• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.11a
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• pp.109-111
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• 2007

Pulsed DC 마그네트론 스퍼터링 장치를 이용하여 Polymer 및 Glass 기판 위에 $SiN_{\chi}$ (Silicon Nitride) 박막을 합성 시키고 이들의 구조적, 광학적 특성을 조사하였다. 막두께는 100 nm로 고정하였으며, power mode 및 질소 가스 유량비를 변수로 합성하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.320-320
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• 2016

Nanocrystalline Carbon thin films have numerous applications in different areas such as mechanical, biotechnology and optoelectronic devices due to attractive properties like high excellent hardness, low friction coefficient, good chemical inertness, low surface roughness, non-toxic and biocompatibility. In this work, we studied the comparison of pure DC power and pulsed DC power in plasma sputtering process of carbon thin films synthesis. Using a close field unbalanced magnetron sputtering system, films were deposited on glass and Si wafer substrates by varying the power density and pulsed DC frequency variations. The plasma characteristics has been studied using the I-V discharge characteristics and optical emission spectroscopy. The films properties were studied using Raman spectroscopy, Hall effect measurement, contact angle measurement. Through the Raman results, ID/IG ratio was found to be increased by increasing either of DC power density and pulsed DC frequency. Film deposition rate, measured by Alpha step measurement, increased with increasing DC power density and decreased with pulsed DC frequency. The electrical resistivity results show that the resistivity increased with increasing DC power density and pulsed DC frequency. The film surface energy was estimated using the calculated values of contact angle of DI water and di-iodo-methane. Our results exhibit a tailoring of surface energies from 52.69 to $55.42mJ/m^2$ by controlling the plasma parameters.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.40-42
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• 2002

Electromigration is atomic diffusion driven by a momentum transfer from conducting electrons. With every new generation of intergrated circuits, interconnect line widths have been reduced and current densities in the interconnect have become higher. This leads to an increase in the threat to interconnect reliability due to electromigration. In this paper, we simulated stress evolution with changing temperature, duty factor(ratio of on time and pulse time), frequency under pulsed DC condition. As a result, we predict MTF(median time to failure) and found that exponent n is affected by changing temperature, duty factor.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.311-311
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• 2012

Boron carbide (B-C) 박막은 높은 경도, 열적 안전성, 화학적 안전성이 우수한 하드 코팅 소재로 사용되고 있다. 우수한 특성을 가지는 B-C 박막에 대한 연구는 B4C 비전도성 타겟을 이용하여 RF Sputtering 법으로 증착 공정변수에 대해서 박막의 물성에 관해 일부 연구자들이 진행하였으나, Pulsed dc margnetron sputtering 법으로 증착 공정변수에 대한 물성의 연구는 미진하였다. 반면에, DLC 박막은 우수한 특성을 가지는 하드 코팅 소재이나 400도 이상에서는 내열성이 떨어지는 단점을 가지고 있다. 연구에서는 B-C 박막의 내열성이 우수한 특성을 이용하여 DLC 박막의 내열성을 높이기 위한 목적으로 B-C 박막과 DLC 박막을 다층막으로 제조함으로서 DLC 박막을 구조적으로 안정화를 시키고자 하였다. 그리고 비전도성 B4C 타겟으로 Pulsed dc 마그네트론 스퍼터링법을 이용하여 증착기술을 개발하기 위해서 공정압력과 인가전력에 따른 B-C 박막을 제조하여 그 물성을 조사하였고, B-C/DLC 다층막을 제조하여 DLC 박막의 내열성을 증가시키고자 하였다. B-C 박막과 B-C/DLC 다층막의 경도와 탄성율은 나노인덴테이션과 마이크로 비커스를 이용하였으며, 박막의 성장구조와 박막의 구조를 조사하기 위해 SEM과 FTIR 및 XRD 을 이용하여 측정하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.44-48
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• 2013

Niobium oxide($Nb_2O_5$) films were deposited on p-type Si wafers at room temperature using in-line pulsed-DC magnetron sputtering system with various frequencies. The different duty ratios were obtained by varying the frequency of pulsed DC power from 100 to 300 kHz at the fixed reverse time of $1.5{\mu}s$. From the thickness of the sputtered $NbO_x$ films, it was possible to obtain much higher deposition rate in case of pulsed-DC sputtering than RF sputtering. However, the similar leakage currents and structural characteristics were obtained from the metal-insulator-semiconductor(MIS) structure fabricated with the $NbO_x$ films and the x-ray photoelectron spectroscopy(XPS) results in spite of the different deposition rates. From the experimental results, the $NbO_x$ films sputtered by pulsed-DC sputtering are expected to be used in the fabrication process instead of RF sputtering.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.67-67
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• 2011

Pulsed DC $BCl_3/SF_6$ 플라즈마를 사용하여 GaAs와 AlGaAs의 건식 식각을 연구하였다. 식각 공정 변수는 가스 유량 (50~100 % $BCl_3$ in $BCl_3/SF_6$), 펄스 파워 (450~600 V), 펄스 주파수 (100~250 KHz), 리버스 시간 (0.4~1.2 ${\mu}s$)이었다. 식각 공정 후 표면 단차 측정기 (Surface profiler)를 사용하여 표면의 단차와 거칠기를 분석하였다. 그 결과를 이용하여 식각률 (Etch rate), 표면거칠기 (Surface roughness), 식각 선택비 (Selectivity)와 같은 특성 평가를 하였다. 실험 후 주사 현미경 (FE-SEM, Field Emission Scanning Electron Microscopy)을 이용, 식각 후 시료의 단면과 표면을 관찰하였다. 실험 결과에 의하면 1) 18 sccm $BCl_3$ / 2 sccm $SF_6$, 500 V (Pulsed DC voltage), 0.7 ${\mu}s$ (Reverse time), 200 KHz (Pulsed DC frequency), 공정 압력이 100 mTorr인 조건에서 GaAs와 Al0.2Ga0.8As의 식각 선택비가 약 48:1로 우수한 결과를 나타내었다. 2) 펄스 파워 (Pulsed DC voltage), 리버스 시간(Reverse time), 펄스 주파수(Pulsed DC frequency)의 증가에 따라 각각 500~550 V, 0.7~1.0 ${\mu}s$, 그리고 200~250 KHz 구간에서 AlGaAs에 대한 GaAs의 선택비가 감소하게 되는 것을 알 수 있었다. 이는 척 (chuck)에 인가되는 전류와 파워를 증가시키고, 따라서 GaAs의 식각률이 크게 증가했지만 AlGaAs 또한 식각률이 증가하게 되면서 GaAs에 대한 식각 선택비가 감소한 것으로 생각된다. 3) 표면 단차 측정기와 주사전자현미경 사진 결과에서는 GaAs의 경우 10% $SF_6$ (18 sccm $BCl_3$ / 2 sccm $SF_6$)가 혼합된 조건에서 상당히 매끈한 표면 (RMS roughness < 1.0 nm)과 높은 식각률 (~0.35 ${\mu}m$/min), 수직의 식각 측벽 확보에서 매우 좋은 결과를 보여주었다. 또한 같은 공정 조건에서 AlGaAs는 식각이 거의 되지 않은 결과 (~0.03 ${\mu}m$/min)를 보여주었다. 위의 결과들을 종합해 볼 때 Pulsed DC $BCl_3/SF_6$ 플라즈마는 GaAs와 AlGaAs의 선택적 식각 공정에서 매우 우수한 공정 결과를 나타내었다.

• IMMUNE NETWORK
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• v.10 no.6
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• pp.206-211
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• 2010

Background: Dendritic cell (DC)-based tumor vaccine is an attractive modality for the treatment of colon cancer because it has been recurred and produced few side effects in patients. Secretory glycoprotein 90K has been found at elevated level in various cancer tissues and sera. We investigated to establish a more effective DC vaccine for the treatment of colon cancer in which the levels of 90K are elevated. Methods: We obtained the concentrated 90K from 293T cells stably expressing 90K. DCs were cultured from peripheral blood monocytes, and a DC vaccine pulsed with tumor lysate was compared with a DC vaccine pulsed with 90K. We measured the functional activity for CTLs by using IFN-${\gamma}$-enzyme linked immunoabsorbent spot (ELISPOT) assay. Results: DCs pulsed with tumor lysate+90K exhibited the enhanced T cell stimulation, polarization of $\ddot{i}$ T cell toward Th1. The CTLs generated by DCs pulsed with 90K efficiently lysed HCT116 cells. The results indicate that 90K-speicifc-CTLs can recognize 90K proteins naturally presented by colon cancer cells. Conclusion: Our study suggests that 90K-specific CTLs generated by 90K-pulsed DCs could be useful effector cells for immunotherapy in colon cancer.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.4
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• pp.265-272
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• 2018

This paper proposes a new control method for the supercapacitor (SC) to compensate the pulsed load and to enhance the power quality of the DC microgrid. By coordinating the operating frequency, the SC is controlled to handle the surge current, while the low-frequency current component is dealt with by the remaining sources in the system. The operation mode of the SC unit is automatically changed based on the state of charge and DC bus voltage level. Meanwhile, the mismatch in the power demand is covered by the SC unit by regulating the DC bus voltage level. The effectiveness of the proposed method is verified experimentally by the prototype with two distributed generators and one SC unit.

• IMMUNE NETWORK
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• v.3 no.4
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• pp.295-301
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• 2003

Background: Carcinoembryonic antigen (CEA) is well-known soluble tumor marker frequently detectable in peripheral blood of carcinoma patients and considered as good target for antigen-specific immunotherapy. In this study, we used a replication-deficient adenovirus containing CEA to study CTL induction in vitro after adenovirus-mediated gene transfer into DC. Methods: DC were obtained from mouse bone marrow and cultured with IL-4 and GM-CSF. For measuring CTL activity, splenocytes were harvested from the mice, which were immunized with DC that had been infected AdV-CEA or pulsed with CEA peptide. Untreated DC was used as a control. Splenocytes were re-stimulated in vitro with DC pulsed with CEA peptide for 7 days and CTL activity with CEA peptide-pulsed EL-4 cells were assessed in a standard $^{51}Cr$-release assay. The frequencies of antigen-specific cytokine-secreting T cell were determined with $mIFN-{\gamma}$ELISPOT. Results: DC infected with recombinant adenovirus expressing CEA induced CEA-specific CTL responses in vivo. Splenocyte induced from mice immunized with AdV-CEA-infected DC increase in the number of $IFN-{\gamma}$ secreting T cells compared with those from mice immunized with CEA peptide-pulsed DC. Conclusion: These results suggested that DC infected with recombinant adenovirus has advantages over other forms of vaccination and could provide an alternative approach vaccination therapies.

• Journal of the Semiconductor & Display Technology
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• v.17 no.4
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• pp.32-36
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• 2018

For various oxygen($O_2$) to argon(Ar) gas ratio, aluminum-doped zinc oxide(AZO) films were deposited for 3 min at different duty ratio by changing reverse pulse times. As the duty ratio increased, the thickness of the AZO film decreased and the sheet resistance increased. It can be concluded that When sputtering AZO Thin film, oxygen interfered with sputtering. When the reverse time was increased, the thickness of AZO was proportional to the real sputtering time and decreased. From the optical transmittance and sheet resistance, it was possible to obtain a higher figure of merits of AZO at a lower reverse pulse time. Even at the short reversed pulse time, it can be concluded that the accumulated charges on the AZO target are completely cleared. At a lower reverse pulse time, pulsed-DC sputtering of AZO is expected to be used instead of DC sputtering in the deposition of transparent conductive oxide(TCO) films without any degradation in thickness and structural/electrical characteristics.