• Resources Recycling
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• v.30 no.2
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• pp.14-23
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• 2021

To investigate the potential for leaching of heavy metals by bacteria from ores stacked on actual mining sites, leaching tests of a complex metallic ore (Pb-Zn-As ore) were conducted over 60 days using acidophile bacteria Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans under initial acidic conditions. Initially, a small amount of heavy metals was leached due to the initial acidic conditions. After 20 days, when A. thiooxidans in the reactor was adapted to the ore, the amount of leached heavy metals rapidly increased; the concentrations of leached arsenic, iron, and zinc reached a maximum of 2800, 3700, and 2500 mg/L, respectively. On the other hand, in the presence of A. ferrooxidans or in the control test without bacteria, heavy metals, except zinc, were barely detected in leaching. Through this study, it was confirmed that (i) bacteria could leach heavy metals at mining sites under acidic conditions and (ii) leaching of heavy metals from a high arsenic-containing ore by A. thiooxidans was more significant than that by A. ferrooxidans.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.1
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• pp.9-15
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• 2019

Here, we present a facile route to fabricate a vertically stacked 3D porous structure-based triboelectric nanogenerator (TENG) that can be used to harvest energy from the friction in a repetitive contact-separation mode. The unit component of TENG consists of thin Al foil electrodes integrated with microstructured 3D foams such as Ni, Cu, and polyurethane (PU), which provide advantageous tribo-surfaces specifically to increase the friction area to the elastomeric counter contact surfaces (i.e., polydimethylsiloxane, PDMS). The periodic contact/separation-induced triboelectric power generation from a single unit of the 3D porous structure-based TENG was up to $0.74mW/m^2$ under a mild condition. To demonstrate the potential applications of our approach, we applied our TENGs to small-scale devices, operating 48 LEDs and capacitors. We envision that this energy harvesting technology can be expanded to the applications of sustainably operating portable electronic devices in a simple and cost-effective manner by effectively harvesting wasted energy resources from the environment.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.3
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• pp.9-15
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• 2021

Miniaturization of semiconductor devices has recently faced a physical limitation. To overcome this, 3D packaging in which semiconductor devices are vertically stacked has been actively developed. 3D packaging requires three unit processes of TSV, wafer grinding, and bonding, and among these, copper bonding is becoming very important for high performance and fine-pitch in 3D packaging. In this study, the effects of Ti nanolayer on the antioxidation of copper surface and low-temperature Cu bonding was investigated. The diffusion rate of Ti into Cu is faster than Cu into Ti in the temperature ranging from room temperature to 200℃, which shows that the titanium nanolayer can be effective for low-temperature copper bonding. The 12nm-thick titanium layer was uniformly deposited on the copper surface, and the surface roughness (R_q) was lowered from 4.1 nm to 3.2 nm. Cu bonding using Ti nanolayer was carried out at 200℃ for 1 hour, and then annealing at the same temperature and time. The average shear strength measured after bonding was 13.2 MPa.

• Journal of the Korean Association of Geographic Information Studies
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• v.23 no.4
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• pp.52-67
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• 2020

Recently, the Arctic has been exposed to snow-covered land due to melting permafrost every year, and the Korea Geographic Information Institute(NGII) provides polar spatial information service by establishing spatial information of the polar region. However, there is a lack of spatial information on vegetation sensitive to climate change. This research used a multi-temporal Sentinel-2 image to perform land cover classification of the Ny-Ålesund in Arctic Svalbard. In the pre-processing step, 10 bands and 6 vegetation spectral index were generated from multi-temporal Sentinel-2 images. In image-classification step is consisted of extracting the vegetation area through 8-class land cover classification and performing the vegetation species classification. The image classification algorithm used Random Forest to evaluate the accuracy and calculate feature importance through Out-Of-Bag(OOB). To identify the advantages of multi- temporary Sentinel-2 for vegetation classification, the overall accuracy was compared according to the number of images stacked and vegetation spectral index. Overall accuracy was 77% when using single-time Sentinel-2 images, but improved to 81% when using multi-time Sentinel-2 images. In addition, the overall accuracy improved to about 83% in learning when the vegetation index was used additionally. The most important spectral variables to distinguish between vegetation classes are located in the Red, Green, and short wave infrared-1(SWIR1). This research can be used as a basic study that optimizes input characteristics in performing the classification of vegetation in the polar regions.

• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.180-186
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• 2011

Isothermal annealing and electromigration tests were performed at $125^{\circ}C$ and $125^{\circ}C$, $3.6{\times}10_4A/cm^2$ conditions, respectively, in order to compare the growth kinetics of the intermetallic compound (IMC) in the Cu/thin Sn/Cu bump. $Cu_6Sn_5$ and $Cu_3Sn$ formed at the Cu/thin Sn/Cu interfaces where most of the Sn phase transformed into the $Cu_6Sn_5$ phase. Only a few regions of Sn were not consumed and trapped between the transformed regions. The limited supply of Sn atoms and the continued proliferation of Cu atoms enhanced the formation of the $Cu_3Sn$ phase at the Cu pillar/$Cu_6Sn_5$ interface. The IMC thickness increased linearly with the square root of annealing time, and increased linearly with the current stressing time, which means that the current stressing accelerated the interfacial reaction. Abrupt changes in the IMC growth velocities at a specific testing time were closely related to the phase transition from $Cu_6Sn_5$ to $Cu_3Sn$ phases after complete consumption of the remaining Sn phase due to the limited amount of the Sn phase in the Cu/thin Sn/Cu bump, which implies that the relative thickness ratios of Cu and Sn significantly affect Cu-Sn IMC growth kinetics.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.4
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• pp.119-125
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• 2020

Transition metal dichalcogenides (TMDCs), two-dimensional atomic layered materials with direct bandgap in the range of 1.1-2.1 eV, have attracted a lot of research interest due to their high response to light and capability to build new types of artificial heterostructures. However, the large-area synthesis of high-quality and uniform TMDC films with vertical-stacked heterostructure still remains challenge. In this study, we have developed a metal-organic chemical vapor deposition (MOCVD) system for TMDCs and conducted a systematic study on the growth of single-layer TMDCs and their heterostructures. In particular, using a bubbler-type organometallic compound sources, the concentration and flow rate of each source can be precisely controlled to obtain uniformly single-layered MoS2 and WS2 films over the centimeter scale. In addition, the MoS2/WS2 vertical heterostructure was achieved by growing WS2 film directly on the MoS2 film, as confirmed by electron microscopy, UV-visible spectrophotometer, Raman spectroscopy, and photoluminescence spectroscopy.

• The Korean Journal of Applied Statistics
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• v.34 no.3
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• pp.427-438
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• 2021

Two-stage sampling allows us to estimate population characteristics by both unit and cluster level together. Given a complex auxiliary information, integrated calibration weighting would better reflect the level-wise characteristics as well as multivariate characteristics between levels. This paper explored the integrated calibration weighting methods by Estevao and Särndal (2006) and Kim (2019) through a simulation study, where the efficiency of those weighting methods was compared using an artificial population data. Two weighting methods among others are shown efficient: single step calibration at the unit level with stacked individualized auxiliary information and iterative integrated calibration at each level. Under both methods, cluster calibrated weights are defined as the average of the calibrated weights of the unit(s) within cluster. Both were very good in terms of the goodness-of-fit of estimating the population totals of mutual auxiliary information between clusters and units, and showed small relative bias and relative mean square root errors for estimating the population totals of survey variables that are not included in calibration adjustments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.5
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• pp.719-730
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• 2021

We have demonstrated a sandwich-type ZnO-based piezoelectric energy harvesting nanogenerator, namely ZCZ-NG device, composed of symmetrically stacked layers of ZnO/carbon tape/ZnO structure. Especially, we have adopted a conductive double-sided adhesive carbon tape in an effort to fabricate a high-quality ZCZ-NG device, leading to its superior output performance in terms of the peak-to-peak output voltage. Effects of the device size, ZnO layer thickness, and bending strain rate on the device performance have been investigated by measuring the output voltage. Moreover, to evaluate the effectiveness of the fabricated ZCZ-NG devices, we have experimentally implemented a sensor network testbed which can utilize the output voltages of ZCZ-NG devices. This sensor network testbed consists of several components such as Arduino-based transmitter and receiver nodes, wirelessly transmitting the sensed information of each node. We hope that this research combining the ZnO-based energy harvesting devices and IoT sensor networks will contribute to the development of more advanced energy harvester-driven IoT sensor networks in the future.

• Journal of Dental Rehabilitation and Applied Science
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• v.37 no.4
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• pp.199-208
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• 2021

Purpose: The purpose of this study was to compare and evaluate the masking ability of three types of high translucent zirconia according to the various thicknesses and backgrounds. Materials and Methods: Using three types of high-translucency zirconia (Ceramill zolid fx white, Ceramill zolid ht+ white, Ceramill zolid ht+ preshade A2), 10 cylindrical specimens were fabricated in 10mm diameter and each with four thicknesses (0.6 mm, 1.0 mm, 1.5 mm, 2.0 mm), respectively by CAD/CAM method. The background was 10 mm in diameter and 10 mm in thickness. A1, A2, A3 flowable resin backgrounds, blue-colored core resin background, and Ni-Cr alloy background were prepared, and black, white backgrounds provided by the spectrophotometer manufacturer (x-rite, Koblach, Austria) were used. zirconia specimens and the background specimen were stacked to measure L, a^*, b^* with Spectrophotometer (Color i5, x-rite, Koblach, Austria) and the ΔE value with the other background is calculated. The Calculated mean ΔE values were compared based on perceptibility threshold 1.0 and acceptability threshold 3.7. Nonparametric tests such as Kruskal-Wallis test were performed to verify statistical significance (α = 0.05). Results: There was a significant difference in the mean ΔE value according to the zirconia type, background and thickness change (P = 0.000). Conclusion: According to the results of this study, the pre-colored high-translucent zirconia can obtain the desired zirconia shade when it is restored on teeth, composite resins, and abutments except for the blue resin core.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.3
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• pp.25-29
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• 2022

Recently, the importance of electronic packaging technology has been attracting attention, and heterogeneous integration technology in which chips are stacked out-of-plane direction is being applied to the electronic packaging field. The 2.5D integration circuit is a technology for stacking chips using an interposer including TSV, and is widely used already. Therefore, it is necessary to make the interposer mechanically reliable in the packaging process that undergoes various thermal processes and mechanical loadings. Considering the structural characteristics of the interposer on which several thin films are deposited, thermal stress due to the difference in thermal expansion coefficients of materials can have a great effect on reliability. In this study, the mechanical reliability of the metal pad for wire bonding on the silicon interposer against thermal stress was evaluated. After heating the interposer to the solder reflow temperature, the delamination of the metal pad that occurred during cooling was observed and the mechanism was investigated. In addition, it was confirmed that the high cooling rate and the defect caused by handling promote delamination of the metal pads.