• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.277-277
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• 2007

$(Bi,La)_4Ti_3O_{12}$ (BLT) 물질은 결정 방향에 따른 강한 이방성의 강유전 특성을 나타낸다. 따라서 BLT 박막을 이용하여 FeRAM 소자 등을 제작하기 위해서는 결정의 방향성을 세심하게 제어하는 것이 매우 중요하다. 현재까지 연구된 BLT 박막의 방향성 조절 결과를 보면, BLT 박막을 스핀 코팅 법 (spin coating method)으로 중착하고, 핵생성 열처리 단계를 조절하여 무작위 방향성 (random orientation)을 갖는 박막을 제조하는 방법이 일반적이었다. 그런데 이러한 스핀 코팅법에서의 핵생성 단계의 제어는 공정 조건 확보가 너무 어려운 단점이 있다. 이러한 어려움을 극복할 수 있는 대안은 스퍼터링 증착법 (sputtering deposition method), PLD법 (pulsed laser deposition method) 등과 같은 PVD (physical vapor deposition) 법의 증착방법을 적용하는 것이다. PVD 법으로 증착하는 경우에는 이미 박막 내에 무수한 결정핵이 존재하기 때문에 핵생성 단계가 필요 없게 된다. PVD 증착법의 적용을 위해서는 타겟 (target)의 제조 및 평가 실험이 선행되어야 한다. 그런데 벌크 BLT 재료의 소결공정 조건과 전기적 특성에 관한 연구 결과는 거의 발표 되지 않고 있다. 본 실험에서는 $Bi_2O_3$, $TiO_2$ and $La_2O_3$ 분말을 이용하여 최적의 조성을 구하기 위하여 Bi양을 변화시키며 타겟을 제조 하였다. 혼합된 분말을 하소 후 pallet 형태로 성형하여 소결을 실시하였다. 시편을 1mm 두께로 연마하고, 표면에 silver 전극을 인쇄하여 전기적 특성을 측정하였다. Bi양이 3.28몰 첨가된 조성에서 최대의 잔류분극 (2Pr) 값을 얻었고, 이때의 값은 약 $18{\mu}C/cm^2$ 정도였다. 최적화된 조성 ($Bi_{3.28}La_{0.75}Ti_3O_{12}$)으로 BLT 타겟을 제조하여 PLD법으로 박막을 제조하였다. 박막 제조 시 압력은 $1{\times}10^{-1}\;{\sim}\;1{\times}10^{-4}\;Torr$ 범위에서 변화시켰다. $1{\times}10^{-1}\;Torr$ 압력을 제외하고는 모든 압력에서 BLT 박막이 증착되었다. 중착된 박막을 $650\;{\sim}\;800^{\circ}C$에서 30분간 열처리를 실시하고 전기적 특성을 평가한 결과, $1{\times}10^{-2}\;Torr$에서 증착한 박막에서 양호한 P-V (polarization-voltage) 이력곡선을 얻을 수 있었고, 이때의 잔류분극 (2Pr) 값은 약 $6\;{\mu}C/cm^2$ 이었다. 주사전자현미경 (SEM)을 이용하여 BLT 박막 표면의 미세구조도 관찰하였는데, 스핀코팅 법으로 증착한 경우에 관찰되었던 조대화된 입자들은 관찰되지 않았고, 상당히 양호한 입자 크기 균일도를 나타내었다.

• Journal of Magnetics
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• v.2 no.1
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• pp.7-11
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• 1997

The dependence of magnetoresistance (MR) ratio on various variables like the thickness of the second Co layer, on the presence of cap layer, on deposition field (Hdep) and on annealing in Co/Cu/Co sandwiches was investigated. Spin-valve sandwiches were deposited on the corning glass by means of the 3-gun dcmagnetron sputtering at a 5 mTorr partial Ar pressure and room temperature. The deposition field was varied from 70 Oe to 720 Oe. The MR curve was measured by the four-terminal method with applied magnetic field up to 1000 Oe perpendicular to the direction of a current in the film plne. The MR ratio of glass/Fe(50${\AA}$)/Co(17${\AA}$)/Cu(24${\AA}$)/Cot(${\AA}$) fabricated by making 50 ${\AA}$ of Fe buffer layer has the maximum value of 8.2% when the thickness of the second Co layer was 17${\AA}$and the deposition field was 350 Oe. In the case of glass/Fe(50${\AA}$)/Co(17${\AA}$)/Cu(24${\AA}$)/Cot(${\AA}$) with Cu cap layer on top, the decrease in the MR ratio seemed to relate with the oxidation of the second Co layer. Samples prepared with deposition field showed greater MR ratios through the formation of more complete spin valve films. After annealing for 2 hours at 300$^{\circ}C$, the MR ratio of the samples prepared with deposition field decreased rapidly while the MR raito of the sample prepared without the field remained.

• Journal of the Korean Magnetics Society
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• v.7 no.2
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• pp.82-89
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• 1997

Dependence of magnetoresistance on the thickness of Cu, type and thickness of buffer layer, and the stacking number of multilayer in the form buffer /$[Co(17{\AA}/Cu(t{\AA})]_{20}$ were investigated. To evaluate effect of annealing on this samples, X-ray diffraction analysis, vibrating sample magnetometer analysis, and magnetoresistance measurement (4-probe method) were performed. The magnetoresistance ratio exhibits a maximum of 21% for the multilayer with Cu thickness of 24$\AA$ and Fe buffer layer thickness of 50$\AA$. Deposition of film under low base pressure induces in increase magnetoresistance ratio by preventing oxidation. The multilayer annealed below 30$0^{\circ}C$ temperature allowed larger textured grain without loss in the periodicity. Magnetoresistance ratios of the multilayer with Cu thickness of 24$\AA$ and 36$\AA$ were increased due to the increase in the antiferromagnetically coupled fraction after annealing.

• Journal of the Korean Magnetics Society
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• v.2 no.3
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• pp.277-281
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• 1992

We have designed, fabricated and tested an integrated planar DC SQUID which incorporates input coil and mofulation coil in thin film structure. The SQUID uses Nb /Al-oxide /Nb Josephson junctions and Pd shunt resistors, and the SQUID loop incorporates two rings connected in series forming figure '8' structure and has the advantage of a negligibly small circulating current for the spatially homogeneous noise fields. The devices were fabricated using photolithographic technique, RF magnetron sputtering, anodic oxidation for insulation and lift-off process. The preliminary test of the fabricated SQUID at 4.2 K showed that the flux-voltage characteristics were smooth enough to adopt standard readout system, and the voltage noise was too small to be measured by direct method and so the white noise was thought to be less than $10^{-4}\;{\phi}_o/\;\sqrt{H_z}$.

• Transactions on Electrical and Electronic Materials
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• v.10 no.2
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• pp.58-61
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• 2009

The electrical stability of ZnO: Al thin films deposited on glass substrate by the RF magnetron sputtering method have been modified by a hydrogen annealing treatment and $SiO_2$ protection layer. AZO thin films were deposited at room temperature and different RF powers of 50, 100, 150, and 200 W to optimize the AZO film growth condition. The lowest value of resistivity of $9.44{\times}10^{-4}{\Omega}cm$ was obtained at 2 mtorr, room temperature, and a power level of 150 W. Then, the AZO thin films were annealed at $250-400^{\circ}C$ for 1 h in hydrogen ambient. The minimum resistivity obtained was $8.32{\times}10^{-4}{\Omega}cm$ as-annealed at $300^{\circ}C$. The electrical properties were enhanced by the hydrogen annealing treatment. After a 72 h damp-heat treatment in harsh conditions of a water steam at $110^{\circ}C$ for four representative samples, a degradation of electrical properties was observed. The sample of hydrogen-annealed AZO thin films with $SiO_2$ protection layer showed a slight degradation ratio(17%) of electrical properties and a preferable transmittance of 90%. The electrical stability of AZO thin films had been modified by hydrogen annealing treatment and $SiO_2$ protection layer.

• Journal of Magnetics
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• v.7 no.3
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• pp.72-79
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• 2002

Local M-H loops have been measured on the free layer of a tunneling magnetoresistance (TMR) junction using the magneto-optical Kerr effect (MOKE) system, with an optical beam size of about 2 $\mu$m diameter. Tunnel junctions were deposited using the DC magnetron sputtering method in a chamber with a base pressure of 3$\times$10$^{-9}$ Torr. The relatively irregular variations of coercive force H$_c$(∼17.5 Oe) and unidirectional anisotropy field H$_{ua}$(∼7.5 Oe) in the as-deposited sample are revealed. After $200{^{\circ}C}$ annealing, He decreases to 15 Oe but H$_{ua}$ increases to 20 Oe with smooth local variations. Two-dimensional plots of H$_c$ and H$_{ua}$ show the symmetric saddle shapes with their axes aligned with the pinned layer, irrespective of the annealing field angle. This is thought to be caused by geometric effects during deposition, together with a minor annealing effect. In addition, the variation of root mean square (RMS) surface roughness reveals it to be symmetric with respect to the center of the pinned-layer axis, with the roughness of 2.5 $\AA$ near the edge and 5.8 $\AA$ at the junction center. Comparison of surface roughness with the variation of H$_{ua}$ suggests that the H$_{ua}$ variation of the free layer is well described by dipole interactions related to surface roughness. As a whole, the reversal magnetization is not uniform over the entire junction area and the macroscopic properties are governed by the average sum of local distributions.

• Korean Journal of Materials Research
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• v.22 no.4
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• pp.190-194
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• 2012

The formation of high-quality polycrystalline silicon (poly-Si) on relatively low cost substrate has been an important issue in the development of thin film solar cells. Poly-Si seed layers were fabricated by an inverse aluminum-induced crystallization (I-AIC) process and the properties of the resulting layer were characterized. The I-AIC process has an advantage of being able to continue the epitaxial growth without an Al layer removing process. An amorphous Si precursor layer was deposited on Corning glass substrates by RF magnetron sputtering system with Ar plasma. Then, Al thin film was deposited by thermal evaporation. An $SiO_2$ diffusion barrier layer was formed between Si and Al layers to control the surface orientation of seed layer. The crystallinity of the poly-Si seed layer was analyzed by Raman spectroscopy and x-ray diffraction (XRD). The grain size and orientation of the poly-Si seed layer were determined by electron back scattering diffraction (EBSD) method. The prepared poly-Si seed layer showed high volume fraction of crystalline Si and <100> orientation. The diffusion barrier layer and processing temperature significantly affected the grain size and orientation of the poly Si seed layer. The shorter oxidation time and lower processing temperature led to a better orientation of the poly-Si seed layer. This study presents the formation mechanism of a poly seed layer by inverse aluminum-induced crystallization.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.393-393
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• 2012

Optically active nanostructures such as subwavelength moth-eye antireflective structures or surface enhanced Raman spectroscopy (SERS) active structures have been demonstrated to provide the effective suppression of unwanted reflections as in subwavelength structure (SWS) or effective enhancement of selective signals as in SERS. While various nanopatterning techniques such as photolithography, electron-beam lithography, wafer level nanoimprinting lithography, and interference lithography can be employed to fabricate these nanostructures, roll-to-roll (R2R) nanoimprinting is gaining interests due to its low cost, continuous, and scalable process. R2R nanoimprinting requires a master to produce a stamp that can be wrapped around a quartz roller for repeated nanoimprinting process. Among many possibilities, two different types of mask can be employed to fabricate optically active nanostructures. One is self-assembled Au nanoparticles on Si substrate by depositing Au film with sputtering followed by annealing process. The other is monolayer silica particles dissolved in ethanol spread on the wafer by spin-coating method. The process is optimized by considering the density of Au and silica nano particles, depth and shape of the patterns. The depth of the pattern can be controlled with dry etch process using reactive ion etching (RIE) with the mixture of SF6 and CHF3. The resultant nanostructures are characterized for their reflectance using UV-Vis-NIR spectrophotometer (Agilent technology, Cary 5000) and for surface morphology using scanning electron microscope (SEM, JEOL JSM-7100F). Once optimized, these optically active nanostructures can be used to replicate with roll-to-roll process or soft lithography for various applications including displays, solar cells, and biosensors.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.231-231
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• 2012

Correct determination of the interface locations is critical for the calibration of the depth scale and measurement of layer thickness in SIMS depth profiling analysis of multilayer films. However, the interface locations are difficult to determine due to the unwanted distortion from the real ones by the several effects due to sputtering with energetic ions. In this study, the layer thicknesses of Si/Ge and Si/Ti multilayer films were measured by SIMS depth profiling analysis using the oxygen and cesium primary ion beam. The interface locations in the multilayer films could be determined by two methods. The interfaces can be determined by the 50 at% definition where the atomic fractions of the constituent layer elements drop or rise to 50 at% at the interfaces. In this method, the raw depth profiles were converted to compositional depth profiles through the two-step conversion process using the alloy reference relative sensitivity factors (AR-RSF) determined by the alloy reference films with well-known compositions determined by Rutherford backscattering spectroscopy (RBS). The interface locations of the Si/Ge and Si/Ti multilayer films were also determined from the intensities of the interfacial composited ions (SiGe+, SiTi+). The determination of the interface locations from the composited ions was found to be difficult to apply due to the small intensity and the unclear variation at the interfaces.

• Proceedings of the IEEK Conference
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• 2000.06b
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• pp.32-35
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• 2000

Oxide-nitride-oxide(ONO) structures were formed by sequential radio frequency reactive magnetron sputtering method. The chemical composition and structure of these films were studied by using of secondary ion mass spectroscopy(SIMS) and Auger electron spectroscopy(AES) SIMS and AES experiments show the existence of nitridation at the SiO$_2$/Si substrate. The electrical characteristics of ONO films were evaluated by I-V and high frequency C-V measurements When the ONO films were annealed at 90$0^{\circ}C$ for 30 sec in $N_2$ ambient, the breakdown voltage increased and flat-band voltage decreased under high electric field.