• 한국재료학회지
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• 제14권3호
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• pp.191-195
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• 2004

Tunnel junctions with AI-N barriers fabricated by microwave-excited plasma were studied. When the Al thickness, nitridation time, and annealing temperature were 1 nm (0.8 nm), 50 s (35 s), and $280^{\circ}C$ ($300^{\circ}C$), TMR ratio and resistance-area product (RA) were 49% (34%) and $3 ${\times}$ 10^4$ $\Omega$$\mu\m^2$ ($1.5 ${\times}$ 10^4$ $\Omega$$\mu\m^2$), respectively. In order to clarify the annealing temperature dependence of TMR ratio, the local transport properties were measured for Ta 5 nm/Cu 20 nm/Ta 5 nm$29_{76}$ $Fe_{24}$ 2 nm/Cu 5 nm/M $n_{75}$$Ir_{25}$ 10 nm/ $Co_{71}$ $Co_{29}$ 4nm/Al-N junction with Al thickness of 0.8 nm and nitridation time of 35s at various temperatures. The increase of TMR ratio after annealing at $300^{\circ}C$, where the TMR ratio of the corresponding MTJ had the maximum value of 34%, can be well explained by the enhancement of the average barrier height ($\Phi_{ave}$) and the reduction of its fluctuation. After further annealing at $340^{\circ}C$, the leakage current was observed and the TMR ratio decreaseded

• 한국추진공학회지
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• 제19권1호
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• pp.25-32
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• 2015

원통 모델에 공기저항저감 효과를 검증하기 위해서 원통형에 적합한 유연성 플라즈마 구동기를 제작하였다. 다양한 풍속에서 플라즈마 유동제어 풍동시험을 수행하였으며, CFD 해석과 유동가시화를 수행하였다. 풍속이 느린 저속 구간에서는 유동박리가 발생하지 않아 플라즈마 유동제어 효과가 없었다. 풍속 14 m/s 에서 14% 정도 항력이 저감되었으며, 풍속이 증가된 17 m/s 의 경우 항력이 27% 저감되었다. CFD 해석과 유동가시화의 비교를 통해 DBD플라즈마 구동기는 원통 주변의 압력차를 감소시켜 와류의 크기가 줄어든 것으로 확인되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.167-167
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• 2011

Magnetic random access memory (MRAM) is one of the prospective semiconductor memories for next generation. It has the excellent features including nonvolatility, fast access time, unlimited read/write endurance, low operating voltage, and high storage density. MRAM consists of magnetic tunnel junction (MTJ) stack and complementary metal-oxide semiconductor (CMOS). The MTJ stack is composed of various magnetic materials, metals, and a tunneling barrier layer. For the successful realization of high density MRAM, the etching process of magnetic materials should be developed. Among various magnetic materials, FePt has been used for pinned layer of MTJ stack. The previous etch study of FePt magnetic thin films was carried out using $CH_4/O_2/NH_3$. It reported only the etch characteristics with respect to the variation of RF bias powers. In this study, the etch characteristics of FePt thin films have been investigated using an inductively coupled plasma reactive ion etcher in various etch chemistries containing $CH_4$/Ar and $CH_4/O_2/Ar$ gas mixes. TiN thin film was employed as a hard mask. FePt thin films are etched by varying the gas concentration. The etch characteristics have been investigated in terms of etch rate, etch selectivity and etch profile. Furthermore, x-ray photoelectron spectroscopy is applied to elucidate the etch mechanism of FePt thin films in $CH_4$/Ar and $CH_4/O_2/Ar$ chemistries.

• 한국공간구조학회:학술대회논문집
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• 한국공간구조학회 2006년도 춘계 학술발표회 논문집 제3권1호(통권3호)
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• pp.91-101
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• 2006

We have conducted the study about the shelter effect against the wind by using the wind fence with various porosities and the measured distance from the wind fence, in three different types of it ; (Circle wind fence, Vertical wind fence, Horizontal wind fence) The shelter effect and turbulence characteristics of the selected wind barrier is throughly investigated by wind tunnel test. flow characteristics of velocities and turbulences behind wind fence were measured using hot-wire anemometer. we characterize the turbulence behind the wind fence by varying the porosity of 0 %, 20 %, 40%, and 60%, and the distances from the wind fence from 1 H to 9 H with maintaining the uniform flow velocity of 6 m/s. In addition, we investigated the overall characterization of the wind fence by measuring total of twenty eight points on the wind fence, which forms the lattice structure on it with seven points in lateral direction and four points in vertical direction. The results of analysis from the circle wind fence indicate that the degree of the turbulence is lowered and the velocity of the wind is decreased when the porosity of 40 % are used at the distance from 3 H to 9 H. On the other hand, the vertical, horizontal wind fence with the porosity of 20% is more advantageous at the distance of 2 H to 9 H. For the effectiveness of the wind fence depending on the position, the center part is the greatest and it decreases at the edges with 10 % to 30 % less than that of at the center.

• 터널과지하공간
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• 제31권5호
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• pp.333-359
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• 2021

고준위방사성폐기물 처분시스템에서는 처분용기 인근에서 용기 금속 물질의 부식 등 여러 이유로 인해 수소, 라돈 등의 기체가 발생할 수 있다. 기체 발생 속도가 투수계수가 낮은 벤토나이트 완충재 공극에서의 기체 확산 속도보다 커질 경우, 형성된 기체가 축적된다. 기체 압력이 증가하여 유입 압력에 도달하면 완충재 내부로 기체의 팽창 흐름 및 이류가 발생하게 된다. 기체의 급격한 팽창 흐름 발생 시 방사성 핵종이 완충재 외부로 유출될 가능성이 있으므로, 처분시설의 설계 과정에서 점토 기반 물질에서의 기체 유동의 영향성 및 공학적방벽의 건전성을 평가하기 위해 기체 이동 현상에 대한 거동 특성을 명확하게 규명할 필요가 있다. 전세계적으로 벤토나이트 완충재 내 기체 이동 현상 규명을 위한 실험적 연구와 이를 모사할 수 있는 전산 수치 모델 개발 연구가 활발히 진행되고 있다. 본 기술보고에서는 현재까지 수행된 기체 주입 시험 및 전산 수치모델 관련 주요연구를 소개하고 향후 기체 이동 현상 규명을 위한 연구 수행 방향에 대해 정리하였다.

• 터널과지하공간
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• 제31권3호
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• pp.167-183
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• 2021

고준위방사성폐기물 처분장의 장기 안전성 확보를 위해서는 공학적방벽 및 천연방벽 내에서 발생하는 복잡한 열-수리-역학-화학적(THMC) 복합거동 해석에 대한 이해가 필수적이다. 특히 고준위방사성폐기물에서 발생하는 열로 인해 암반 및 완충재 내의 지하수에서 압력 증가 및 상변화가 발생하게 되며, 지하수의 유입으로 인해 공학적방벽 내 포화도가 변화하게 된다. 또한 포화도의 변화는 완충재 내에서의 열전달 및 다상 유동 특성에 영향을 미치게 된다. 따라서 복합거동 특성의 복잡성으로 인해 수치해석은 처분시스템에서의 THMC 복합거동 평가와 예측 및 안전성 평가에 있어 강점을 지니고 있으며, DECOVALEX 국제공동연구는 THMC 복합거동에 대한 이해도 증진 및 해석기법 검증을 목적으로 1992년부터 시작되었다. 국내에서는 2008년부터 한국원자력연구원이 지속적으로 참여하여 연구를 수행하고 있으며, 본 기술보고에서는 현재 진행 중인 DECOVALEX-2023의 주요 연구내용을 국내 암반 및 지반공학자들에게 소개하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.128-129
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• 2008

The annealing effects of $SiO_2/Si_3N_4$ stacked tunneling dielectrics were investigated. I-V characteristics of band gap engineered tunneling gate stacks consisted of $Si_3N_4/SiO_2/Si_3N_4$(NON), $SiO_2/Si_3N_4/SiO_2$(ONO) dielectrics were evaluated and compared with $SiO_2$ single layer using the MOS(Metal-Oxide-Semiconductor) capacitor structure. The leakage currents of engineered tunneling barriers (ONO, NON stacks) are lower than that of the conventional $SiO_2$ single layer at low electrical field. Meanwhile, the engineered tunneling barriers have larger tunneling current at high electrical field and improved electrical characteristics by annealing processes than $SiO_2$ layer.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.21-21
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• 2003

Microstructure and magnetic transport phenomina in rf sputtered AlN/Co type ten-layered discontinuous films of nanoscaled [AlN (3 nm)/Co (t nm)]...$\sub$10/ with t$\sub$Co/=1.0∼2.0 nm have been investigated. The microstructure and tunneling magnetic resistance of the samples are strongly dependent on the thickness of Co layer. Negative tunneling magneto-resistance due to the spin-dependent transport has been observed along the current-in-plane configuration in the samples having the Co layers below 1.6 nm thick. When the thickness of Co layer was less than 1,2 nm, randomly oriented granular Co particles were completely isolated and embedded in amorphous AlN matrix, and the films showed the superparamagnetic behavior with a high MR value of Δ$\rho$/$\rho$$\sub$0/=1.8 %. As t$\sub$Co/ increases, a transition from the regime of co-existence of superparamagnetic and ferromagnetic behaviors to ferromagnetic behavior was observed. Tunneling barrier called "decay length for tunneling" for the films having the thickness of Co layer from 1.4 to 1.6 nm was measured to be ranged from 0.004 to 0.021 ${\AA}$$\^$-1/.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.29-29
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• 1999

The synthesis of layered structures on the nanometer scale has become essential for continued improvements in the operation of various electronic and magnetic devices. Abrupt metal-metal interfaces are desired for applications ranging from metallization in semiconductor devices to fabrication of magnetoresistive tunnel junctions for read heads on magnetic disk drives. In particular, characterizing the interface structure between various transition metals (TM) and aluminum is desirable. We have used the techniques of MeV ion backscattering and channeling (HEIS), x-ray photoemission (ZPS), x-ray photoelectron diffraction(XPD), low-energy ion scattering (LEIS), and low-energy electron diffraction(LEED), together with computer simulations using embedded atom potentials, to study solid-solid interface structure for thin films of Ni, Fe, Co, Pd, Ti, and Ag on Al(001), Al(110) and Al(111) surfaces. Considerations of lattice matching, surface energies, or compound formation energies alone do not adequately predict our result, We find that those metals with metallic radii smaller than Al(e.g. Ni, Fe, Co, Pd) tend to form alloys at the TM-Al interface, while those atoms with larger atomic radii(e.g. Ti, Ag) form epitaxial overlayers. Thus we are led to consider models in which the strain energy associated with alloy formation becomes a kinetic barrier to alloying. Furthermore, we observe the formation of metastable fcc Ti up to a critical thickness of 5 monolayers on Al(001) and Al(110). For Ag films we observe arbitrarily thick epitaxial growth exceeding 30 monolayers with some Al alloying at the interface, possible driven by interface strain relief. Typical examples of these interface structures will be discussed.

• Journal of Magnetics
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• 제8권2호
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• pp.98-102
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• 2003

Microstructure and magnetic transport phenomina in rf sputtered AIN/CO type ten- layered discontinuous films of nanoscaled [AIN(3 nm)/Co(t nm)]…$_10$ with t$_Co$=1.0∼2.0 nm have been investigated. The microstructure and tunneling magnetic resistance of the samples are strongly dependent on the thickness of Co layer, Negative tunneling magneto-resistance due to the spin-dependent transport has been observed along the current-in-plane configuration in the samples having the Co layers below 1.6 nm thick. When the thickness of Co layer was less than 1.2 nm, randomly oriented granular Co particles were completely isolated and embedded in amorphous AIN matrix, and the films showed the superparamagnetic behavior with a high MR value of ${\Delta}p/p_0$=1.8%. As t$_Co$ increases, a transition from the regime of co-existence of superparamagnetic and ferromagnetic behaviors to ferromagnetic behavior was observed. funneling barrier called “decay length far tunneling” fur the films haying the thickness of Co layer from 1.4 to 1.6 nm was measured to be ranged from 0.004 to 0.021 ${\AA}$$^{-1}$.