SiC SiO2 Research Articles

Impact of interface traps/defects and self‐heating on the degradation of performance of a 4H‐SiC VDMOSFET

The reliability of silicon carbide metal oxide semiconductor field-effect transistors remains a challenge in power applications and relates to the SiO2–SiC interface. The presence of unwanted interface traps/defects degrades the device performance. The impact of acceptor traps/defects on the performance of a 4H-SiC vertical Diffused Metal Oxide Semiconductor Field Effect Transistor (DMOSFET) with a breakdown voltage of 1700 V is investigated. - and - characteristics were simulated, using a drift-diffusion model coupled to Fourier heat equations, and are in a good agreement with experimental results. The presence of interface traps/defects were shown to produce degradation of threshold voltage, but the impact diminishes as temperature increases. A threshold voltage shift of 3.5 V occurs for a trap concentration of 2 × 1013 cm–2/eV at room temperature. The transfer characteristics obtained from electro-thermal modelling show a larger degradation than those at a constant temperature. This degradation increases with the drain bias increase. The threshold voltage from the electro-thermal simulations is 5 V compared to 4 V observed in constant 423 K temperature simulations at. Finally, the interface traps/defects increases breakdown voltage exhibiting a strong dependency on the trap density and their energy decay characteristics.

Atomic Coordination Analysis of Nitrogen Introduced in SiO<sub>2</sub>/ SiC Interface and SiO<sub>2</sub> Layer by XAFS Measurement

Although the nitridation by N2O or NO oxidation with annealing has been used in order to reduce interface trap density, the atomic location or coordination environment of nitrogen atom have been still unclear. In this study, we have investigated atomic coordination environment of nitrogen atom in both SiO2/SiC interface and SiO2 layer after nitridation by N2O annealing using XAFS measurements and ab initio multiple scattering calculations. Nitrogen in SiO2 layer was suggested to have the same atomic coordination environments as general SiON thin film. On the other hand, in SiO2/SiC region, nitrogen atoms were isolated and occupied the C-site of SiC structure, and it was confirmed that nitrogen atoms were surrounded by silicon atoms and strong Si-N bonds were formed in the interface region that was not eliminated by HF etching.

Application of Empirical Si–O–C Potential to Simulate Amorphous Atomic Structures and Transition Layers by the Bond Switching Method

The parameters of REBO2 empirical potential for the Si–O–C system are presented. The results of the calculations using this potential agree well with the experimental values of the lengths and angles of unit cells, bond energy, and surface energy for Si, SiO2, and SiC. The algorithm of bond switching in a multicomponent system has been developed and tested. A method is proposed to simulate the structure of the transition layer between crystalline Si and amorphous SiO2, as well as between crystalline SiC and amorphous SiO2.

Effect of Si/O doping on the thermal stability of non-bonded hydrogenated diamondlike carbon coatings

Diamond-like carbon coatings containing Si and O (a-C:H:SiOx) were deposited onto 316L steel and silicon wafer substrates using a mixture precursor of hexamethyldisiloxane (HMDSO) and acetylene under a high bias voltage. Then, the coated coupons were annealed in an argon media. The hydrogen content in the coating was measured by 2 MeV 4He+ elastic recoil detection analysis (ERDA). The structure and morphology evolution during annealing were characterized by scanning electron microscopy (SEM), mass spectrometry (MS), Fourier transformation infrared spectroscopy (FTIR), Raman spectra, and X-ray photoelectron spectroscopy (XPS). The mechanical properties were investigated using a residual stress tester and nanoindentor. The results showed that under a high bias voltage a large amount of the hydrogen of the a-C:H:SiOx coatings did not bond with carbon. Si and O preferred to form SiC bonds and SiO bonds respectively to enhance C sp3 fraction, relax the residual stress, and depress the graphite cluster growth. During annealing, combining with C sp3 rehybridization, the transformation of the SiC bond to SiO or Si-C-O bonds caused hardness and residual stress variation. The a-C:H:SiOx coatings still held more than 12 GPa hardness after annealing at 590 °C for 4 h, while the hardness was approximately 8 GPa for the pure a-C:H coating.

Research in the Field of Composite Materials Based on HCBS and Refractory Materials Based on the System Al2O3–SiO2–SiC. Part 41

The effect of heat treatment duration of the properties of specimens prepared on the basis of composite composition HCBS in the Al2O3–SiO2–SiC system is studied. With a content of 10 and 30% SiC in specimens its fineness varies within the limits 3 – 200 μm. Amethod is proposed for evaluating the degree of SiC oxidation within composite material. Depending on specimen composition this index is within the limit 50 – 100%. Maximum values of σben and σco for SiC-containing specimens reach 80 and 390 MPa respectively.

A novel two-stage synthesis for 3C–SiC nanowires by carbothermic reduction and their photoluminescence properties

A large quantity of 3C–SiC nanowires (SiCnws) with high purity were fabricated via carbothermic reduction method combined with a novel two-stage temperature program. At the first temperature stage, the reactants were kept at 1600 °C for 4 h to promote the formation of SiC nucleus and SiO intermediate gas. Then they were cooled to 1350 °C for 2 h at the second stage for the growth of SiCnws with fewer defects. Compared with the conventional single temperature method at 1600 °C for 6 h, the product prepared by this new strategy exhibits large yield and high purity with a narrow diameter range. As for the reaction mechanism, “solid–solid” and “solid–vapor” reactions occurring between SiO2, SiO and C dominate at the first stage. While “vapor–vapor” reaction between SiO and CO plays an important role at the second stage. Furthermore, photoluminescence (PL) properties were measured under the room temperature. A sharp violet light emission peak with a significant blue shift is observed at 401 nm compared to bulk 3C–SiC.

Research in the Field of Composite Materials Based on HCBS and Refractory Materials Based on the System Al2O3–SiO2–SiC. Part 31

Research in the Field of Composite Materials Based on HCBS and Refractory Materials Based on the System Al2O3–SiO2–SiC. Part 31

Research in the Field of Composite Materials Based on HCBS and Refractory Materials Based on the System Al2O3–SiO2–SiC. Part 2

Research in the Field of Composite Materials Based on HCBS and Refractory Materials Based on the System Al2O3–SiO2–SiC. Part 2

Self‐crack healing ability and strength recovery in ytterbium disilicate/silicon carbide nanocomposites

AbstractThe SiO2 volatility and SiC recession in hydrocarbon‐rich combustion atmosphere is the main problem of SiC‐reinforced ceramics when they are utilized as coating materials for gas turbine blades. The composite of Yb2Si2O7‐Yb2SiO5/SiC is expected as a self‐crack healing material that can avoid this problem because the monosilicate can react with the SiO2 glass to form disilicate and hence further reinforce the composite. In this study, the composites, fabricated with various morphology of SiC nanofillers, were precracked and then heat‐treated in an oxidizing environment to activate their crack healing behavior. The healing effect as a function of filler morphology and annealing time was investigated. Healing mechanism and future applications of these composites were also discussed.

Mullite-bonded SiC-whisker-reinforced SiC matrix composites: Preparation, characterization, and toughening mechanisms

A novel mullite-bonded SiC-whisker-reinforced SiC matrix composite (SiCw/SiC, SiC whisker-to-SiC powder mass ratio of 1:9) was designed and successfully prepared. Before preparing the composite, the inexpensive lab-made SiCw was first modified by an oxidation/leaching process and then coated with Al2O3. The kinetics results indicate that the oxidation process can be described by improved shrinking-cylinder models. The aspect ratio of SiCw improved after modification. Subsequently, raw materials with a SiC–SiO2–Al2O3 triple-layered structure were obtained after the Al2O3-coating process and used as feedstocks during the subsequent hot-pressing sintering. Finally, the characterization of the composites indicates that the mullite-bonded sample performs better (relative density of 93.8 ± 1.4%, flexural strength of 533.3 ± 18.2 MPa, fracture toughness of 13.6 ± 2.1 MPa m1/2, and Vickers hardness of 20.6 ± 2.5 GPa) than the reference sample without the mullite interface. The improved toughness could essentially be attributed to the moderately strong interface bonding and effective load transfer effects of the mullite interface.

Researches in the field of composite HCBS and of the refractory materials on their base in the Al2O3‒SiO2‒SiC system. Part 2

The influence was investigated of the prolonged heat treatment on the samples properties prepared on base of the composite Al2O3‒SiO2‒SiC HCBS. The dispersion degree of the samples containing either 10 or 30 % of SiC varied within 3‒200 microns. The estimating method was proposed for the SiC oxidation degree in the composite. Depending on the samples composition the oxidation degree was within 50‒100 %. The ultimate bend strength and compressing strength SiC-containing samples attained the values of 80 and 390 MPa respectively. `````````````````````````````

Research in the Field of Composite Materials Based on HCBS and Refractory Materials Based on the System Al2O3–SiO2–SiC. Part 1

Research in the Field of Composite Materials Based on HCBS and Refractory Materials Based on the System Al2O3–SiO2–SiC. Part 1

X-ray absorption spectroscopy study on SiC-side interface structure of SiO2–SiC formed by thermal oxidation in dry oxygen

Extended X-ray absorption fine structure (EXAFS) spectroscopy is demonstrated to measure the fine atomic structure of SiO2–SiC interfaces. The SiC-side of the interface can be measured by fabricating thin SiO2 films and using SiC-selective EXAFS measurements. Fourier transforms of the oscillations of the EXAFS spectra correspond to radial-structure functions and reveal a new peak of the first nearest neighbor of Si for m-face SiC, which does not appear in measurements of the Si-face. This finding suggests that the m-face interface could include a structure with shorter Si–C distances. Numerical calculations provide additional support for this finding.

Research in the Field of Preparing Molded and Unmolded Refractories Based on High-Alumina HCBS. Part 14. Composition and Some Properties of Composite Composition Ceramic Concretes in the System Al2O3–SiO2–SiC–C1

Research is conducted on specimens of composite composition ceramic concrete specimens in the Al2O3 –SiO2 –SiC–C system molded by pneumatic ramming. Ramming refractory mixes of similar composition are used extensively in preparing monolithic linings for blast furnace runners. The effect of firing temperature and heat treatment duration (50 and 100 h) is studied in the range 1300 – 1390°C for specimens on the main material properties. A considerable increase in specimen weight is detected caused by high-temperature oxidation of silicon carbide contained within the concrete. A method is proposed for evaluating the degree of silicon carbide oxidation.

A New Route to High Yield Mesostructure Boron Carbide Powder from SiC/Si3N4 Whiskers

Boric acid/Mg (magnesiothermic or metal sintering aid)/C (activated carbon)/N2 or Ar (atmosphere)/additives (mesoporous SiO2 or mesoporous SiC or SiC/Si3N4 whiskers) systems were used in the one‐step synthesis of mesostructured B4C (221.04 m2/g). In this study, a mixture of the active precursors was allowed to react via a self‐sustaining reaction (high‐energy ball milling process). Also, the properties of the samples prepared using powdered activated carbon (PAC) and SiC/Si3N4 whiskers (concentration in the range 5–10 wt%) as sources of carbon were investigated. X‐ray diffraction results proved the presence of crystalline boron carbide in the peak positions of B4C (B12C3). The advantage of the present route for yielding mesostructured B4C powder seems to be limited by the growth of carbide crystals. This restriction is believed to be imposed by a lack of whisker additives around the pores where B4C crystals grow. The results also show that the best mesoporous additive for the synthesis of nanoscale boron carbide is mesoporous SiC. The effect of the concentration of CO (reduction of α‐Fe2O3 to Fe by CO) on the B4C synthesis suggests that, in addition to the concentration of CO, the pressure of the N2 atmosphere is an important factor in the synthesis of mesostructured B4C.

The Use of the D-Optimal Mixture Design to Develop a Novel Refractory Ramming Mix of the MgO–SiO2–SiC–C System for Blast Furnace Pig Iron Runners

In this study, to develop a ramming mix, the D-optimal mixture design method was used, which makes it possible to achieve in the new type of ramming mix the optimal concentration of carbonaceous raw materials – silicon carbide, graphite, pitch. Using the expert-design software and a special preparation methodology, 16 samples of varying compositions were prepared, and their physical properties, such as dried and fired strength, were evaluated. In order to determine the optimal formulation, 12 models were studied. The model with the highest percentage of desired properties at 78.5% contained 11.7 wt.% silicon carbide, 2.6 wt.% graphite, and 5.7 wt.% pitch. Thus, this is the optimal composition of a ramming mix of the MgO–SiO2–SiC–C system for a blast furnace pig iron runner.

Improved sandwich structured ceramic matrix composites with excellent thermal insulation

An improved sandwich structured composite with low thermal conductivity used in high temperature is discussed, which have a great potential to be used in thermal protection system. This composite was composed of compound core material and C/SiC laminates. It is crucially noted that the compound core material is composed of reticulated SiC foam and SiO2 powders. In this paper, the thermal conductivity of compound core was much lower than that of unfilled SiC foam in high temperature. It was also observed that the thermal conductivities of compound cores with the density ranged from 1.23 to 1.38 g/cm3 increased accordingly. A mathematical relation was derived to calculate the theoretical effective thermal conductivity of sandwich structured composite, and the results agreed with the measured data with an error of 5%.

The Effect of Charge Redistribution on Flat-Band Voltage Turnaround in 4H-SiC MOS Capacitors

The existence of a turnaround in flat-band voltage shift of stressed MOS capacitors, fabricated on N-type 4H–SiC substrates, is reported in this paper. The turnaround is observed by room-temperature C–V measurements, after two minutes gate-bias stressing of the MOS capacitors at different temperatures. The existence of this turnaround effect demonstrates that a mechanism, in addition to the well-stablished tunneling to the near-interface oxide traps, is involved in the threshold voltage instability of 4H–SiC MOSFETs. This newly identified mechanism occurs due to charge redistribution of the compound polar species that exist in the SiO2–SiC transitional layer.

Synthesis of novel hierarchical SiC–SiO2heterostructures via a catalyst free method

Novel hierarchical SiC–SiO2heterostructures were synthesized on a graphite paper substrateviaa catalyst free method.

Study of Artificial Ceramic Binder Properties in the System Al2O3–SiO2–SiC

Artificial ceramic binders based on silicon carbide and high-alumina chamotte are studied. Rheological and physicomechanical properties of mixed ACB are determined. An optimum content is revealed for silicon carbide and high-alumina chamotte ACB. It is established that a thin film of mullite forms at the surface with a firing temperature of 1300°C for ACB specimens of optimum composition.