Nb 버퍼층과 거대자기저항-스핀밸브 하이브리드 다층박막의 자기저항 특성

양우일(Woo-Il Yang),최종구(Jong-Gu Choi),이상석(Sang-Suk Lee) 한국자기학회 2017 韓國磁氣學會誌 Vol.27 No.3

The IrMn based GMR-SV films with three different buffer layers were prepared on Corning glass by using ion beam deposition and DC magnetron sputtering method. The major and minor magnetoresistance curves for three different buffer layers beneath the structure of NiFe(15 ㎚)/CoFe(5 ㎚)/Cu(2.5 ㎚)/CoFe(5 ㎚)/NiFe(7 ㎚)/IrMn(10 ㎚)/Ta(5 ㎚) at room temperature have shown different magnetoresistance properties. When the samples were annealed at 250 ℃ in vacuum, the magnetoresistance ratio, the coercivity of pinned ferromagnetic layer, and the interlayer coupling field of free ferromagnetic layer were enhanced while the exchange bias coupling field did not show noticeable changes.

거대자기저항-스핀밸브와 고온초전도체 사이에 있는 틈 층에 의한 전류전달효과 특성연구

양우일(Woo-Il Yang),강병욱(Byeong-Uk Kang),최종구(Jong-Gu Choi),카지드마(Purevdorj Khajidmaa),이상석(Sang-Suk Lee) 한국자기학회 2018 韓國磁氣學會誌 Vol.28 No.5

A giant magnetoresistive - spin valve (GMR-SV) NiFe/CoFe/Cu/CoFe/IrMn/Ta multilayer film was fabricated by ion beam deposition on a commercial high - temperature superconductor Y₁Ba₂Cu₃O<SUB>7 - x</SUB> (YBCO) film. The thickness of the hybrid YBCO thin film was 300 nm and one of the antiferromagnetic IrMn-based GMR-SV thin film was 55 nm. The superconductor characteristics of the YBCO thin films were confirmed by the R-T curve measured with 4-terminal and the Q-T and I-V curves measured with a microwave cavity resonator. In particular, the phenomenon of negative magnetoresistance (MR) ratio in the reversed MR curve of -7.4% is explained by the current transfer effect from the MR and the I-V curves measured by the 2-, 3-, and 4-probe methods at 77 K below the critical temperature. It was also confirmed by SEM image that a gap layer of 9.3 nm was present between the YBCO film and the GMR-SV multilayer. The residual resistance of 0.456 Ω was measured due to the presence of the gap layer and the difference in current transfer was caused by the superconductor depending on the change of the spin magnetization array configuration of GMR-SV.

초전도체 YBCO/NiFe/CoFe/Cu/CoFe/IrMn 다층박막에서의 스핀밸브 효과에 의한 반전된 자기저항비 특성 연구

양우일(Woo-Il Yang),최종구(Jong-Gu Choi),이상석(Sang-Suk Lee) 한국자기학회 2018 韓國磁氣學會誌 Vol.28 No.1

The antiferromagnetic IrMn based GMR-SV (giant magnetoresistance-spin valve) multilayer on the high-Tc superconductor YBCO film fabricated by using ion beam deposition and dc magnetron sputtering systems. The hybrid multilayer structure performed with the typical GMR-SV film and the superconducting YBCO film was compared two different magnetoresistance curves, which are measured at a room and a liquid nitrogen temperatures below the critical temperature. The exchange biased coupling field (H<SUB>ex</SUB>), coercivity (H<SUB>c</SUB>), magnetoresistance ratio (MR (%)) for the pure GMR-SV multilayer measured at 77 K are enhanced to the increment values of 80 Oe, 43 Oe, and 6.6% more than those measured at room temperature, respectively. In case of YBCO/GMR-SV mulitlayer, the H<SUB>ex</SUB>, H<SUB>c</SUB>, and MR (%) are 410 Oe, 240 Oe, −4.6% more than those measured at 77 K, respectively. The phenomenon having a negative MR (%) below the critical temperature is explained the current in plane tunneling (CIPT) effect when the resistance of the middle G layer between the high-temperature superconductor YBCO and the GMR-SV multilayer reaches a level comparable to the plane resistance of the upper metal layer.

High-Q $Yba_2Cu_3O_{7-\delta}$ 고온초전도체 공진기를 이용한 주파수 튜닝이 가능한 고성능 발진기 제작

양우일,이재훈,허정,이상영,Yang Woo Il,Lee Jae Hun,Hur Jung,Lee Sang Young 대한전자공학회 2005 電子工學會論文誌-TC (Telecommunications) Vol.42 No.7

위상잡음(phase noise)이 작은 발진기(oscillator)는 주파수 대역의 효율적 활용과 고속의 데이터 전송을 가능하게 하는 통신 시스템의 구축과 Doppler 효과를 이용하는 RADAR의 제작을 위한 핵심소자로서 발진기의 위상잡음은 공진부의 loaded Q($Q_{L}$)값이 클수록 작아진다. 본 논문에서는 고온초전도 $YBa_2Cu_3O_{7-\delta}$(YBCO) 박막을 사용하여 $TE_{011}$ 모드 고온초전도 YBCO-루타일 공진기를 제작하고 이 공진기가 공진단으로 사용된 발진기 특성의 시뮬레이션, 발진기 제작 및 위상잡음 측정 연구를 수행하였다. 23.5 K 및 $TE_{01\delta}$ 모드 공진주파수인 8.545 GHz에서 $Q_{L}$=180000 인 고온초전도 YBCO-루타일 공진기를 사용하여 제작된 발진기의 위상잡음은 1 KHz offset에서 -104.8 dBc/Hz 정도의 매우 작은 값을 지님을 확인하였다. Piezoactuator를 이용한 상온에서의 발진기 주파수의 튜닝 결과를 제시하고, 이러한 공진기가 사용된, 튜닝 가능한 고성능 발진기의 제작 가능성에 대해 논의하였다. We investigated the phase noise of an oscillator with a extremely high-Q resonator used as the resonant element. A TE$_{011}$ mode rutile-loaded resonator with high-temperature superconductive (HTS) $YBa_2Cu_3O_{7-\delta}$(YBCO) films used as the endplates is prepared for this purpose. At 23.5 K, the unloaded Q and the loaded Q are 863000 and 180000, respectively. The phase noise of -104.8 dBc/Hz at 1 KHz offset was observed for the oscillator having a resonator with $Q_{L}$ =180000 at the $TE_{01\delta$ mode resonant frequency of 8.545 GHz at 23.5 K Such oscillators with very low phase noise are expected to be used for building up communication systems capable of efficient use of the frequency band and high-speed data transmission as well as for Doppler radars. Frequency tuning could be realized for the resonator by using a piezoactuator Applicability of the tunable rutile resonator for fabricating tunable oscillators of high performances is discussed.

초전도체 박막의 표면저항 측정용 유전체 공진기에 대한 Geometrical factor의 비교 : 전자기장 해석 대 시뮬레이션

양우일,정호상,김명수,조남순,주기남,이상영,Yang, Woo-Il,Jung, Ho-Sang,Kim, Myung-Su,Cho, Man-Soon,Choo, Kee-Nam,Lee, Sang-Young 한국초전도학회 2011 Progress in superconductivity Vol.13 No.2

유전체 공진기법을 이용하여 초전도체 박막의 표면저항을 측정할 경우, 공진기의 $Q_U$로부터 초전도체 박막의 표면저항을 구하기 위해 알아야 하는 G-factor를 시뮬레이션과 전자기장 해석을 이용해서 구한 후 두 값을 비교하였다. 시뮬레이션 과정에서 사용된 mesh 수가 증가할수록 시뮬레이션으로 구한 G-factor의 크기와 전자기장 해석을 통해 얻은 값 간의 차이가 줄어들게 됨을 확인하였다. 공진기에 따라 mesh 수 증가에 따른 G-factor의 정확도 증가가 조금씩 다르게 나타났는데, 이는 공진기와 유전체의 크기에 따라 simulation program이 계산하는 개당 mesh의 크기가 각기 다르기 때문으로 여겨진다. 19.6 GHz의 공진주파수를 지닌 사파이어 공진기의 경우 시뮬레이션과 전자기장 해석을 통해 구한 G-factor의 차이를 이용하여 표면저항의 불확도 추정치를 온도의 함수로 구했으며 $Q_U$를 2 % 이내의 상대 불확도로 측정할 경우 G-factor의 불확도 변화에 따른 표면저항의 상대 불확도 변화를 확인하였다. 본 연구 결과는 전자기장 해석이 매우 어렵거나 불가능한 구조의 유전체 공진기 (예로서 open-ended 평행판 유전체 공진기)의 G-factor를 시뮬레이션을 이용하여 구하여 초전도체 박막의 표면저항을 $Q_U$로부터 측정하고자 할 때 측정 온도 구간에서 허용되는 표면저항의 불확도를 고려하여 G-factor의 시뮬레이션 시 사용되는 mesh 수가 결정되어야 함을 보여준다. In the dielectric resonator method, which has been widely used for measuring the microwave surface resistance of superconductors, accuracies in the geometrical factors (G-factors) affect the uncertainty in the measured surface resistance. We compare the G-factors of short-ended sapphire resonator as obtained by using field analysis with those by using computer simulations: The former is obtained by using the analytic expressions for the electric and the magnetic field components inside the resonator, and the latter by using computer software. The G-factors as obtained by using the latter appear to be closer to those obtained by using the former as the resonator space is divided into larger number of sub-space, i.e., a tighter mesh, with a difference of ~8 % observed for a mesh of 14400 sub-spaces reduced to ~2 % for 114996 sub-spaces. Variations in the relative uncertainty in the surface resistance of typical $YBa_2Cu_3O_{7-\delta}$ superconductor films with those in the G-factors are studied, which provides an upper limit of the relative uncertainty in the G-factors required for realizing the target uncertainty in the surface resistance. These results could be useful in estimating the optimum number of meshes for obtaining the G-factors through computer simulations.

마이크로파 공진기를 이용한 YBCO 박막 두께의 비파괴적 측정: 캘리브레이션 박막 두께의 불확도의 역할

김명수,정호상,양우일,이상영,Kim, Myung-Su,Jung, Ho-Sang,Yang, Woo-Il,Lee, Sang-Young 한국초전도학회 2012 Progress in superconductivity Vol.14 No.1

마이크로파 측정법으로 ~40 GHz의 공진주파수를 지닌 공진기를 이용하여 비파괴적으로 YBCO 초전도체 박막의 두께를 측정할 경우 calibration용 YBCO 박막의 두께의 불확도가 마이크로파로 측정된 두께의 불확도에 미치는 영향을 70 - 360 nm 두께를 지닌 5 개의 YBCO 박막에 대해 연구하였다. Calibration용 박막으로는 약 150 nm의 두께를 지닌 박막이 사용되었는데, 이 박막의 두께의 불확도는 박막 표면의 거칠기를 고려하여 결정하였다. 본 연구 결과, calibration용 박막의 불확도가 마이크로파로 측정된 박막의 두께에 상당한 영향을 준다는 것을 확인하였으며, ~ 40 GHz에서 연구에 사용된 모든 박막에 대해 측정 두께가 5% 이내의 상대 불확도를 지니기 위해서는 calibration용 박막의 두께의 상대 표준불확도가 2.7% 이내의 값을 가져야 함을 알 수 있었다. 본 연구 결과는 마이크로파를 이용하여 박막의 두께를 측정할 경우 측정 두께의 상대 불확도의 목표치를 구현하기 위해서는 표면 거칠기로 인한 두께의 불확도가 일정 값 이하인 박막 만이 calibration용 박막으로 사용될 수 있음을 보여준다. Microwave metrology for the thickness of metallic or superconductive films provides a new way to measure the film thickness in a non-invasive way by using microwave resonators, with the measurement accuracy affected by standard uncertainties in the resonator quality factor, temperature-dependent resonant frequency and the dimensions of the resonators. Here we study effects of the standard uncertainty in the thickness, $t_{cal}$, of a calibration $YBa_2Cu_3O_{7-{\delta}}$ (YBCO) film on the measured thicknesses, $t_{RF}$, by using a ~ 40 GHz microwave resonator. For the study, we used five YBCO films having the thicknesses of 70 - 360 nm, for which relative standard uncertainties in $t_{RF}$ due to that in $t_{cal}$ are obtained. The standard uncertainty in $t_{cal}$ was determined with the surface roughness of the film taken into account. It appeared that relative standard uncertainty in $t_{cal}$ significantly affects the $t_{RF}$ values, with the values of 1% (5%) in the former resulting in those of 1-2% (5-9%) for the latter at 10 K. Our results show that, for realizing relative standard uncertainties less than 5% in $t_{RF}$ for all the YBCO films, the surface roughness of the calibration films should be small enough to realize a relative standard uncertainty of less than 2.7% in $t_{cal}$.

산소 결핍된 TiO<SUB>2 − δ</SUB> 박막의 상온 강자성 연구

박영란(Young Ran Park),김광주(Kwang Joo Kim),양우일(Woo Il Yang),이상영(Sang Young Lee),김성철(Chul Sung Kim) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.4

A room-temperature ferromagnetism has been observed for oxygen-deficient rutile and anatase TiO<SUB>2 ? δ</SUB> films. XPS data revealed the existence of Ti<SUP>3+</SUP> ions, for compensating the charge imbalance caused by oxygen vacancies in the film. The observed ferromagnetism is attributable to the spin (3d¹) alignment of the Ti<SUP>3+</SUP> ions. Such spin alignment can happen through magnetic polaron formed by trapped electron in oxygen vacancy and magnetic Ti<SUP>3+</SUP> ions around it.

블록 암호를 이용한 안전한 심층 암호

유정재(Jeong-Jae Yu),김종현(Jong-Hyun Kim),박종혁(Jong-Hyuck Park),양우일(Woo-Il Yang),이상진(Sang-Jin Lee) 한국정보보호학회 2003 정보보호학회논문지 Vol.13 No.3

NiFe/Cu/NiFe 박막과 YBa₂Cu₃O<SUB>7−x </SUB>박막 사이 NiO 층의 두께에 따른 전류전달효과에 의한 음의 자기저항비 특성 연구

카지드마(Purevdorj Khajidmaa),강병욱(Byeong-Uk Kang),최종구(Jong-Gu Choi),이상석(Sang-Suk Lee),양우일(Woo-Il Yang) 한국자기학회 2019 韓國磁氣學會誌 Vol.29 No.2

The magnetoresistance (MR) curves of giant magnetoresistive-spin valve (GMR-SV) multilayer on Corning glass and sapphire/high-temperature superconductor (HTS) YBa₂Cu₃O<SUB>7−x</SUB> (YBCO) film fabricated by magnetron sputtering were compared and analyzed. Hybrid type HTS and GMR-SV multilayer film with antiferromagnetic NiO thickness of 10 nm has a negative MR ratio of−7.7 %, an exchange coupling field (H<SUB>ex</SUB>) of 120 Oe, a coercive force (H<SUB>c</SUB>) of 125 Oe, respectively. However, there is exist a positive MR ratio of +7.3 % in case of NiO thickness of 60 nm. The glass/NiO/NiFe/Cu/NiFe/Ta multilayer showed linear current-voltage (IV) curve, but the Al₂O₃/YBCO/NiO(10 nm, 60 nm)/NiFe/Cu/NiFe/Ta multilayer showed a nonlinear I-V curve in which the resistance value of 1.15 Ω and 59.4 Ω decreased to 1.02 Ω and 50.2 Ω when the current of 15.7 mA increased to 1.67 mA, respectively. This results are explained by the current transfer effect in the 4-probe electrode measurement method occurred when the resistance of the YBCO film is 0.

수치해석을 이용한 코그메틱용 스프레이 미립화를 위한 부품설계 및 금형 설계에 과한 연구

서형진,손창우,장영주,양우,서태일,Seo, Hyoung-Jin,Son, Chang-Woo,Jang, Young-Ju,Yang, Woo,Seo, Tae-Il 한국금형공학회 2015 한국금형공학회지 Vol.9 No.2

This paper presented characterization of spray velocity and angle of spray nozzle systems for cosmetic products. Diameter and length of nozzle orifice were chosen as shape factors of the spray system. Spray orifice of the spray pattern is a factor influencing the quality of the product. Fluid analysis was conducted by using "Fluent" to obtain spray angle and velocity. RSM (Response Surface Method) was used to approximate the relationship between these 2 factors and spray characteristics. To evaluate the proposed method, experimental work with existing was conducted and good agreement between simulation and experimental results.