protecting C/SiC components from oxidation for extended periods at 1600°C. Conventional coatings consist of multilayers of different materials designed to seal cracks by forming glassy phases on exposure to oxygen. The objective of this work was to develop a coating which was inherently crack resistant and would, therefore, not require expensive sealing layers. Yttrium silicate has been shown to possess the required properties for use in oxidation protection coatings. These requirements can be summarised as being low Young’s modulus, low thermal expansion coefficient, good erosion resistance, and low oxygen permeability. The development of protective coatings based on a SiC bonding layer combined with an outer yttrium silicate erosion resistant layer and oxygen barrier is described. Thermodynamic computer calculations and finite element analysis have been used to design the coating. C/SiC samples have been coated using a combination of chemical vapour deposition and slip casting. The behaviour against oxidation of the coating has been evaluated.

A Tough, Thermally Conductive Silicon Carbide Composite with High Strength up to 1600°C in Air

Abstract: A sintered silicon carbide fiber-bonded ceramic, which consists of a highly ordered, close-packed structure of very fine hexagonal columnar fibers with a thin interfacial carbon layer between fibers, was synthesized by hot-pressing plied sheets of an amorphous silicon-aluminum-carbon-oxygen fiber prepared from an organosilicon polymer. The interior of the fiber element was composed of sintered beta-silicon carbide crystal without an obvious second phase at the grain boundary and triple points. This material showed high strength (over 600 megapascals in longitudinal direction), fibrous fracture behavior, excellent high-temperature properties (up to 1600 degreesC in air), and high thermal conductivity (even at temperatures over 1000 degreesC).

High surface area silicon carbide as catalyst support characterization and stability

Abstract: High surface area silicon carbide (SiC) of 30 m 2 /g has been synthesized by the catalytic conversion of activated carbon. The stability of this SiC in aqueous hydrogen fluoride and a boiling nitric acid solution is shown to be excellent. No corrosion is encountered by treatment with boiling HNO 3 , HF treatment causes the dissolution of the silica surface layer present on the SiC while the SiC remains intact. Oxidation in air at elevated temperatures has been analyzed by thermal gravimetric analysis, diffuse reflectance infrared spectroscopy, nitrogen adsorption, and X-ray diffraction. The thermal stability in non-oxidizing environments is shown to be excellent; no significant sintering has been observed after ageing in nitrogen for 4 h at 1273 K. The presence of 2 v% steam at 1273 K results in partial SiC oxidation into SiO 2 and considerable sintering. Air oxidation at 1273 K of pure SiC, SiC loaded with 5 wt.% nickel, and HNO 3 treated SiC is shown to cause substantial SiC conversion, viz. 60% to 70% after 10 h. Air oxidation at 1080 K will result in complete conversion in about 100 days. This rate of oxidation agrees with reports on the oxidation of non-porous Acheson SiC and SiC coatings formed by Chemical Vapour Deposition. It is concluded that at high surface area SiC cannot be used as a catalyst support in processes operating in oxidizing environments and temperatures above 1073 K. SiC based catalysts are very well suited for (1) high-temperature gas-phase reactions operating in the absence of oxidizing constituents (O 2 or H 2 O) and (2) strong acidic liquid-phase processes.

Development of a silicon carbide radiation detector

Abstract: The radiation detection properties of semiconductor detectors made of 4H silicon carbide were evaluated. Both Schottky and p-n junction devices were tested. Exposure to alpha particles from a /sup 238/Pu source led to robust signals from the detectors. The resolution of the Schottky SiC detector was 5.8% (FWHM) at an energy of 294 keV, while that of the p-n junction was 6.6% (FWHM) at 260 keV. No effect of temperature in the range of 22 to 89/spl deg/C was observed on the characteristics of the /sup 238/Pu alpha-induced signal from the SiC detector. In addition, testing in a gamma field of 10,000 rad-Si h/sup -1/ showed that the alpha-induced signal was separable from the gamma signal.

Silicon carbide power devices

Abstract: The more and more demanding requirements of the power device users bring the silicon technology very close to its own physical limits. Silicon carbide (SiC) appears today as the only semiconductor having the capability for significantly improving the ratings of major power components (such as high voltage Schottky rectifiers), indeed for creating novel devices for new applications. The choice of SiC comes from superior physical properties, an existing substrate commercialization, and an experimental confirmation of several potentialities (at high voltage, temperature, or frequency) via demonstrative prototypes. However, such a young technology still suffers from a too poor quality of the available basic materials, and from the fabrication step immaturity, delaying the SiC power electronics emergence.

Negative-U centers in 4H Silicon Carbide

Abstract: Characterization of two negative-U centers in 4H SiC has been performed using various capacitance transient techniques. Each center gives rise to one acceptor level (-/0) and one donor level (0/+), where the electron ionization energy of the acceptor level is larger than that of the donor level. The two-electron emissions from the two acceptor levels give rise to the previously reported deep level transient spectroscopy peak associated with the so-called ${Z}_{1}$ center. Direct evidence for the inverted ordering and temperature dependence studies of the electron-capture cross sections of the acceptor levels will be presented.

Meteoritic oxide grain from supernova found

Abstract: Meteorites contain tiny (0.002-10 μm) mineral grains which formed around stars or in stellar explosions1,2. These grains have unusual isotope compositions that reflect those of the stars in which they formed. Stardust composed of nanodiamonds, silicon carbide (SiC), silicon nitride (Si3N4) or graphite are believed to derive from a range of stellar types1,2, whereas the oxygen-rich grains found to date are thought to originate only in red giants and asymptotic giant branch stars3. We report here an oxide grain that is extremely rich in the isotope oxygen-16 (16O), in an acid-resistant residue of the Tieschitz meteorite. This grain, T84, probably derives from the ejecta of a type II supernova and is the first reported oxide grain derived from such a source, despite 16O being the third most abundant isotope ejected by supernovae (after hydrogen and helium)4.

Absorption coefficient of 4H silicon carbide from 3900 to 3250 Å

Abstract: We report the values of the absorption coefficient of 4H SiC at room temperature, in the wavelength range from 3900 to 3350 A and at 3250 A. By using the known shift in the band gap with temperature, we also present an estimate of the absorption coefficient of 4H SiC at 2 K.

SiC materials and devices

Abstract: K. Jarrendahl and R.F. Davis, Materials Properties and Characterization of SiC. V.A. Dmitriev and M.G. Spencer, SiC Fabrication Technology: Growth and Doping. V. Saxena and A.J. Steckl, Silicon Carbide Materials and Devices. M. Shur, SiC Transistors. C.D. Brandt, R.C. Clarke, R.R. Siergiej, J.B. Casady, and A.W. Morse, SiC for Applications in High Power Electronics. R.J. Trew, SiC Microwave Devices. C. Carter, J. Edmond, H. Kong, G. Negley, M. Leonard, K. Doverspike, W. Weeks, A. Suvorov, and D. Waltz, SiC-Based UV Photodiodes and Light Emitting Diodes. H. Morkoc, Beyond Silicon Carbide! II-V Nitride Based Heterostructures and Devices. Subject Index.

High temperature mechanical behaviour of liquid phase sintered silicon carbide

Abstract: Silicon carbide was liquid phase sintered using Y 2 O 3 and AlN as sintering additives. A globular grained microstructure was obtained from α-SiC powder whereas a mixture of β-SiC, with a small amount of α-SiC seeds, revealed platelet shaped grains with an aspect ratio of eight. Beside this difference in grain morphology of the α-SiC grains, the phase content of the grain boundary phase is different. The influence of both aspects onto the mechanical behaviour, i.e. four-point bending strength between room temperature and 1400°C and fracture toughness between room temperature and 1100°C, are investigated.

Joining of reaction-bonded silicon carbide using a preceramic polymer

Abstract: Ceramic joints between reaction-bonded silicon carbide (RBSiC) were produced using a preceramic polymer (GE SR350 silicone resin) as joining material; samples were heat treated in an argon flux at temperatures ranging from 800–1200°C without applying any pressure. The strength of the joints was determined by four-point bending, shear and indentation tests. Microstructural and microchemical analyses were performed by optical microscopy, SEM, TEM and AEM. The room-temperature strength of the joints increased with the joining temperature. Maximum values as high as 220 MPa in bending and 39 MPa in shear tests were reached for samples joined at 1200°C. No detectable residual stresses were observed both in the joining material and the joined parts, and the fracture mechanism was nearly always cohesive. The joint thickness was shown to depend on the processing temperature, and ranged from about 2–7 μm. The joining material was a silicon oxycarbide amorphous ceramic, with no oxygen diffusion occurring between this and the RBSiC joined parts. The lack of compositional gradients, precipitates or reaction layers indicate that the SiOC ceramic acted as an inorganic adhesive, and that the joining mechanism involved the direct formation of chemical bonds between the RBSiC parts and the joining material. © 1998 Chapman & Hall

MOSgated trench type power semiconductor with silicon carbide substrate and increased gate breakdown voltage and reduced on-resistance

Abstract: A MOSgated trench type power semiconductor device is formed in 4H silicon carbide with the low resistivity direction of the silicon carbide being the direction of current flow in the device drift region. A P type diffusion at the bottom of the U shaped grooves in N− silicon carbide helps prevent breakdown of the gate oxide at the trench bottom edges. The gate oxide may be shaped to increase its thickness at the bottom edges and has a trapezoidal or spherical curvature. The devices may be implemented as depletion mode devices.

Study of avalanche breakdown and impact ionization in 4H silicon carbide

Abstract: Epitaxial p-n diodes in 4H SiC are fabricated with uniform avalanche multiplication and breakdown. Photomultiplication measurements were performed to determine electron and hole ionization rates. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained. We discuss ionization mechanisms in 4H SiC and make a comparison between silicon carbide and gallium nitride.

Silicon carbide semiconductor device and its manufacture

Abstract: PROBLEM TO BE SOLVED: To provide a silicon carbide semiconductor device which can improve ON-resistance by improving channel mobility. SOLUTION: An n - -type silicon carbide epitaxial layer 2 is formed on a main surface of an n + -type silicon carbide semiconductor board 1, p-type silicon carbide base regions 3a, 3b with a specified depth are formed in a specified region of a surface layer of the n - -type silicon carbide epitaxial layer 2, and n + -type source regions 4a, 4b are formed in a specified region of a surface layer of the base regions 3a, 3b. A surface channel epitaxial layer 5 is arranged to connect the source regions 4a, 4b and the n - -type silicon carbide epitaxial layer 2 in a surface layer of the base regions 3a, 3b. A gate electrode 8 is formed in a surface of the surface channel epitaxial layer 5 through a gate insulation film 7. A source electrode 10 is formed to come into contact with the base regions 3a, 3b and the source regions 4a, 4b, and a drain electrode 11 is formed in a rear of the board 1. COPYRIGHT: (C)1998,JPO

Lateral n-channel inversion mode 4H-SiC MOSFETs

Abstract: Advances in MOS devices on silicon carbide (SiC) have been greatly hampered by the low inversion layer mobilities. In this paper, the electrical characteristics of lateral n-channel MOSFETs fabricated on 4H-SiC are reported for the first time. Inversion layer electron mobilities of 165 cm/sup 2//V/spl middot/s in 4H-SiC MOSFETs were measured at room temperature. These MOSFETs were fabricated using a low temperature deposited oxide, with subsequent oxidation anneal, as the gate dielectric.

Crack Deflection in Ceramic Laminates Using Porous Interlayers

Abstract: Ceramic laminates have been made from alternating layers of silicon carbide and silicon carbide containing a fugitive polymer, which can be pyrolysed to produce porous interlayers. It is shown that such interlayers can be used to deflect cracks and that the volume fraction of porosity, due to the added polymer, that is required to cause crack deflection is approximately 0·4. A simple model has been developed which describes the fracture behaviour of porous solids and also predicts the volume fraction of porosity required to give crack deflection in the laminate and which is in good agreement with experiment.

Silicon carbide semiconductor device and process for manufacturing same

Abstract: A n - -type source region 5 is formed on a predetermined region of the surface layer section of the p-type silicon carbide semiconductor layer 3 of a semiconductor substrate 4. A low-resistance p-type silicon carbide region 6 is formed on a predetermined region of the surface layer section in the p-type silicon carbide semiconductor layer 3. A trench 7 is formed in a predetermined region in the n + -type source region 5, which trench 7 passes through the n + -type source region 5 and the p-type silicon carbide semiconductor layer 3, reaching the n - -type silicon carbide semiconductor layer 2. The trench 7 has side walls 7a perpendicular to the surface of the semiconductor substrate 4 and a bottom side 7b parallel to the surface of the semiconductor substrate 4. The hexagonal region surrounded by the side walls 7a of the trench 7 is an island semiconductor region 12. A high-reliability gate insulating film 8 is obtained by forming a gate insulating layer on the side walls 7a which surround the island semiconductor region 12.

Method for doping semiconductor materials

Abstract: Method is provided for controlling the concentration of a dopant introduced into an epitaxial film during CVD or sublimation growth by controlling the energy of dopant atoms impinging on the film in a supersonic beam. Precursor materials may also be introduced by supersonic beam. Energy of the dopant atoms may be changed by changing flow conditions in the supersonic beam or changing carrier gases. Flow may be continuous or pulsed. Examples of silicon carbide doping are provided.