• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.201-208
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• 2023

The dependence of the electrical characteristics on the fast neutron fluence of an epitaxial 4H-SiC Schottky barrier diode (SBD) was investigated. The 30 MeV cyclotron was used for fast neutron irradiation. The neutron fluences evaluated through Monte Carlo simulation were in the 2.7 × 10¹¹ to 1.45 × 10¹³ neutrons/cm² range. Current-voltage and capacitance-voltage measurements were performed to characterize the samples by extracting the parameters of the irradiated SBDs. Neutron-induced defects in the epitaxial layer were identified and quantified using a deep-level transient spectroscopy measurement system developed at the Korea Atomic Energy Research Institute. As the neutron fluence increased from 2.7 × 10¹¹ to 1.45 × 10¹³ neutrons/cm², the concentration of the Z_1/2 defects increased by approximately 20 times. The maximum defect concentration was estimated as 1.5 × 10¹⁴ cm^-3 at a neutron fluence of 1.45 × 10¹³ neutrons/cm².

• Journal of IKEEE
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• v.24 no.1
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• pp.170-177
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• 2020

This paper presents an open-fault tolerance control method for active neutral point clamped (ANPC) inverter with high frequency/low frequency (HF/LF) modulation. By applying the ANPC inverter with SiC MOSFETs and Si IGBTs, the system efficiency and performance can be improved compared to a Si-based inverter. HF/LF modulation is used for a megawatt-scale inverter to minimize the commutation loop. The open-switch failure in megawatt-scale inverter causes severe damage to load and huge expenses when the inverter has been shut-down. The proposed tolerance control of open-switch failure provides continuous operation and improved reliability to the ANPC inverter. The effectiveness of the proposed fault tolerance control is verified by simulation results.

• Resources Recycling
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• v.25 no.6
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• pp.73-81
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• 2016

Geopolymers produced from aluminosilicate materials such as metakaolin and coal ash react with alkali activators and show higher fire resistance than portland cement, due to amorphous inorganic polymer. The percentage of thermal shrinkage of geopolymers ranges from less than 0.5 % to about 3 % until $600^{\circ}C$, and reaches about 5 ~ 7 % before melting. In this study, geopolymers paste having Si/Al = 1.5 and being mixed with carbon nanofibers, silicon carbide, pyrex glass, and vermiculite, and ISO sand were studied in order to understand the compressive strength and the effects of thermal shrinkage of geopolymers. The compressive strength of geopolymers mixed by carbon nanofibers, silicon carbide, pyrex glass, or vermiculite was similar in the range from 35 to 40 MPa. The average compressive strength of a geopolymers mixed with 30 wt.% of ISO sand was lowest of 28 MPa. Thermal shrinkage of geopolymers mixed with ISO sand decreased to about 25 % of paste. This is because the aggregate particles expanded on firing and to compensate the shrinkage of paste. The densification of the geopolymer matrix and the increase of porosity by sintering at $900^{\circ}C$ were observed regardless of fillers.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.2
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• pp.112-120
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• 1998

A nondestructive evaluation technique was developed for the quantitative determination of the reinforcement volume fractions in particulate reinforced metal matrix composites. The proposed technique employed a composite micromechanics which accounts for the microstructure of the composite medium together with the measurement of anisotropic electrical conductivity. When the measured conductivity was coupled with the theoretically predicted conductivity, the unknown reinforcement volume fraction was calculated. An analytical model based on the Mori-Tanaka method was described which relates the NDE signatures to the composite microstructure. The volume fractions were calculated using eddy current measurements made on a wide range of silicon carbide particulate ($SiC_p$) reinforced aluminum (Al) matrix composites. The calculated $SiC_p$ volume fractions were in good agreement with the measured volume fractions in the range of 0-30%. The technique was also found to be effective in estimating the total volume percentage of reinforcement and intermetallic compound formed during the processing stage.

• Korean Journal of Materials Research
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• v.26 no.11
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• pp.656-661
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• 2016

4H- and 6H-SiC grown by physical vapor transport method were investigated by transmission electron microscopy (TEM). From the TEM diffraction patterns observed along the [11-20] zone axis, 4H- and 6H-SiC were identified due to their additional diffraction spots, indicating atomic stacking sequences. However, identification was not possible in the [10-10] zone axis due to the absence of additional diffraction spots. Basal plane dislocations (BPDs) were investigated in the TEM specimen prepared along the [10-10] zone axis using the two-beam technique. BPDs were two Shockley partial dislocations with a stacking fault (SF) between them. Shockley partial BPDs arrayed along the [0001] growth direction were observed in the investigated 4H-SiC. This arrayed configuration of Shockley partial BPDs cannot be recognized from the plan view TEM with the [0001] zone axis. The evaluated distances between the two Shockley partial dislocations for the investigated samples were similar to the equilibrium distance, with values of several hundreds of nanometers or even values as large as over a few micrometers.

• Composites Research
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• v.35 no.1
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• pp.23-30
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• 2022

Polycarbosilane(PCS) is an important precursor for melt-spinning the silicon carbide(SiC) fibers and manufacturing ceramics. The PCS is a metal-organic polymer precursor capable of producing continuous SiC fibers having excellent performance such as high-temperature resistance and oxidation resistance. The SiC fibers are manufactured through melt-spinning, stabilization, and heat treatment processes using the PCS manufactured by synthesis, purification, and control of the molecular structure. In this paper, we analyzed the effect of purification of unreacted substances and low molecular weight through solvent treatment of PCS and the effect of heat treatment at various temperatures change the polymerization and network rearrangement of PCS. Especially, we investigated the complex viscosity and structural arrangement of PCS precursors according to solvent treatment and heat treatment through the rheological properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.8
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• pp.486-490
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• 2014

$Al_2O_3$ films on silicon carbide were fabricated by Aerosol deposition with annealing temperature at $800^{\circ}C$ and $1,000^{\circ}C$. The effect of thermal treatment on physical properties of $Al_2O_3$ thin films has been investigated by XRD (X-ray diffraction), AFM (atomic force microscope), SEM (scanning electron microscope), and AES (auger electron spectroscopy). Also electrical properties have been investigated by Keithley 4,200 semiconductor parameter analyzer to explain the interface trapped charge density ($D_{it}$), flatband voltage ($V_{FB}$) and leakage current ($I_o$). $Al_2O_3$ films become crystallized with increasing temperature by calculating full width at half maximum (FWHM) of diffraction peaks, also surface morphology is observed by topography measurement in non-contact mode AFM. $D_{it}$ was $2.26{\times}10^{-12}eV^{-1}.cm^{-2}$ at $800^{\circ}C$ annealed sample, which is the lowest value in all samples. Also the sample annealed at $800^{\circ}C$ has the lowest leakage current of $4.89{\times}10^{-13}A$.

• Tribology and Lubricants
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• v.35 no.5
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• pp.274-285
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• 2019

Chemical mechanical polishing (CMP), which is a material removal process involving chemical surface reactions and mechanical abrasive action, is an essential manufacturing process for obtaining high-quality semiconductor surfaces with ultrahigh precision features. Recent rapid growth in the industries of digital devices and semiconductors has accelerated the demands for processing of various substrate and film materials. In addition, to solve many issues and challenges related to high integration such as micro-defects, non-uniformity, and post-process cleaning, it has become increasingly necessary to approach and understand the processing mechanisms for various substrate materials and abrasive particle behaviors from a tribological point of view. Based on these backgrounds, we review recent CMP R&D trends in this study. We examine experimental and analytical studies with a focus on substrate materials and abrasive particles. For the reduction of micro-scratch generation, understanding the correlation between friction and the generation mechanism by abrasive particle behaviors is critical. Furthermore, the contact stiffness at the wafer-particle (slurry)-pad interface should be carefully considered. Regarding substrate materials, recent research trends and technologies have been introduced that focus on sapphire (${\alpha}$-alumina, $Al_2O_3$), silicon carbide (SiC), and gallium nitride (GaN), which are used for organic light emitting devices. High-speed processing technology that does not generate surface defects should be developed for low-cost production of various substrates. For this purpose, effective methods for reducing and removing surface residues and deformed layers should be explored through tribological approaches. Finally, we present future challenges and issues related to the CMP process from a tribological perspective.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.1
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• pp.34-40
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• 1998

Conductive metal matrix composite(MMC) material of 30% silicon carbide particulated based on aluminum matrix was machined by die sinking electrical discharge machining(EDM) process according to different current and duty factor for reverse polarity of electrode. Material removal rate(MRR) was examined by process under various operation conditions. The surface morphology was evaluated by surface roughness parameter and scanning electron microscopy(SEM) research. The MRR was suddenly increased over 11 ampere of current, and it was slightly changed over 0.3 of duty factor. The maximum surface roughness of EDMed surface was affected by the duty factor. The SEM photograghs of EDMed surface showed wide recast distribution region of melting materials as increased of current and duty factor.

• 전기의세계
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• v.21 no.2
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• pp.25-33
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• 1972

The main focus of this paper is on the study of voltage-current characteristics in disk-type siliconcarbide resistors. For each of the 15 different sintering and other process conditions, 10 samples were prepared. Experiments performed with each sample consist of supplying sinusoidal AC current of a few miliamperes after conditioning-shots with 400ma. Experimental data were examined with regard to the relationship between the process conditions and the nonlinear resistivity. The examination suggests several possibilities of improving the nonlinlinear characteristics of siliconcarbide resistors while maintaining low resitance. One of those possible conditions is to sinter the powdered SiC and the binding materials approximately 2 hours in nitrogen. In addition to describing the nonlinear characteristics of siliconcarbide resistors, this paper also presents the distortion characteristics of current waves vs. the nonlinear exponent, n. Photographical results show that the more nonlinear characteristics samples have, the more distorted current waves are.