• 한국진공학회지
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• 제12권4호
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• pp.218-227
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• 2003

AlGaAs/GaAs HBT 에미터 오믹 접촉을 위해 n형 InGaAs에 대한 Pd/Si/Ti/Pt 및 Pd/Si/Pd/Ti/Au 오믹 접촉 특성을 조사하였다. Pd/Si/Ti/Pt 오믹 접촉의 경우, 증착 상태에서는 접촉 비저항을 측정할 수 없을 정도의 비오믹 특성을 보였으며, $375^{\circ}C$에서 10초 동안 열처리한 경우 $5\times10^{-3}\Omega\textrm{cm}^2$의 높은 접촉 비저항을 나타내었다. 그러나 열처리 조건을 $425^{\circ}C$, 10초로 변화시킬 경우 $2\times10^{-6}\Omega\textrm{cm}^2$의 낮은 접촉 비저항을 나타내었다. Pd/Si/Pd/Ti/Au 오믹 접촉의 경우, $450^{\circ}C$까지의 열처리 동안에 전반적으로 우수한 오믹 특성을 나타내어 $400^{\circ}C$, 20초의 급속 열처리 조건에서 최저 $3.9\times10^{-7}\Omega\textrm{cm}^2$의 접촉 비저항을 나타내었다. 두 오믹 접촉 모두 오믹 재료와 InGaAs의 평활한 계면을 유지하면서 우수한 오믹 특성을 나타내어, 화합물 반도체 소자의 오믹 접촉으로 충분히 응용 가능하였다. Pd/Si/Ti/Pt 및 Pd/Si/Pd/Ti/Au를 AlGaAs/GaAs HBT의 에미터 오믹 접촉으로 사용하여 제작된 HBT 소자의 고주파 특성을 측정한 결과, 차단 주파수가 각각 63.9 ㎓ 및 74.4 ㎓로, 또한 최대공진 주파수가 각각 50.1 ㎓ 및 52.5 ㎓로 우수한 작동특성을 보였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권2호
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• pp.80-84
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• 2003

The mechanical and electrical properties of the hot-pressed and pressureless annealed SiC-Ti $B_2$electroconductive ceramic composites were investigated as functions of the liquid additives of $Al_2$ $O_3$+ $Y_2$ $O_3$. The result of phase analysis for the SiC-Ti $B_2$ composites by XRD revealed $\alpha$-SiC(6H), Ti $B_2$, and YAG(A $l_{5}$ $Y_3$ $O_{12}$ ) crystal phase. The relative density of SiC-Ti $B_2$ composites was increased with increased $Al_2$ $O_3$+ $Y_2$ $O_3$ contents. The fracture toughness showed the highest value of 6.04 Mpa $m^{\frac{1}{2}}$ for composites added with l2wt% A1$_2$ $O_3$+ $Y_2$ $O_3$ additives at room temperature. The electrical resistivity showed the lowest value of 6.2$\times$10$^{-3}$ $\Omega$ㆍcm for composite added with l6wt% $Al_2$ $O_3$+ $Y_2$ $O_3$ additives at room temperature. The electrical resistivity of the SiC-Ti $B_2$ composites was all positive temperature cofficient resistance(PTCR) in the temperature ranges from $25^{\circ}C$ to $700^{\circ}C$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.208-209
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• 2008

Ni/Ti/Al multilayer system was tested for low-resistance ohmic contact formation to Al-implanted p-type 4H-SiC. Compared with conventional process using Ni, Ni/Ti/Al contact shows perfect ohmic behavior, and possesses much lower contact resistance of about $2.5\times10^{-4}\Omega{\cdot}cm^2$ after $930^{\circ}C$ RTA, which is about 2 orders of magnitude smaller than that of Ni contact. Contact resistance gradually increased as the RTA temperature was lowered in the range of 840 ~ $930^{\circ}C$, and about $3.4\times10^{-4}\Omega{\cdot}cm^2$ was obtained at the lowest RTA temperature of $840^{\circ}C$. Therefore, it was shown that RTA temperature for ohmic contact formation can be lowered to at least $840^{\circ}C$ without significant compromise of contact resistance.

• 한국분말재료학회지
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• 제2권1호
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• pp.36-43
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• 1995

Rapidly solidified and mechanically alloyed Al-Ti base alloys were prepared by gas atomization and attritor milling separately. The gas atomized and the mechanically alloyed powders were consolidated after preheating at $450^{\circ}C$, and then heat treated isochronally for 1 hour to observe the microstructures and to investigate the mechanical properties. Stable phases of precipitates in the Al-Ti-Si and the Al-Ti-Zr alloys were identified as DO22-$(Al,Si)_3Ti$ and $Do_{23}-Al_3(Ti, Zr)$ each. Among the alloys, the mechanically alloyed Al-l0Ti-2Si alloy showed superior thermal stability and mechanical properties at elevated temperature. The additions of third elements, such as Si and Zr, to Al-Ti alloys seemed to improve the mechnical properties remarkably by stabilizing the microstructure and the precipitate phases in the consolidated alloys.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1228-1229
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• 2008

The composites were fabricated 61[vol.%] ${\beta}$-SiC and 39[vol.%] $TiB_2$ powders with the liquid forming additives of 12[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid by pressure or pressureless annealing at 1,650[$^{\circ}C$] for 4 hours. Reactions between SiC and transition metal $TiB_2$ were not observed in the microstructure and the phase analysis of the SiC-$TiB_2$ electroconductive ceramic composites. Phase analysis of SiC-$TiB_2$ composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $TiB_2$, and In Situ $YAG(Al_5Y_3O_{12})$. The relative density, the flexural strength and the Young's modulus showed the highest value of 88.32[%], 136.43[MPa] and 52.82[GPa] for pressure annealed SiC-$TiB_2$ composites at room temperature. The electrical resistivity showed the lowest value of 0.0162[${\Omega}{\cdot}cm$] for pressure annealed SiC-$TiB_2$ composite at 25[$^{\circ}C$]. The electrical resistivity of the pressure annealed SiC-$TiB_2$ composite was positive temperature coefficient resistance (PTCR) but the electrical resistivity of the pressureless annealed SiC-$TiB_2$ composites was negative temperature coefficient resistance(NTCR) in the temperature ranges from 25[$^{\circ}C$] to 700[$^{\circ}C$].

• 한국주조공학회지
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• 제15권4호
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• pp.368-376
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• 1995

An Al-composite material was fabricated with using the rheocompocasting process and the microstructure of the Al-Cu/SiCp composite material was investigated depending on the stirring times and the amount of Ti additions. The distribution of SiC dispersion shows the good result at the stirring time of 30 min. The degree of microdistribution of the $Al_2Cu$ and SiCp is improved when the amount of Ti addition is increased. At the compositon of 0.3%Ti, the primary solid is the compound of $Al_3Ti$ and no exist of the SiCp and $Al_2Cu$ phase around the primary $Al_3Ti$. In the process of compositization, SiCp is found at the primary and final solid parts and is found at the final solid part after remelting. $Al_2Cu$ and SiCp are distributed around and outside of dendrite or independently after remelting, which is different from the process of compositization.

• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2288-2292
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• 2007

The catalytic activities of nickel-based catalysts were estimated for oxidizing acetaldehyde of VOCs exhausted from industrial facilities. The catalysts were prepared by sol-gel methods of SiO2 and SiO2-TiO2 as a xerogel followed by impregnating Al2O3 powder with the nickel nitrate precursor. The crystalline structure and catalytic properties for the catalysts were investigated by use of BET surface area, X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) techniques. These results show that nickel oxide is transformed to NiAl2O4 spinel structure at the calcination temperature of 400 °C in response to the steps with after- and co-impregnation of Al2O3 powder in sol-gel process. The NiAl2O4 could suppress the oxidation reaction of acetaldehyde by catalysts. The NiO is better dispersed on SiO2-TiO2/Al2O3 support than SiO2/Al2O3 and SiO2-TiO2-Al2O3 supports. From the testing results of catalytic activities for oxidation of acetaldehyde, Catalysts showed a big difference in conversion efficiencies with the way of the preparation of catalysts and the loading weight of nickel. The catalyst of 8 wt.% Ni/TiO2-SiO2/Al2O3 showed the best conversion efficiency on acetaldehyde oxidation with 100% conversion efficiency at 350 °C.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제55권10호
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• pp.467-474
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• 2006

The effect of pressureless-sintered temperature on the densification behavior, mechanical and electrical properties of the $SiC-TiB_2$ electroconductive ceramic composites was investigated. The $SiC-TiB_2$ electroconductive ceramic composites were pressureless-sintered for 2 hours at temperatures in the range of $1,750{\sim}1,900[^{\circ}C]$, with an addition of 12[wt%] $Al_2O_3+Y_2O_3(6:4\;mixture\;of\;Al_2O_3\;and\;Y_2O_3)$ as a sintering aid. The relative density, flexural strength, vicker's hardness and fracture toughness showed the highest value of 84.92[%], 140[MPa], 4.07[GPa] and $3.13[MPa{\cdot}m^{1/2}]$ for $SiC-TiB_2$ composites of $1,900[^{\circ}C]$ sintering temperature at room temperature respectively. The electrical resistivity was measured by the Pauw method in the temperature ranges from $25[^{\circ}C]\;to\;700[^{\circ}C]$. The electrical resistivity showed the value of $5.51{\times}10^{-4},\;2.11{\times}10^{-3},\;7.91{\times}10^{-4}\;and\;6.91{\times}10^{-4}[\Omega{\cdot}cm]$ for ST1750, ST1800, ST1850 and ST1900 respectively at room temperature. The electrical resistivity of the composites was all PTCR(Positive Temperature Coefficient Resistivity). The resistance temperature coefficient showed the value of $3.116{\times}10^{-3},\;2.717{\times}10^{-3},\;2.939{\times}10^{-3},\;3.342{\times}10^{-3}/[^{\circ}C]$ for ST1750, ST1800, ST1850 and ST1900 respectively in the temperature ranges from $25[^{\circ}C]\;to\;700[^{\circ}C]$. It is assumed that because polycrystallines, such as recrystallized $SiC-TiB_2$ electroconductive ceramic composites, contain of porosity and In Situ $YAG(Al_5Y_3O_{12})$ crystal grain boundaries, their electrical conduction mechanism are complicated. In addition, because the condition of such grain boundaries due to $Al_2O_3+Y_2O_3$ additives widely varies with sintering temperature, electrical resistivity of the $SiC-TiB_2$ electroconductive ceramic composites with sintering temperature also varies with sintering condition. It is convinced that ${\beta}-SiC$ based electroconductive ceramic composites for heaters or ignitors can be manufactured by pressureless sintering.

• 대한금속재료학회지
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• 제49권2호
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• pp.121-127
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• 2011

The mechanical properties of the various heat treatment conditions on Ti-15Mo-3Nb-3Al-0.2Si alloy plates were examined. XRD patterns from the surface of Ti-15Mo-3Nb-3Al-0.2Si were analyzed as a solution-treated Ti alloy has the single-phase ${\beta}$ structure whereas the aged Ti alloys have the ${\beta}$ matrix embedded with ${\alpha}$ needles. High strength (~1500 MPa) with decent ductility (7%) was obtained by the Ti alloy double aged at $300^{\circ}C$ and $520^{\circ}C$ for 8 hours each. The double-aged alloy exhibits the finer structure than the single-aged alloy at $300^{\circ}C$ for 8 hours because of the higher nucleation rate of ${\alpha}$ needles at an initial low aging temperature ($320^{\circ}C$). TEM observation revealed that the fine nanostructure with ${\alpha}$ needles in the ${\beta}$ matrix ensured the excellent mechanical properties in the double aged Ti-15Mo-3Nb-3Al-0.2Si alloy. In the solution treated alloy, the yield drop, stress-serrations and the ductility minimum typically associated with dynamic strain aging can be attributed to the dynamic interaction between dislocations and oxygen atoms. The yield drop and the stress serration were not observed in aged samples because the geometrically introduced dislocations due to phase precipitates suppressed the dynamic strain aging.

• 한국세라믹학회지
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• 제28권9호
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• pp.661-666
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• 1991

Microstructure, room temperature resistivity and temperature coefficient of resistance of BaTiO3 ceramics were studied by varying cooling rates and additives such as TiO2, SiO2 and Al2O3. The basic composition of the BaTiO3 ceramics was formed by adding 0.25 mol% Dy2O3 and 0.07 mol% MnO2 to the BaTiO3 composition. Unlike the additives of SiO2 and Al2O3, an addition of 2 mol% TiO2 to the basic composition was effective to control the grain size of the fired specimens. The room temperature resistivity and the temperature coefficient of resistance for the specimen of this particular compostion were measured as about 102 ohm.cm and 16.5%/$^{\circ}C$, respectively. The observed grain boundary phase of the sample with Al2O3 additive was BaTi3O7, while that of the samples with SiO2 additive was confirmed as BaTiSiO5.