• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.746-755
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• 2017

In this study, $CeO_2/TiO_2$ nanoparticle with structure of core and shell was synthesized by growing $TiO_2$ onto the surface of $CeO_2$ according to hydrolysis of $Ti(SO_4)_2$. Reaction time, temperature, concentration of $CeO_2$ slurry, pH control of $Ti(SO_4)_2$ were optimized about synthesis of $CeO_2/TiO_2$ core-shell nanoparticle. It was found that optimal mole ratio range of $CeO_2:TiO_2$ was 1:0.2~1.1, the optimal concentration of $CeO_2$ slurry was 1 %, and the optimal reaction temperature was $50^{\circ}C$. The optimal concentration of $CeO_2$ slurry could be increased up to 10 % by adjusting the pH of $Ti(SO_4)_2$ to 1 using $NH_4OH$ and adding to $CeO_2$ slurry. If reaction was carried at $80^{\circ}C$ or higher, the separated $TiO_2$ particles were obtained instead of $CeO_2/TiO_2$ core-shell nanoparticles. The optimal reaction temperature was $50^{\circ}C$ at which good shaped core-shell structure of $CeO_2/TiO_2$ was obtained.

• Journal of the Korean Ceramic Society
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• v.35 no.9
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• pp.981-987
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• 1998

$La_{0.5}Sr_{0.5}MnO_{3-\delta}$ as air electrode for soild oxide fuel cell was synthesized by a citrate process and its cathodic polarization was determinated by the current interruption method on the Gd-doped ceria as electrolyte. The addition of citric acid increased the exothermic heat for the formation of $La_{0.5}Sr_{0.5}MnO_{3-\delta}$ perovskite oxide. The degree of the initial particle agglomeration was affected by the exothermic heat. Also the increase of cal-cination temperature enlarged the particle size and the higher sintering temperature accelerated the den-sification of $La_{0.5}Sr_{0.5}MnO_{3-\delta}$ layer after its being painted on $Ce_{0.8}Gd_{0.2}O_{1.9}$ electrolyte. In this study $La_{0.5}Sr_{0.5}MnO_{3-\delta}$ synthesized by citrate process of which the molar ratio of citric acid to metal nitrate was 2 calcined at $650^{\circ}C$ for 2hr and sintered at 1100 at $1200^{\circ}C$ for 4 hrs after slurry coating on Ce0.8Gd0.2O1.9 electrlyte showed the lowest cathodic polarization.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.61-61
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• 2003

CMP(Chemical Mechanical Polishing)는 VLSI의 제조공정에서 실리콘웨이퍼의 절연막내에 있는 토포그래피를 제어할 수 있는 광역 평탄화 기술이다. 또한 최근에는 실리콘웨이퍼의 나노토포그래피(Nanotopography)가 STI의 CMP 공정에서 연마 후 필름의 막 두께 변화에 많은 영향을 미치게 됨으로 중요한 요인으로 대두되고 있다. STI CMP에 사용되는 CeO$_2$ 슬러리에서 첨가되는 계면활성제의 농도에 따라서 나노토포그래피에 미치는 영향을 제어하는 것이 필수적 과제로 등장하고 있다. 본 연구에서는 STI CMP 공정에서 사용되는 CeO$_2$ 슬러리에서 계면활성제의 농도에 따른 나노토포그래피의 의존성에 대해서 연구하였다. 실험은 8 "단면연마 실리콘웨이퍼로 PETEOS 7000$\AA$이 증착 된 것을 사용하였으며, 연마 시간에 따른 나노토포그래피 의존성을 알아보기 위해 연마 깊이는 3000$\AA$으로 일정하게 맞췄다. 그리고 CMP 공정은 Strasbaugh 6EC를 사용하였으며, 패드는 IC1000/SUBA4(Rodel)이다. 그리고 연마시 적용된 압력은 4psi(Pounds per Square Inch), 헤드와 정반(table)의 회전속도는 각각 70rpm이다 슬러리는 A, B 모두 CeO$_2$ 슬러리로 입자크기가 다른 것을 사용하였고, 농도를 달리한 계면활성제가 첨가되었다. CMP 전 후 웨이퍼의 막 두께 측정은 Nanospec 180(Nanometrics)과 spectroscopic ellipsometer (MOSS-ES4G, SOPRA)가 사용되었다.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.8
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• pp.929-935
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• 2011

As a deterministic finishing process for the optical parts having complex surface, machining performance of the magnetorheological(MR) fluid jet polishing of optical glass are studied and compared with a general water jet polishing. First, design of the jet polishing system which has the special electromagnet-nozzle unit for stabilizing the slurry jet based on MR fluid and the change of jet shape as magnetic field is applied are explained. Second, for the BK7 glass, machining spot and its cross section profile are analyzed and the unique effect of MR fluid jet polishing is shown. Third, both material removal depth and surface roughness are explored in order to investigate the polishing performance of MR fluid jet. With the same ceria abrasives and amount in the polishing slurries, MR fluid jet shows superior machining performance compared to water jet and the difference of material removal mechanism and its resulting performance are described.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.78-83
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• 2009

In general, Light-hardening polymer was used UV nanoimprint technology. A light-hardening polymer was had the problem of poor hardness, durability. In order to overcome the problem of polymer, inter change optical glass. However glass is very manufacture and a lowering of standars transmittance. In order to glass recover was necessary polishing process. The process is magnetorheological fluids polishing. MR polishing has been developed as a new precision finishing technique to obtain a fine surface. Hence, Magnetorheological fluids has been used for micro polishing to get micro parts. This polishing process guarantees high polishing quality by controlling the fluid density electrically. The applied material in experiments is fused silica glass. Fused silica glass is widely used in the optical field because of high degree of purity. For MR polishing experiments, MR fluid was composed with DI-water, carbonyl iron and nano slurry ceria. The wheel speed and electric current were chosen as the variables for analyzing the characteristics of MR polishing process. Outstanding surface roughness of Ra=1.58nm was obtained on the fused silica glass specimen. And originally glass transmittance was recover on the fused silica glass.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.119-120
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• 2008

ILD CMP process has been well accepted for the planarization of the dielectric oxide film and becomes a critical process in ULSI manufacturing due to the rapid shrinkage of the design rule for the device. In total manufacturing process steps for a device, the proportion of ILD CMP process has been gradually increased. Ever since ILD CMP has been introduced, the scratches have been a major defects on polished surfaces which cause the electrical shorts between vias or metal lines [1,2]. It was reported that micro-scratches are caused by large, irregularly shaped particles during CMP process. Therefore, most of the CMP users have used < 5 m POU filter to remove and reduce the scratch source from the slurry. However, the scratch has always been the biggest concern in ILD polishing whatever preventive actions are taken. Silica and ceria slurries are widely used for ILD CMP process. There are not much differences in generated scratches and their formation mechanism. In this study, the scratches were investigated as a function of polishing conditions with possible explanation on formation mechanism in ILD CMP.