• Journal of the Semiconductor & Display Technology
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• v.10 no.3
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• pp.67-74
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• 2011

In this study, we have investigated the effect of the substrate temperature on the structural and the electrical characteristics of IZO thin films for the OLED (organic light emitting diodes) devices. For this purpose, IZO thin films were deposited by RF magnetron sputtering under various substrate temperature. The substrate temperature has been changed from room temperature to $400^{\circ}C$. Samples which were deposited under $250^{\circ}C$ show amorphous structure. The electrical resistivity of crystalline-IZO (c-IZO) film was higher than that of amorphous-IZO (a-IZO) film. And the electrical resistivity showed minimum value near $150^{\circ}C$ of deposition temperature. The OLED device was fabricated with different IZO substrates made by configuration of IZO/$\acute{a}$-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of IZO substrate. OLED devices with the amorphous-IZO (a-IZO) anode film show better current density-voltage-luminance characteristics than that of OLED devices with the commercial crystalline-ITO (c-ITO) anode film. It can be explained that very flat surface roughness and high work function of a-IZO anode film lead to more efficient hole injection by reduction of interface barrier height between anode and organic layers. This suggests that a-IZO film is a promising anode materials substituting conventional c-ITO anode in OLED devices.

• Journal of the Optical Society of Korea
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• v.13 no.1
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• pp.65-74
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• 2009

Device quality indium tin oxide (ITO) films are deposited on glass substrates and ultra-thin diamond-like carbon films are deposited as a buffer layer on ITO by a pulsed Nd:YAG laser at 355 nm and 532 nm wavelength. ITO films deposited at room temperature are largely amorphous although their optical transmittances in the visible range are > 90%. The resistivity of their amorphous ITO films is too high to enable an efficient organic light-emitting device (OLED), in contrast to that deposited by a KrF laser. Substrate heating at $200^{\circ}C$ with laser wavelength of 355 nm, the ITO film resistivity decreases by almost an order of magnitude to $2{\times}10^{-4}\;{\Omega}\;cm$ while its optical transmittance is maintained at > 90%. The thermally induced crystallization of ITO has a preferred <111> directional orientation texture which largely accounts for the lowering of film resistivity. The background gas and deposition distance, that between the ITO target and the glass substrate, influence the thin-film microstructures. The optical and electrical properties are compared to published results using other nanosecond lasers and other fluence, as well as the use of ultra fast lasers. Molecularly doped, single-layer OLEDs of ITO/(PVK+TPD+$Alq_3$)/Al which are fabricated using pulsed-laser deposited ITO samples are compared to those fabricated using the commercial ITO. Effects such as surface texture and roughness of ITO and the insertion of DLC as a buffer layer into ITO/DLC/(PVK+TPD+$Alq_3$)/Al devices are investigated. The effects of DLC-on-ITO on OLED improvement such as better turn-on voltage and brightness are explained by a possible reduction of energy barrier to the hole injection from ITO into the light-emitting layer.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.41 no.6
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• pp.17-25
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• 2004

In this paper, we propose a new small swing domino logic for low-power consumption. To reduce the power consumption, both the precharge node and the output node swing the range from 0 to $V_{REF}$- $V_{THN}$, where $V_{REF}$=VDD-n $V_{THN}$ (n=1, 2, and 3). This can be done by adding the inverter structure on domino logic that allows a full swing or a small swing on its input terminal without leakage current. Compared to previous works, the proposed structure can save the power consumption of more than 30% for n=0, 1, 2, and 3 in the equation of $V_{REF}$=VDD-n $V_{THN}$. A multiplier applying the proposed domino logic has been designed and fabricated using a 0.35-${\mu}{\textrm}{m}$ n-well CMOS process under 3.3-V supply voltage. Compared with other previous works, it shows a 30% power reduction and a better feature in power-delay product.lay product.

• Journal of the Semiconductor & Display Technology
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• v.10 no.2
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• pp.39-44
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• 2011

In this study, we have investigated the structural and electrical characteristics of IZO thin films deposited on flexible substrate for the OLED (organic light emitting diodes) devices. For this purpose, PES was used for flexible substrate and IZO thin films were deposited by RF magnetron sputtering under oxygen ambient gases (Ar, $Ar+O_2$) at room temperature. In order to investigate the influences of the oxygen, the flow rate of oxygen in argon mixing gas has been changed from 0.1sccm to 0.5sccm. All the samples show amorphous structure regardless of flow rate. The electrical resistivity of IZO films increased with increasing flow rate of $O_2$ under $Ar+O_2$. All the films showed the average transmittance over 85% in the visible range. The OLED device was fabricated with different IZO electrodes made by configuration of IZO/a-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of IZO substrate. OLED devices with the amorphous-IZO (a-IZO) anode film show better current density-voltage-luminance characteristics than that of OLED devices with the commercial crystalline-ITO (c-ITO) anode film. It can be explained that very flat surface roughness and high work function of a-IZO anode film lead to more efficient hole injection by reduction of interface barrier height between anode and organic layers. This suggests that a-IZO film is a promising anode materials substituting conventional c-ITO anode in OLED devices.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.2
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• pp.353-360
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• 2017

Recently, due to physical limitation of Si based power semiconductor, development speed of switching power semiconductors is falling and it is difficult to expect any further performance improvements. SiC based power semiconductor with superior characteristic than Si-based power semiconductor have been developed to overcome these limitations. however, there is not method to apply for real system. Therefore, suggested the feasibility and solution for SiC-based power semiconductor system. design to 1kW class DC-DC boost converter and demonstrated the superiority of SiC MOSFET under the same operating conditions by analyzing switching frequency, duty ratio, voltage and current, and comparing with Si based power semiconductor through experimental efficiency according to each system load. The SiC MOSFET has high efficiency and fast switching speed, and can be designed with small inductors and capacitors which has the advantage of volume reduction of the entire system.

• Journal of Powder Materials
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• v.15 no.2
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• pp.114-118
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• 2008

Functional nanomaterial is expected to have improved capacities on various fields. Especially, metal nanoparticles dispersed in polymer matrix and metal nanofiber, one of the functional nanomaterials, are able to achieve improvement of property in the electric and other related fields. In this study, the fabrication of metal (Ag) nanoparticle dispersed nanofibers were attempted. The Ag nanoparticle dispersed polymer nanofiber and Ag nanofiber were fabricated by electrospinning method using electric force. First, PVP/$AgNO_3$ nanofibers were synthesized by electrospinning in $18{\sim}22kV$ voltage with the starting materials (Ag-nitrate) added polymer (PVP; poly (vinylpyrrolidone)). Then Ag nanoparticle dispersed polymer nanofibers were fabricated to reduce hydrogen reduction at $150^{\circ}C$ for 3hr. And Ag nanofibers were synthesized by the decomposited of PVP at $300{\sim}500^{\circ}C$ for 3hr. The nanofibers were analyzed by XRD, TGA, FE-SEM and TEM. The experimental results showed that the Ag nanofibers could be applied in many fields as an advanced material.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.363-368
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• 2007

Lithium-ion batteries providing high gravimetric energy density are rapidly replacing Ni-Cd and Ni-H2 in aerospace applications. The main advantage is the weight reduction of the battery system. Weight is a major concern in aerospace applications. Also, lithium-ion offer low thermal dissipation, high energy efficiency, and low cell cost. The Onboard battery module for KSLV-I(Korea Space Launch Vehicle) contains 80 Sony US18650 cells configured as 10 strings in parallel, with each string containing 8 series connected cells. This allows to meet voltage and capacity requirements specified for the mission. In this paper design description and specifications of lithium-ion battery developed are presented. Qualification test flow is also shown to make sure the performance in the predicted space environment. Electrical performance was simulated by dedicated program, and verified with electronic load. Lastly, the capacity was proven on real equipment load assembly.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.5
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• pp.416-422
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• 2001

The BLDC(Brushless DC) Motor is characterized by linear torque to current and speed to voltage. It has low acoustic noise and fast dynamic response. Moreover, it has high power density with high proportion of torque to inertia in spite of small size drive. However, when armature current is commutated, the current ripple is generated by the motor inductance components in stator windings and back-EMF. This current ripple caused to torque ripple. Therefore, it is difficult to apply the BLDC motor to a precision servo drive system. In this paper, a new current control algorithm using fourier series coefficients is proposed. This proposed algorithm can minimize torque ripple due to the phase current commutation of BLDC motor. Simulation and Experimental results prove the effectiveness at the Proposed algorithm through comparison with the conventional unipolar PWM method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.9
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• pp.25-31
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• 2008

The field of induction motor is magnetized and demagnetized for each reversal of the current. This field component of the motor accounts for most of the reactive component of inductive load. Reactive power needs to sustain the electromagnetic field required for the induction motor to operate. Power factor of induction motor is usually low and power factor correction needs. Power factor becomes low by the effect of the reduction operation of load capacity. In most cases, Capacitor capacity for the power factor correction should be complied with the recommendation by the motor capacity. But Capacitor value for power factor correction can't change during the normal operation. In this paper, we analyzed characteristics of power and power factor changing by load fluctuation of low-voltage small size induction motor and show that lower power factor correction's parameter of existing recommendation should be revised by new value.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.9
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• pp.82-87
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• 2008

Faster, safer and cheaper mailing of the postal matter is essential for surviving in the competitive market of home-delivery service. In the past, the domestic delivery business has been nu by only a few number of companies. But more and more number of companies including medium size ones are participating in the business, and the competition is getting severe. This paper proposes a method to select the optimal location of mail distribution centers that minimally connect the local mail centers of some major cities in Korea using the Steiner Tree theory, which is about connecting a finite number of points with a minimal length of paths and has been used in the distribution system optimization and optimal routing of the transmission lines of the electric power system. By using Steiner Tree theory in finding the best location of the postal delivery hub, we may expect the reduction of transportation cost and the increase of profit, resulting in acquiring the superior position in the competitive delivery business. It is expected that we may use the Steiner Tree theory in finding the best location of the electric power substation for the nott higher EHV(extreme high voltage) transmission network.