• 한국세라믹학회지
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• 제43권11호
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• pp.688-692
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• 2006

Ferroelectric lanthanides-substituted $Bi_4Ti_3O_{12}$ $(Bi_{4-x}Ln_xTi_3O_{12}, BLnT)$ thin films approximately 200 nm in thickness were deposited by metal organic chemical vapor deposition onto Pt(111)/Ti/SiO$_2$/Si(100) substrates. Many researchers reported that the lanthanides substitution for Bi in the pseudo-perovskite layer caused the distortion of TiO$_6$ octahedron in the a-b plane accompanied with a shift of the octahedron along the a-axis. In this study, the effect of lanthanides (Ln=Pr, Eu, Gd, Dy)-substitution and crystallization temperature on their ferroelectric properties of bismuth titanate $(Bi_4Ti_3O_{12}, BIT)$ thin films were investigated. As BLnT thin films were substituted to lanthanide elements (Pr, Eu, Gd, Dy) with a smaller ionic radius, the remnant polarization (2P$_r$) values had a tendency to increase and made an exception of the Eu-substituted case because $Bi_{4-x}Eu_xTi_3O_{12}$ (BET) thin films had the smaller grain sizes than the others. In this study, we confirmed that better ferroelectric properties can be expected for films composed of larger grains in bismuth layered peroskite materials. The crystallinity of the thin films was improved and the average grain size increased as the crystallization temperature,increased from 600 to 720$^{\circ}C$. Moreover, the BLnT thin film capacitor is characterized by well-saturated polarization-electric field (P-E) curves with an increase in annealing temperature. The BLnT thin films exhibited no significant degradation of switching charge for at least up to $1.0\times10^{11}$ switching cycles at a frequency of 1 MHz. From these results, we can suggest that the BLnT thin films are the suitable dielectric materials for ferroelectric random access memory applications.

• 한국세라믹학회지
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• 제43권11호
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• pp.715-723
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• 2006

Perovskite oxide materials are very important for the electronics industry, because they exhibit promising properties. With an interest in the obvious applications, significant effort has been invested in the growth of highly crystalline epitaxial perovskite oxide thin films in our laboratory. And the desired structure of films was formed to achieve excellent properties. $Y_1Ba_2Cu_3O_{7-x}$ (YBCO) superconducting thin films were simultaneously deposited on both sides of 3 inch wafer by inverted cylindrical sputtering. Values of microwave surface resistance R$_2$ (75 K, 145 GHz, 0 T) smaller than 100 m$\Omega$ were reached over the whole area of YBCO thin films by pre-seeded a self-template layer. For implementation of voltage tunable high-quality varactor, A tri-layer structured SrTiO$_3$ (STO) thin films with different tetragonal distortion degree was prepared in order to simultaneously achieve a large relative capacitance change and a small dielectric loss. Highly a-axis textured $Ba_{0.65}Sr_{0.35}TiO_3$ (BST65/35) thin films was grown on Pt/Ti/SiO$_2$/Si substrate for monolithic bolometers by introducing $Ba_{0.65}Sr_{0.35}RuO_3$ (BSR65/35) thin films as buffer layer. With the buffer layer, the leakage current density of BST65/35 thin films were greatly reduced, and the pyroelectric coefficient of $7.6\times10_{-7}$ C $cm^{-2}$ $K^{-1}$ was achieved at 6 V/$\mu$m bias and room temperature.

• 한국전기전자재료학회논문지
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• 제31권4호
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• pp.226-230
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• 2018

Pure $BiFeO_3$ (BFO) and codoped $Bi_{0.9}A_{0.1}Fe_{0.975}Zn_{0.025}O_{3-{\delta}}$ (A=Eu, Dy) thin films were prepared on Pt(111)/Ti/$SiO_2$/Si(100) substrates by chemical solution deposition. The remnant polarizations (2Pr) of the $Bi_{0.9}Eu_{0.1}Fe_{0.975}Zn_{0.025}O_{3-{\delta}}$ (BEFZO) and $Bi_{0.9}Dy_{0.1}Fe_{0.975}Zn_{0.025}O_{3-{\delta}}$ (BDFZO) thin films were about 36 and $26{\mu}C/cm^2$ at the maximum electric fields of 900 and 917 kV/cm, respectively, at 1 kHz. The codoped BEFZO and BDFZO thin films showed improved electrical properties, and leakage current densities of 3.68 and $1.21{\times}10^{-6}A/cm^2$, respectively, which were three orders of magnitude lower than that of the pure BFO film, at 100 kV/cm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1345-1346
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• 2007

다양한 게이트 절연막의 펜타신 박막 트랜지스터의 전기적 특성을 atomic force microscope (AFM), X-선 회절을 사용하여 분석하였다. 펜타신 박막 트랜지스터는 thermal evaporator 방법을 사용하여 여러 폴리며 기판위에 제작하였다. Hexamethylsilasane (HMDS), polyvinyl acetate (PVA), polymethyl methacrylate (PMMA)등의 폴리머 기판을 사용하여 다양한 온도에서 증착시켰다. 이 때 PMMA위에 증착시킨 펜타신의 경우가 가장 큰 그레인 크기를 보였고, 가장 적은 트랩 농도를 보였다. 그리고 상부 전극 구조를 가진 박막 트랜지스터를 HMDS 처리를 한 $SiO_2$와 PMMA 절연막을 사용하여 제작하고 비교하였다. 이때 PMMA기판 위에 제작한 트랜지스터는 전계효과 이동도가 ${\mu}_{FET}=0.03cm^{2}/Vs$ 이고, 문턱이전 기울기 0.55V/dec, 문턱전압 $V_{th}=-6V$, on/off 전류비 $>10^5$의 전기적 특성을 보였고, $SiO_2$ 기판위에 제작한 트랜지스터는 전계효과 이동도 ${\mu}_{FET}=0.004cm^{2}/Vs$, 문턱이전 기울기 0.518 V/dec, 문턱전압 $V_{th}=5V$, on/off 전류비 $>10^4$의 전기적 특성을 보였다.

• 한국정밀공학회지
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• 제33권5호
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• pp.385-392
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• 2016

Recently in the display industry, demands for high-luminance and resolution of display devices have been steadily increasing. Generally, micro linear patterns are applied to an optical film in order to improve its properties of light. However, these patterns are easily viewed to eyes and moire phenomenon can be occurred. Micro random patterns are proposed as a method to solve these problems, increasing light-luminance and light-diffusion. However, conventional pattern manufacturing technologies have long processing times and high costs making it difficult to apply to large area molds. In order to combat this issue, micro-random patterns are formed by using a roll to plate indentation method along with abrasive paper tools composed of AlSiO2, SiC, and diamond grains. Also, forming properties, such as size and fill-factor of random patterns, are analyzed depending on type, mesh of abrasive paper tools, and indentation forces.

• 열처리공학회지
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• 제10권1호
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• pp.10-19
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• 1997

This study has been conducted to investigate the effects of initial structure on the microstructure and tensile properties of high strength trip steel sheet. The initial structure before austempering remarkably influenced the second phase. The specimen with normalized initial structure showed mainly bainitic ferrite and retained austenite, while the as rolled specimen and spherodized specimen showed martensite plus retained austenite and martensite plus bainitic ferrite with small retained austenite, respectively. Two type of retained austenite, film type and granual type were observed in all specimens. The as rolled specimen appeared the highest contents of retained austenite owing to the compressive stress by cold rolling. The contents of retained austenite increased with increasing intercritical annealing temperature and austempering time. Tensile strength showed the highest in the as rolled specimen, while the highest elongation were obtained in the normalized specimen. The maximum T.S.${\times}$El. Value showed in normalized initial structure and increased with increasing intercritical annealing and austempering time. The highest Value of T.S.${\times}$El. obtained at austempering temperature of $400^{\circ}C$ and retained austenite of 12%.

• Journal of Magnetics
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• 제10권3호
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• pp.95-98
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• 2005

We report hole-induced ferromagnetism in diluted magnetic semiconductor $Zn_{0.99}Mn_{0.01}$ films grown on $SiO_2/Si$ substrates by reactive sputtering. The p-type conduction with hole concentration over $10^{18}\;cm^{-3}$ is achieved by P doping followed by rapid thermal annealing at $800^{\circ}C$ in a $N_2$ atmosphere. The p-type $Zn_{0.99}Mn_{0.01}O:P$ is carefully examined by x-ray diffraction and transmission electron microscopy. The magnetic measurements for $p-Zn_{0.99}Mn_{0.01}O:P$ clearly reveal ferromagnetic characteristics with a Curie temperature above room temperature, whereas those for $n-Zn_{0.99}Mn_{0.01}O:P$ show paramagnetic behavior. The anomalous Hall effect at room temperature is observed for the p-type film. This result strongly supports hole-induced room temperature ferromagnetism in $p-Zn_{0.99}Mn_{0.01}O:P$.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.348-351
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• 1999

Cold 층을 입힌 저항형 초전도 한류기의 전류 제한 특성을 통하여 다음과 같은 결론을 얻었다. 고장발생후 3.2 msec 후에 quench가 발생하였으며, 부분적인 quench가 발생한 다음 시간이 지나면서 완전한 quench로 진행되었다. 즉, 선로고장에 따른 quench 발생 후 YBCO 초전도체의 gold층으로 대부분의 전류가 흐르게 되고, quench 되면서 발생하는 열도 대부분 gold층에서 흡수하여저항이 증가하였으며 이에 따른 전류감소, 전압증가 및 소비전력증가가 발생하였다. 인가전압 V$_0$=65 V$_{peak}$이고 R$_0$는 1 ${\omega}$, 그리고 R$_L$을 7.7 ${\omega}$으로 하였을 때 사고모의 위상각 0$^{\circ}$에서 고장발생후 0.9 msec 후인 9.6 A$_{peak}$ 되는 지점에서 quench가 발생하여 13.0 A$_{peak}$의 최대한류전류값을 보인후 11.4 A$_{peak}$의 전류값에서 fast quench가 완료되었다. 이때 quench 시간은0.63 msec 이었다. 저항값은 gold층에서 발생한 열때문에 점진적인 상승을 보이다가 약 3주기후에 일정한 값에 도달하였다. 한류소자의 온도는 약 11 msec 후에 상온에 도달하였으며, 3 주기후인 54 msec에는 150 $^{\circ}C$까지 상승하였다. gold 박막을 입힌 meander line은 임계전류 이상의 전류를 통전하였을 때에 용단되지 않았으며 ??치된 상태에서 3 사이클 이상 유지하였다. 약65 A$_{rms}$가 흘렀을 때에야 ??치후 3 사이클 지나용단되었다. 이러한 YBCO/gold에 의한 초전도한류기의 용량은 gold에 발생하는 열을 gold가감당할 수 있는 전류의 크기와 관련이 있으며, gold층이 YBCO 한류소자가 quench되었을 때 발생하는 열을 효과적으로 분산시킬 뿐만 아니라 전기적으로 shunt 회로 역할을 하고 있음을 확인할 수 있다. 이에 더하여 앞으로 quench 후 한류소자에서 발생할 수 있는 인덕턴스의 저감방안에 대한 설계 및 모델 탐구를 통하여 좀더 효율적인 한류소자 구성에 대한 연구를 병행하고자 한다.

• 한국전기전자재료학회논문지
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• 제33권3호
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• pp.214-218
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• 2020

In this study, Mg_xZn_1-xO thin films, which can be applied not only to active layers of light-emitting devices (LEDs), such as UV-LEDs, but also to solar cells, high mobility field-effect transistors, and power semiconductor devices, are fabricated using the sol-gel method. ZnO and Mg_0.3Zn_0.7O solution synthesized by the sol-gel method and the thin film were grown by spin coating on a Si (100) substrate and sapphire substrate. The solutions are synthesized by dissolving precursor materials in 2-methoxyethanol (2-ME) solvent, and then monoethanolamine (MEA) was added to the mixed solution as a sol stabilizer. Zinc acetate dihydrate is used as a ZnO precursor, while Mg nitrate hexahydrate and Mg acetate tetrahydrate are used as an MgO precursor. Then, the optical and structural characteristics of the fabricated thin films are compared. The molar concentration of the Zn precursor in the solvent is fixed at 0.3 M, and the amount of the Mg precursor is 30% of Mg²⁺/Zn²⁺. The optical characteristics are measured using an UV-vis spectrophotometer, and the transmittance of each wavelength is measured. Structural characteristics are measured using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Composition analyses are performed using energy dispersive X-ray spectroscopy (EDS). The Mg_0.3Zn_0.7O thin film was well formed at the ratio of the Mg precursor added regardless of the type of Mg precursor, and the c-axis of the thin film was decreased, while the band gap was increased to 3.56 eV.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.144.2-144.2
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• 2016

Diamond-like carbon (DLC) coatings have been widely applied to the mechanical components, cutting tools due to properties of high hardness and wear resistance. Among them, hydrogenated amorphous carbon (a-C:H) coatings are well-known for their low friction properties, stable production of thin and thick film, they were reported to be easily worn away under high temperature. Non-hydrogenated tetrahedral amorphous carbon (ta-C) is an ideal for industrial applicability due to good thermal stability from high $sp^3$-bonding fraction ranging from 70 to 80 %. However, the large compressive stress of ta-C coating limits to apply thick ta-C coating. In this study, the thick ta-C coating was deposited onto Inconel alloy disk by the FCVA technique. The thickness of the ta-C coating was about $3.5{\mu}m$. The tribological behaviors of ta-C coated disks sliding against $Si_3N_4$ balls were examined under elevated temperature divided into 23, 100, 200 and $300^{\circ}C$. The range of temperature was setting up until peel off observed. The experimental results showed that the friction coefficient was decreased from 0.14 to 0.05 with increasing temperature up to $200^{\circ}C$. At $300^{\circ}C$, the friction coefficient was dramatically increased over 5,000 cycles and then delaminated. These phenomenon was summarized two kinds of reasons: (1) Thermal degradation and (2) graphitization of ta-C coating. At first, the reason of thermal degradation was demonstrated by wear rate calculation. The wear rate of ta-C coatings showed an increasing trend with elevated temperature. For investigation of relationship between hardness and graphitization, thick ta-C coatings(2, 3 and $5{\mu}m$) were additionally deposited. As the thickness of ta-C coating was increased, hardness decreased from 58 to 49 GPa, which means that graphitization was accelerated. Therefore, now we are trying to increase $sp^3$ fraction of ta-C coating and control the coating parameters for thermal stability of thick ta-C at high temperatures.