• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.377-377
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• 2011

Organic solar cells (OSCs) with low cost have been studied to apply on flexible substrate by solution process in low temperature [1]. In previous researches, conventional organic solar cell was composed of metal oxide anode, buffer layer such as PEDOT:PSS, photoactive layer, and metal cathode with low work function. In this structure, indium tin oxide (ITO) and Al was generally used as metal oxide anode and metal cathode, respectively. However, they showed poor reliability, because PEDOT:PSS was sensitive to moisture and air, and the low work function metal cathode was easily oxidized to air, resulting in decreased efficiency in half per day [2]. Inverted organic solar cells (IOSCs) using high work function metal and buffer layer replacing the PEDOT:PSS have focused as a solution in conventional organic solar cell. On the contrary to conventional OSCs, ZnO and TiO2 are required to be used as a buffer layer, since the ITO in IOSC is used as cathode to collect electrons and block holes. The ZnO is expected to be excellent electron transport layer (ETL), because the ZnO has the advantages of high electron mobility, stability in air, easy fabrication at room temperature, and UV absorption. In this study, the IOSCs based on poly [N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) : [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) were fabricated with the ZnO electron-transport layer and MoO3 hole-transport layer. Thickness of the ZnO for electron-transport layer was controlled by rotation speed in spin-coating. The PCDTBT and PC70BM were mixed with a ratio of 1:2 as an active layer. As a result, the highest efficiency of 2.53% was achieved.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.386-386
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• 2011

탄소나노튜브는 큰 길이 대 직경 비와 뛰어난 전기적 특성으로 인해 차세대 전계 방출 소자로 주목 받고 있다. 실질적인 전계방출 디스플레이로의 응용을 위한 대면적 제작과 유리 기판 사용을 위해 이용되었던 페이스트(paste)법은 높은 전기장 하에서 장시간 전계방출시 탄소나노튜브 전계방출원과 페이스트(paste)간의 낮은 접착력 때문에 발생하는 탄소나노튜브의 탈루현상(omission)과 유기물질(organic paste)에서 발생하는 탈기체(out-gassing) 문제점이 있었다. 최근 이런 문제점을 개선하기 위해 유기물질(organic paste)를 대체하여 금속바인더(metal binder) 물질을 사용한 결과들이 보고되고 있다. 본 연구에서는 유리기판 위에 제작된 탄소나노튜브 전계방출원의 수명 향상을 위하여 금속바인더와 후속 열처리법의 변화에 따른 전계방출 안정성을 분석하였다. 금속바인더는 접합층/ 접착층(soldering layer/ adhesive layer)으로 구성되어 있으며, 일반적인 소다석회유리(soda-lime glass)에 스퍼터(DC magnetron sputtering system)를 이용하여 증착하였다. 접착층은 유리기판과 접합층의 접착력 향상을 위해 사용되며, 접합층은 기판과 탄소나노튜브 전계방출원을 접합하는 역할과 전계방출 측정시 전극이 되기 때문에 우수한 전기 전도성과 내산화성을 필요로 한다. 본 실험에서는 일반적으로 유리기판과 접착력이 좋다고 알려진 Cr, Ti, Ni, Mo을 접착층으로 사용하였으며, 접합성과 전기전도성, 내산화성이 뛰어난 귀금속 계열의 금속을 접합층으로 사용하였다. 탄소나노튜브를 1,2-디클로로에탄(1,2-dichloroethane, DCE)에 분산시킨 용액을 스프레이방법을 이용하여 증착시켰으며, 후속 열처리 방법을 통하여 접합층과 결합시켰다. 금속바인더와 후속 열처리법의 변화에 따른 접착력과 표면형상(morphology)의 변화를 주사전자현미경(scanning electron microscopy)를 이용하여 분석하였으며, 다이오드 타입에 디씨 바이어스(DC bias)를 사용하여 전계방출특성을 측정하였다[1,2].

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.129-129
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• 2018

Hard coating application is effective way of cutting tool for hard-to-machine materials such as Inconel, Ti and composite materials focused on high-tech industries which are widely employed in aerospace, automobile and the medical device industry also Information Technology. In cutting tool for hard-to-machine materials, high hardness is one of necessary condition along with high temperature stability and wear resistance. In recent years, high-entropy alloys (HEAs) which consist of five or more principal elements having an equi-atomic percentage were reported by Yeh. The main features of novel HEAs reveal thermodynamically stable, high strength, corrosion resistance and wear resistance by four characteristic features called high entropy, sluggish diffusion, several-lattice distortion and cocktail effect. It can be possible to significantly extend the field of application such as cutting tool for difficult-to-machine materials in extreme conditions. Base on this understanding, surface coatings using HEAs more recently have been developed with considerable interest due to their useful properties such as high hardness and phase transformation stability of high temperature. In present study, the nanocomposite coating layers with high hardness on WC substrate are investigated using high entropy alloy target made a powder metallurgy. Among the many surface coating methods, reactive magnetron sputtering is considered to be a proper process because of homogeneity of microstructure, improvement of productivity and simplicity of independent control for several critical deposition parameters. The N2 is applied to reactive gas to make nitride system with transition metals which is much harder than only alloy systems. The acceleration voltage from 100W to 300W is controlled by direct current power with various deposition times. The coating layers are systemically investigated by structural identification (XRD), evaluation of microstructure (FE-SEM, TEM) and mechanical properties (Nano-indenter).

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.219-223
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• 2000

The ferroelectric SBT films were deposited on Pt/Ti/SiO$_2$/Si substrates by liquid injection metalorganic chemical vapor deposition (MOCVD) with single-mixture solution of Sr[Ta(OEt)$_5$(dmae)]$_2$and Bi(C$_6$ 6/H$_5$)$_3$. The Sr/Ta and Bi/Ta ratio in SBT films depended on deposition temperature and mol ratio of precursor in the single-mixture solution. At the substrate temperature of 40$0^{\circ}C$, Sr/Ta and Bi/Ta ratio were close to 0.4 and 1 at precursor mol ratio of 0.5~1.0, respectively. As-deposited film was amorphous. However, after annealing at 75$0^{\circ}C$ for 30 min in oxygen atmosphere, the diffraction patterns indicated polycrystalline SBT phase. The remanent polarization (Pr) and coercive field (Ec) of SBT film annealed at 75$0^{\circ}C$ were 4.7$\mu$C/$\textrm{cm}^2$ and 115.7kV/cm at an applied voltage of 5V, respectively. The SBT films annealed at 75$0^{\circ}C$ showed practically no polarization fatigue up to 10$^10$ switching cycles.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 제5회 영호남 학술대회 논문집
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• pp.85-88
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• 2003

$Sr_xBa_{1-x}Nb_2O_6$(SBN, $025{\leq}x{\leq}0.75$) ceramic is a ferroelectric material with tetragonal tungsten bronze (TTB) type structure, which has a high pyroelectric coefficient and a nonlinear electro-optic coefficient value. In spite of its advantages, SBN has not been investigated well compared to other ferroelectric materials with perovskite structure. In this study, SBN thin film was manufactured by ion beam sputtering technique using the prepared SBN target in Ar/$O_2$ atmosphere. SBN30 thin film of 500 ${\AA}$ was pre-deposited as a seed layer on Pt(l00)/$TiO_2$/$SiO_2$/Si substrate followed by SBN60 deposition up to 4500 ${\AA}$ in thickness. SBN60/SBN30 layer was deposited at different Oxygen amount of 0, 8.1, 17, and 31.8 sccm, respectively. The crystallinity and orientation behavior as well as electric properties of SBN60/SBN30 multi-layer were examined. The deposited layer was uniform and the orientation was shown primarily along (001) plane from XRD pattern. The crystal structure and the electric properties depended on the Oxygen amount, heating temperature and was the best at O2 = 8.1 seem, $750^{\circ}C$. In electric properties of Pt/SBN60/SBN30/Pt thin film capacitor prepared, the remnant polarization (2Pr) value was 13 ${\mu}C/cm^2$, the coercive field (Ec) 75 kV/cm, and the dielectric constant 1492, respectively.

• 한국전기전자재료학회논문지
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• 제29권3호
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• pp.147-151
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• 2016

Graphene has a monolayer crystal structure formed with C-atoms and has been used as a base layer of HETs (hot electron transistors). Graphene HETs have exhibited the operation at THz frequencies and higher current on/off ratio than that of Graphene FETs. In this article, we report on the preliminary results of current characteristics from the HETs which are fabricated utilizing highly doped Si collector, graphene base, and 5 nm thin $Al_2O_3$ tunnel layers between the base and Ti emitter. We have observed E-B forward currents are inherited to tunneling through $Al_2O_3$ layers, but have not noticed the Schottky barrier blocking effect on B-C forward current at the base/collector interface. At the common-emitter configuration, under a constant $V_{BE}$ between 0~1.2V, $I_C$ has increased linearly with $V_{CE}$ for $V_{CE}$ < $V_{BE}$ indicating the saturation region. As the $V_{CE}$ increases further, a plateau of $I_C$ vs. $V_{CE}$ has appeared slightly at $V_{CE}{\simeq}V_{BE}$, denoting forward-active region. With further increase of $V_{CE}$, $I_C$ has kept increasing probably due to tunneling through thin Schottky barrier between B/C. Thus the current on/off ration has exhibited to be 50. To improve hot electron effects, we propose the usage of low doped Si substrate, insertion of barrier layer between B/C, or substrates with low electron affinity.

• 한국재료학회지
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• 제15권12호
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• pp.796-801
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• 2005

In order to reduce the weight of glass in architecture, automobile, bottles, displays, a new technique that can strengthen glass was developed using various method. Generally, the strength achieved of glass-ceramics is higher as is 1.he fracture toughness by the formation of a crystalline phase inside glass. In this study, $70SiO_2-20Na_2O-10CaO-10TiO_2$ glasses were irradiated to strengthen by heterogeneous phase using femto-second laser pulse. Laser pulse irradiation of samples was analyzed by DTA, TMA, XRD, nano-indenter and SEM. Samples irradiated by laser had lower value$(3\~4\times10^{-3}Pa)$ of nano indentation which related with mother glass$(8\times10-3Pa)$ than values. Microcracks were occurred around laser irradiation area when femtosecond laser with the repetition rate of 1kHz was used as the light source to induced heterogeneous phase.

• 한국세라믹학회지
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• 제35권10호
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• pp.1107-1112
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• 1998

We could obtan c-axis oriented $SrBi_2$$Ta_2$$O_9$ thin films on usual Pt(111)/Ti/$SiO_2$/Si(100) substrate using a r. f. magnetron sputtering technique. According to the increase of sputtering pressure from 250 to 300 mTorr the Bi content and degree of the c-a xis preferred orientation of $SrBi_2$$Ta_2$$O_9$ thin films were increased. By controlling Bi(or $Bi_2O_3$) loss from $SrBi_2$$Ta_2$$O_9$ thin films during post annealing and by inserting $Bi_2O_3$ layer in $SrBi_2$$Ta_2$$O_9$ thin films the effect of Bi content on the c-axis oriented growth of $SrBi_2$$Ta_2$$O_9$ thin films could be investigated without the effect of sputtering pressure. The degree of the c-axis preferred orientation of $SrBi_2$$Ta_2$$O_9$ thin films was increased with increasing with increasing Bi content by control of Bi(or $Bi_2O_3$) loss of $SrBi_2$$Ta_2$$O_9$ thin films. But the c-axis oriented growth of $SrBi_2$$Ta_2$$O_9$ thin films disappeared by the inserting of $Bi_2O_3$ lay-er in $SrBi_2$$Ta_2$$O_9$ thin films.

• 한국세라믹학회지
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• 제44권5호
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• pp.179-183
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• 2007

BCB $Resin-BaNd_2Ti_4O_{12}$(BNT) composites with BNT contents were prepared by tape casting method and epoxy resin-BNT composites were prepared by using heating press. Their dielectric properties and microstructures were investigated. The dielectric properties such as dielectric constant and dielectric loss at 1 MHz for epoxy resin-BNT composites and BCB resin-BNT composites are improved with an increase of BNT volume fraction. The dielectric constant of the Epoxy-BNT composite increased from 5.9 to 7.8 as the volume fraction of BNT increased from 15 to 25. The dielectric constant of the BCB-BNT composite increased from 9.1 to 15.5 as the volume fraction of BNT increased from 30 to 50. The dielectric behavior of BCB-BNT system can be explained by Lichtenecker's equation. The dielectric constant of epoxy resin-BNT composite is smaller than that of BCB resin-BNT composite. These results are considered to be related with the dispersion of BNT filler in polymer matrix from the result of SEM photograph.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제51권9호
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• pp.449-454
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• 2002

A rectangular straight microchannel, integrated with the resistance temperature detectors(RTDs) for temperature sensing and a micro-heater for generating the Temperature gradient along the channel, was fabricated. Its dimension is 57${\mu}{\textrm}{m}$(H)$\times$200${\mu}{\textrm}{m}$(W)$\times$48,050${\mu}{\textrm}{m}$(L), and RTDs were placed at the inner-channel wall. Si wafer was used as a substrate. For the fabrication of RTDs, 5300$\AA$ thick Pt/Ti layer was sputtered on a Pyrex glass wafer. Finally, the glass wafer was bonded with Si wafer by anodic bonding, so that the RTDs are located inside the microchannel. Temperature coefficient of resistance(TCR) values of the fabricated Pt-RTDs were 2800~2950ppm$^{\circ}C$ and the variation of TCR value In the range of O~10$0^{\circ}C$ was less than 0.3％. Therefore, it was proved that the fabricated Pt-RTDs without annealing were excellent as temperature sensors. The temperature distribution in the microchannel was investigated as a function of mass flow rate and heating power. The temperature increase rate diminished with decreasing the applied power and increasing the mass flow rate. It was confirmed from the comparison with the simulation results that the temperature measured inside the microchannel is more accurate than measuring the temperature measured at the outer wall. The proposed temperature sensing method and microchannel are expected to be useful in microfluidics researches.