• 한국재료학회:학술대회논문집
• /
• 한국재료학회 2012년도 춘계학술발표대회
• /
• pp.110.1-110.1
• /
• 2012

Recently, advances in ZnO based oxide semiconductor materials have accelerated the development of thin-film transistors (TFTs), which are the building blocks for active matrix flat-panel displays including liquid crystal displays (LCD) and organic light-emitting diodes (OLED). However, the electrical performances of oxide semiconductors are significantly affected by interactions with the ambient atmosphere. Jeong et al. reported that the channel of the IGZO-TFT is very sensitive to water vapor adsorption. Thus, water vapor passivation layers are necessary for long-term current stability in the operation of the oxide-based TFTs. In the present work, $Al_2O_3$ and $TiO_2$ thin films were deposited on poly ether sulfon (PES) and $SnO_x$-based TFTs by electron cyclotron resonance atomic layer deposition (ECR-ALD). And enhancing the WVTR (water vapor transmission rate) characteristics, barrier layer structure was modified to $Al_2O_3/TiO_2$ layered structure. For example, $Al_2O_3$, $TiO_2$ single layer, $Al_2O_3/TiO_2$ double layer and $Al_2O_3/TiO_2/Al_2O_3/TiO_2$ multilayer were studied for enhancement of water vapor barrier properties. After thin film water vapor barrier deposited on PES substrate and $SnO_x$-based TFT, thin film permeation characteristics were three orders of magnitude smaller than that without water vapor barrier layer of PES substrate, stability of $SnO_x$-based TFT devices were significantly improved. Therefore, the results indicate that $Al_2O_3/TiO_2$ water vapor barrier layers are highly proper for use as a passivation layer in $SnO_x$-based TFT devices.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 초전도 자성체 연구회
• /
• pp.30-33
• /
• 2003

YBCO coated conductor, also called the 2nd generation high temperature superconducting wire, consists of oxide multi-layer hetero-epitaxial thin films. Pulsed laser deposition (PLD) is one of many film deposition methods used to make coated conductor, and is the one known to be the best to make superconducting layer so far. As a part of the effort to make long length coated conductor, the optimum deposition condition of YBCO film on single crystal substrate (SrTiO3) was investigated using PLD. Substrate temperature, oxygen partial pressure, and laser fluence were varied to find the best combination to grow high quality YBCO film.

• 한국자기학회지
• /
• 제8권6호
• /
• pp.350-356
• /
• 1998

Sol-gel법을 이용하여 합성한 자성 garnet Y3-xLaxFe5O12(x=0.0, 0.25, 0.5, 0.75, 1.0) 분말과 박막의 결정 및 자기적 성질에 관하여 X-선 회절기, atomic force microscopy(AFM), scanning electron microscopy(SEM), 진동시료자화기 (VSM)와 Mossbauer 부노강기를 이용하여 연구하엿다. X-선 회절분석 결과와 Mossbauerqnsrhkd 실험으로부터 100$0^{\circ}C$에서 열처리한 x=0.75 이하의 Y3-xLaxFe5O12 분말의 경우 모두 순수한 cubic의 garnet 구조가 형성되었음을 확인 할 수 있었으나, x=1.0인 경우는 LaFeO3상이 함께 관측되었다. Garnet 박막의 성장을 위하여 75$0^{\circ}C$에서 2시간의 열처리로 결정화를 이루었으며, 성장한 박막은 특정한 방향성 없이 성장하였음을 알 수 있었다. Mossbauer 분광기를 이용하여 측정한 결과는 산화물을 통하여 제조한 garnet 분말의 Mossbauer spectrumthk 일치함을 알 수 있었다. 전자 현미경의 측정을 통한 분말의 입자크기는 200~300nm이며, AFM의 측정으로부터 박막의 평균 표면 거칠기가 3.17nm임을 알 수 있었다. 진동시료자화기를 이용하여 측정한 garnet 분말과 박막의 자기적 특성은 전형적인 연자성의 자기적 속성을 가지며, garnet 분말의 경우 최대 포화자화 (30 emu/g)와 최소 보자력 (52 Oe)을 가짐을 알 수 있엇다. 80$0^{\circ}C$에서 열처리한 순수한 garnet 박막시료의 경우 수직 및 수평방향으로 측정한 자화곡선은 수직방향으로 측정한 자화곡선이 낮은 포화자화를 가지며 보자력은 양방향 모두 37 Oe를 나타냈다.

• 한국결정성장학회지
• /
• 제9권1호
• /
• pp.126-131
• /
• 1999

Hot-wall epitaxy법으로 $Cd_{1-x}Mn_xTe$박막을 GaAs (100) 기판위에 성장시켰다. XRD 측정으로부터 CdTe/GaAs(100) 박막은 기판과 같은 (100)면의 단결정 박막으로, $Cd_{1-x}Mn_xTe$박막은 Mn의 조성비 x가 증가함에따라 다결정 박막으로 성장되었으며, 박막의 격자상수는 x의 증가에 따라 덩어리 결정의 경우와 비슷한 기울기로 감소함을 확인하였다. x의 변화에 대한 $Cd_{1-x}Mn_xTe$ 박막의 PL 측정으로부터 받개와 퍼텐셜 요동에 의하여 포획된 엑시톤의 재결합 피크인 $L_1$과 $L_2$를 관측하였으며, $L_1$피크는 x=0.09 시료에서만 관측되었고 x값이 증가하면 사라졌다. x $\ge$0.2의 경우에는 $L_2$피크가 강하게 나타나고 x$\ge$ 0.4에서는 $Mn^{2+}$이온의 intra 천이에 의한 2.0eV 근처의 피크가 강하게 나타났다. x>0.4에서 $Mn^{2+}$이온에 의한 2.0eV 피크는 pinning이 일어나 변화가 거의 없이 일정하였다.

• Tribology and Lubricants
• /
• 제11권5호
• /
• pp.128-135
• /
• 1995

Atomic force microscopy/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales, ranging from atomic and molecular to microscales. These techniques have been used to study surface roughness, adhesion, friction, scratching/wear, indentation, detection of material transfer, and boundary lubrication and for nanofabrication/nanomachining purposes. Micro/nanotribological studies of single-crystal silicon, natural diamond, magnetic media (magnetic tapes and disks) and magnetic heads have been conducted. Commonly measured roughness parameters are found to be scale dependent, requiring the need of scale-independent fractal parameters to characterize surface roughness. Measurements of atomic-scale friction of a freshly-cleaved highly-oriented pyrolytic graphite exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography were displaced relative to each other. Variations in atomic-scale friction and the observed displacement has been explained by the variations in interatomic forces in the normal and lateral directions. Local variation in microscale friction is found to correspond to the local slope suggesting that a ratchet mechanism is responsible for this variation. Directionality in the friction is observed on both micro- and macro scales which results from the surface preparation and anisotropy in surface roughness. Microscale friction is generally found to be smaller than the macrofriction as there is less ploughing contribution in microscale measurements. Microscale friction is load dependent and friction values increase with an increase in the normal load approaching to the macrofriction at contact stresses higher than the hardness of the softer material. Wear rate for single-crystal silicon is approximately constant for various loads and test durations. However, for magnetic disks with a multilayered thin-film structure, the wear of the diamond like carbon overcoat is catastrophic. Breakdown of thin films can be detected with AFM. Evolution of the wear has also been studied using AFM. Wear is found to be initiated at nono scratches. AFM has been modified to obtain load-displacement curves and for nanoindentation hardness measurements with depth of indentation as low as 1 mm. Scratching and indentation on nanoscales are the powerful ways to screen for adhesion and resistance to deformation of ultrathin fdms. Detection of material transfer on a nanoscale is possible with AFM. Boundary lubrication studies and measurement of lubricant-film thichness with a lateral resolution on a nanoscale have been conducted using AFM. Self-assembled monolyers and chemically-bonded lubricant films with a mobile fraction are superior in wear resistance. Finally, AFM has also shown to be useful for nanofabrication/nanomachining. Friction and wear on micro-and nanoscales have been found to be generally smaller compared to that at macroscales. Therefore, micro/nanotribological studies may help def'me the regimes for ultra-low friction and near zero wear.

• Progress in Superconductivity
• /
• 제9권1호
• /
• pp.96-101
• /
• 2007

[ $YBa_2Cu_3O_{7-{\delta}}$ ] films have been prepared on $LaAlO_3$ (100) single-crystal substrates by a metalorganic deposition using dichloroacetate precursors (DCA-MOD). Calcination conditions were varied in order to optimize the microstructure and the superconducting properties of YBCO film. Coated films were calcined at various temperatures ranging from $400{\sim}700^{\circ}C$ in flowing humid oxygen atmosphere. Ramping rate to calcination tempertures was $2.22^{\circ}C/min$. Conversion heat treatment was performed at $800^{\circ}C$ for 2 h in flowing Ar gas containing 1000 ppm oxygen with a humidity of 9.45%. Observations of surface and cross sectional SEM microstructure showed that the particle size in the calcined film increased in the range of 100-200 nm with heating rate and the calcination temperature. SEM EDS analysis showed that 13 a/o of chlorine was contained in the calcined film. It was also observed that the porosity increased with the heating rate and temperature. Porous microstructure was developed when YBCO films were prepared using porous calcined film. Dense microstructure and high $J_c$ over $1\;MA/cm^2$ was obtained when calcination was carried out at the temperature of $500^{\circ}C$ with a heating rate of $2.22^{\circ}C/min$.

• 대한화학회지
• /
• 제37권4호
• /
• pp.401-407
• /
• 1993

티타늄 금속판을 공기산화와 수증기 산화하여 만든 $TiO_{2-x}$ 박막을 전극으로 사용하여 1M NaOH 용액에서 전기화학적 성질을 연구하였다. 순환 전압 전류법에 의한 산소의 환원전위는 SCE에 대해 -0.9 ∼ -1.0 V 근처에서 나타났으며 이들 반응은 전체적으로 비가역적으로 진행되었다. 수증기 산화법에 의해 제조된 $TiO_{2-x}$ 전극들의 전기화학적 성질들은 공기 산화법에 의해 제조된 것과 다르게 나타났으며 900$^{\circ}$이상의 온도에서 제조된 전극들은 단결정 $TiO_2$ 전극들의 전기화학적 성질과 비슷하였다. $TiO_{2-x} $전극에서 산소위 환원전위는 flat band 전위보다 더 양전위 쪽에서 나타났으며 pH 증가에 따라 60mV/pH 정도 감소되었다.

• 한국재료학회지
• /
• 제1권2호
• /
• pp.93-98
• /
• 1991

The as-grown $YBa_2Cu_3O_{7-x}$ superconducting thin films on MgO(100) substrate have been prepared by a reactive coevaporation method. The superconducting transition temperature, surface morphology and crystalline quality were examined as a function of the substrate temperature ranging from $450^{\circ}C$ to $590^{\circ}C$. From the reflection high energy electron diffraction (RHEED) analysis, it was found the film consisted of almost amorphous phase with a halo pattern deposited at the substrate temperature of $450^{\circ}C$. The film deposited at the substrate temperature of $510^{\circ}C$ consisted of polycrystalline phase, showing a broad ring pattern. On the other hand, for the film deposited at $590^{\circ}C$, RHEED showed spotty pattern indicating that this film consisted of single crystal phase. It has rough film surface due to the surface outgrowth. The surface outgrowth increased as the substrate temperature increased from $510^{\circ}C$ to $590^{\circ}C$. the surface outgrowth may be due to the anisotropic growth rate. The highest transition temperature obtained in this study was $Tc_{zero}$ of 83K with $Tc_{onset}$ of 88K for the film deposited at $590^{\circ}C$ using activated RF oxygen plasma.

• 한국세라믹학회지
• /
• 제49권6호
• /
• pp.620-624
• /
• 2012

The role of moisture remaining inside the deposition chamber during the formation of the cubic boron nitride (c-BN) phase in BN film was investigated. BN films were deposited by an unbalanced magnetron sputtering (UBM) method. Single-crystal (001) Si wafers were used as substrates. A hexagonal boron nitride (h-BN) target was used as a sputter target which was connected to a 13.56 MHz radiofrequency electric power source at 400 W. The substrate was biased at -60 V using a 200 kHz high-frequency power supply. The deposition pressure was 0.27 Pa with a flow of Ar 18 sccm - $N_2$ 2 sccm mixed gas. The inside of the deposition chamber was maintained at a moisture level of 65% during the initial stage. The effects of the evacuation time, duration time of heating the substrate holder at $250^{\circ}C$ as well as the plasma treatment on the inside chamber wall on the formation of c-BN were studied. The effects of heating as well as the plasma treatment very effectively eliminated the moisture adsorbed on the chamber wall. A pre-deposition condition for the stable and repeatable deposition of c-BN is suggested.

• 대한화학회지
• /
• 제37권12호
• /
• pp.1010-1018
• /
• 1993

티타늄 금속판을 양극산화하여 제조한 $TiO_2$ 박막을 전극으로 사용하여 1M NaOH 용액에서 광전기화학적 성질을 연구하였다. $TiO_2$ 전극들의 flatband potential은 대략 -0.8V 정도로 이들 값은 단결정 $TiO_2$에서 보다 0.2V만큼 양전위 방향으로 이동되어 나타났다. 순환 전압 전류법에 의한 산소의 환원전위는 SCE에 대해 -0.95V 근처에서 나타났으며, 반응은 전체적으로 비가역적으로 진행되었다. 또한 전극의 광전류는 단결정 $TiO_2$에서 보다 더 단파장에서 나타났으며 전류밀도는 감소되었다.