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윤대식,이영,박범찬,김철기,김종오,Yoon, Tae-Sick,Tsunoda, Masakiyo,Takahashi, Migaku,Li, Ying,Park, Bum-Chan,Kim, Cheol-Gi,Kim, Chong-Oh 한국재료학회 2003 한국재료학회지 Vol.13 No.4
Ferromagnetic tunnel junctions, Ta/Cu/Ta/NiFe/Cu/$Mn_{75}$ $Ir_{25}$ $Co_{70}$ $Fe_{30}$/Al-oxide, were fabricated by do magnetron sputtering and plasma oxidation process. The effect of annealing temperature on the local transport properties of the ferromagnetic tunnel junctions was studied using contact-mode Atomic Force Microscopy (AFM). The current images reflected the distribution of the barrier height determined by local I-V analysis. The contrast of the current image became more homogeneous and smooth after annealing at $280^{\circ}C$. And the average barrier height $\phi_{ave}$ increased and its standard deviation $\sigma_{\phi}$ X decreased. For the cases of the annealing temperature more than $300^{\circ}C$, the contrast of the current image became large again. And the average barrier height $\phi_{ave}$ decreased and its standard deviation $\sigma_{\phi}$ increased. Also, the current histogram had a long tail in the high current region and became asymmetric. This result means the generation of the leakage current that is resulted from the local generation of a low barrier height region. In order to obtain the high tunnel magnetoresistance(TMR) ratio, the increase of the average barrier height and the decrease of the barrier height fluctuation must be strictly controlled.led.
질화법으로 제작한 강자성 터널링 접합의 국소전도 및 자기저항 특성
윤대식,박범찬,이영우,이영,김종오,Yoon Tae Sick,Tsunoda Masakiyo,Takahashi Migaku,Park Bum Chan,Lee Young-Woo,Li Ying,Kim Chong Oh 한국재료학회 2004 한국재료학회지 Vol.14 No.3
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
마이크로파 여기 프라즈마법으로 제조한 강자성 터널링 접합의 국소전도특성
윤대식(Tae Sick Yoon),김철기(Cheol Gi Kim),김종오(Chong-Oh Kim),Masakiyo Tsunoda(Masakiyo Tsunoda),Migaku Takahashi(Migaku Takahashi),Ying Li(Ying Li) 한국자기학회 2003 韓國磁氣學會誌 Vol.13 No.2
Ferromagnetic tunnel junctions were fabricated by dc magnetron sputtering and plasma oxidation process. The local transport properties of the ferromagnetic tunnel junctions were studied using contact-mode Atomic Force Microscopy (AFM) and the local current-voltage analysis. Tunnel junctions with the structure of sub./Ta/Cu/Ta/NiFe/Cu/Mn_(75)Ir_(25)/Co_(70)Fe_(30)/Al-oxide were prepared on thermally oxidized Si wafers. Al-oxide layers were formed with microwave excited plasma using radial line slot antenna (RLSA) for 5 and 7 sec. Kr gas was used as the inert gas mixed with O₂ gas for the plasma oxidization. No correlation between topography and current image was observed while they were measured simultaneously. The local current distribution was well identified with the distribution of local barrier height. Assuming the gaussian distribution of the local barrier height, the ferromagnetic tunnel junction with longer oxidation time was well fitted with the experimental results. As contrast, in the case of the shorter time oxidation junction, the current mainly flow through the low barrier height area for its insufficient oxygen. Such leakage current might result in the decrease of tunnel magnetoresistance (TMR) ratio.
김현빈(Hyun Bin Kim),윤대식(Tae Sick Yoon),N. D. Ha(N. D. Ha),김종오(Chong Oh Kim) 한국자기학회 2005 韓國磁氣學會誌 Vol.15 No.1
The influence of O₂ partial pressure on saturation magnetization, coercivity, anisotropy field and effective permeability(over 1 ㎓) of as-deposited Co-Fe-Al-O thin films, which were fabricated by RF magnetron reactive sputtering method, were investigated. The Co_(69.9)Fe_(20.5)A_(14.4)O_(5.2) thin film fabricated at O₂ partial pressure of 4% exhibits the best magnetic softness with saturation magnetization (4πMs) of 18.1 kG, coercivity (Hc) of 0.82 Oe, anisotropy field (Hk) of 24 Oe, and effective permeability (μeff) about 1,024 above 1 ㎓. The electrical resistivity of Co-Fe-Al-O thin films were increased with increasing O₂ partial pressure, the electrical resistivity of Co_(69.9)Fe_(20.5)A_(14.4)O_(5.2) thin film with the best soft magnetic properties was 560.7 μΩ㎝. Therefore, It is assumed that the good soft magnetic properties of Co_(69.9)Fe_(20.5)A_(14.4)O_(5.2) thin film results from high electrical resistivity and large anisotropy field.
2차원 자화벡터를 이용한 퍼멀로이 박막의 이방성자기저항 해석
이영우(Young-woo Lee),호영강(Yongkang Hu),임재준(Jae-joon Lim),김철기(CheolGi Kim),김종오(Chong Oh Kim),윤대식(Tae Sick Yoon) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.4
We measured in-plane 2 dimensional magnetization vector using two pick-up coil sets and investigate the relationship between magnetization vector and anisotropic magnetoresistance. We can determine magnetization vector by measuring magnetic moment in x and y direction simultaneously. As the uniaxial magnetic anisotropy of permalloy film increases, magnetoresistance approaches the expectation which is calculated from the angle between current vector and magnetization vector. Magnetoresistance ratio is linearly proportional to the y moment magnitude which is parallel to the current direction.