• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.7
• /
• pp.669-674
• /
• 2013

A three-dimensional hydrogel scaffold has been proposed for the effective production of biomimetic intestinal villi to reduce ethical and cost problems caused by animal testing in pharmaceutical development. This study explores an experimental approach to develop a new technique based on laser machining and microdrilling processes to produce a plastic mold for the fabrication of a three-dimensional hydrogel scaffold. For process optimization, both the laser machining and the microdrilling experiments are conducted by varying the experimental conditions, and structural characterization of the mold and intestinal villi were performed using SEM (scanning electron microscope) and OM (optical microscope) images. Polycarbonate (PC) was used as a candidate material. The experimental results show that intestinal villi can be fabricated by both laser and microdrilling machining processes.

• Progress in Medical Physics
• /
• v.28 no.1
• /
• pp.33-38
• /
• 2017

Creating individualized build-up material for superficial photon beam radiation therapy at irregular surface is complex with rice or commonly used flat shape bolus. In this study, we implemented a workflow using 3D printed patient specific bolus and describe our clinical experience. To provide better fitted build-up to irregular surface, the 3D printing technique was used. The PolyLactic Acid (PLA) which processed with nontoxic plant component was used for 3D printer filament material for clinical usage. The 3D printed bolus was designed using virtual bolus structure delineated on patient CT images. Dose distributions were generated from treatment plan for bolus assigned uniform relative electron density and bolus using relative electron density from CT image and compared to evaluate the inhomogeneity effect of bolus material. Pretreatment QA is performed to verify the relative electron density applied to bolus structure by gamma analysis. As an in-vivo dosimetry, Optically Stimulated Luminescent Dosimeters (OSLD) are used to measure the skin dose. The plan comparison result shows that discrepancies between the virtual bolus plan and printed bolus plan are negligible. (0.3% maximum dose difference and 0.2% mean dose difference). The dose distribution is evaluated with gamma method (2%, 2 mm) at the center of GTV and the passing rate was 99.6%. The OSLD measurement shows 0.3% to 2.1% higher than expected dose at patient treatment lesion. In this study, we treated Mycosis fungoides patient with patient specific bolus using 3D printing technique. The accuracy of treatment plan was verified by pretreatment QA and in-vivo dosimetry. The QA results and 4 month follow up result shows the radiation treatment using 3D printing bolus is feasible to treat irregular patient skin.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.110-110
• /
• 2010

현재 박막 트랜지스터는 비정질 실리콘 기반의 개발이 주를 이루고 있으며, 이 비정질 실리콘은 성막공정이 간단하고 대면적에 용이하지만 전기적인 특성이 우수하지 않기 때문에 디스플레이의 적용에 어려움을 겪고 있다. 이에 따라 poly-Si을 이용한 박막 트랜지스터의 연구가 진행되고 있는데, 이는 공정온도가 높고, 대면적에의 응용이 어렵다. 따라서 앞으로 저온 공정이 가능하며 대면적 응용이 용이한 박막 트랜지스터의 연구가 필수적이다. 한편 최근 박막 트랜지스터의 채널층으로 사용되는 물질에는 oxide 기반의 ZnO, SnO2, In2O3 등이 주로 사용되고 있고, 보다 적합한 채널층을 찾기 위한 연구가 많이 진행되어 왔다. 최근 Hosono 연구팀에서 IGZO를 채널층으로 사용하여 high mobility, 우수한 on/off ratio의 특성을 가진 소자 제작에 성공함으로써 이를 시작으로 IGZO의 연구 또한 세계적으로 활발한 연구가 이루어지고 있다. 특히, ZnO는 wide band gap (3.37eV)을 가지고 있어 적외선 및 가시광선의 투과율이 좋고, 전기 전도성과 플라즈마에 대한 내구성이 우수하며, 낮은 온도에서도 성막이 가능하다는 특징을 가지고 있다. 그러나 intrinsic ZnO 박막은 bias stress 같은 외부 환경이 변했을 경우 전기적인 성질의 변화를 가져올 뿐만 아니라 고온에서의 공정이 불안정하다는 요인을 가지고 있다. ZnO의 전기적인 특성을 개선하기 위해 본 연구에서는 hafnium을 doping한 ZnO을 channel layer로 소자를 제작하고 전기적 특성을 평가하였다. 이를 위해 DC magnetron sputtering을 이용하여 ZnO 기반의 박막 트랜지스터를 제작하였다. Staggered bottom gate 구조로 ITO 물질을 전극으로 사용하였으며, 제작된 소자는 semiconductor analyzer를 이용하여 출력특성과 전이 특성을 평가하였으며, ZnO channel layer 증착시 hafnium이 도핑 되는 양을 조절하여 소자를 제작한 후 intrinsic ZnO의 소자 특성과 비교 분석하였다. 그 결과 hafnium을 doping 시킨 소자의 field effect mobility가 $6.42cm^2/Vs$에서 $3.59cm^2/Vs$로 낮아졌지만, subthreshold swing 측면에서는 1.464V/decade에서 0.581V/decade로 intrinsic ZnO 보다 좋은 특성을 나타냄을 알 수 있었다. 그리고 intrinsic ZnO의 경우 외부환경에 대한 안정성 문제가 대두되고 있는데, hafnium을 도핑한 ZnO의 경우 temperature, bias temperature stability, 경시변화 등의 다양한 조건에서의 안정성이 확보된다면 intrinsic ZnO 박막트랜지스터의 문제점을 해결할 수 있는 물질로 될 것이라고 기대된다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.117-117
• /
• 2011

유기물과 무기물이 결합한 나노 복합체를 사용하여 제작한 비휘발성 메모리 소자는 공정이 간단하고 저렴할 뿐만 아니라 휘어짐이 가능하다는 장점 때문에 많은 연구가 진행되고 있다. 코어-쉘 나노 입자를 포함한 고분자 박막으로 제작한 비휘발성 메모리 소자에서 쉘의 종류와 유무에 따른 메모리 윈도우와 기억시간에 미치는 영향에 대한 연구는 아주 적다. 본 연구에서는 CdTe-CdSe 코어-쉘 나노 입자 및 CdTe 나노 입자가 Poly(9-vinylcarbazol) (PVK) 박막에 분산되어 있는 나노복합체를 기억 매체로 사용하는 비휘발성 메모리 소자들을 제작하여 쉘의 유무에 따른 메모리 윈도우와 기억시간의 변화를 관찰하였다. 소자를 제작하기 위해 두 가지의 나노 입자를 각각 PVK와 함께 톨루엔에 용해시킨 후에 초음파 교반기를 사용하여 나노입자가 PVK가 고르게 섞인 두 가지의 나노복합체를 형성하였다. 두 가지 용액을 p-Si 기판위에 스핀 코팅 방법으로 도포한 후, 열을 가해 용매를 제거하여 CdTe-CdSe 나노 입자가 PVK에 분산되어 있는 나노복합체 박막과 CdTe 나노 입자가 PVK에 분산되어 있는 나노복합체 박막을 각각 형성하였다. 나노 입자가 분산된 각각의 나노복합체 박막 위에 Al을 게이트 전극으로서 열증착하여 소자를 완성하였다. 제작된 두 소자의 정전용량-전압 (C-V) 측정을 하여 CdSe의 유무에 따른 메모리 소자에 대한 C-V 곡선의 다른 평탄 전압 이동을 관찰 하였다. 정전용량-시간 측정을 하여 CdSe 쉘의 유무에 따라 포획된 전하를 유지하는 능력에 차이가 있는 것을 관찰하였다. 측정 결과 모두 CdSe 쉘이 존재하는 메모리 소자에서 우수한 메모리 윈도우와 기억시간 특성이 나타났다. 에너지 대역도를 사용하여 소자의 전하 수송 메커니즘과 CdSe 쉘의 존재에 의해 소자의 메모리 윈도우와 기억시간 특성이 향상되는 원인을 설명 할 것이다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.566-566
• /
• 2012

그래핀(Graphene)은 모든 탄소 동소체의 기본구성 요소로 2 차원 결정구조를 가지며, 양자홀 효과(quantum Hall effect), 뛰어난 열 전도도, 고 탄성, 광학적 투과성 등과 같은 탁월한 물리적 성질을 보이는 물질이다. 이러한 그래핀의 우수한 특성은 전계 효과 트랜지스터(field effect transistor), 화학/바이오 센서, 투명 전극(transparent electrode) 등의 다양한 전자소자를 개발하는 응용 가능하다. 그 중, 그래핀 투명전극의 제조는 가장 응용가능성이 높은 분야이다. 현재 투명전극 물질로는 인듐-주석 산화물(indium tin oxide; ITO)가 널리 이용되고 있으나, 인듐의 고갈로 인한 공급부족 문제 및 고 생산비용, 휘어지지 않는 취성 등의 단점을 지니고 있다. 따라서, 우수한 광학적 투과성과 전기전도성을 지닌 그래핀이 ITO의 대체 물질로서 각광받고 있다.[1-5] 본 연구에서는 그래핀의 투명전도필름의 응용을 위해 면저항을 낮추기 위한 방법으로 화학적 도핑(doping)을 이용하였다. 그래핀은 구리(copper; Cu) 호일을 촉매로 사용하여 열 화학증착법(Thermal Chemical Vapor Deposition)을 이용하여 합성하였다. 합성된 그래핀은 PMMA(Poly(methyl methacrylate)) 전사법을 이용하여 산화실리콘(SiO2) 기판에 전사 후, 염화은(AgCl)과 클로로벤젠(C6H5Cl)으로 만든 콜로이드(colloid) 용액에 디핑(dipping)하여 그래핀에 은 입자를 도핑 하였다. 그 결과, 은 입자 도핑 농도에 따라 면저항이 감소하는 양상을 보였다. 제작된 그래핀 투명전도성 필름의 투과도는 자외선-가시광선-근적외선 분광법(UV-Vis-NIR spectroscopy)를 이용하여 측정하였고, 라만 분광법(Raman spectroscopy)을 통해 그래핀 필름의 질적 우수성과 성장 균일도를 조사하였다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.68-68
• /
• 2011

As feature size is smaller, new technology are needed in semiconductor factory such as gap-fill technology for sub 100nm, development of ALD equipment for Cu barrier/seed, oxide trench etcher technology for 25 nm and beyond, development of high throughput Cu CMP equipment for 30nm and development of poly etcher for 25 nm and so on. We are focus on gap-fill technology for sub-30nm. There are many problems, which are leaning, over-hang, void, micro-pore, delaminate, thickness limitation, squeeze-in, squeeze-out and thinning phenomenon in sub-30 nm gap fill. New gap-fill processes, which are viscous oxide-SOD (spin on dielectric), O3-TEOS, NF3 Based HDP and Flowable oxide have been attempting to overcome these problems. Some groups investigated SOD process. Because gap-fill performance of SOD is best and process parameter is simple. Nevertheless these advantages, SOD processes have some problems. First, material cost is high. Second, density of SOD is too low. Therefore annealing and curing process certainly necessary to get hard density film. On the other hand, film density by Flowable oxide process is higher than film density by SOD process. Therefore, we are focus on Flowable oxide. In this work, dielectric film were deposited by PECVD with TSA(Trisilylamine - N(SiH3)3) and NH3. To get flow-ability, the effect of plasma treatment was investigated as function of O2 plasma power. QMS (quadruple mass spectrometry) and FTIR was used to analysis mechanism. Gap-filling performance and flow ability was confirmed by various patterns.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.659-659
• /
• 2013

Recently, graphene has been intensively studied due to the fascinating physical, chemical and electrical properties. It shows high carrier mobility, high current density, and high thermal conductivity compare with conventional semiconductor materials even it has single atomic thickness. Especially, since graphene has fantastic electrical properties many researchers are believed that graphene will be replacing Si based technology. In order to realize it, we need to prepare the large and uniform graphene. Chemical vapor deposition (CVD) method is the most promising technique for synthesizing large and uniform graphene. Unfortunately, CVD method requires transfer process from metal catalyst. In transfer process, supporting polymer film (Such as poly (methyl methacrylate)) is widely used for protecting graphene. After transfer process, polymer layer is removed by organic solvents. However, it is impossible to remove it completely. These organic residues on graphene surface induce quality degradation of graphene since it disturbs movement of electrons. Thus, in order to get an intrinsic property of graphene completely remove of the organic residues is the most important. Here, we introduce modified wet graphene transfer method without PMMA. First of all, we grow the graphene from Cu foil using CVD method. And then, we deposited several metal films on graphene for transfer layer instead of PMMA. Finally, we fabricate graphene FET devices. Our approaches show low defect density and non-organic residues in comparison with PMMA coated graphene through Raman spectroscopy, SEM and AFM. In addition, clean graphene FET shows intrinsic electrical characteristic and high carrier mobility.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.117-117
• /
• 2008

In MIM capacitor, poly-Si bottom electrode is replaced with metal bottom electrode. Noble metals can be used as bottom electrodes of capacitors because they have high work function and remain conductive in highly oxidizing conditions. In addition, they are chemically very stable. Among novel metals, Ru (ruthenium) has been suggested as an alternative bottom electrode due to its excellent electrical performance, including a low leakage of current and compatibility to high dielectric constant materials. Chemical mechanical planarization (CMP) process has been suggested to planarize and isolate the bottom electrode. Even though there is a great need for development of Ru CMP slurry, few studies have been carried out due to noble properties of Ru against chemicals. In the organic chemistry literature, periodate ion ($IO_4^-$) is a well-known oxidant. It has been reported that sodium periodate ($NaIO_4$) can form $RuO_4$ from hydrated ruthenic oxide ($RuO_2{\cdot}nH_2O$). $NaIO_4$ exist as various species in an aqueous solution as a function of pH. Also, the removal mechanism of Ru depends on solution of pH. In this research, the static etch rate, passivation film thickness and wettability were measured as a function of slurry pH. The electrochemical analysis was investigated as a function of pH. To evaluate the effect of pH on polishing behavior, removal rate was investigated as a function of pH by using patterned and unpatterned wafers.

• Macromolecular Research
• /
• v.12 no.3
• /
• pp.316-321
• /
• 2004

We have performed copolymerizations of ethylene with 1-hexene using various ansa-metallocene compounds in the presence of the non-coordinative [CPh$_3$][B(C$\_$6/F$\_$5/)$_4$ion pair as a cocatalyst. The metallocenes chosen for this study are isospecific metallocene diamide compounds, rac-(EBI)Zr(NMe$_2$)$_2$ [1, EBI = ethylene-l ,2-bis(1-indenyl)], rac-(EBI)Hf(NMe$_2$)$_2$ (2), rac-(EBI)Zr(NC$_4$H$\_$8/)$_2$ (3), and rac-(CH$_3$)$_3$Si(1-C$\_$5/H$_2$-2-CH$_3$-4-$\^$t/C$_4$H$\_$9/)2 Zr(NMe$_2$)$_2$ (4), and syndiospecific metallocene dimethyl compounds, ethylidene(cyclopentadienyl)(9-fluorenyl) ZrMe$_2$ [5, Et(Flu)(Cp )ZrMe$_2$] and isopropylidence (cyclopentadienyl)(9-fluorenyl)ZrMe$_2$ [6, iPr(Flu)(Cp)ZrMe$_2$]. The copolymerization rate decreased in the order 4 ＞1-3＞2 ＞5＞6. The reactivity of I -hexene decreased in the order 2 ＞6＞1- 3-5＞ 4. We characterized the microstructure of the resulting poly(ethylene-co-l-hexene) by $\^$l3/C NMR spectroscopy and investigated various other properties of the copolymers in detail.

• Advances in Energy Research
• /
• v.1 no.2
• /
• pp.97-106
• /
• 2013

This study designs and tests a photovoltaic system with distributed maximum power point tracking (DMPPT) methodology using a field programmable gate array (FPGA) controller. Each solar panel in the distributed PV system is equipped with a newly designed DC/DC converter and the panel's voltage output is regulated by a FPGA controller using PI control. Power from each solar panel on the system is optimized by another controller where the quadratic maximization MPPT algorithm is used to ensure the panel's output power is always maximized. Experiments are carried out at atmospheric insolation with partial shading conditions using 4 amorphous silicon thin film solar panels of 2 different grades fabricated by Chi-Mei Energy. It is found that distributed MPPT requires only 100ms to find the maximum power point of the system. Compared with the traditional centralized PV (CPV) system, the distributed PV (DPV) system harvests more than 4% of solar energy in atmospheric weather condition, and 22% in average under 19% partial shading of one solar panel in the system. Test results for a 1.84 kW rated system composed by 8 poly-Si PV panels using another DC/DC converter design also confirm that the proposed system can be easily implemented into a larger PV power system. Additionally, the use of NI sbRIO-9642 FPGA-based controller is capable of controlling over 16 sets of PV modules, and a number of controllers can cooperate via the network if needed.