Showing papers on "Silicon carbide published in 2009"

Towards wafer-size graphene layers by atmospheric pressure graphitization of silicon carbide

Abstract: Graphene, a single monolayer of graphite, has recently attracted considerable interest owing to its novel magneto-transport properties, high carrier mobility and ballistic transport up to room temperature. It has the potential for technological applications as a successor of silicon in the post Moore's law era, as a single-molecule gas sensor, in spintronics, in quantum computing or as a terahertz oscillator. For such applications, uniform ordered growth of graphene on an insulating substrate is necessary. The growth of graphene on insulating silicon carbide (SiC) surfaces by high-temperature annealing in vacuum was previously proposed to open a route for large-scale production of graphene-based devices. However, vacuum decomposition of SiC yields graphene layers with small grains (30-200 nm; refs 14-16). Here, we show that the ex situ graphitization of Si-terminated SiC(0001) in an argon atmosphere of about 1 bar produces monolayer graphene films with much larger domain sizes than previously attainable. Raman spectroscopy and Hall measurements confirm the improved quality of the films thus obtained. High electronic mobilities were found, which reach mu=2,000 cm (2) V(-1) s(-1) at T=27 K. The new growth process introduced here establishes a method for the synthesis of graphene films on a technologically viable basis.

SiC Graphene Suitable For Quantum Hall Resistance Metrology

Abstract: We report the first observation of the quantum Hall effect in epitaxial graphene. The result described in the submitted manuscript fills the yawning gap in the understanding of the electronic properties of this truly remarkable material and demonstrate suitability of the silicon carbide technology for manufactiring large area high quality graphene. Having found the quantum Hall effect in several devices produced on distant parts of a single large-area wafer, we can confirm that material synthesized on the Si-terminated face of SiC promises a suitable platform for the implementations of quantum resistance metrology at elevated temperatures and, in the longer term, opens bright prospects for scalable electronics based on graphene.

Development of Aluminium Based Silicon Carbide Particulate Metal Matrix Composite

Abstract: Metal Matrix Composites (MMCs) have evoked a keen interest in recent times for potential applications in aerospace and automotive industries owing to their superior strength to weight ratio and high temperature resistance. The widespread adoption of particulate metal matrix composites for engineering applications has been hindered by the high cost of producing components. Although several technical challenges exist with casting technology yet it can be used to overcome this problem. Achieving a uniform distribution of reinforcement within the matrix is one such challenge, which affects directly on the properties and quality of composite material. In the present study a modest attempt has been made to develop aluminium based silicon carbide particulate MMCs with an objective to develop a conventional low cost method of producing MMCs and to obtain homogenous dispersion of ceramic material. To achieve these objectives two step-mixing method of stir casting technique has been adopted and subsequent property analysis has been made. Aluminium (98.41% C.P) and SiC (320-grit) has been chosen as matrix and reinforcement material respectively. Experiments have been conducted by varying weight fraction of SiC (5%, 10%, 15%, 20%, 25%, and 30%), while keeping all other parameters constant. The results indicated that the ‘developed method’ is quite successful to obtain uniform dispersion of reinforcement in the matrix. An increasing trend of hardness and impact strength with increase in weight percentage of SiC has been observed. The best results (maximum hardness 45.5 BHN & maximum impact strength of 36 N-m.) have been obtained at 25% weight fraction of SiC. The results were further justified by comparing with other investigators.

Epitaxial graphene: How silicon leaves the scene

Abstract: Large and homogeneous layers of graphene are obtained by annealing silicon carbide in a dense noble gas atmosphere that controls the way in which silicon sublimates. Epitaxial graphene thus gets back on track towards future electronic applications.

Silicon Carbide as a Platform for Power Electronics

Abstract: For high-voltage, high-current devices that can be operated at elevated temperatures, silicon carbide (SiC) has been the material of choice Efforts to produce single-crystal SiC began 30 years ago, but intrinsic problems in growing high-quality single-crystal boules free of micropipe defects—micrometer-scale pinholes created by dislocations—have only recently been overcome A series of developments in crystal growth have made large-area, high-quality SiC substrates readily available for applications such as high-frequency transmitters and solid-state white lighting Additional reductions in defects in the active region of devices have been achieved through epitaxial approaches, in which single-crystal layers are grown on the substrate SiC is now poised as the linchpin to “green energy” that will replace less energy-efficient switches now based on silicon technology

Joining of engineering ceramics

Abstract: Engineering ceramics such as alumina, zirconia, silicon nitride and silicon carbide can now be manufactured reliably with reproducible properties As such, they are of increasing interest to industry, particularly for use in demanding environments, where their thermomechanical performance is of critical importance, with applications ranging from fuel cells to cutting tools One aspect common to virtually all applications of engineering ceramics is that eventually they must be joined with another material, most usually a metal The joining of engineering ceramics to metals is not always easy There are two main considerations The first consideration is the basic difference in atomic bonding: the ionic or covalent bonding of the ceramic, compared to the metallic bond The second consideration is the mismatch in the coefficient of thermal expansion In general, ceramics have a lower coefficient of thermal expansion than metals and, if high tensile forces are produced in the ceramic, either a

Correlating Raman spectral signatures with carrier mobility in epitaxial graphene: a guide to achieving high mobility on the wafer scale.

Abstract: We report a direct correlation between carrier mobility and Raman topography of epitaxial graphene (EG) grown on silicon carbide (SiC). We show the Hall mobility of material on SiC(0001) is highly dependent on thickness and monolayer strain uniformity. Additionally, we achieve high mobility epitaxial graphene (18100 cm(2)/(V s) at room temperature) on SiC(0001) and show that carrier mobility depends strongly on the graphene layer stacking.

Mechanism for material removal in diamond turning of reaction-bonded silicon carbide

Abstract: Reaction-bonded silicon carbide (RB-SiC) is a new ceramic material that has extremely high strength and hardness. Diamond turning experiments were performed on RB-SiC to investigate the microscopic material removal mechanism. Diamond tools with large nose radii of 10 mm were used for machining. It was found that the surface roughness was not significantly affected by the tool feed rate, but was strongly dependent on the tool rake angle. The mechanism for material removal involved plastic deformation, microfracture and dislodgement of 6H-SiC grains. Raman spectroscopy revealed that the silicon bond component underwent amorphization, while no phase transformation of 6H-SiC grains was observed. Tool wear was also investigated and two types of wear patterns were identified. Under the experimental conditions used, a surface finish of 23 nm Ra was obtained even at an extremely high tool feed rate of 72 μm/rev. This study demonstrates the feasibility of precision machining of RB-SiC by diamond turning at a very high material removal rate.

Light-emitting device

Abstract: PROBLEM TO BE SOLVED: To provide a light-emitting device employing silicon carbide, in particular, a light-emitting device such as a silicon carbide light-emitting element for the visible light wavelength range. SOLUTION: The light-emitting device is provided in which, for example, an n-type region and a p-type region formed by an ion implantation method constitute a pn junction on an insulating layer buried type semiconductor silicon carbide substrate. The semiconductor silicon carbide substrate is preferably a semiconductor silicon carbide substrate in which surface silicon of an SOI substrate is made thin, the extremely thin silicon layer is denatured into a silicon carbide layer through carbonization, and a silicon carbide epitaxial film is deposited thereon by a CVD (chemical vapor-deposition) method. COPYRIGHT: (C)2009,JPO&INPIT

SiC power semiconductors in HEVs: Influence of junction temperature on power density, chip utilization and efficiency

Abstract: With SiC, junction temperatures of power semiconductors of more than 700 _C are theoretically possible due to the low intrinsic charge carrier concentration of SiC. Hence, a lot of research on package configurations for power semiconductor operation above 175 _C is currently carried out, especially within the automotive industry due to the possible high ambient temperatures occurring in hybrid electric vehicles (HEVs). This paper shows, that a higher junction temperature though does not necessarily guarantee a higher utilization of the SiC chips with respect to the current that the device can conduct without overheating. The reason is, that for most power devices the power losses start to increase very rapidly at high junction temperatures while the power that can be dissipated always increases linearly with the junction temperature. The junction temperature, where the device current starts to decrease at, is derived for different SiC chips using measured onstate conduction and switching losses in this paper. This paper furthermore analyzes in detail, how the junction temperature on the one hand is influenced by boundary conditions and on the other hand influences itself the core parameters of a converter such as efficiency, the required chip area (i. e. cost) as well as the volumetric power density and thus forms an additional degree of freedom in the design of a power electronic converter. While calculating the optimum junction temperature and analyzing its impact on the system performance, it is demonstrated, how these results can help to find the best suited power semiconductor device for the particular application. The performance of the calculations is shown on a design applied to a drive inverter for hybrid electric vehicles with normally-off SiC JFETs. Operated close to the optimum junction temperature of the SiC JFETs, it reaches a power density of 51 kW/l for the power modules and the air-cooling system, which is shown to be doubled by increasing chip size and using an advanced power semiconductor package with a lower thermal resistance from junction to ambient than the for this case assumed 1 K/W.

Chemical Properties of Oxidized Silicon Carbide Surfaces upon Etching in Hydrofluoric Acid

Abstract: Hydrogen termination of oxidized silicon in hydrofluoric acid results from an etching process that is now well understood and accepted. This surface has become a standard for studies of surface science and an important component in silicon device processing for microelectronics, energy, and sensor applications. The present work shows that HF etching of oxidized silicon carbide (SiC) leads to a very different surface termination, whether the surface is carbon or silicon terminated. Specifically, the silicon carbide surfaces are hydrophilic with hydroxyl termination, resulting from the inability of HF to remove the last oxygen layer at the oxide/SiC interface. The final surface chemistry and stability critically depend on the crystal face and surface stoichiometry. These surface properties affect the ability to chemically functionalize the surface and therefore impact how SiC can be used for biomedical applications.

Transfer of graphene layers grown on SiC wafers to other substrates and their integration into field effect transistors

Abstract: This letter presents a simple method for transferring epitaxial sheets of graphene on silicon carbide to other substrates. The graphene was grown on the (0001) face of 6H-SiC by thermal annealing at 1550 °C in a hydrogen atmosphere. Transfer was accomplished using a peeling process with a bilayer film of gold/polyimide, to yield graphene with square millimeters of coverage on the target substrate. Raman spectroscopy provided evidence that the transferred material is single layer. Back gated field-effect transistors fabricated on oxidized silicon substrates with Cr/Au as source-drain electrodes exhibited ambipolar characteristics with hole mobilities of ∼100 cm2/V-s, and negligible influence of resistance at the contacts.

Relationship between 4H-SiC∕SiO2 transition layer thickness and mobility

Abstract: The interfacial region between silicon carbide (SiC) and its native oxide contains a high density of interfacial traps, which is considered a major problem leading to a lower mobility that has hindered SiC metal oxide semiconductor field effect transistors from reaching their theoretical expectations. We investigate the microstructure and chemistry of the 4H-SiC∕SiO2 interface due to variations in nitric oxide annealing and aluminum implantation using Z-contrast imaging and electron energy loss spectroscopy. A transition layer with a carbon to silicon ratio greater than 1 is consistently observed on the SiC side of the interface in each of these samples, and the width of this transition layer is found to be inversely related to the effective channel mobility measured on fabricated devices.

Polishing liquid and polishing method

Abstract: A polishing liquid which is used for chemical mechanical polishing of a body to be polished in a planarization process for manufacturing of a semiconductor integrated circuit, the body to be polished including at least a first layer containing polysilicon or modified polysilicon and a second layer containing at least one selected from the group consisting of silicon oxide, silicon nitride, silicon carbide, silicon carbonitride, silicon oxycarbide, and silicon oxynitride, the polishing liquid having a pH of 1.5 to 7.0, including (1) colloidal silica particles, (2) an organic acid, and (3) an anionic surfactant, and being capable of selectively polishing the second layer with respect to the first layer.

Recovery of silicon from kerf loss slurry waste for photovoltaic applications

Abstract: The constantly rising price of silicon feedstock has been the most important factor preventing photovoltaic (PV) energy from reaching grid parity. On the other hand, large amount of silicon gets wasted during slicing. We report a promising approach to recycle kerf loss silicon from cutting slurry waste for solar cell applications. Silicon carbide (SiC) and metal impurities were successfully removed by chemical/ physical processing from the slurry waste to recover solar grade silicon. The effects of centrifugation using heavy fluids and high-temperature treatment in the removal of SiC particles are discussed in detail. Ingots from the recycled silicon were grown by using directional solidification. The average resistivity and minority carrier lifetime of the grown crystals were found to be about 0·7 Ω cm and 1·02 µs, respectively, which were close to the original sawing silicon ingots. Solar cells using multi-crystalline wafers of recovered silicon were fabricated and the best energy conversion efficiency was found to be 12·6% comparable to those from the high-purity silicon. Copyright © 2008 John Wiley & Sons, Ltd.

A 55-kW Three-Phase Inverter With Si IGBTs and SiC Schottky Diodes

Abstract: Silicon carbide (SiC) power devices are expected to have an impact on power converter efficiency, weight, volume, and reliability. Currently, only SiC Schottky diodes are commercially available at relatively low current ratings. Oak Ridge National Laboratory has collaborated with Cree and Semikron to build a Si insulated-gate bipolar transistor-SiC Schottky diode hybrid 55-kW inverter by replacing the Si p-n diodes in Semikron's automotive inverter with Cree's made-to-order higher current SiC Schottky diodes. This paper presents the developed models of these diodes for circuit simulators, shows inverter test results, and compares the results with those of a similar all-Si inverter.

On the lattice parameters of silicon carbide

Abstract: The thermal expansion coefficients of the hexagonal SiC polytypes 4H and 6H and with Al and N dopants have been determined for temperatures between 300 and 1770 K. Further, a set of the room temperature lattice parameters in dependence on doping with N, Al, and B has been obtained. Data for the thermal expansion were taken on a triple axis diffractometer for high energy x rays with a photon energy of 60 keV, which allows the use of large single crystals with a volume of at least 6×6×6 mm3 without the need to consider absorption. The room temperature measurements for samples with different dopants have been performed on a four-circle diffractometer. The thermal expansion coefficients along the a- and c-directions, α11 and α33, increase from 3×10−6 K−1 at 300 K to 6×10−6 K−1 at 1750 K. It is found that α11 and α33 are isotropic within 107 K−1. At high temperatures both coefficients for doped samples are ∼0.2×10−6 and 0.3×10−6 K−1 lower than for the undoped material.

Oxidation Behavior of Zirconium Diboride Silicon Carbide Produced by the Spark Plasma Sintering Method

Abstract: Dense samples of ZrB2–20 vol% SiC were successfully fabricated by spark plasma sintering without the use of sintering aids. Oxidation behavior of these samples was characterized by exposing them to 1400°, 1500°, and 1600°C in an ambient atmosphere for 150 min, and by measuring the weight gains of the sample and crucible, as well as the thickness of the oxide scale and the glassy outer layer. The effects of gravity on the viscous outer layer are shown to result in significant heterogeneity within a sample. The oxidation scales were characterized by scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy analysis. The oxide scale was found to be composed of three layers: (1) a SiO2-rich glassy outer layer, (2) an intermediate layer of a ZrO2 matrix with interpenetrating SiO2, and (3) a layer containing a ZrO2 matrix enclosing partially oxidized ZrB2 with Si–C–B–O glass inclusions.

A Kinetic Model of Silicon Carbide Oxidation Based on the Interfacial Silicon and Carbon Emission Phenomenon

Abstract: We proposed a kinetic model for thermal oxidation of silicon carbide, termed "silicon and carbon emission model", taking into account the Si and C emissions from the oxidation interface, which lead to a reduction of interfacial reaction rate. We used this model to calculate oxide growth rates and found that the derived growth rates showed a good fit with the measured rates over the entire oxide thickness for both the C and Si faces. We discussed the difference in oxidation mechanism between these polar faces in terms of the difference in parameter values deduced from the curve fits.

Maximum Junction Temperatures of SiC Power Devices

Abstract: This paper presents a detailed physical analysis on the junction temperatures, thermal stabilities, and thermal runaway effects of self-heating unipolar SiC power devices. Results reveal that the risk of thermal runaway could limit the usable junction temperature of these SiC devices to substantially lower than 200°C, regardless of the device size and the cooling method used.