• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1429-1436
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• 1994

We have prepared Ba0.5Sr0.5TiO3 thin films on Si substrate without buffer layer. Deposition was carried out by off-axis rf magnetron sputtering method using Ba0.5Sr0.5TiO3 stoichiometric target. The substrate temperature was changed from 40$0^{\circ}C$ to $700^{\circ}C$ during deposition. As the substrate temperature increased, relative intensity of (110) peak increased up to $600^{\circ}C$, however preferred orientation changed from (110) to (h00) beyond $650^{\circ}C$ of substrate temperature. Deposited films showed microstructures with fine grains whose diameters are less than 100 nm, and columnar structure was observed in the cross-sectional SEM micrograph. AES depth profile showed no significant diffusion at the interfacial reaction area. The effective dielectric constant of films showed maximum value at $600^{\circ}C$, and the leakage current increased with increasing substrate temperature, which may be ascribed to the crystallization of amorphous phases at grain boundary.

• Journal of Magnetics
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• v.19 no.3
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• pp.221-226
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• 2014

Significantly enhanced low-field magnetoresistance (LFMR) and maximum dMR/dH {$(dMR/dH)_{max}$} values were successfully achieved from $La_{0.7}Sr_{0.3}MnO_3$(LSMO)-manganese oxide composite samples prepared by liquid phase sintering, compared with those of the same composites prepared by solid state reaction. For this study, pure LSMO and LSMO-manganese oxide composites with various nominal compositions of (1-x)LSMO-$xMn_2O_3$ (x = 0.1, 0.2, 0.3, 0.4, and 0.8) were sintered at $1450^{\circ}C$, above the eutectic temperature of $1430^{\circ}C$, for 1 h in air. The highest LFMR value of 1.28% with the highest $(dMR/dH)_{max}$ value of 21.1% $kOe^{-1}$ was obtained from the composite sample with x = 0.3 at 290 K in 500 Oe. This enhancement of LFMR and $(dMR/dH)_{max}$ values is ascribed to efficient suppression of magnetic disorder at the LSMO grain boundary, by forming a characteristic LSMO-manganese eutectic structure.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.47-47
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• 2009

용착금속의 미세조직은 크게 Acicular ferrite(AF), Ferrite with aligned second phase(FS), Primary ferrite(=Grain boundary Ferrite) 등으로 나눌 수 있다. 이 중 침상형 페라이트(AF)는 인성과 강도를 동시에 증가시킬 수 있으므로 이를 다량 확보하는 것이 용접산업의 관건이다. 본 연구에서는 침상형 페라이트 발생에 기여한다고 알려진 Ti 함량을 용착금속에서 단계적으로 조절하여 나타나는 미세조직과 특성변화를 관찰하였다. 모재는 HSB-600을 사용하였으며 용접재료는 ER100S-G급의 Ti가 함유되어 있는 것(A)과 미함유된 것(B)을 사용하였다. 모재 성분의 희석을 방지하기 위해 V-Groove 가공 후 Buttering 용접을 실시하였다. 중앙에 가공된 V-그루브에 이들 재료를 적절히 조합하고 용접(입열량 20kJ/cm)하여 Ti함유량을 총 4가지(0.002~0.025% Ti)로 제어하였다. 용접 후 각각의 시편에 대해 미세조직, 충격시험, O/N분석, 성분분석 등의 시험을 진행하였다. 미세조직 관찰결과 Ti함량이 증가할수록 AF는 증가하고 FS는 감소함을 확인할 수 있었으며 충격시험결과 Ti가 많이 함유된 시편일수록 더 낮은 연성취성 천이온도(DBTT)를 나타내었다. EDS와 SEM으로 관찰한 결과 Ti함량 증가에 따라 비금속개재물의 크기는 작아지고 밀도는 높아지는 것을 확인할 수 있었으며 개재물 내에서의 Ti함량도 더 많아지는 것을 확인 할 수 있었다.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.258-261
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• 2000

Highly (h00)-oriented (Ba, Sr)TiO$_3$(BST) thin films were grown by pulsed laser deposition on the perovskite LaNiO$_3$(LNO) metallic oxide layer as a bottom electrode. The LNO films were deposited on SiO$_2$/Si substrates by rf-magnetron sputtering method. The crystalline phases of the BST film were characterized by x-ray $\theta$-2$\theta$, $\omega$-rocking curve and $\psi$-scan diffraction measurements. The surface microsturcture observed by scanning electron microscopy was very dense and smooth. The low-frequency dielectric responses of the BST films grown at various substrate temperatures were measured as a function of frequency in the frequency range from 0.1 Hz to 10 MHz. The BST films have the dielectric constant of 265 at 1 kHz and showed multiple dielectric relaxation at the low frequency region. The origin of these low-frequency dielectric relaxation are attributed to the ionized space charge carriers such as the oxygen vacancies and defects in BST film, the interfacial polarization in the grain boundary region and the electrode polarization. We studied also on the capacitance-voltage characteristics of BST films.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.386-390
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• 2015

Fe-base superalloy powders with $Y_2O_3$ dispersion were prepared by high energy ball milling, followed by spark plasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50 mm were used for the preparation of $Fe-20Cr-4.5Al-0.5Ti-O.5Y_2O_3$ powder mixtures (wt%). The milling process of the powders was carried out in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation (350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) were applied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclic operation and was about 15 nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constant milling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at $1100^{\circ}C$ for 30 min in vacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, a homogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1574-1576
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• 2003

Carbon nanotubes (CNTs) were grown on the TiN-coated silicon substrate with different thickness of Ni and Co catalysts layer at $600^{\circ}C$ using inductively coupled plasma-chemical vapor deposition (ICP-CVD). The Ni and Co catalysts were formed using the RF magnetron sputtering system with various deposition times. It was found that the growth of CNTs was strongly influenced by the surface morphology of Ni and Co catalysts. With increasing deposition time, the thickness of catalysts increased and the grain boundary size of catalysts increased. The surface morphology of catalysts and CNTs were elucidated by SEM. The Raman spectrum further confirmed the graphitic structure of the CNTs. The turn-on field of CNTs grown on Ni and Co catalysts was about 2.7V/pm and 1.9V/pm respectively. Field emission current density of CNTs grown on Ni and Co catalysts was measured as $11.67mA/cm^2$ at $5.5V/{\mu}m$ and $1.5mA/cm^2$ at $5.5V/{\mu}m$ respectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.9
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• pp.1615-1622
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• 2008

We have fabricated the poly-silicon thin film transistor(TFT) which has the LDD-region with graded spacer. The devices of n-channel poly-si TFT's hydrogenated by $H_2$ and $H_2$/plasma processes were fabricated for the devices reliability. We have biased the devices under the gate voltage stress conditions of maximum leakage current. The parametric characteristics caused by gate voltage stress conditions in hydrogenated devices are investigated by measuring/analyzing the drain current, leakage current, threshold voltage($V_{th}$), sub-threshold slope(S) and transconductance($G_m$) values. As a analyzed results of characteristics parameters, the degradation characteristics in hydrogenated n-channel polysilicon TFT's are mainly caused by the enhancement of dangling bonds at the poly-Si/$SiO_2$ interface and the poly-Si grain boundary due to dissolution of Si-H bonds. The structure of novel proposed poly-Si TFT's are the simplicities of the fabrication process steps and the decrease of leakage current by reduced lateral electric field near the drain region.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.6
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• pp.303-313
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• 2022

The purpose of this study was to test and analyze the effects of the mechanical properties and structural changes of the austenitized and tempered martensite STS 410 stainless steel containing 11.5~13%Cr and 0.10%C on its temper embrittlement. The STS 410 stainless steel test pieces for each 3 hours at 960℃, 1000℃ and then, tempered them for 2 hours at 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃ and 700℃ known as the intervals vulnerable to temper embrittlement to observe the changes of their structures and mechanical properties. In case autenitizing was insufficient due to lower temperature of thermal treatment for solution, unsolved carbides and ferrites remained in the structure after quenching, which meant that the parts could wear out and corrode to embrittle at the room temperature. Elongation and impact energy changes with Tempering conditions showed minimum results in range of 400~500℃. The decrease in elongation and impact energy at 400~500℃ was the hardening effect of the subgrain due to the precipitation of many M₃C or M₇C₃, M₂₃C₆. And STS 410 stainless steel corrosion tested in 10% NaCl solution at 30℃ after tempering treatment. The degree of corrosion sensitization showed increasing tendency with increase of tempering temperature and Cr carbide precipitation were observed in grain boundary.

• Journal of the Korean Vacuum Society
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• v.16 no.4
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• pp.262-266
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• 2007

Polycrystalline $Mn_xFe_{3-x}O_4$ thin films were synthesized on Si(100) substrates using sol-gel method and the effects of Mn substitution on the structural, magnetic, and magnetotransport properties were analyzed. X-ray diffraction revealed that cubic structure is maintained up to x = 1.78 with increasing lattice constant for increasing x. Such increase of the lattice constant is attributable to the substitution of $Mn^{2+}$ (with larger ionic radius) ions into tetrahedral $Fe^{3+}$(with smaller ionic radius) sites. VSM measurements revealed that $M_s$ does not vary significantly with x, qualitatively explainable by comparing spin magnetic moments of Mn and Fe ions. On the other hand, $H_c$ was found to decrease with increasing x, attributable to the decrease of magnetic anisotropy due to the decrease of $Fe^{2+}$ density through $Mn^{2+}$ substitution. Magnetoresistance (MR) of the $Mn_xFe_{3-x}O_4$ films was found to decrease with increasing x. Analysis of the MR data in comparison with the VSM results gives an indication of the tunneling of spin-polarized carriers through the grain boundaries of the polycrystalline samples at low external field and spin-flip of the carriers at high external field.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.102-102
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• 2018

Electronic industry had required the finer size and the higher performance of the device. Therefore, 3-D die stacking technology such as TSV (through silicon via) and micro-bump had been used. Moreover, by the development of the 3-D die stacking technology, 3-D structure such as chip to chip (c2c) and chip to wafer (c2w) had become practicable. These technologies led to the appearance of HBM (high bandwidth memory). HBM was type of the memory, which is composed of several stacked layers of the memory chips. Each memory chips were connected by TSV and micro-bump. Thus, HBM had lower RC delay and higher performance of data processing than the conventional memory. Moreover, due to the development of the IT industry such as, AI (artificial intelligence), IOT (internet of things), and VR (virtual reality), the lower pitch size and the higher density were required to micro-electronics. Particularly, to obtain the fine pitch, some of the method such as copper pillar, nickel diffusion barrier, and tin-silver or tin-silver-copper based bump had been utillized. TCB (thermal compression bonding) and reflow process (thermal aging) were conventional method to bond between tin-silver or tin-silver-copper caps in the temperature range of 200 to 300 degrees. However, because of tin overflow which caused by higher operating temperature than melting point of Tin ($232^{\circ}C$), there would be the danger of bump bridge failure in fine-pitch bonding. Furthermore, regulating the phase of IMC (intermetallic compound) which was located between nickel diffusion barrier and bump, had a lot of problems. For example, an excess of kirkendall void which provides site of brittle fracture occurs at IMC layer after reflow process. The essential solution to reduce the difficulty of bump bonding process is copper to copper direct bonding below $300^{\circ}C$. In this study, in order to improve the problem of bump bonding process, copper to copper direct bonding was performed below $300^{\circ}C$. The driving force of bonding was the self-annealing properties of electrodeposited Cu with high defect density. The self-annealing property originated in high defect density and non-equilibrium grain boundaries at the triple junction. The electrodeposited Cu at high current density and low bath temperature was fabricated by electroplating on copper deposited silicon wafer. The copper-copper bonding experiments was conducted using thermal pressing machine. The condition of investigation such as thermal parameter and pressure parameter were varied to acquire proper bonded specimens. The bonded interface was characterized by SEM (scanning electron microscope) and OM (optical microscope). The density of grain boundary and defects were examined by TEM (transmission electron microscopy).