Showing papers on "Silicon carbide published in 2007"

Graphene: mind the gap.

Abstract: Research now shows that interaction with silicon carbide substrate leads to the opening of a semiconductor gap in epitaxial graphene. This is an important first step towards bandgap engineering in this two-dimensional crystal, and its incorporation in electronic devices.

Evolution of structure during the oxidation of zirconium diboride–silicon carbide in air up to 1500 °C

Abstract: The structures that developed as dense ZrB2–SiC ceramics were heated to 1500 °C in air were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction. The oxidation behavior was also studied using thermal gravimetric analysis (TGA). Below 1200 °C, a protective B2O3-rich scale was observed on the surface. At 1200 °C and above, the B2O3 evaporated and the SiO2-rich scale that formed was stable up to at least 1500 °C. Beneath the surface, layers that were rich in zirconium oxide, and from which the silicon carbide had been partially depleted, were observed. The observations were consistent with the oxidation sequence recorded by thermal gravimetric analysis.

Dielectric metamaterials based on electric and magnetic resonances of silicon carbide particles.

Abstract: Silicon carbide particles exhibit both electric and magnetic optical resonances, allowing unexplored dielectric metamaterial designs. Experimental extinction spectra and Mie theory calculations of single microscale rod-shaped particles reveal three observable midinfrared resonant modes. Two of the modes are degenerate, with a frequency that can be tuned according to a resonance condition derived within the Letter. The existence of both electric and magnetic resonances may enable a novel negative refractive index metamaterial design.

Power Conversion With SiC Devices at Extremely High Ambient Temperatures

Abstract: This paper evaluates the capability of SiC power semiconductor devices, in particular JFET and Schottky barrier diodes (SBD) for application in high-temperature power electronics. SiC JFETs and SBDs were packaged in high temperature packages to measure the dc characteristics of these SiC devices at ambient temperatures ranging from 25degC (room temperature) up to 450degC. The results show that both devices can operate at 450degC, which is impossible for conventional Si devices, at the expense of significant derating. The current capability of the SiC SBD does not change with temperature, but as expected the JFET current decreases with rising temperatures. A 100 V, 25 W dc-dc converter is used as an example of a high-temperature power-electronics circuit because of circuit simplicity. The converter is designed and built in accordance with the static characteristics of the SiC devices measured under extremely high ambient temperatures, and then tested up to an ambient temperature of 400degC. The conduction loss of the SiC JFET increases slightly with increasing temperatures, as predicted from its dc characteristics, but its switching characteristics hardly change. Thus, SiC devices are well suited for operation in harsh temperature environments like aerospace and automotive applications.

Influence of silicon carbide particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide ceramics

Abstract: The influence of silicon carbide (SiC) particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide (ZrB2–SiC) ceramics was investigated. ZrB2-based ceramics containing 30 vol.% SiC particles were prepared from four different α-SiC precursor powders with average particle sizes ranging from 0.45 to 10 μm. Examination of the dense ceramics showed that smaller starting SiC particle sizes led to improved densification, finer grain sizes, and higher strength. For example, ceramics prepared from SiC with the particle size of 10 μm had a strength of 389 MPa, but the strength increased to 909 MPa for ceramics prepared from SiC with a starting particle size of 0.45 μm. Analysis indicates that SiC particle size controls the strength of ZrB2–SiC.

Playing with carbon and silicon at the nanoscale.

Abstract: Because of its superior properties silicon carbide is one of the most promising materials for power electronics, hard- and biomaterials. In the solid phase, the electronic and optical properties are controlled by the stacking of double layers of Si and C atoms. In thin films, a change in the stacking order often requires stress, which can be achieved naturally in systems with nanometre length scale. For this reason, nanotubes, nanowires and clusters can be used as building blocks for the synthesis of novel materials. Furthermore, playing at the nanometre length scale enables the nature of the SiC bonding to be modified, which is of prime importance for atomic engineering of nanostructures. In this review, emphasis is placed on the theoretical principles associated with SiC cage-like clusters and experimental work resulting from them.

SiC sensors: a review

Abstract: Silicon carbide has attracted considerable attention in recent years as a potential material for sensor devices. This paper reviews the current status of SiC technology for a wide range of sensor applications. It is shown that SiC MEMs devices are well-established with operational devices demonstrated at high temperatures (up to 500 °C) for the sensing of motion, acceleration and gas flow. SiC sensors devices using electrical properties as the sensing mechanism have also been demonstrated principally for gas composition and radiation detection and have wide potential use in scientific, medical and combustion monitoring applications.

Superabrasive compact including diamond-silicon carbide composite, methods of fabrication thereof, and applications therefor

Abstract: Embodiments of the present invention relate to diamond-silicon carbide composites, superabrasive compacts including such diamond-silicon carbide composites, and methods of fabricating such diamond-silicon carbide composites and superabrasive compacts. In one embodiment, a superabrasive compact includes a substrate and a superabrasive table bonded to the substrate. The superabrasive table comprises diamond-silicon carbide composite including a matrix comprising nanometer-sized silicon carbide grains and micrometer-sized diamond grains dispersed through the matrix. In another embodiment, a method of fabricating a superabrasive compact is disclosed. An assembly comprising a mixture including diamond particles and silicon is formed. The silicon comprises amorphous silicon, crystalline silicon crystallized from amorphous silicon formed by a milling process, or combinations thereof. A substrate is positioned in proximity to the mixture. The assembly is subjected to heat and pressure to form a superabrasive compact comprising a superabrasive table bonded to the substrate. The superabrasive table comprises diamond-silicon carbide composite including diamond grains dispersed through a matrix of silicon carbide grains.

Silicon Carbide Power MOSFET Model and Parameter Extraction Sequence

Abstract: A compact circuit simulator model is used to describe the performance of a 2-kV, 5-A 4-H silicon carbide (SiC) power DiMOSFET and to perform a detailed comparison with the performance of a widely used 400-V, 5-A Si power MOSFET. The model's channel current expressions are unique in that they include the channel regions at the corners of the square or hexagonal cells that turn on at lower gate voltages and the enhanced linear region transconductance due to diffusion in the nonuniformly doped channel. It is shown that the model accurately describes the static and dynamic performance of both the Si and SiC devices and that the diffusion-enhanced channel conductance is essential to describe the SiC DiMOSFET on-state characteristics. The detailed device comparisons reveal that both the on-state performance and switching performance at 25degC are similar between the 400-V Si and 2-kV SiC MOSFETs, with the exception that the SiC device requires twice the gate drive voltage. The main difference between the devices is that the SiC has a five times higher voltage rating without an increase in the specific on-resistance. At higher temperatures (above 100degC), the Si device has a severe reduction in conduction capability, whereas the SiC on-resistance is only minimally affected

A SiC MEMS Resonant Strain Sensor for Harsh Environment Applications

Abstract: In this paper, we present a silicon carbide MEMS resonant strain sensor for harsh environment applications. The sensor is a balanced-mass double-ended tuning fork (BDETF) fabricated from 3C-SiC deposited on a silicon substrate. The SiC was etched in a plasma etch chamber using a silicon oxide mask, achieving a selectivity of 5:1 and etch rate of 2500 Aring/min. The device resonates at atmospheric pressure and operates from room temperature to above 300degC. The device was also subjected to 10 000 g shock (out-of-plane) without damage or shift in resonant frequency. The BDETF exhibits a strain sensitivity of 66 Hz/muepsiv and achieves a strain resolution of 0.11 muepsiv in a bandwidth from 10 to 20 kHz, comparable to state-of-the-art silicon sensors

Method, system, and apparatus for the growth of SiC and related or similar material, by chemical vapor deposition, using precursors in modified cold-wall reactor

Abstract: An approach for the growth of high-quality epitaxial silicon carbide (SiC) films and boules, using the Chemical Vapor Deposition (CVD) technique is described here. The method comprises modifications in the design of the typical cold-wall CVD reactors, providing a better temperature uniformity in the reactor bulk and a low temperature gradient in the vicinity of the substrate, and an approach to increase the silicon carbide growth rate and to improve the quality of the growing layers, using halogenated carbon-containing precursors (carbon tetrachloride CCl 4 or halogenated hydrocarbons, CHCl 3 , CH 2 Cl 2 , CH 3 Cl, etc.), or introducing other chlorine-containing species in the gas phase in the growth chamber. The etching effect, proper ranges, and high temperature growth are also examined.

High-Temperature Operation of SiC Power Devices by Low-Temperature Sintered Silver Die-Attachment

Abstract: In this paper, we present the realization of high-temperature operation of SiC power semiconductor devices by low-temperature sintering of nanoscale silver paste as a novel die-attachment solution. The silver paste was prepared by mixing nanoscale silver particles with carefully selected organic components which can burn out within the low-temperature firing range. SiC Schottky diodes were placed onto stencil-printed layers of the nanoscale silver paste on Au or Ag metallized direct bonded copper (DBC) substrates for the die-attachment. After heating up to 300degC and dwell for 40 min in air to burn out the organic components in the paste and to sinter the nanoscale silver, the paste consolidated into a strong and uniform die-attach bonding layer with purity >99% and density >80%. Then the die-attached SiC devices were cooled down to room temperature and their top terminals were wire-bonded to achieve the high-temperature power packages. Then the power packages were heated up from room temperature to 300degC for high-temperature operation and characterization. Results of the measurement demonstrate the low-temperature silver sintering as an effective die-attach method for high-temperature electronic packaging. An advanced packaging structure for future SiC transistors with several potential advantages was also proposed based on the low-temperature sintering technology.

Comparisons of SiC MOSFET and Si IGBT Based Motor Drive Systems

Abstract: With the rapid development of silicon carbide (SiC) material quality, SiC power devices are gaining tremendous attentions in power electronics. In this paper, a SiC device based motor drive system is performed to provide a quantitative estimate of the system improvement. Two 60 kW motor drive systems based on SiC MOSFET/Schottky diode and Si IGBTs are designed. The power losses of the two inverters with sinusoidal pulse width modulation (SPWM) control are calculated analytically. By comparing the efficiencies, sizes and temperatures of the two designed systems, SiC device shows the superior advantages of smaller loss, better efficiency and smaller size in the same motor drive application.

Method of manufacturing silicon carbide semiconductor device

Abstract: A method of manufacturing a silicon carbide semiconductor device having a MOS structure includes preparing a substrate made of silicon carbide, and forming a channel region, a first impurity region, a second impurity region, a gate insulation layer, and a gate electrode to form a semiconductor element on the substrate. In addition, a film is formed on the semiconductor element to provide a material of an interlayer insulation layer, and a reflow process is performed at a temperature about 700° C. or over in an wet atmosphere so that the interlayer insulation layer is formed from the film and an edge portion of the gate electrode is rounded and oxidized.

Pressureless Sintering of ZrB2–SiC Ceramics

Abstract: A pressureless sintering process was developed for the densification of zirconium diboride ceramics containing 10-30 vol% silicon carbide particles. Initially, boron carbide was evaluated as a sintering aid. However, the formation of a borosilicate glass led to significant coarsening, which inhibited densification. Based on thermodynamic calculations, a combination of carbon and boron carbide was added, which enabled densification (relative density > 98%) by solid-state sintering at temperatures as low as 1950°C. Varying the size of the starting silicon carbide particles allowed the final silicon carbide particle morphology to be controlled from equiaxed to whisker-like. The mechanical properties of sintered ceramics were comparable with hot-pressed materials with Vickers hardness of 22 GPa, elastic modulus of 460 GPa, and fracture toughness of ∼4 4 MPa· m 1/2 . Flexure strength was ∼ 460 MPa, which is at the low end of the range reported for similar materials, due to the relatively large size (∼ 13 μm long) of the silicon carbide inclusions.

Strain Measurements of Silicon Dioxide Microspecimens by Digital Imaging Processing

Abstract: Silicon dioxide thin film is a common component in electronic devices and in MEMS, but its mechanical properties have rarely been studied. Techniques have been adapted and developed to conduct tensile tests on 1.0 μm thick silicon dioxide specimens that are 100, 150, and 200 μm wide and either 1 or 2 mm long. One end of the specimen remains fastened to the substrate, and the other is glued to a silicon carbide fiber attached to a 30 g load cell mounted on a piezoelectric translation stage. Strain is measured by digital imaging of two gold lines applied to the gage section of the transparent specimen. Twenty-five tests yield a Young’s modulus of 60.1 ± 3.4 GPa and a fracture strength of 364 ± 57 MPa.

Comparison of GaN HEMTs on Diamond and SiC Substrates

Abstract: The performance of AlGaN/GaN high-electron-mobility transistors (HEMTs) on diamond and SiC substrates is examined. We demonstrate GaN-on-diamond transistors with periphery WG = 250 mum, exhibiting ft = 27.4 GHz and yielding a power density of 2.79 W/mm at 10 GHz. Additionally, the temperature rise in similar devices on diamond and SiC substrates is reported. To the best of our knowledge, these represent the highest frequency of operation and first-reported thermal and X -band power measurements of GaN-on-diamond HEMTs.

Methods of fabricating superabrasive articles

Abstract: In one embodiment of the present invention, a method of fabricating a superabrasive article is disclosed. A mass of unsintered diamond particles may be infiltrated with metal-solvent catalyst from a metal-solvent- catalyst-containing material to promote formation of a sintered body of diamond grains including interstitial regions. At least a portion of the interstitial regions may also be infiltrated with silicon from a silicon- containing material. The silicon reacts with the sintered body to form silicon carbide within a portion of the interstitial regions.

High Thermal Conductivity of Gallium Nitride (GaN) Crystals Grown by HVPE Process

Abstract: A relatively large sample of gallium nitride (GaN) was grown as a single crystal using the hydride vapor phase epitaxy (HVPE) process. The thermal diffusivity of the single crystal has been measured using a vertical-type laser flash method. The thermal expansion was measured using a dilatometer in order to estimate the thermal diffusivity with sufficient reliability. The effect of sample thickness and temperature on thermal diffusivity was evaluated. The specific heat capacity of GaN was also measured by using a differential scanning calorimeter. The thermal properties of single-crystal GaN have been compared with the measured thermal properties of single-crystal silicon carbide (SiC). The thermal conductivity of single-crystal GaN at room temperature is found to be 253 � 8:8% W/mK, which is approximately 60% of the value obtained for SiC. The excellent thermal property that is obtained in this study clearly indicates that GaN crystals are one of the promising materials for use in high-power-switching devices. [doi:10.2320/matertrans.MRP2007109]

Silicon Quantum Dots in a Dielectric Matrix for All-Silicon Tandem Solar Cells

Abstract: We report work progress on the growth of Si quantum dots in different matrices for future photovoltaic applications. The work reported here seeks to engineer a wide-bandgap silicon-based thin-film material by using quantum confinement in silicon quantum dots and to utilize this in complete thin-film silicon-based tandem cell, without the constraints of lattice matching, but which nonetheless gives an enhanced efficiency through the increased spectral collection efficiency. Coherent-sized quantum dots, dispersed in a matrix of silicon carbide, nitride, or oxide, were fabricated by precipitation of Si-rich material deposited by reactive sputtering or PECVD. Bandgap opening of Si QDs in nitride is more blue-shifted than that of Si QD in oxide, while clear evidence of quantum confinement in Si quantum dots in carbide was hard to obtain, probably due to many surface and defect states. The PL decay shows that the lifetimes vary from 10 to 70 microseconds for diameter of 3.4 nm dot with increasing detection wavelength.

Effects of silicon carbide reinforcement on microstructure and properties of cast Al–Si–Fe/SiC particulate composites

Abstract: The effects of silicon carbide (SiC) particles on the as-cast microstructure and properties of Al–Si–Fe alloy composites produced by double stir-casting method have been studied. A total of 5–25 wt% silicon carbide particles were added. The microstructure of the alloy particulate composites produced was examined, the physical and mechanical properties measured include: densities, porosity, ultimate tensile strength, yield strength, hardness values and impact energy. The results revealed that, addition of silicon carbide reinforcement, increased the hardness values and apparent porosity by 75 and 39%, respectively, and decreased the density and impact energy by 1.08 and 15%, respectively, as the weight percent of silicon carbide increases in the alloy. The yield strength and ultimate tensile strength increased by 26.25 and 25% up to a maximum of 20% silicon carbide addition, respectively. These increases in strength and hardness values are attributed to the distribution of hard and brittle ceramic phases in the ductile metal matrix. The microstructure obtained reveals a dark ceramic and white metal phases, which resulted into increase in the dislocation density at the particles–matrix interfaces. These results show that better properties is achievable by addition of silicon carbide to Al–Si–Fe alloy.

Interfacial design of Cu/SiC composites prepared by powder metallurgy for heat sink applications

Abstract: In order to dissipate the heat generated in electronic packages, suitable materials must be developed as heat spreaders or heat sinks. Metal matrix composites (MMCs) offer the possibility to tailor the properties of a metal (Cu) by adding an appropriate reinforcement phase (SiC) to meet the demands for high thermal conductivities in thermal management applications. Copper/SiC composites have been produced by powder metallurgy. Silicon carbide is not stable in copper at the temperature needed for the fabrication of Cu/SiC. The major challenge in development of Cu/SiC is the suppression of this reaction between copper and SiC. Improvements in bonding strength and thermo-physical properties of the composites have been achieved by a vapour deposited molybdenum coating on SiC powders to control the detrimental interfacial reactions.

Power Device Packaging Technologies for Extreme Environments

Abstract: Silicon carbide is a wide-bandgap semiconductor capable of operation at temperatures in excess of 300degC. However, high-temperature packaging to interface with the other elements of the electrical system is required. Die attach, wire bonding, and passivation materials and techniques have been demonstrated for use at 300degC. Transient liquid phase bonding has been developed with Au:Sn/Au, yielding high die shear strength after 2000 h at 400degC. Large diameter (250 mum) gold and platinum wire bonding was evaluated for top side electrical contact. Au wire was reliable after 2000 h at 300degC with Ti/Ti:W/Au pads over passivation on the SiC. However, Au wire on Ti/Pt/Au and Pt wire on both Ti/Tl:W/Au and Ti/Pt/Au exhibited passivation fracture with aging. Polyimide has been demonstrated for 2000 h at 300degC in air as a high-voltage passivation layer.

Strengthening in a WE54 magnesium alloy containing SiC particles

Abstract: The microstructure and the mechanical properties of the WE54 magnesium alloy reinforced by 13 vol.% of silicon carbide particulates were studied. The composite material was prepared using a powder-metallurgical technique. Compressive deformation properties of the composite were investigated in the temperature range from room temperature up to 300 °C. Transmission electron microscopy revealed cuboidal precipitates in the matrix. Various strengthening mechanisms originating from the matrix and the reinforcing particles are discussed.

Beveled LED Chip with Transparent Substrate

Abstract: A light emitting diode is disclosed that includes a transparent (and potentially low conductivity) silicon carbide substrate, an active structure formed from the Group III nitride material system on the silicon carbide substrate, and respective ohmic contacts on the top side of the diode. The silicon carbide substrate is beveled with respect to the interface between the silicon carbide and the Group III nitride.