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Regular Paper

Study on OCP Optimization and EIS-Based SOH Estimation for LiFePO4 Battery Packs Under Motor Load Conditions
Woo-Geun Jung, Jae-Ha Ko, Keon-Sik Hong
J Electr Electron Mater 2026;39(4):407-417.
Published online July 1, 2026
DOI: https://doi.org/10.4313/JEEM.2026.39.4.11
This study proposes an optimization strategy for the over-current protection (OCP) parameters of a lithium iron phosphate (LiFePO₄, LFP) battery system used in electric golf carts operating under high motor-load conditions. Real-world hillclimbing tests were conducted under four clearly defined payload/passenger conditions to analyze the transient discharge-current pro-file, voltage sag, and cell-temperature response. The maximum discharge current reached -238.2 A under the 200 kg cargopayload and one-passenger condition, and the current interval exceeding 150 A lasted up to 27 s. The maximum instantaneous power was 11.05 kW. Thermal analysis showed that the cell-temperature rise was within 2°C and the maximum measured cell temperature was 22.3°C. Linear regression of voltage and current yielded R² = 0.9368 and dV/dI = 0.0126 Ω, which was used as the DC internalresistance estimate. Based on these quantitative results and the cell specification limit of 300 A continuous discharge, the OCP threshold was reviewed from 250 A to 280 A to improve driving continuity while remaining below the allowable continuous-discharge current. EIS-based SOH estimation and the AI-BMS variable protection logic are presented as an extension framework for reflecting temperature and aging effects in future OCP-setting decisions.
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This paper proposes a circular sequential lighting control method to reduce current imbalance and luminance deviation among multiple LED modules in AC-powered LED lighting systems. Conventional fixed-sequence lighting control repeatedly prioritizes the same LED modules in every rectified voltage cycle, which leads to unequal current distribution, luminance non-uniformity, and the accelerated degradation of specific modules during long-term operation. To address these limitations, a circular sequential lighting strategy is introduced, in which the lighting order is cyclically rotated at every rectified cycle, ensuring that all LED modules experience equal lighting opportunities. A prototype AC-LED lighting system consisting of four series-connected LED modules was implemented and experimentally evaluated. The results demonstrate that, while the conventional fixed-sequence method produces a maximum average current deviation of up to 1.6 mA among modules, the proposed method equalizes the average current across all modules to approximately 17.1 mA. Furthermore, the flicker index remains at 0.13, which is comparable to that of the conventional method, indicating that luminance uniformity is improved without degradation of optical performance. The proposed circular sequential lighting control effectively distributes electrical stress, enhances luminance uniformity, and improves long-term reliability, making it a practical and efficient solution for high-quality AC-LED lighting applications.
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Quench Behavior of Wires for Superconducting Fault Current Limiters at DC Faults
Hye-rim Kim, Bong-man Ahn, Byoung-sung Han
J Electr Electron Mater 2026;39(1):19-26.   Published online January 1, 2026
DOI: https://doi.org/10.4313/JEEM.2026.39.1.3
The quench behavior of wires for superconducting fault current limiters at DC faults was simulated, with a focus on the effect of capacitor discharge on the quench. The behavior was also expressed in mathematical forms to facilitate a better understanding of the simulation results and for rough analytical estimations of the wire length suitable for the circuit voltage and capacitance. The quench resistance development behavior for various wire lengths and circuit capacitances was simulated using the model developed in the previous work. The quench behavior was expressed in mathematical forms, reflecting the concept of heat balance. During the quench, the wire temperature increased more slowly for longer wires, but was found to increase in a similar pattern. The wire length estimated by the mathematical formula was close to the one obtained by the simulation, with an error range of a few %. The calculations will be used to estimate effectively the length of wires needed to build superconducting fault current limiters for applications in DC power systems.
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Effect of Porous SiC Film Thickness on the Performance of UV Photodetectors Fabricated by Aerosol Deposition
Sabin Hwang, Kwangyeol An, Jihyun Kim, Jin-woo Choi, Minseok Kim, Geonhee Lee, Jong-min Oh, Sang-mo Koo
J Electr Electron Mater 2025;38(6):690-695.   Published online November 1, 2025
DOI: https://doi.org/10.4313/JEEM.2025.38.6.13
Silicon carbide (SiC), with its wide bandgap and strong resistance to radiation and thermal conditions, is a promising material for ultraviolet (UV) photodetector applications under harsh environments. In this study, porous SiC thin films with thicknesses of 20, 50, and 80 nm were fabricated on 4H-SiC substrates using aerosol deposition (AD), which enables roomtemperature film formation. The device with a 50 nm-thick film exhibited the highest photoresponse under UV-C illumination (260 nm), achieving a maximum photo-to-dark current ratio (PDCR) of 205.2, a responsivity of 0.058 A/W, an external quantum efficiency (EQE) of 27.71%, and a specific detectivity (D*) of 7.9×1011 Jones. These results are attributed to an optimized balance between photon absorption and carrier transport in the porous structure. The findings confirm the potential of ADfabricated porous SiC films for highly sensitive and scalable UV photodetector applications.
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Effect of Concurrent Low-Temp Plasma Annealing on a-IGZO TFT Performance Over Time
Jeong Hun Choi, Jae-yun Lee, Beom Gu Lee, Jeong Moo Seo, Sung-jin Kim
J Korean Inst Electr Electron Mater Eng 2025;38(3):265-271.   Published online May 1, 2025
DOI: https://doi.org/10.4313/JKEM.2025.38.3.4
Recently, oxide semiconductors have assumed a pivotal role in electronic displays and transparent electronic devices such as amorphous indium gallium zinc oxide (a-IGZO), characterized by high electron mobility and excellent stability. a- IGZO is very suitable for next-generation applications such as flexible displays because it is possible to manufacture highperformance transistors even at low temperatures. However, since the electrical properties tend to deteriorate in hightemperature environments, research aimed at improving thermal stability is needed. In this study, a low-temperature plasma annealing process was introduced to improve the high-temperature stability of the a-IGZO thin film. This process enhances electron mobility by reducing defects in the a-IGZO film and provides stable device performance even under high-temperature conditions. As a result of the experiments of 5 min, 10 min, 15 min, and 20 min, the a-IGZO TFT, which was subjected to plasma annealing at 160℃ for 5 min, showed the best electrical performance, especially in charge mobility and current-voltage characteristics. The technical potential for improving the performance of a-IGZO-based display device was emphasized, and the foundation for applying this power generation to flexible displays and next-generation electronic devices was laid. Future research will focus on determining the optimal annealing conditions by exploring various temperature ranges and plasma parameters to integrate these results into the actual device manufacturing process. These efforts are expected advance significantly to advancing next-generation high-performance display technology.
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Electrical Characteristics of Solution-Based TiO₂ Resistive Switch
Jae Mo Yun, Ha Na Kang, Jin Tae Park, Soon Joo Yoon, Yoon Kyeung Lee
J Korean Inst Electr Electron Mater Eng 2025;38(3):330-335.   Published online May 1, 2025
DOI: https://doi.org/10.4313/JKEM.2025.38.3.14
The solution-based fabrication process for resistive random-access memory (ReRAM) offers several advantages over conventional vapor deposition processes, including simplicity, cost-effectiveness, and high versatility for coating complex structures over large areas. In this study, a TiO₂-based ReRAM device was fabricated using a solution process with Pt top and P++-Si bottom electrodes. The synthesized TiO₂ films contain a residual Cl element as revealed by X-ray photoelectron spectroscopy (XPS). Reversible volatile resistance switching was observed due to the formation of conductive Ti-O-Ti networks in the TiO₂ layer. Post-annealing led to an increase in the threshold voltage (Vth). Asymmetric Current-Voltage characteristics was observed due to the different in the work functions of the electrodes. Additionally, the influence of compliance current settings on filament formation and hysteresis behavior was systematically investigated. The results demonstrated that higher compliance currents enhanced the hysteresis width for both positive and negative voltage bias conditions.

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  • Pulse Response Measurement Optimization of ReRAM-Based Neuromorphic Devices
    Soon Joo Yoon, Yoon Kyeung Lee
    Journal of Electrical and Electronic Materials.2026; 39(3): 258.     CrossRef
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Quench Simulation and Calculation of Current Limitation at DC Faults for Superconductors
Hye-rim Kim, Bong-man Ahn, Byoung-sung Han
J Korean Inst Electr Electron Mater Eng 2025;38(3):311-318.   Published online May 1, 2025
DOI: https://doi.org/10.4313/JKEM.2025.38.3.11
The quench behavior of coated conductors (CCs) was simulated with a focus on the initial stage of quenches, and the current limiting behavior of superconducting fault current limiters (SFCLs) at DC faults was calculated. Since the fault current reaches the peak in several ms in DC lines due to capacitor discharge, it is necessary to understand the initial quench behavior well. Considered in the simulation are characteristics of CCs in the flux-flow state, current sharing, non-uniform critical current distribution in CCs, and heat transfer to surroundings. The simulation fit data well. Using the CC model developed in the simulation, the current limiting behavior of SFCLs made of CCs at DC faults was calculated. Critical current distribution and heat transfer were found to affect the current limiting behavior of SFCLs less at DC faults. The calculation will contribute to the effective design of SFCLs for applications in DC lines.
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Impact of Hydrogen-Doped Indium Oxide Films on the Performance of Silicon Heterojunction Solar Cells
Hyeong Gi Park, Jaehyeong Lee, Junsin Yi
J Korean Inst Electr Electron Mater Eng 2024;37(6):582-589.   Published online November 1, 2024
DOI: https://doi.org/10.4313/JKEM.2024.37.6.2
We investigated the potential of IO:H thin films and hydrogen doping to improve current density and fill factor for enhancing the performance of silicon heterojunction solar cells. We revealed that a transmittance of 86.7% and work function of 5.4 eV could be achieved by injecting 3 sccm of hydrogen gas. The lattice constant of 1.037 nm at the AB site indicates an anion antibonding tendency, and the work function increases as the Fermi level shifts to the valence band. Based on these findings, we fabricated a silicon heterojunction solar cell and achieved an efficiency of 18.53%, while computer simulation confirmed a conversion efficiency of 24.65%, an open-circuit voltage of 724 mV, and a fill factor of 82.72% at a current density of 41.15 mA/㎠.

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  • A Review on Energy Yield Enhancement Characteristics of Bifacial Photovoltaic Systems Combined with Solar Tracking
    Hyeong Gi Park
    Journal of Electrical and Electronic Materials.2026; 39(4): 309.     CrossRef
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Quest for Comparing Direct-Current (DC) and Alternating-Current (AC) Poling Effects on Ferroelectric and Piezoelectric Materials
Jihun Choi, Hyunseung Kim, Sang-il Yoon, Chang Kyu Jeong
J Korean Inst Electr Electron Mater Eng 2024;37(6):563-581.   Published online November 1, 2024
DOI: https://doi.org/10.4313/JKEM.2024.37.6.1
Piezoelectricity refers to the phenomenon where mechanical stress is converted into electrical signals or, conversely, electrical signals are converted into mechanical stress. Ferroelectric materials, characterized by high dielectric permittivity and spontaneous polarization, retain their polarization even after the removal of an electric field. In such materials, poling plays a crucial role in enhancing the piezoelectric effect, with the process of aligning dipoles being known as poling. This review focuses on studies that have compared and analyzed the enhancement of piezoelectric properties in ceramics and polymers through two representative poling methods: AC poling (ACP) and DC poling (DCP). Even within the same category of ceramics or polymers, variations in piezoelectric properties are observed based on the material type, poling method, and poling conditions. Under certain conditions, ACP has been shown to provide superior poling effects compared to DCP. Through this review, we propose that ACP has the potential not only to replace the traditionally used DCP in the poling of piezoelectric materials but also to serve as a more effective method. This could spark increased interest in the study of poling methods for piezoelectric polymers, a field that has received relatively less attention.
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A Study on State Analysis of Substation Using PMU
Tae-hee Kim, Kyung-min Lee, Cheol-won Park, Dong-hoon Jeon, Dae-yoon Kwon, Yong-sung Choi
J Korean Inst Electr Electron Mater Eng 2024;37(3):304-308.   Published online May 1, 2024
DOI: https://doi.org/10.4313/JKEM.2024.37.3.10
In this paper, in order to analyze the PMU data of the accident section, we collected the raw data of a total of 35 PMU installed at the Yeonggwang substation and tried to find a way to analyze the data, and analyzed the data using Excel format and formula. As a result, the three-phase voltage and current data of the PMU were calculated using formulas in Excel and interpreted as effective and reactive power, and it was possible to check the effective and reactive power of the accident section through the graph to see why it was different from before the accident. As a result, it was confirmed that each power was greatly reduced in the graph of the effective and reactive power of the accident section, and it was confirmed that the loss occurred as the power of the accident section was greatly reduced.
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Advanced Tellurium-Based Threshold Switching Devices for High-Density Memory Arrays
Seunghwan Kim, Changhwan Kim, Namwook Hur, Joonki Suh
J Korean Inst Electr Electron Mater Eng 2023;36(6):547-555.   Published online November 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.6.2
High-density crossbar arrays based on storage class memory (SCM) are ideally suited to handle an exponential increase in data storage and processing as a central hardware unit in the era of AI-based technologies. To achieve this, selector devices are required to be co-integrated with SCM to address the sneak-path current issue that indispensably arises in such crossbar-type architecture. In this perspective, we first summarize the current state of tellurium-based threshold-switching devices and recent advances in the material, processing, and device aspects. We thoroughly review the physicochemical properties of elemental tellurium (Te) and representative binary tellurides, their tailored deposition techniques, and operating mechanisms when implemented in two-terminal threshold switching devices. Lastly, we discuss the promising research direction of Te-based selectors and possible issues that need to be considered in advance.
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Analysis on Fault Current Limiting Characteristics of Three-Phase Transformer Type SFCL using Double Quench According to Three-Phase Ground-Fault Types
Shin-won Lee, Tae-hee Han, Sung-hun Lim
J Korean Inst Electr Electron Mater Eng 2023;36(6):614-619.   Published online November 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.6.13
The fault current limiting characteristics of three-phase transformer type superconducting fault current limiter (SFCL), which consisted of three-phase primary and secondary windings wound on E-I iron core, one high-TC superconducting (HTSC) element connected with the secondary winding of one phase and another HTSC element connected in parallel with other two secondary windings of two phases, were analyzed. Unlike other three-phase transformer type SFCLs with three HTSC elements, three-phase transformer type SFCL using double quench has the merit to perform fault current limiting operation for three-phase ground faults with two HTSC elements. To verify its proper three-phase ground fault current limiting operation, three-phase ground faults such as single-line ground, double-line ground and triple-line ground faults were generated in three-phase simulated power system installed with three-phase transformer type SFCL using double quench. From analysis of its fault current limiting characteristics based on tested results, three-phase transformer type SFCL using double quench was shown to be effectively operated for all three-phase ground faults.
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Verification of Algorithm for Arc Detection Using High Pass Filter and FFT
Min-ho Yoon, You-jung Cho, Kyoung-tak Kim, Sung-hun Lim
J Korean Inst Electr Electron Mater Eng 2023;36(5):520-524.   Published online September 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.5.13
An algorithm was developed to detect and block serial arc currents using HPF. The AC series arc problem is that the load current is greater than the fault current and no leakage current occurs. As a solution, an arc detection method utilizing differences in high- frequency amplitudes was developed. HPT was applied to the load current and FFT was applied to eliminate low frequencies. An algorithm has been developed to detect arc waveforms when they exceed a certain value compared to the average of normal waveforms. Using one cycle of data, arc detection is faster and arc accidents are prevented.
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Quantum Efficiency Measurement and Analysis of Solar Cells
Youngkuk Kim, Donghyun Oh, Jinjoo Park, Junsin Yi
J Korean Inst Electr Electron Mater Eng 2023;36(4):351-361.   Published online July 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.4.5
The purpose of this paper is to help those who research and develop solar cells in university laboratories and industrial sites understand the most basic and important quantum efficiency measurement and analysis method in analyzing solar cell performance. Starting with the definition of quantum efficiency, we calculate the theoretical current density according to the band gap of the solar cell material from the solar spectrum, along with a detailed introduction to the measurement and analysis methods, and measure and analyze the theoretical current density and quantum efficiency. We discuss in depth how to analyze the performance of solar cells through Quantum efficiency measurement and analysis of solar cells is a very useful method that can give intuition to solar cell performance analysis as it can analyze solar cells according to depth (front emitter, bulk, rear surface). Students and researchers who study solar cells with a deep understanding of theoretical current density and quantum efficiency measurement analysis are expected to use it as a basis for analyzing solar cell performance.
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A Study on How to Minimize the Luminance Deviation of AC-LED Lighting
Dong Won Lee, Bong Hee Lee, Byungcheul Kim
J Korean Inst Electr Electron Mater Eng 2023;36(3):255-260.   Published online May 1, 2023
DOI: https://doi.org/10.4313/JKEM.2023.36.3.7
In order to spread LED lighting, LED lighting technology directly driven by alternating current (AC) commercial power has recently been introduced. Since current does not flow at a voltage lower than the threshold voltage of the LED, a nonconductive section occurs in the current waveform, and the higher the threshold voltage of the LED, the more discontinuous current waveforms are generated. In this paper, multi-LED modules are connected in series so that the threshold voltage can be adjusted according to the number of LED modules. A small number of LED modules are driven at a low instantaneous rectified voltage, and a large number of LED modules are driven at a high instantaneous rectified voltage to lengthen the overall lighting time of AC-LED lighting, thereby minimizing the luminance deviation of AC-LED lighting. In addition, the load current flowing through the LED module is adjusted to be the same as the design current even at the maximum rectified voltage higher than the design voltage, so that the light brightness of the LED module is kept constant. Therefore, even if the rectified voltage applied to the LED module changes, the AC-LED lighting in which the light brightness is constant and the luminance deviation is minimal has been realized.

Citations

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  • Reduction of Luminance Deviation in Multi-Module AC-LED Lighting Systems Using a Circular Sequential Lighting Control Method
    Dong Won Lee, Byungcheul Kim
    Journal of Electrical and Electronic Materials.2026; 39(3): 267.     CrossRef
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Alternating Current (AC) Powered LED Lighting Technology with Constant Brightness
Dong Won Lee, Ho-myoung Ahn, Byungcheul Kim
J Korean Inst Electr Electron Mater Eng 2022;35(5):466-470.   Published online September 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.5.7
In order to widely disseminate LED lighting, LED lighting technology that directly uses AC commercial power has been recently introduced. AC powered LED lighting technology has a problem in that the light brightness of the LED changes because the voltage applied to the LED and the current flowing through the LED continuously change. In this study, when the LED current is greater than the design current, the current control signal generated by the controller is supplied to the current source to supply only the design current to the LED by increasing the voltage drop at the current source. If it is smaller than the design current, the controller is adjusted so that the current is supplied only to the LED without a voltage drop in the current source. It can be seen that the higher the maximum rectified voltage, the faster the lighting time of the LED light emitting block is, so that the power factor of the LED lighting is improved. The LED lighting technology proposed in this study enables LED lighting with constant light brightness, reduced power consumption, and long lifetime.

Citations

Citations to this article as recorded by  
  • Reduction of Luminance Deviation in Multi-Module AC-LED Lighting Systems Using a Circular Sequential Lighting Control Method
    Dong Won Lee, Byungcheul Kim
    Journal of Electrical and Electronic Materials.2026; 39(3): 267.     CrossRef
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Study on Current Conditioning Process for Improving Withstand Voltage Performance of Vacuum Interrupter
Young-kwang Cha, Il-hoi Lee, Ki-beom Jeon, Ji-hoon Jang, Heung-jin Ju
J Korean Inst Electr Electron Mater Eng 2022;35(5):480-487.   Published online September 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.5.9
As a process to improve the insulation performance of VIs (Vacuum Interrupters), AC voltage conditioning is generally adopted by many manufacturers. Although the insulation performance is enhanced easily with AC Voltage conditioning, it has limitations when high recovery voltage is required due to high voltage rate or capacitive current switching. In particular, impurities such as oxides segregated on the electrode surface can be removed not by the energy level of the voltage conditioning but by the higher energy level achieved by the current conditioning process In this article, the current conditioning was carried out in various conditions and its validity was examined. The current conditioning was processed by changing the amplitude of applied current, arc time, the number of tests, and frequency. The insulation performance and the status of contact surface were checked as well. We concluded that as the applied charge quantity and the conditioning coverage area increase, the conditioning effect is much higher.
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Analysis on Fault Current Limiting Operation of Three-Phase Transformer Type SFCL Using Double Quench
Tae-hee Han, Seok-cheol Ko, Sung-hun Lim
J Korean Inst Electr Electron Mater Eng 2022;35(2):184-189.   Published online March 1, 2022
DOI: https://doi.org/10.4313/JKEM.2022.35.2.12
In this paper, the fault current limiting operations of three-phase transformer type superconducting fault current limiter (SFCL) using double quench, which consisted of E-I iron core with three legs wound by primary and secondary windings and two superconducting modules (SCMs), were analyzed according to three-phase ground fault types. To verify the effective operation of the three-phase transformer type SFCL using double quench, the test circuit for three-phase ground faults was constructed, and the fault current tests were carried out. Through analysis on the fault current test results, the different fault current limiting characteristics of three-phase transformer type SFCL using double quench from three-phase transformer type SFCL using three SCMs were discussed.
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Effect of Internal Bias Field on Poling Behavior in Mn-Doped Pb(Mg1/3Nb2/3)O3-29 mol%PbTiO3 Single Crystal
Geon-ju Lee, Hwang-pill Kim, Ho-yong Lee, Wook Jo
J Korean Inst Electr Electron Mater Eng 2021;34(5):382-385.   Published online September 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.5.382
Electrical poling is a crucial step to convert ferroelectrics to piezoelectrics. Nevertheless, no systematic investigation on the effect of poling has been reported. Given that the poling involves an alignment of spontaneous polarization, the condition for poling should be different when a material has an internal bias field that influences the domain stability. Here, we present the effect of poling profile on the dielectric and piezoelectric properties in Mn-doped Pb(Mg1/3Nb2/3)O3-29 mol%PbTiO3 single crystal with an internal bias field. We showed that both the dielectric permittivity and the piezoelectric coefficient were further enhanced when the poling procedure ends with a field application along the opposite direction to the internal bias field. We expect that the current finding would give a clue to understanding the true mechanism for the electrical poling.
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We fabricated plate typed shunt resistors composed of carbon nanotube (CNT) and metal alloy for measuring DC current. CNT plates were prepared from dispersed CNT/Urethane solution by squeezing method. Cu/Ni alloys were prepared from composition-designed alloy wires for adjusting the temperature coefficient of resistance (TCR) by pressing them. As well, we fabricated a hybrid resistor by squeezing the CNT/Urethane solution on the metal alloy plate directly. In order to confirm the composition ratio of the Cu/Ni alloy, we used an energy-dispersed X-ray spectroscopy (EDX). Cross-section and surface morphology were analyzed by using a scanning electron microscopy (SEM). Finally, we measured the initial resistance of 2.35 Ω at 25℃ for the CNT paper resistor, 7.56 mΩ for the alloy resistor, and 7.38 mΩ for the hybrid resistor. The TCR was also measured to be -778.72 ppm/℃ at the temperature range between 25℃ to 125℃ for the CNT paper resistor, 824.06 ppm/℃ for the alloy resistor, and 17.61 ppm/℃ for the hybrid resistor. Some of the hybrid resistors showed a near-zero TCR of 1.38, -2.77, 2.66, and 5.49 ppm/℃, which might be the world best-value ever reported. Consequently, we could expect an error-free measurement of the DC current using this resistor.
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A Study on the Surface Properties of Polymer Insulators for Improving Electrical Insulation Performance
Yong Seob Park, Jae Sung Bae, Byungyou Hong, Jae Hyeong Lee
J Korean Inst Electr Electron Mater Eng 2021;34(1):63-67.   Published online January 1, 2021
DOI: https://doi.org/10.4313/JKEM.2021.34.1.063
In this paper, we investigated the surface properties of polymer insulators to improve electrical insulation performance. First, after washing the polymer insulator in various ways, its contact angle was increased, thereby improving the hydrophobic properties and electrical insulation properties. In addition, TiO2 thin films, which have been used as a photocatalytic material and have been applied to the polymer insulator surface of to enhance the surface and electrical insulating properties. For the sputtering method, the contact angle after coating the TiO2 thin film increased with increasing RF power, but it was lower compared to that before coating, indicating that the hydrophobic properties of the surface were slightly deteriorated. Consequently, the electrical properties of the polymer-insulating material were maintained or improved after the TiO2 thin-film coating.
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Analysis on Current Characteristics According to Injection Method and Driving Waveform in Electrophoretic-Type E-Paper Display
Joo-won Lee, Young-cho Kim
J Korean Inst Electr Electron Mater Eng 2020;33(5):386-392.   Published online September 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.5.9
In this study, the drift current characteristics of charged particles are analyzed for panels fabricated by varying the waveform biasing of the active particle loading method (APLM), which is a method driven by the electrophoretic principle of loading charged particles into a cell of a barrier rib-type electronic paper. We prepare 3 panels using APLM and 1 panel without APLM. The waveform of APLM uses square wave and ramp wave, and the step voltage wave is applied to the driving voltage. The drift currents measured from the square wave and ramp wave with the same period applied by APLM are 4.872 μC and 5.464 μC, respectively, and the ramp wave is shown to be relatively advantageous for loading charged particles that have a large q/m. The time–current curve results confirm that the abrupt movement of charged particles is occurring. When the step form wave signal with a short time of 1s is first applied, initial large movement of the charged particles is confirmed to occur in all samples, which is understood as the effect of applying the voltage necessary to remove the imaging force. The results of this study are expected to improve the loading of charged particles into the electronic paper cell, driven by the electrophoretic principle and optimization of the driving conditions.
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Analysis of the Output Characteristics of IGZO TFT with Double Gate Structure
Ji Won Kim, Kee Chan Park, Yong Sang Kim, Jae Hong Jeon
J Korean Inst Electr Electron Mater Eng 2020;33(4):281-285.   Published online July 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.4.6
Oxide semiconductor devices have become increasingly important because of their high mobility and good uniformity. The channel length of oxide semiconductor thin film transistors (TFTs) also shrinks as the display resolution increases. It is well known that reducing the channel length of a TFT is detrimental to the current saturation because of drain-induced barrier lowering, as well as the movement of the pinch-off point. In an organic light-emitting diode (OLED), the lack of current saturation in the driving TFT creates a major problem in the control of OLED current. To obtain improved current saturation in short channels, we fabricated indium gallium zinc oxide (IGZO) TFTs with single gate and double gate structures, and evaluated the electrical characteristics of both devices. For the double gate structure, we connected the bottom gate electrode to the source electrode, so that the electric potential of the bottom gate was fixed to that of the source. We denote the double gate structure with the bottom gate fixed at the source potential as the BGFP (bottom gate with fixed potential) structure. For the BGFP TFT, the current saturation, as determined by the output characteristics, is better than that of the conventional single gate TFT. This is because the change in the source side potential barrier by the drain field has been suppressed.
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Design for a Fuse of High Durability Protection Elements for Improving the Safety of DC Current Measurement Device
Ye Ji Lee, Jae Seo Youn, Sung Chul Cho, Sung Yeo Noh
J Korean Inst Electr Electron Mater Eng 2020;33(3):201-207.   Published online May 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.3.8
With the expansion in the use of DC power systems and increased need for system maintenance, the development of measurement devices for maintenance requires high stability. Of the different kinds of DC current measurement devices, the single-shot measurement device causes the input signal of the current measuring unit to initially generate a high inrush current. The high inrush current flows into the signal processor of the meter, shortening the life of the internal fuses and causing failure. Therefore, in this study, the I2t value for increasing the durability of the fuse is designed using the available wire diameter. Operating characteristics for 210~400% over-current of the rated current, which is relatively low over-current, are realized by the plating of low melting tin metal. As a result, a method of designing a fuse element for a DC power supply, which improves the safety of the DC current measurement device by blocking the failure caused by the inrush current, is presented.
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Analysis on Current and Optical Characteristics by Electronic Ink Loading Method in Charged Particles Type Display
Hyeong-jin An, Young-cho Kim
J Korean Inst Electr Electron Mater Eng 2020;33(2):123-129.   Published online March 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.2.9
We analyzed the drift current by charged particles according to the loading methods applied into a closed cell by electronic ink at a reflective-type display panel using an electrophoretic mechanism. For this experiment, various panels were fabricated with injection voltages for electronic ink taking values in the range -4~0 V. The size of each cell was 220 μm × 220 μm and height of the barrier rib was 54.28 μm. The electronic ink was fabricated by mixing electrically neutral fluid and single-charge white particles. Drift current was measured by moving charged particles. A biasing voltage of 6 V was applied to the display panel. As a result, the drift current was proportional to the injection voltage for electronic ink, but it decreased in case of an injection voltage above -3 V. Our experimentation ascertained that the concentration of charged particles injected into closed cells is controlled by the injection voltage and the selective injection of charged particles above movable q/m is possible.
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Design and Fabrication of a Surge Generator with Coupling/Decoupling Networks
Nam-hoon Kim, Tae-ho Kang, Han-sin Shin, Gyung-suk Kil
J Korean Inst Electr Electron Mater Eng 2020;33(2):130-134.   Published online March 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.2.10
Metal oxide varistors (MOVs) protect circuits and devices from transient overvoltages in electric power systems. However, a MOV continuously deteriorates owing to manufacturing defects or repetitive protective operations from transient overvoltages. A deteriorated MOV may result in a short circuit or a line-ground accident. Previous studies focused on the analysis of deterioration mechanisms and condition diagnosis techniques for MOVs owing to their recent growth of use. An accelerated deterioration experiment under the same conditions in which a MOV operates is essential. In this study, we designed and fabricated a surge generator that can apply a surge current to a MOV connected to AC mains. The coupling network operates at a low impedance against the surge current from the surge generator and transfers the surge current to the MOV under test. It also acts as a high impedance against AC mains for the AC voltage not to be applied to the surge generator. The decoupling network operates at a high impedance against the surge current and blocks the surge current from AC mains. It also acts as a low impedance against AC mains for the AC voltage to be applied to the MOV under test. The prototype surge generator can apply the 8/20 us up to 15 kA on AC voltages in the approximate range of 110~450 V, and it fully operates on a LabVIEW-based program.
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Limited Current Characteristics of Carbon Nanotube Elements Miniature Fuses
Seong Yeo Noh, Sang Jun Jin, Sunwoo Lee
J Korean Inst Electr Electron Mater Eng 2020;33(1):45-49.   Published online January 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.1.9
In this paper, we prepared miniature fuse fabricated with carbon nanotube (CNT) fiber for the use of low rated current under 1 A and high speed operation under 4ms. CNT fuses were fabricated in the form of universal modular fuse (UMF) with different diameter of CNT fibers defined by multiplying the CNT threads. Electrical properties of the CNT fuses were measured such as resistance, rated current, and operation time with current. Resistance of the CNT fuse decreased and rated current increased with the diameter of the CNT fuses, respectively. Consequently, the operation time with current increased with the diameter of the CNT fuses. The CNT fuses fabricated in this work had broad range of low rated current from 0.05 to 1.25 A by multiplying the CNT threads. Operation time was measured about 3.6ms which was applicable to the UMF.
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Current Properties and Evaluation of Electronic Ink in Electrophoretic Display
Hyeong-jin An, Young-cho Kim
J Korean Inst Electr Electron Mater Eng 2020;33(1):31-36.   Published online January 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.1.7
An investigation was conducted to determine whether the ratio of the fluid to the charged particles affects the panel reflexibility rate and the drifting current flowing in the panel, in electrophoretic-based electronic paper. In this regard, three panels were produced in this study with the ratio of the charged particles to the fluid set as 1:5, 1:1, and 5:1. Each sample was driven using an identical input pulse, for which the current flowing in the panel and the output voltage of the photodiode were measured for the panel reflexibility rate. Consequently, the drifting current initially exhibited a peak value and a saturated value at a later point. This value was proportional to the ratio of the charged particles, and it was similar to this ratio when it is higher than 1:1. The output voltage of the photodiode due to the panel reflexibility rate was proportional to the ratio of the charged particles. However, the response speed decreased if the ratio was higher than 1:1. It is expected that the results of this study will contribute to the analysis of the charging of charged particles in electrophoretic-based electronic paper, and the selection of an appropriate concentration.
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Characteristics of Circular β-Ga2O3 MOSFETs with High Breakdown Voltage (>1,000 V)
Kyu Jun Cho, Jae-kyong Mun, Woojin Chang, Hyun-wook Jung
J Korean Inst Electr Electron Mater Eng 2020;33(1):78-82.   Published online January 1, 2020
DOI: https://doi.org/10.4313/JKEM.2021.33.1.15
In this study, MOSFETs fabricated on Si-doped, MBE-grown β-Ga2O3 are demonstrated. A Si-doped Ga2O3 epitaxial layer was grown on a Fe-doped, semi-insulating 1.5 cm × 1 cm Ga2O3 substrate using molecular beam epitaxy (MBE). The fabricated devices are circular type MOSFETs with a gate length of 3 μm, a source-drain spacing of 20 μm, and a gate width of 523 μm. The device exhibited a good pinch-off characteristic, a high on-off drain current ratio of approximately 2.7×109, and a high breakdown voltage of 1,080 V, which demonstrates the potential of Ga2O3 for power device applications including electric vehicles, railways, and renewable energy.
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Safety Improvement of Military Primary Lithium Batteries by New Protection Circuit for Low Current System
Seong Gi Youn, Yu Seup Cho
J Korean Inst Electr Electron Mater Eng 2019;32(3):256-261.   Published online May 1, 2019
DOI: https://doi.org/10.4313/JKEM.2019.32.3.256
The use of military lithium batteries in this field accelerates the generation of internal pressure because the active materials, lithium and the electrolyte, react to form sulfur dioxide gas. This also reduces the amount of electrolyte. In this condition, batteries can ‘vent’ or ‘explode’ especially when completely discharged. Such venting and explosion can be regarded as a safety accident, as toxic gases and shrapnel are ejected from the batteries which can harm the user. A DTaQ was carried out in 2017 as a quality problem solution project to solve this safety issue. A protection circuit was thereby developed, which included a micro controller unit (MCU) which can stop battery usage when in an over-discharging state by sensing its low-voltage condition. In 2018, this concept was expanded to lithium batteries for the remote controlled ammunition system. This paper reports results of the improved performance.
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