• Journal of IKEEE
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• v.24 no.1
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• pp.284-292
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• 2020

SiC-based devices perform well in high-voltage environments of more than 1200V compared to silicon devices, and are particularly stable at very high temperatures. Therefore, 1700V UMOSFET has been actively researched and developed for the use of electric power systems such as electric vehicles and aircrafts. In this paper, we analysed thermal variations of critical variables (breakdown voltage (BV), on-resistance (R_on), threshold voltage (v_th), and transconductance (g_m)) for the three type 1700V UMOSFETs-Conventional UMOSFET (C-UMOSFET), Source Trench UMOSFET (ST-UMOSFET), and Local Floating Superjunction UMOSFET (LFS-UMOSFET). All three devices showed BV increase, R_on increase, v_th decrease, and g_m decrease with increasing temperature. However, there are differences in BV, R_on, v_th, g_m according to the structural differences of the three devices, and the degree and cause of the analysis were compared. All results were simulated using sentaurus TCAD.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.1
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• pp.74-80
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• 2009

In the structure of ITO/N,N'-diphenyl-N,N' bis (3-methylphenyl)-1,1'-biphenyl-4,4'-diamine(TPD)/tris (8-hydroxyquinoline)aluminum($Alq_3$)/Al device, we studied the efficiency improvement of organic light-emitting diodes due to variation of deposition rate of hole transport layer (TPD) materials using hole-size of crucible boat. The thickness of TPD and $Alq_3$ was manufactured 40 nm, 60 nm, respectively under a base pressure of $5{\times}10^{-6}$ Torr using a thermal evaporation. The $Alq_3$ used for an electron-transport and emissive layer were evaporated to be at a deposition rate of $2.5\;{\AA}/s$. When the deposition rate of TPD increased from 1.5 to $3.0\;{\AA}/s$, we studied the efficiency improvement of TPD using the hole-size of crucible is 1.0 mm. When the deposition rate of TPD is $2.5\;{\AA}/s$, we found that the average roughness is rather smoother, the luminous efficiency the external quantum efficiency is superior to the others. Compared to the two from the devices made with the deposition rate of TPD is $2.0\;{\AA}/s$ and $3.0\;{\AA}/s$, the external quantum efficiency was improved by four-times and two-times, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.131-131
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• 2008

Silicon carbide (SiC) has attracted significant attention for high frequency, high temperature and high power devices due to its superior properties such as the large band gap, high breakdown electric field, high saturation velocity and high thermal conductivity. We performed Al ion implantation processes on n-type 4H-SiC substrate using a SILVACO ATHENA numerical simulator. The ion implantation model used a Monte-Carlo method. We studied the effect of channeling by Al implantation simulation in both 0 off-axis and 8 off-axis n-type 4H-SiC substrate. We have investigated the Al distribution in 4H-SiC through the variation of the implantation energies and the corresponding ratio of the doses. The implantation energies controlled 40, 60, 80, 100 and 120 keV and the implantation doses varied from $2\times10^{14}$ to $1\times10^{15}cm^{-2}$. In the simulation results, the Al ion distribution was deeper as increasing implantation energy and the doping level increased as increasing implantation doses. After the post-implantation annealing, the electrical properties of Al-implanted p-n junction diode were investigated by SILV ACO ATLAS numerical simulator.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.87-88
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• 2008

In the structure of ITO/N,N'-diphenyl-N,N' bis (3-methylphenyl)-1,1'-biphenyl-4,4'-diamine(TPD)/tris (8-hydroxyquinoline)aluminum$(Alq_3)$/Al device, we studied the efficiency improvement of organic light-emitting diodes due to variation of deposition rate of TPD materials. The thickness of TPD and $Alq_3$ was manufactured 40 nm, 60 nm, respectively under a base pressure of $5\times10^{-6}$Torr using a thermal evaporation. The $Alq_3$ used for an electron-transport and emissive layer were evaporated to be at a deposition rate of 2.5 $\AA$/s. When the deposition rate of TPD increased from 1.5 to 3.0 $\AA$/s, we found that the average roughness is rather smoother, external quantum efficiency is superior to the others when the deposition rate of TPD is 2.5 $\AA$/s. Compared to the ones from the devices made with the deposition rate of TPD 3.0 $\AA$/s, the external quantum efficiency was improved by a factor of eight.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.239-242
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• 1998

Ca $F_2$ films have superior gate insulator properties than conventional gate insulator such as $SiO_2$, Si $N_{x}$, $SiO_{x}$, and T $a_2$ $O_{5}$ to the side of lattice mismatch between Si substrate and interface trap charge density( $D_{it}$). Therefore, this material is enable to apply Thin Film Transistor(TFT) gate insulator. Most of gate oxide film have exhibited problems on high trap charge density, interface state in corporation with O-H bond created by mobile hydrogen and oxygen atom. This paper performed Ca $F_2$ property evaluation as MIM, MIS device fabrication. Ca $F_2$ films were deposited at the various substrate temperature using a thermal evaporation. Ca $F_2$ films was grown as polycrystalline film and showed grain size variation as a function of substrate temperature and RTA post-annealing treatment. C-V, I-V results exhibit almost low $D_{it}$(1.8$\times$10$^{11}$ $cm^{-1}$ /le $V^{-1}$ ) and higher $E_{br}$ (>0.87MV/cm) than reported that formerly. Structural analysis indicate that low $D_{it}$ and high $E_{br}$ were caused by low lattice mismatch(6%) and crystal growth direction. Ca $F_2$ as a gate insulator of TFT are presented in this paper paperaper

• Progress in Superconductivity and Cryogenics
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• v.16 no.1
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• pp.9-13
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• 2014

Effects of neutron irradiation on the superconducting properties of the undoped $MgB_2$ and the carbon(C)-doped $MgB_2$ bulk superconductors, prepared by an in situ reaction process using Mg and B powder, were investigated. The prepared $MgB_2$ samples were neutron-irradiated at the neutron fluence of $10^{16}-10^{18}n/cm^2$ in a Hanaro nuclear reactor of KAERI involving both fast and thermal neutron. The magnetic moment-temperature (M-T) and magnetization-magnetic field (M-H) curves before/after irradiation were obtained using magnetic property measurement system (MPMS). The superconducting critical temperature ($T_c$) and transition width were estimated from the M-T curves and critical current density ($J_c$) was estimated from the M-H curves using a Bean's critical model. The $T_cs$ of the undoped $MgB_2$ and C-doped $MgB_2$ before irradiation were 36.9-37.0 K and 36.6-36.8 K, respectively. The $T_cs$ decreased to 33.2 K and 31.6 K, respectively after irradiation at neutron fluence of $7.16{\times}10^{17}n/cm^2$, and decreased to 22.6 K and 24.0 K, respectively, at $3.13{\times}10^{18}n/cm^2$. The $J_c$ cross-over was observed at the high magnetic field of 5.2 T for the undoped $MgB_2$ irradiated at $7.16{\times}10^{17}n/cm^2$. The $T_c$ and $J_c$ variation after the neutron irradiation at various neutron fluences were explained in terms of the defect formation in the superconducting matrix by neutron irradiation.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.60-69
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• 2013

An optimum configuration of the hybrid/dual swirl jet combustor for a micro-gas turbine was investigated experimentally. Location of pilot nozzle, angle and direction of swirler vane were varied systematically as main parameters under the conditions of constant thermal load. The results showed that the variation in locations of inner fuel nozzle and pilot burner resulted in significant change in flame shape and swirl intensity due to the changes in recirculating flow pattern and minimum flow area near burner exit, in particular, with the significant reduction of CO emission near lean-flammability limit. In addition, it was observed that the co-swirl configuration produced less CO and NOx emissions compared to the counter-swirl configuration.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1043-1050
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• 2010

Fuel stratification and thermal stratification occur in the HCCI combustion chamber on a microscopic scale. They affect the ignition and combustion processes. In this study, the effect of the inhomogeneity in the mixture gas on the HCCI combustion process was investigated. Two-dimensional chemiluminescence images were captured using a framing camera to evaluate the flame structure. DME was used as the test fuel. First, the effect of inhomogeneity in the fuel distribution in the premixture was investigated for the four-stroke optically accessible engine. Then, by comparing the combustion of the homogeneous mixture in the rapid compression machine, which does not contain any residual gas, with the combustion in the four-stroke engine, the effect of inhomogeneity in temperature due to the residual gas was analyzed. The results showed that a time lag appears spatially in combustion under inhomogeneous conditions in the four-stroke engine. The spatial variation in the combustion without the residual gas in the rapid compression machine is less than that in the combustion in the four-stroke engine.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.1
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• pp.25-36
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• 1995

We have investigated the structure and the conductivity of the $Cd_{1-y}Zn_{y}$ Te films evaporated on the glass substrates (Corning 7059) by Electron Beam Evaporator (EBE) in pressure of approximately $1 {\times} 10^{-6}$ torr.The structure temperatures were held at both room temperature and $300^{\circ}C$, and the samples have annealed for an hour at $300^{\circ}C$ The survace com-position of the as-prepared films were slightly different from those of CdZn Te source material.Cd losses on the CdZnTe surface was measured about 4% of atomic ratio at room temperature substrate, whereas Zn atomic ratio was nearly constant, relatively. The strure is observed to be polycrystalline whose phase is mainly cubic phase. Thermal expansion coefficient was $6.30 {\times} 10^{-5}/^{\circ}C$ which was calculated from the variation of lattice parameter by X-ray powder pat-terns measured at $400^{\circ}C$.Diffraction peaks were slightly increased by annealing for an hour at $300^{\circ}C $, but they werey highly affected by substrate temperature during evaporation.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.224-228
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• 2008

A highly sensitive integrated photonic temperature sensor was proposed and developed incorporating a polymeric microring resonator. The change in the ambient temperature was estimated by observing the shift in the resonant wavelength of the resonator induced via the thermooptic effect. For the purpose of enhancing its sensitivity, the sensor was built by implementing a polymeric resonator exhibiting a high thermooptic coefficient on a silicon substrate with a small coefficient of thermal expansion. For the range of from $20^{\circ}C$ to $30^{\circ}C$ near the room temperature, the fabricated sensor yielded a sensitivity of as high as 165 ${\pm}/^{\circ}C$ and a resolution of better than $0.1^{\circ}C$. And its performance was found to be hardly affected by the variation in the refractive index of the target analyte, which was applied to the surface of the sensor. It is hence expected that the sensor could be integrated with other refractormetric optical sensors, thereby compensating for the fatal error caused by the change in the ambient temperature.