• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.4
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• pp.67-72
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• 1989

Room Temperature Plasma Nitridation of silicon was investigated as a new LOCOS (local oxidation of silicon) process in order to reduce the bird's beak length. In $N_2$ plasma formed by 100kHz, 400W AC power, a thin silicon nitride film (<100${\AA}$) was uniformly grown on a silicon substrate. SEM studies showed that the nitride layer formed by this method can effectively protect the silicon from oxidation and reduce the bird's beak length to $0.2{mu}m$ when 4000${\AA}$ field oxide is grown. This is a considerable improvement comparing with 0.7${mu}m,$ the bird's beak, for the conventional LOCOS process using a thick LPCVD nitride. No appreciable crystalline defect could be found around the bird's beak with SEM cross-section afrer Secco etch. Leakage current tests were carried out on the $N^+/P^-$ well and $P^+/N^-$ well diodes formed by this new LOCOS process. The electrical tests indicate that this new process has electrical properties similar or superior to those of the conventional LOCOS process.

• Journal of the Korea Safety Management & Science
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• v.16 no.2
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• pp.237-246
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• 2014

Researches on the elimination of sulfur and nitrogen oxides with catalysts and absorbents reported many problems related with elimination efficiency and complex devices. In this study, decomposition efficiency of harmful gases was investigated. It was found that the efficiency rate can be increased by moving the harmful gases together with SPCP reactor and the catalysis reactor. Calcium hydroxide($Ca(OH)_2$), CaO, and $TiO_2$ were used as catalysts. Harmful air polluting gases such as $SO_2$ were measured for the analysis of decomposition efficiency, power consumption, and voltage according to changes to the process variables including frequency, concentration, electrode material, thickness of electrode, number of electrode winding, and additives to obtain optimal process conditions and the highest decomposition efficiency. The standard sample was sulfur oxide($SO_2$). Harmful gases were eliminated by moving them through the plasma generated in the SPCP reactor and the $Ca(OH)_2$ catalysis reactor. The elimination rate and products were analyzed with the gas analyzer (Ecom-AC,Germany), FT-IR(Nicolet, Magna-IR560), and GC-(Shimazu). The results of the experiment conducted to decompose and eliminate the harmful gas $SO_2$ with the $Ca(OH)_2$ catalysis reactor and SPCP reactor show 96% decomposition efficiency at the frequency of 10 kHz. The conductivity of the standard gas increased at the frequencies higher than 20 kHz. There was a partial flow of current along the surface. As a result, the decomposition efficiency decreased. The decomposition efficiency of harmful gas $SO_2$ by the $Ca(OH)_2$ catalysis reactor and SPCP reactor was 96.0% under 300 ppm concentration, 10 kHz frequency, and decomposition power of 20 W. It was 4% higher than the application of the SPCP reactor alone. The highest decomposition efficiency, 98.0% was achieved at the concentration of 100 ppm.

• Journal of the Korean Magnetics Society
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• v.5 no.4
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• pp.304-308
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• 1995

In order to measure magnetic field difference, we have constructed a fluxgate magnetometer which is based on the measurement of apparent coreci ve field strength from the magnetizing current of two sensors. 'Co-based amorphous ribbon, which has square shape of ac hysteresis loop, was used as core material. Two sensors have 315 turns of the primary and the secondary windings respectively, and core size of 2 mm wide and 30 mm long. The primary windings are connected parallel to measure external magnetic field difference and the secondary windings serieally for the averaged magnetic induction of the cores. The constructed magnetometer could measure magnetic field difference with sensitivity of $1.6{\times}10^{6}V/T$ and resolution of 1 nT at 1 Hz bandwidth.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.2
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• pp.54-58
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• 2007

This paper describes an atomic force microscope (AFM)-based instrument for measuring the nanoscale cutting edge profiles of diamond cutting tools. The instrument consists of a combined AFM unit and an optical sensor to align the AFM tip with the top of the diamond cutting tool edge over a submicron range. In the optical sensor, a aser beam is emitted from a laser diode along the Y-axis and focused to a small beam spot with a diameter of approximately $10{\mu}m$ at the beam waist, which is then received by a photodiode. The top of the tool edge is first brought into the center of the beam waist by adjusting it in the X-Z-plane while monitoring the variation in the photodiode output. The cutting tool is then withdrawn and its top edge position at the beam center is recorded. The AFM tip can also be positioned at the beam center in a similar manner to align it with the top of the cutting edge. To reduce electronic noise interference on the photodiode output and thereby enhance the alignment accuracy, a technique is applied that can modulate the photodiode output to an AC signal by driving the laser diode with a sinusoidal current. Alignment experiments and edge profile measurements of a diamond cutting tool were carried out to verify the performance of the proposed system.

• Journal of the Korean Electrochemical Society
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• v.2 no.4
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• pp.202-208
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• 1999

Composite cathodes of $50/50\;vol\%$ LSM-YSZ $(La_{-x}Sr_xMnO_3-yttria\;stabilized\;zirconia)$ were deposited onto dense YSZ electrolytes by colloidal deposition technique. The cathode characteristics were then examined by scanning electron microscopy (SEM) and studied by ac-impedance spectroscopy (IS). The conditioning effects on LSM-YSZ cathodes were seen and remedies for these effects were noted in order to improve the performance of a solid oxide fuel cell (SOFC). The effects of temperature on impedance, surface contamination on cathode bonding to YSZ electrolyte, changing Pt paste, aerosol spray technique applied to curved surface on microstructure and cell to cell variability were solved by testing at $900^{\circ}C$, sanding the YSZ surface, using only one batch of Pt paste, using flat YSZ plates and using consistent procedures and techniques, respectively. And then, reproducible impedance spectra were confirmed by using the improved cell and the typical spectra measured for an (air)LSM-YSZ/YSZ/LSM-YSZ(air) cell at $900^{\circ}C$ were composed of two depressed arcs. Impedance characteristics of the LSM-YSZ cathodes were also affected by experimental conditions such as catalytic interlayer, composite cathode compositions and applied current.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1682-1691
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• 2018

Natural ester is a suitable substitute for mineral oil and has been widely used in AC transformer in many countries. In order to further application of natural ester in direct current (DC) equipment, it is needed to investigate its long term insulation property under DC condition. In this paper, a thermal ageing experiment was conducted for both mineral oil-paper and natural ester-paper insulation. The DC breakdown and space charge characteristics of insulation paper impregnated with natural ester and mineral oil was compared. Results show that the resistivity of the paper immersed in natural ester and mineral oil both increase as the ageing goes on. While insulation paper impregnated with natural ester has higher resistivity and DC breakdown voltage than the paper impregnated with mineral oil. The DC breakdown voltage for the oil impregnated insulation paper being DC pre-stressing is higher than that without pre-stressing. The average DC breakdown field strength difference between the test with pre-stressing and without pre-stressing clearly shows that there is an apparent enhancement effect for the homo-charge injection on the DC breakdown.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.4
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• pp.38-46
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• 1999

Measurerments of ultrasonic signals caused by corona discharges were perforrred by using an ultrasonic meeasurerment technique to analyze the deve1qxrent states of coronas in a high-voltage power apparatus. We also examined the relationship between discharge magnitude and ultrasonic pulse number to diagnose the deterioration of electrical insulation by corona discharges. From these results, it was found that ultrasonic signals due to corona discharges can be firstly detected at the peak value of positive polarities prior to the breakdown voltages, and the magnitude of ultrasonic signals was closely related to the current pulses by the corona discharges when ac voltages were gradually raised, and it appeared that ultrasonic pulse number was proportional to discharge magnitude. Attenuation, tirre-delaying and directivity charocteristics of ultrasonic signals propagated to air by using ultrasonic oscillation and receiving systems are feJXlrt.ed as a basic data of ultrasonic measurements in out-door HV apparatus.aratus.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.545-549
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• 2001

We have produced electrolyte solution out of 1.15M LiPF$\sub$6/ EC/EMC/DEC/PC(30/55/10/5 by vol%) as a reference, and at the same time, performed basic physical property test using a single solvent of 1.15M LiPF$\sub$6/DEC, DMC, EMC and a 2 component electrolyte solution of 1.15M LiPF$\sub$6/ EC/DEC(1/2 by vo%%) and PC/DEC(1/2 by vol%). Cyclic Voltammetry Analysis showed that, compared to existing carbonate organic solvent, the addition of DEC, DMC and EMC brought the de-decomposition peak of salt anion of PF$\sub$6/$\^$-/ and the solvent at lower oxidization potential of 2.3V, 0.7V and 2.1V(vs. Li/Li$\^$+/\`). In addition, a kinetics current peak, in which intercalation of Li$\^$+/ is proceeded at 750mv, 450mv(vs. Li/Li$\^$+/), was confirmed. These findings suggest that the DEC solvent decomposition occurred at an electric potential lower than that of oxidization of existing carbonate organic solvent. Through the impedance analysis, we checked electric charge transfer resistance(R$\sub$ct/) according to the electric potential of Li$\^$+/ intercalation at 750mv(vs. Li/Li$\^$+/), which was the same as the resistance (R$\sub$f/) and cyclic voltammetry of SEI film that was formed at Reference. By doing so, we found that the significant decrease of polarization resistance(R$\sub$p/) when Reference was played a part in the formation of compact SEI layer at the initial decomposition reaction.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.1
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• pp.46-54
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• 2008

In this paper, a low-cost impedance spectroscopy system(LCISS) suitable for modeling the electrochemical power sources such as fuel cells, batteries and supercapacitors is designed and implemented. Since the developed LCISS is composed of simple sensor circuits, commercial data acquisition board and LabVIEW software, a graphic language with powerful HMI(Human-Machine Interface), it is expected ta be widely used in substitution of the expensive EIS instruments. In the proposed system, the digital lock-in amplifier is adopted to achieve the accurate measurements even in the presence of the high level of noises. The developed hardware and software is applied to measure the impedance spectrum of the Ballard Nexa 1.2kW proton exchange membrane fuel cell stack and an equivalent impedance model is proposed based on the measurement results. The validity of the proposed equivalent circuit and the developed system is proven by the measurement of the ac power losses of the PEM fuel celt stack by the ripple current.

• Journal of Sensor Science and Technology
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• v.25 no.1
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• pp.1-7
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• 2016

Bioelectrical impedance (BI) at popliteal regions was measured using a bioelectrical impedance measurement system (BIMS), which employs the multi-frequency and the two-electrode method. Experiments were performed as follows. First, a constant AC current of $800{\mu}A$ was applied to the popliteal regions (left and right) and the BI was measured at eight different frequencies from 10 to 500 kHz. When the applied frequency greater than 50 kHz was applied to human's popliteal regions, the BI was decreased significantly. Logarithmic plot of impedance vs. frequency indicated two different mechanisms in the impedance phenomena before and after 50 kHz. Second, the relationship between resistance and reactance was obtained with respect to the applied frequency using BI (resistance and reactance) acquired from the popliteal regions. The phase angle (PA) was found to be strongly dependent on frequency. At 50 kHz, the PA at the right popliteal region was $7.8^{\circ}$ slightly larger than $7.6^{\circ}$ at the left popliteal region. Third, BI values of extracellular fluid (ECF) and intracellular fluid (ICF) were calculated using BIMS. At 10 kHz, the BI values of ECF at the left and right popliteal regions were $1664.14{\Omega}$ and $1614.08{\Omega}$, respectively. The BI values of ECF and ICF decreased sharply in the frequency range of 10 to 50 kHz, and gradually decreased up to 500 kHz. Logarithmic plot of BI vs. frequency shows that the BI of ICF decreased noticeably at high frequency above 300 kHz because of a large decrease in the capacitance of the cell membrane.