• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.9
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• pp.818-824
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• 2006

The effects of high-temperature process required to fabricate the SiC devices on the surface morphology and the electrical characteristics were investigated for 4H-SiC Schottky diodes. The 4H-SiC diodes without a graphite cap layer as a protection layer showed catastrophic increase in an excess current at a forward bias and a leakage current at a reverse bias after high-temperature annealing process. Moreover it seemed to deviate from the conventional Schottky characteristics and to operate as an ohmic contact at the low bias regime. However, the 4H-SiC diodes with the graphite cap still exhibited their good electrical characteristics in spite of a slight increase in the leakage current. Therefore, we found that the graphite cap layer serves well as the protection layer of silicon carbide surface during high-temperature annealing. Based on a closer analysis on electric characteristics, a conductive surface transfiguration layer was suspected to form on the surface of diodes without the graphite cap layer during high-temperature annealing. After removing the surface transfiguration layer using ICP-RIE, Schottky diode without the graphite cap layer and having poor electrical characteristics showed a dramatic improvement in its characteristics including the ideality factor[${\eta}$] of 1.23, the schottky barrier height[${\Phi}$] of 1.39 eV, and the leakage current of $7.75\{times}10^{-8}\;A/cm^{2}$ at the reverse bias of -10 V.

• Journal of the Korean Institute of Landscape Architecture
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• v.33 no.5 s.112
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• pp.94-103
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• 2005

This study was carried out to investigate growth and morphological characteristics of leaf, flower and winter bud of Corylopsis species such as C. coreana, C. spicata, C. sinensis, C. willmottiae, C. willmottiae 'Spring Purple', C. wilsonii, C. spicata 'Yellow Spring', C. gotoana, and C. vechiana. In the Corylopsis species, C. coreana, C. willmottiae, and C. vetchiana had larger flowers, longer flower cluster, and more flowers than other species. C. sinensis and C. veitchiana had fragrant flowers. In addition, species with beautiful leaf color were C. spicata 'Yellow spring' with yellow color and C. willmottiae 'Spring purple' with purple color, which eventually changed to green. The winter bud of C. sinensis, C. willmottiae, C. willmottiae 'Spring Purple', and C. vechiana were oval and different from those of other species. Comparison of the morphological characteristics among C. coreana, C. spicata, and C. sinensis, C. coreana showed they had earlier flowering dates and brighter yellow flowers than those of other species. Flower cluster of C. sinensis was shortest, but it had most number of flowers and fragrance. In addition, the winter buds of C. coreana and C. spicata with elliptical shape were different from that of C. sinensis with oval shape. Therefore, based on these characteristics, the following Corylopsis species were found to be promising as woody landscape plants: C. coreana, C. sinensis, C. willmottiae 'Spring Purple', C. spicata 'Yellow Spring', and C. vechiana.

• Journal of the Korean Ceramic Society
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• v.46 no.3
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• pp.330-335
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• 2009

We investigated the effects of the re-oxidation temperature and time on the positive temperature coefficient (PTC) of resistivity characteristics of Sm-doped $BaTiO_3$ sintered at $1200{\sim}1260^{\circ}C$ for 2 h in a reducing atmosphere (3% $H_2/N_2$), followed by re-oxidization processes in air, in which re-oxidization temperature and time were $600{\sim}1000^{\circ}C$ and $1{\sim}10$h, respectively. The result reveals that Smdoped (Ba,Ca)$TiO_3$ ceramics fired in a reducing atmosphere exhibit low PTC characteristics, whereas the sample re-oxidized at $800^{\circ}C$ for 1 h in air exhibit pronounced PTC characteristics. The room-temperature resistivity and jumping characteristics of resistivity (${\rho}_{max}/{\rho}25^{\circ}C$) decrease with Sm contents. The PTC characteristics with reoxidization time at $800^{\circ}C$ have improved about $2{\sim}3$ orders of magnitude whereas differed according to the sintering temperature. The 0.7 at% Sm-doped (Ba,Ca)$TiO_3$ samples reveal the best PTC characteristics in the present range of formula and processes.

• 전기의세계
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• v.30 no.4
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• pp.231-236
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• 1981

It has been known that D.C. breakdown Voltage is lower than A.C. breakdown Voltage in insulatingoil, but there are still many unvivid points at electric conduction in breakdown or under of high electric field. This study measured the electric current-electric field characteristics (I-E characteristics) and the breakdown Voltage under of D.C. electric field of insulating oil using the system of electrodes that are near the Uniform electric field with a result. I can study, electric conduction in area of high electric field depends upon the Schottky effect. The liquidity of breakdown electric field takes place by the local concentration of electric field. The longer gap is and the more electric current is the more breakdown Voltage decreased. There are not almost the change of electric current-electric field characteristics by materials of electrode.

• Korean Journal of Materials Research
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• v.13 no.1
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• pp.11-17
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• 2003

DC characteristics of recessed gate 4H-SiC MESFET were investigated using the device/circuit simulation tool, PISCES. Results of theoretical calculation were compared with the experimental data for the extraction of modeling parameters which were implemented for the prediction of DC and gate leakage characteristics at high temperatures. The current-voltage analysis using a fixed mobility model revealed that the short channel effect is influenced by the defects in SiC. The incomplete ionization models are found out significant physical models for an accurate prediction of SiC device performance. Gate leakage is shown to increase with the device operation temperatures and to decrease with the Schottky barrier height of gate metal.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.11
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• pp.908-913
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• 2000

CoSi$_2$/p+/n diodes(bilayer diodes) were fabricated by using epitaxial CoSi$_2$grown from Co/Ti bilayer as a diffusion source. The I-V characteristics of p+/n diodes were measured and compared with those of diode made from Co monolayer (monolayer diode). Monolayer diodes showed typical p+n junction characteristics with the leakage current of as low as 10$^{-12}$ A and forward current 6-orders higher than the leakage current, when drive-in annealed at 90$0^{\circ}C$ for 20 sec.. On the other hand, bilayer diodes showed the Schottky-like behaviors with forward currents rather higher than those of monolyer diodes, but with too high leakage currents, when drive-in annealed at $700^{\circ}C$ or higher. However, when the annealing temperature was lowered to $700^{\circ}C$ and annealing time was increased to 60 sec., the leakage current was reduced to 10$^{-11}$ A and thus sho3wed typical diode characteristics. The high leakage currents for diodes annealed at $700^{\circ}C$ or higher was attributed to Shannon contacts formed due to unremoved Co-Ti-Si precipitates. But when annealed at 50$0^{\circ}C$, B ions diffused in the direction of the surface layer, and thus the leakage currents were reduced by removing Shannon contacts.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.5
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• pp.79-84
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• 2011

In this study, breakdown characteristics of a vertical sphere-plane air gap in the presence of combustion flame were examined under the application of a.c. and d.c. high-voltages in order to investigate the effect of flame on the dielectric strength of air. Propane gas is used as the fuel of the flame, and the temperature distribution of air around the flame is measured. The polarity effects for the d.c. voltages and breakdown voltages of air when applied both of a.c. and d.c. voltages were examined in the case of the variation of the gap length and the horizontal distance between the flame and the high-voltage sphere electrode. The influence of relative air density, electrification and shape changes of the flame as factors that affect the breakdown voltages were discussed.

• Transactions on Electrical and Electronic Materials
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• v.12 no.3
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• pp.102-105
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• 2011

This work describes the characteristics of zinc oxide (ZnO) thin films formed on a polycrystalline (poly) 3C-SiC buffer layer using a sol-gel process. The deposited ZnO films were characterized using X-ray diffraction, scanning electron microscopy, and photoluminescence (PL) spectra. ZnO thin films grown on the poly 3C-SiC buffer layer had a nanoparticle structure and porous film. The effects of post-annealing on ZnO film were also studied. The PL spectra at room temperature confirmed the crystal quality and optical properties of ZnO thin films formed on the 3C-SiC buffer layer were improved due to close lattice mismatch in the ZnO/3C-SiC interface.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.275-275
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• 2008

This paper describe the fabrication of a Pd/polycrystalline 3C-SiC schottky diode and its characteristics, in which the polycrystalline 3C-SiC layer and Pd Schottky contact were deposited by using APCVD and sputter, respectively. Crystalline quality, uniformity, and preferred orientations of the Pd thin film were evaluated by SEM and XRD, respectively. Pd/poly 3C-SiC Schottky diodes were fabricated and characterized by I-V and C-V measurements. Its electric current density Js and barrier height voltage were measured as $2\times10^{-3}$ A/$cm^2$ and 0.58 eV, respectively. These devices were operated until about $400^{\circ}C$. Therefore, from these results, Pd/poly 3C-SiC Schottky devices have very high potential for high temperature chemical sensor applications.

• Journal of Magnetics
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• v.4 no.4
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• pp.131-135
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• 1999

The HDDR characteristics of the Nd-Fe-B-type isotropic and anisotropic HDDR alloys were investigated using three types of alloys: alloy A $(Nd_{12.6}Fe_{81.4}B_6), alloy B (Nd_{12.6}Fe_{81.3}B_6Zr_{0.1}), and alloy C (Nd_{12.6}Fe_{68.8}Co_{11.5}B_6Ga_{1.0}Zr_{0.1}$). The alloy A is featured with the isotropic HDDR character, while alloy B and C are featured with the anisotropic HDDR character. Hydrogenation and disproportionation characteristics of the alloys were examined using DTA under hydrogen gas. Recombination characteristics of the alloys were examined by observing the coercivity variation as a function of recombination time. The present study revealed that the alloy C exhibits slightly higher hydrogenation and disproportionation temperatures compared to the alloy A and B. Recombination of the anisotropic alloy B and C takes place more rapidly with respect to the isotropic alloy A. The intrinsic coercivities of the recombined materials rapidly increased with increasing the recombination time and then showed a peak, after which the coercivities decreased gradually. The degraded coercivity was, however, recovered significantly on prolonged recombination treatment. Compared with the isotropic HDDR alloy A the anisotropic HDDR alloy B and C are notable for their greater recovery of coercivity. The significant recovery of coercivity was accounted for the in terms of the development of well-defined smooth grain boundary between the recombined grains on prolonged recombination.