Chemical and Nanomechanical Characteristics of Fluorocarbon Thin Films Deposited by Using Plasma Enhanced Chemical Vapor Deposition

Nam-Kyun Kim,Nam-Goo Cha,박진구,Kyu-Chae Kim,Tae-Gon Kim 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.4

In this study, the chemical and nanomechanical characteristics of fluorocarbon (FC) films deposited by using plasma-enhanced chemical vapor deposition on Al were evaluated to apply them as antistiction layers. The calculated deposition rate with C4F8 was 325 nm/min at an optimized process condition of 10 sccm, 30 W, and 340 mTorr. The contact angles of the FC thin films on Al were around 110, regardless of the deposition time. The surface energies were around 14 mN/m, and the contact angle hysteresis was lower than 35. FTIR-ATR (Fourier transform infrared attenuated total reflection) spectra showed the presence of fluorocarbon groups. The adhesion and friction force after FC film deposition showed lower and more stable values than those of bare Al. Depositing the FC films at powers above 50 W increased the hysteresis, the adhesion force, the roughness and the friction force. The addition of Ar resulted in a decrease in the thickness of the FC film during deposition. The deposited FC films gradually decomposed at 200 C.

접착방지막과 접착막을 동시에 적용한 대면적 Au/Pd 트랜스퍼 프린팅 공정 개발

차남구,Cha, Nam-Goo 한국재료학회 2009 한국재료학회지 Vol.19 No.8

This paper describes an improved strategy for controlling the adhesion force using both the antiadhesion and adhesion layers for a successful large-area transfer process. An MPTMS (3-mercaptopropyltrimethoxysilane) monolayer as an adhesion layer for Au/Pd thin films was deposited on Si substrates by vapor self assembly monolayer (VSAM) method. Contact angle, surface energy, film thickness, friction force, and roughness were considered for finding the optimized conditions. The sputtered Au/Pd ($\sim$17 nm) layer on the PDMS stamp without the anti-adhesion layer showed poor transfer results due to the high adhesion between sputtered Au/Pd and PDMS. In order to reduce the adhesion between Au/Pd and PDMS, an anti-adhesion monolayer was coated on the PDMS stamp using FOTS (perfluorooctyltrichlorosilane) after $O_2$ plasma treatment. The transfer process with the anti-adhesion layer gave good transfer results over a large area (20 mm $\times$ 20 mm) without pattern loss or distortion. To investigate the applied pressure effect, the PDMS stamp was sandwiched after 90$^{\circ}$ rotation on the MPTMS-coated patterned Si substrate with 1-${\mu}m$ depth. The sputtered Au/Pd was transferred onto the contact area, making square metal patterns on the top of the patterned Si structures. Applying low pressure helped to remove voids and to make conformal contact; however, high pressure yielded irregular transfer results due to PDMS stamp deformation. One of key parameters to success of this transfer process is the controllability of the adhesion force between the stamp and the target substrate. This technique offers high reliability during the transfer process, which suggests a potential building method for future functional structures.

리아프노프 함수에 기초한 과학기술위성 2호 펄스형 플라즈마 전기추력기의 동작 안정성 연구

신구환(Goo-Hwan Shin),차원호(Won-Ho Cha),남명용(Myeong-Ryong Nam),강경인(Kyung-In Kang),임종태(Jong-Tae Lim) 한국항공우주학회 2006 韓國航空宇宙學會誌 Vol.34 No.1

펄스형 플라즈마 전기추력기의 설계기술과 제어기법에 있어서는 과거의 기술에 비하여 많은 도약을 하였다. 그리고, 펄스형 플라즈마 전기추력기의 충전된 전기에너지는 추력기구동시 중요한 비중을 차지함을 알 수 있다. 펄스형 플라즈마 전기추력기는 매 분사시 축전기에 충전된 전기에너지를 방전시켜 분사 시키므로서 추력을 얻는 장치이다. 따라서, 매 분사시 균일한 추력을 얻고자 할 경우에는 동작시점에서 균일한 전기 에너지가 충전되어 있어야 한다. 따라서, 본 논문에서는 매 분사시 균일한 추력을 얻기 위한 기법과 축전기와 추력기 엔진간의 기하학적 연결에 따른 안정성을 연구하였다. The PPT being currently developed for the flight model represents a Significant leap in techniques and technology compared to the previous flight ones. The electrical energy to be charged in the pulsed plasma thruster (PPT) is a very important aspect to provide an uniform impulse bit ,Ib, and a specific impulse ,Isp, for satellite attitude control. In this paper, we propose a nonlinear control technique and a stability analysis based on the Lyapunov function for the pulsed plasma thruster. Specifically, the proposed control law guarantees to charge and discharge the electrical energy generated from the power processing unit (PPU) within the specified time.

거울을 이용한 시각적 되먹임 훈련이 편마비 환자의 균형능력에 미치는 효과

지상구 ( Sang Goo Ji ),남기원 ( Gi Won Nam ),김명권 ( Myoung Kyun Kim ),차현규 ( Hyun Kyu Cha ) 대한물리의학회 2011 대한물리의학회지 Vol.6 No.2

Purpose:This study was conducted to compare the effect of visual feedback training using mirror and the training without mirror on the balance in people with hemiplegic paralysis. Methods:A total of 26 stroke patients were enrolled in this study. The participants were allocated randomly to 2 groups : visual feedback training group(n=13) and control group(n=13). Both groups received PNF(proprioceptive neuromuscular facilitation) for 5 times(each 30 minutes) per week over 6 weeks period. The group, which is enrolled in visual feed back training, performed additional exercise in front of mirror for 30 minutes. The control group performed same exercise without mirror. The data was analyzed using a paired t-test and independent t-test to determine the statistical significance. Results:The visual feedback training group showed significantly increased foot pressure and total pressure compared to the control group(p<.05) and significantly decreased body sway compared to the control group (p<.05). Also, visual feedback training group showed significant increase on the Berg Balance Scale(BBS), Timed Up and Go test(TUG) compared to the control group(p<.05). Conclusion:These results support the perceived benefits of visual feedback training using mirror to augment the balance of stroke patients. Therefore, visual feedback training using mirror is feasible and suitable for stroke patients.

Effects of High Frequency Repetitive Transcranial Magnetic Stimulation on Function in Subacute Stroke Patients

Hyun-Gyu Cha,Myoung-Kwon Kim,Hyoung-Chun Nam,Sang-Goo Ji 한국자기학회 2014 Journal of Magnetics Vol.19 No.2

The aim of the present study was to examine the effects of high and low frequency repetitive transcranial magnetic stimulation on motor cortical excitability and the balance function in subacute stroke patients. Twenty-four subjects were randomly assigned to either the high frequency (HF) rTMS group, or the low frequency (LF) rTMS group, with 12 subjects each. All subjects received routine physical therapy. In addition, both groups performed a total of 20 sessions of rTMS for 20 minutes, once a day, 5 times per week, for a 4- week period. In the HF rTMS group, 10 Hz rTMS was applied daily to the hotspot of the lesional hemisphere; and in the LF rTMS group, 1 Hz rTMS was applied daily to the hotspot of the nonlesional hemisphere. Motor cortex excitability was determined by motor evoked potentials, and the balance function was evaluated by use of the Balance Index (BI) and the Berg Balance Scale (BBS), before and after the intervention. The change rate in the value of each variable differed significantly between the two groups ( p<0.05). Furthermore, significant differences were observed between all post-test variables of the two groups ( p<0.05). In the HF rTMS, significant differences were found in all the pre- and post-test variables ( p<0.05). On the other hand, in the LF rTMS, significant difference was observed only between the pre- and post-test results of BI and BBS ( p<0.05). The findings demonstrate that HF rTMS can be more helpful in improving the motor cortical excitability and balance function of patients with subacute stroke treatment than LF rTMS, and that it may be used as a practical adjunct to routine rehabilitation.

Effect of processing parameters, antistiction coatings, and polymer type when injection molding microfeatures

Yoon, Sung-Hwan,Cha, Nam-Goo,Lee, Jun S.,Park, Jin-Goo,Carter, David J.,Mead, Joey L.,Barry, Carol M.F. Wiley Subscription Services, Inc., A Wiley Company 2010 Polymer engineering and science Vol.50 No.2

<P>Thermoplastic polyurethane (TPU) and silicon tooling with microscale features on its surface was employed to investigate the impact of three factors on the quality of injection molded microscale features: (1) optimized process parameters, (2) use of a more flexible thermoplastic material, and (3) used as an antistiction coating. The molded parts and tooling surface were characterized by atomic force, confocal, and scanning electron microscopy. Although both improved filling of the tooling trenches, higher mold temperatures significantly enhanced replication, but faster injection velocities contributed moderately to replication quality. With medium aspect ratio (2.3:1) trenches, the antistiction coating doubled depth ratios, enhanced the edge definition and flatness of the features, and significantly reduced tearing of the features during ejection. The flexibility of the TPU permitted easier part ejection and left less polymer residue on the tooling surface in comparison to polycarbonate and other thermoplastic polymers. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers</P>

식생지역 모니터링이 가능한 침식센서의 현장 적용

차경훈(Kyeong-Hun Cha),류정옥(Jeong-Ok Ryu),노진구(Jin-Goo Nho),김정용(Jeong-Yong Kim),조희남(Heuy-Nam Cho),정교철(Gyo-Cheol Jeong) 대한지질학회 2017 대한지질학회 학술대회 Vol.2017 No.10

Trimethylamine 및 Ranitidine의 N-산화대사능을 이용하여 측정한 FMO 활성도와 FMO3 유전자형의 상관성

이경훈,성송기,차영남,신상구 大韓臨床藥理學會 2000 臨床藥理學會誌 Vol.8 No.1

핫 엠보싱용 점착방지막으로 사용되는 10nm급 두께의 Teflon-like 박막의 형성 및 특성평가

차남구,김인권,박창화,임현우,박진구,Cha Nam-Goo,Kim In-Kwon,Park Chang-Hwa,Lim Hyung-Woo,Park Jin-Goo 한국재료학회 2005 한국재료학회지 Vol.15 No.3

Teflon like fluorocarbon thin films have been deposited on silicon and oxide molds as an antistiction layer for the hot embossing process by an inductively coupled plasma (ICP) chemical vapor deposition (CVD) method. The process was performed at $C_4F_8$ gas flow rate of 2 sccm and 30 W of plasma power as a function of substrate temperature. The thickness of film was measured by a spectroscopic ellipsometry. These films were left in a vacuum oven of 100, 200 and $300^{\circ}C$ for a week. The change of film thickness, contact angle and adhesion and friction force was measured before and after the thermal test. No degradation of film was observed when films were treated at $100^{\circ}C$. The heat treatment of films at 200 and $300^{\circ}C$ caused the reduction of contact angles and film thickness in both silicon and oxide samples. Higher adhesion and friction forces of films were also measured on films treated at higher temperatures than $100^{\circ}C$. No differences on film properties were found when films were deposited on either silicon or oxide. A 100 nm silicon template with 1 to $500\;{\mu}m$ patterns was used for the hot embossing process on $4.5\;{\mu}m$ thick PMMA spun coated silicon wafers. The antistiction layer of 10 nm was deposited on the silicon mold. No stiction or damages were found on PMMA surfaces even after 30 times of hot embossing at $200^{\circ}C$ and 10 kN.

연마제 특성에 따른 차세대 금속배선용 Al CMP (chemical mechanical planarization) 슬러리 평가

차남구,강영재,김인권,김규채,박진구,Cha, Nam-Goo,Kang, Young-Jae,Kim, In-Kwon,Kim, Kyu-Chae,Park, Jin-Goo 한국재료학회 2006 한국재료학회지 Vol.16 No.12

It is seriously considered using Al CMP (chemical mechanical planarization) process for the next generation 45 nm Al wiring process. Al CMP is known that it has a possibility of reducing process time and steps comparing with conventional RIE (reactive ion etching) method. Also, it is more cost effective than Cu CMP and better electrical conductivity than W via process. In this study, we investigated 4 different kinds of slurries based on abrasives for reducing scratches which contributed to make defects in Al CMP. The abrasives used in this experiment were alumina, fumed silica, alkaline colloidal silica, and acidic colloidal silica. Al CMP process was conducted as functions of abrasive contents, $H_3PO_4$ contents and pressures to find out the optimized parameters and conditions. Al removal rates were slowed over 2 wt% of slurry contents in all types of slurries. The removal rates of alumina and fumed silica slurries were increased by phosphoric acid but acidic colloidal slurry was slightly increased at 2 vol% and soon decreased. The excessive addition of phosphoric acid affected the particle size distributions and increased scratches. Polishing pressure increased not only the removal rate but also the surface scratches. Acidic colloidal silica slurry showed the highest removal rate and the lowest roughness values among the 4 different slurry types.