• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.69-69
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• 2000

(Ba, Sr)TiO3 (BST)[1-3] 박막은 유전상수가 크고 고주파에서도 유전특성 저하가 적기 때문에 ULSI DRAM(Dynamic Random Access Memory)에 응용 가능한 물질로 최근 각광을 받고 있다. 하지만, 아직 BST 박막을 DRSM에 바로 적용하기 위해선 몇 가지 문제점이 있다. 그 중 누설전류 문제는 디바이스 응용시 매우 중요한 요소이다. 특히, DRAM에서 refresh time와 직접적인 관련이 있어 디바이스 내의 신뢰도 및 전력소모를 결정하는 주된 인자가 된다. 지금까지, BST 박막의 인가전업, 온도, 그리고 전극물질에 따른 누설전류 현상들이 고찰되었고, 이에 관한 많은 전도기구 모델들이 제시되었다. Schottky emission, Poole-Frenkel emission, space charge limited conduction 등이 그 대표적인 예이다. 하지만 아쉽게도 BST 박막의 정확한 누설 전류 전도 기구를 완전히 설명하는데는 아직 한계가 있다. 따라서 본 연구에서는 제작된 BST 커패시터 내의 기본적인 전기적 성질을 조사하고, 정확한 누설전류 기구 규명에 초점을 두고자 한다. 이를 위해 기존의 여러 기구들과 비교 분석할 것이다. 하부전극으로 사용하기 위해 스퍼터링 방법으로 p-Si(100) 기판위에 RuO2 박막을 약 120nm 증착하였다. 증착전의 chamberso의 초기압력은 5$\times$10-6 Torr이하의 압력으로 유지시켰다. Ar/O2의 비는 이전 실험에서 최적화된 9/1로 하였다. BST 박막 증착 시 5분간 pre-sputtering을 실시한 후 하부전극 기판위에 BST 박막을 증착하였다. 증착이 끝난 후 시편을 상온까지 냉각시킨 후 꺼내었다. 전기적 특성을 측정하기 상부전극으로 RuO2와 Al 박막을 각각 상온에서 100nm 증착하였다. 이때 hole mask를 이용하여 반경이 140um인 원형의 상부전극을 증착하였다. BST 박막의 증착온도가 증가하고 Ar/O2 비가 감소할수록 제작된 BST-커패시터의 전기적 성질이 우수하였다. 증착온도 $600^{\circ}C$, ASr/O2=5/5에서 증착된 막의 누설전류는 4.56$\times$10-8 A/cm2, 유전상수는 600 정도의 값을 나타내었다. 인가전압에 따른 BST 커패시터의 transition-current는 Curie-von Schweider 모델을 따랐다. BST 박막의 누설전류 전도기구는 기존의 Schottky 모델이 아니라 modified-Schottky 무델로 잘 설명되었다. Modified-Schottky 모델을 통해 BST 박막의 광학적 유전율 $\varepsilon$$\infty$=4.9, 이동도 $\mu$=0.019 cm2/V-s, 장벽 높이 $\psi$b=0.79 eV를 구하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.448-448
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• 2010

Magnetic random access memory (MRAM) has made a prominent progress in memory performance and has brought a bright prospect for the next generation nonvolatile memory technologies due to its excellent advantages. Dry etching process of magnetic thin films is one of the important issues for the magnetic devices such as magnetic tunneling junctions (MTJs) based MRAM. CoFeB is a well-known soft ferromagnetic material, of particular interest for magnetic tunnel junctions (MTJs) and other devices based on tunneling magneto-resistance (TMR), such as spin-transfer-torque MRAM. One particular example is the CoFeB - MgO - CoFeB system, which has already been integrated in MRAM. In all of these applications, knowledge of control over the etching properties of CoFeB is crucial. Recently, transferring the pattern by using milling is a commonly used, although the redeposition of back-sputtered etch products on the sidewalls and the low etch rate of this method are main disadvantages. So the other method which has reported about much higher etch rates of >$50{\AA}/s$ for magnetic multi-layer structures using $Cl_2$/Ar plasmas is proposed. However, the chlorinated etch residues on the sidewalls of the etched features tend to severely corrode the magnetic material. Besides avoiding corrosion, during etching facets format the sidewalls of the mask due to physical sputtering of the mask material. Therefore, in this work, magnetic material such as CoFeB was etched in an ICP etching system using the gases which can be expected to form volatile metallo-organic compounds. As the gases, carbon monoxide (CO) and ammonia ($NH_3$) were used as etching gases to form carbonyl volatiles, and the etched features of CoFeB thin films under by Ta masking material were observed with electron microscopy to confirm etched resolution. And the etch conditions such as bias power, gas combination flow, process pressure, and source power were varied to find out and control the properties of magnetic layer during the process.

• Korean Journal of Materials Research
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• v.7 no.6
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• pp.505-509
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• 1997

FRAM(Ferroelectric Random Access memory)에의 응용을 위해 rf magnetron sputtering법을 이용하여 SrB $i_{2}$T $a_{2}$ $O_{9}$(SBT)박막을 증착하였다. 사용된 기판은 Pt/Ti/Si $o_{2}$Si이었으며 50$0^{\circ}C$에서 증착한 후 80$0^{\circ}C$의 산소 분위기 하에서 1시간 동안 열처리하였다. 증착시 증착 압력을 변화시켜 가면서 이에 따른 특성의 변화를 고찰하였다. 박막내의 Bi와 Sr의 부족을 보상하기 위해 20mole%의 Bi $O_{2}$와 30mole%의 SrC $O_{3}$를 과잉으로 넣어 타겟을 제조후 사용하였고 박막들의 두께는 300nm의 두께를 가지며 증착압력에 따라 다른 미세 구조르 보였다. 10mtorr에서 증착한 박막의 조성은 S $r_{0.6}$B $i_{3.8}$Ta/ sub 2.0/ $O_{9.0}$이었다. 이 SBT 박막의 잔류 분극(2 $P_{r}$)과 보전계(2 $E_{c}$)값은 각각 인가 전압 5V에서 18.5 $\mu%C/$\textrm{cm}^2$과 150kV/cm이었고, signal/noise비는 3V에서 4.6을 나타내었다. 5V의 bipolar pulse하에서 $10^{10}$cycle까지 피로 현상이 나타나지 않았으며, 누설 전류 밀도는 133kV/cm에서 약 1x$10^{-7A}$$\textrm{cm}^2$의 값을 보였다.을 보였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.5
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• pp.581-588
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• 2019

In this paper, I propose an modified back-off algorithm to improve the fairness for slotted ALOHA sensor networks. In hierarchical networks, the performance degradation of a specific node can cause degradation of the overall network performance in case the data transmitted by lower nodes is needed to be synthesized and processed by an upper node. Therefore it is important to ensure the fairness of transmission performance to all nodes. The proposed scheme choose a back-off time of a node considering the previous transmission results as well as the current transmission result. Moreover a node that failed to transmit consecutively is given gradually shorter back-off time but a node that is success to transmit consecutively is given gradually longer back-off time. Through simulations, I compare and analyze the performance of the proposed scheme with the binary exponential back-off algorithm(BEB). The results show that the proposed scheme reduces the throughput slightly compared to BEB but improves the fairness significantly.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.6
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• pp.15-26
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• 2001

Visual cryptography is a simple method in which secret information can be directly decoded in human visual system without any cryptographic computations. When the secret image is scattered to n random shares(slides), this scheme has some week point such as pixel expansion and contrast degradation. Therefore, it is necessary to reduce the pixel expansion and improve the contrast in recovered image. In this paper, we propose a new construction method for (k, n) visual cryptography using the cumulative matrix. In case k is odd, we can construct the cumulative matrix perfectly. For even k, the contrast of special pair in decoded image can be achieved best by permitting multiple contract. The proposed method is more simple than that of S. Droste\`s in construction and the average contrast of decoded image is improved for the most part. Also, we show that the basis matrices depending on the cumulative matrix are able to be applied for the general access structure.

• Journal of Korea Planning Association
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• v.54 no.2
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• pp.54-66
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• 2019

This study analyzed whether a subway accessibility impact on house price is constant since its operation over time or not. The study was approached specifically to answer two research questions. One is "Are there significant temporal variations in the relationship between subway accessibility and housing price transacted after its opening?" The other one is "How the pattern of its temporal variation in housing price is formed as a function of the distance from the nearest station?" The study area is the subway station areas in the Daejeon metropolitan city, South Korea. Its first subway line has started to be opened in 2006 with 12 stations and then opened its additional 10 stations in 2007. It can be more appropriate to observe its impacts of subway accessibility on housing price because it has only one transit line with more than 10-year reaction term to its operation. The study employed alternative models to estimate yearly variation of subway accessibility on house price for the station areas with 500-meter and 1-kilometer radius respectively. While the study originally considered both a hedonic price model with interaction terms of its access distance to yearly transacted housing and a time-variant random coefficient model, the former model was finally selected because it is better fitted. Based on our analysis results, the reaction of house price to its transit line had significant temporal variation over time after opening. In addition, the pattern in its variation from our analysis results indicates that its capitalization impact on house price is over-estimated in its first several years after the opening. In addition, its positive capitalization impact is more effective in the 1000-meter station area than in the 500-meter one.

• Korean Journal of Clinical Pharmacy
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• v.30 no.4
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• pp.270-278
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• 2020

Background: Although the identification of clinical and laboratory features in pediatric COVID-19 patients is essential in establishing an appropriate treatment plan, a systematic review and meta-analysis on the topic has yet to be reported. Methods: We searched MEDLINE, Embase, and Web of Science to access clinical and laboratory characteristics as well as clinical outcomes of children with COVID-19 infection. A meta-analysis using random-effect model was performed to estimate pooled prevalence and 95% confidence intervals. Results: Among the 532 studies initially collected, 12 articles were finally included in the meta-analysis. Among the investigated 320 pediatric patients with COVID-19, fever (48.2%) and cough (39.3%) were the most common symptoms. Almost one third of patients (30.4%) were asymptomatic. In laboratory findings, only 11.4% of pediatric patients experienced lymphocytopenia. Increased inflammatory markers including c-reactive protein (18.6%) and procalcitonin (32.4%) were observed. Only a few patients needed mechanical ventilation and intensive care support, and only one death was reported. Conclusion: Pediatric patients with COVID-19 infection exhibited milder symptoms and more favorable outcomes compared to adults. However, considering the high rate of asymptomatic pediatric patients, close monitoring is required to prevent community infection in asymptomatic conditions and hidden disease progression.

• KIPS Transactions on Software and Data Engineering
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• v.10 no.11
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• pp.529-534
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• 2021

Computing thinking is regarded as one of the important skills required in the 21st century, and many countries have introduced and implemented computing thinking training courses. Among computational thinking education methods, educational game-based methods increase student participation and motivation, and increase access to computational thinking. Autothinking is an educational game developed for the purpose of providing computational thinking education to learners. It is an adaptive system that dynamically provides feedback to learners and automatically adjusts the difficulty according to the learner's computational thinking ability. However, because the game was designed based on rules, it cannot intelligently consider the computational thinking of learners or give feedback. In this study, game data collected through Autothikning is introduced, and game score prediction that reflects computational thinking is performed in order to increase the adaptability of the game by using it. To solve this problem, a comparative study was conducted on linear regression, decision tree, random forest, and support vector machine algorithms, which are most commonly used in regression problems. As a result of the study, the linear regression method showed the best performance in predicting game scores.

• Safety and Health at Work
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• v.11 no.4
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• pp.526-532
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• 2020

Background: The high incidence of work-related diseases and injuries among day-laborers and workers with no legal contracts (informal workers) has received the attention of the Thai authorities. Workers' low occupational health literacy (OHL) has been reasoned as one contributing factor. Absence of a valid tool has prevented assessment of informal workers' OHL. The aim of this study was to create a valid and reliable Occupational Health Literacy Scale within the context of Thai working culture (TOHLS-IF). Methods: This study used the mixed method approach to develop TOHLS-IF. Questions were generated using in-depth interviews and an extensive review of the literature. Experts' assessment confirmed the content validity of TOHLS-IF. The scales of its psychometric properties were assessed in a sample of 400 informal workers using cluster random sampling. Results: The final version of the TOHLS-IF comprises 38 items within 4 dimensions: Ability to Gain Access, Understanding, Evaluation, and Use of occupational health and safety information. Factor analysis identified items explaining 50.22% of the total variance. The final confirmatory analysis confirmed the model estimates were satisfactory for the construct. TOHLS-IF demonstrated a high internal consistency and satisfactory reliability (Cronbach's alpha = .98). Conclusion: The TOHLS-IF is a valid and reliable instrument to assess informal workers' OHL. The structural dimensions of this instrument are based on the concept of health literacy and Thai culture. Thai health professionals are encouraged to benefit from this instrument to assess their workers' OHL and apply findings as guidelines for effective occupational health and safety interventions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.2
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• pp.435-449
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• 2023

The state-of-the-art video-based point cloud compression(V-PCC) has a high efficiency of compressing 3D point cloud by projecting points onto 2D images. These images are then padded and compressed by High-Efficiency Video Coding(HEVC). Pixels in padded 2D images are classified into three groups including origin pixels, padded pixels and unoccupied pixels. Origin pixels are generated from projection of 3D point cloud. Padded pixels and unoccupied pixels are generated by copying values from origin pixels during image padding. For padded pixels, they are reconstructed to 3D space during geometry reconstruction as well as origin pixels. For unoccupied pixels, they are not reconstructed. The rate distortion optimization(RDO) used in HEVC is mainly aimed at keeping the balance between video distortion and video bitrates. However, traditional RDO is unreliable for padded pixels and unoccupied pixels, which leads to significant waste of bits in geometry reconstruction. In this paper, we propose a new RDO scheme which takes 3D-Distortion into account instead of traditional video distortion for padded pixels and unoccupied pixels. Firstly, these pixels are classified based on the occupancy map. Secondly, different strategies are applied to these pixels to calculate their 3D-Distortions. Finally, the obtained 3D-Distortions replace the sum square error(SSE) during the full RDO process in intra prediction and inter prediction. The proposed method is applied to geometry frames. Experimental results show that the proposed algorithm achieves an average of 31.41% and 6.14% bitrate saving for D1 metric in Random Access setting and All Intra setting on geometry videos compared with V-PCC anchor.