• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.29-29
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• 2009

현재 고집적 비휘발성 메모리 소자로는 MRAM (Magnetic Random Access Memory)과 PRAM (Phase Magnetic Random Access Memory)이 활발하게 미국과 일본, 한국 등에서 다양한 연구가 진행되어 오고 있다. 이 중에서 MRAM은 DRAM과 비슷한 10 ns의 빠른 읽기/쓰기 속도와 비휘발성 특성을 가지고 있으며, 전하를 저장할 커패시터가 필요 없고, 두 개의 자성충에 약 10 mA 정도의 전류를 가하면 그때 발생하는 약 10 Oe의 자장을 개개의 비트를 write하고, read 시에는 각 비트의 자기저항을 측정함으로써 데이터를 저장하고 읽을 있으므로, 고집적화가 가능성하다 [1]. 현재 우수한 박막 재료가 개발 되었으나, 고집적 MRAM 소자의 양산에는 해결 하여야 하는 문제점이 있다. 특히 다층 박막으로 구성되어 있으므로 식각 공정의 개발이 필수적이다. 지금까지 MRAM 재료의 식각은 주로 Ion milling, ICP, ECR등의 플라즈마 장치를 되었고, 식각 가스로는 할로겐 기체와 금속카보닐 형성을 위한 Co/$NH_3$와 $Ch_3OH$ 기체가 이용되고 있다. 그러나 할로겐 계열의 기체를 사용할 경우, 식각 부산물들의 높은 끓는점 때문에 식각 부산물이 박막의 표면에서 열적 탈착에 의하여 제거되지 않기 때문에 높은 에너지를 가지는 이온의 도움에 의한 식각이 필요하다. 또한 Cl 계열의 기체를 사용할 경우, 식각 공정 후, 시료가 대기에 노출되면 대기 중의 수분과 식각 부산물이 결합하여 부식 현상이 발생하게 된다. 그러므로 이를 방지하기 위한 추가 공정이 요구된다. 최근에는 부식 현상이 없고, MTJ 상부에 사용되는 Ta 또는 Ti Hard mask와의 높은 선택비를 가지는 $CH_3OH$ 또는 CO/$NH_3$가 사용되고 있다. 하부 박막에 따른 식각 특성에 연구와 다층의 박막의 식각 공정에 발생에 관한 발표는 거의 없다. MRAM을 양산에 적용하기 위하여서는 Main etch 공정에서 빠른 식각 공정이 필요하고, Over etch 공정에서 하부박막에 대한 높은 선택비가 요구된다. 그러므로 본 논문에서는 식각 변수에 따른 플라즈마 측정과 표면 반응을 비교하여 각 공정의 식각 메커니즘을 규명하고, Main Etch 공정에서는 $Cl_2$/Ar 또는 $BCl_3$/Ar 가스를 이용하여 식각 실험을 수행하고, Over etch 공정에는 낮은 Ta 박막 식각 속도를 가지는 $Ch_4/O_2$/Ar 또는 $Ch_3OH$/Ar 가스를 이용하고자 한다. 플라즈마 내의 식각종과 Ta 박막과의 반응을 XPS와 AES를 이용하여 분석하고, 식각 공정 변수에 따른 식각 속도, 식각 선택비와 식각 프로파일 변화를 SEM을 이용하여 관찰한다.

• Journal of Life Science
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• v.29 no.11
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• pp.1294-1303
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• 2019

Perchlorate is an anionic pollutant that is very soluble and stable in water. It has been detected not only in soil/ground water but also in surface water, drinking water, food, fish, and crops. Perchlorate inhibits iodine uptake by the thyroid gland and reduces production of thyroid hormones that are primarily responsible for regulation of metabolism. Although various technologies have been developed to remove perchlorate from the environment, biodegradation is the method of choice since it is economical and environmentally friendly. However there is limited information on perchlorate biodegradation in salt environment such as salt water. Therefore this paper reviews biodegradation of perchlorate in salt water and related microorganisms. Most biodegradation research has employed heterotrophic perchlorate removal using organic compounds such as acetate as electron donors. Biodegradation research has focused on perchlorate removal from spent brine generated by ion exchange technology that is primarily employed to clean up perchlorate-contaminated ground water. Continuous removal of perchlorate at up to 10% NaCl was shown when bioreactors were inoculated with enriched salt-tolerant perchlorate-reducing bacteria. However the reactors did not show long-term stable removal of perchlorate. Microorganisms belonging to ${\beta}$- and ${\gamma}$-Proteobacteria were dominant in bioreactors used to remove perchlorate from salt water. This review will help our understanding of perchlorate removal from salt water to develop a decent biotechnology for the process.

• Membrane Journal
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• v.32 no.6
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• pp.411-426
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• 2022

Energy plays a significant role in modern lifestyle because of our extensive reliance over energy-operating devices. Therefore, there is a need for alternative and green energy resources that can fulfill the energy demand. For this, fuel cell (FCs) especially anion exchange membrane fuel cells (AEMFCs) have gained tremendous attention over the other (FCs) due to their fast reaction kinetics without using noble catalyst and allow to use of cheaper polymers with high performance. But lack of highly conductive, chemically, and mechanically stable anion exchange membrane (AEM) still main obstacle to the development of high performance AEMFCs. Therefore, graphene-based polymer composite membranes came into the existence as AEMs for the FCs. The exceptional properties of the graphene help to improve the performance of AEMs. Still, there are lot of challenges in the graphene derivatives based AEMs because of their high tendency of agglomeration in polymer matrix which reduced their potential. To overcome this issue surface modification of graphene derivatives is necessary to restrict their agglomeration and conserved their potential features that can help to improve the performance of AEM. Therefore, this review focus on the surface modification of graphene derivatives and their role in the fabrication of AEMs for the FCs.

• Korean Journal of Weed Science
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• v.1 no.1
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• pp.57-68
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• 1981

To clarify the mode of uptake of butachlor (2-chloro-2', 6'-diethyl-N-(butoxymethyl) acetanilide) by rice seedlings, its phytotoxic action to growth and physiological activities, studies were conducted with rice seedlings, at the 6th or 7th leaf-stage, which were treated with nutrient solution containing butachlor 0, 1.8, 3.6, 7.2, 10.8 or 14.4 ppm for 1, 2 or 4 days, in other case, the solutions were thereafter renewed with the untreated nutrient solution for further growth. Uptake of butachlor by rice seedlings increased linearly with increase of its concentration and duration of uptake. Butachlor inhibited root growth more than shoot growth, furthermore, the inhibitory effect on the shoot growth was greater in height than in weight or leafing rate. After 4 day-treatment, the rates of shoot growth in weight were delayed for 4 days. Butachlor inhibited water uptake rapidly and linearly with increase of its external concentration. The reduced uptake of water was followed by slow increase in the stomatal resistance of leaves. Upon completion of butachlor treatment, rate of water uptake was recovered rapidly, but the stomatal resistance with lag in time. Butachlor did not affect the uptake of cation such as ammonium, potassium and calcium, but inhibited substantially uptake of nitrate in proportion to its concentration. Especially, butachlor did not affect synthesis and degradation of nitrate reductase. In addition, butachlor has shown much greater binding to the lipidic substances from rice roots than the proteinous material. The primary mechanism of phytotoxic action of butachlor does not seem to be its effect on the protein synthesis, but great affinity to membranes. The inhibition of water uptake, and its subsequent closure of stomates is thought very important for reduced growth under mild phytotoxicity.

• Korean Journal of Ecology and Environment
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• v.45 no.2
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• pp.158-173
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• 2012

The objectives of this study were to analyze the longitudinal gradient and temporal variations of water quality in Daecheong Reservoir in relation to the major inflowing streams from the watershed, during 2001~2010. For the study, we selected 7 main-stream sites of the reservoir along the main axis of the reservoir, from the headwater to the dam and 8 tributary streams. In-reservoir nutrients of TN and TP showed longitudinal declines from the headwater to the dam, which results in a distinct zonation of the riverine ($R_z$, M1~M3), transition ($T_z$, M4~M6), and lacustrine zone ($L_z$, M7) in water quality, as shown in other foreign reservoirs. Chlorophyll-a (CHL) and BOD as an indicator of organic matter, were maximum in the $T_z$. Concentration of total phosphorus (TP) was the highest (8.52 $mg\;L^{-1}$) on March in the $R_z$, and was the highest (165 ${\mu}g\;L^{-1}$) in the $L_z$ on July. Values of TN was the maximum (377 ${\mu}g\;L^{-1}$) on August in the $R_z$, and was the highest (3.76 $mg\;L^{-1}$) in the $L_z$ on August. Ionic dilution was evident during September~October, after the monsoon rain. The mean ratios of TN : TP, as an indicator of limiting factor, were 88, which indicates that nitrogen is a surplus for phytoplankton growth in this system. Nutrient analysis of inflowing streams showed that major nutrient sources were headwater streams of T1~T2 and Ockcheon-Stream of T5, and the most influential inflowing stream to the reservoir was T5, which is located in the mid-reservoir, and is directly influenced by the waste-water treatment plants. The key parameters, influenced by the monsoon rain, were TP and suspended solids (SS). Empirical models of trophic variables indicated that variations of CHL in the $R_z$ ($R^2$=0.044, p=0.264) and $T_z$ ($R^2$=0.126, p=0.054) were not accounted by TN, but were significant (p=0.032) in the $L_z$. The variation of the log-transformed $I_r$-CHL was not accounted ($R^2$=0.258, p=0.110) by $I_w$-TN of inflowing streams, but was determined ($R^2$=0.567, p=0.005) by $I_w$-TP of inflowing streams. In other words, TP inputs from the inflowing streams were the major determinants on the in-reservoir phytoplankton growth. Regression analysis of TN : TP suggested that the ratio was determined by P, rather than N. Overall, our data suggest that TP and suspended solids, during the summer flood period, should be reduced from the eutrophication control and P-input from Ockcheon-Stream should be controlled for water quality improvement.