• Korean Journal of Materials Research
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• v.24 no.9
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• pp.502-507
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• 2014

Recently, improvement in the conversion efficiency of silicon-based solar cells has been achieved by decreasing emitter doping concentration, because the lightly doped emitter can effectively prevent the recombination of electrons and holes generated by solar light irradiation. This type of emitter is very thin due to the low doping concentration, thus conductive materials (i.e., silver) used for front electrodes can easily penetrate the emitter during a firing process because of their large diffusivity in silicon. This results in junction leakage currents which might reduce cell efficiencies. In this study, $Al_2O_3$-coated Ag powders were synthesized by an ultrasonic spray pyrolysis method and applied to the conductive materials of the front electrode to control the junction leakage current. The $Al_2O_3$ shell obstructs the Ag diffusion into the emitter during the firing process. The powder is spherical with a core-shell structure and the thickness of the $Al_2O_3$ shell is tens of nanometers. Solar cells were fabricated using pure Ag powders or the $Al_2O_3$-coated Ag powder as front electrode materials, and the conversion efficiency and junction leakage current were compared to investigate the role of the $Al_2O_3$ shell during the firing processes.

• Korean Journal of Metals and Materials
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• v.56 no.12
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• pp.915-920
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• 2018

With the development of modern microelectronics technologies, the power density of electronic devices is rapidly increasing, due to the miniaturization or integration of device elements which operate at high frequency, high power conditions. Resulting thermal problems are known to cause power leakage, device failure and deteriorated performance. To relieve heat accumulation at the interface between chips and heat sinks, thermal interface materials (TIMs) must provide efficient heat transport in the through-plane direction. We report on the enhanced thermal conduction of $Al_2O_3-based$ polymer composites, fabricated by the surface wetting and texturing of thermally conductive hexagonal boron nitride(h-BN) nanoplatelets with large anisotropy in morphology and physical properties. The thermally conductive polymer composites were prepared with hybrid fillers of $Al_2O_3$ macro beads and surface modified h-BN nanoplatelets. Hexagonal boron nitride (h-BN) has high thermal conductivity and is one of the most suitable materials for thermally conductive polymer composites, which protect electronic devices by efficient heat dissipation. In this study, we synthesized hexagonal boron nitride nanoparticles by the pyrolysis of cost effective precursors, boric acid and melamine. Through pyrolysis at $900^{\circ}C$ and subsequent annealing at $1500^{\circ}C$, hexagonal boron nitride nanoparticles with diameters of ca. 50nm were synthesized. We demonstrate that the addition of a small amount of calcium fluoride ($CaF_2$) during the preparation of the melamine borate adduct significantly enhanced the crystallinity of the h-BN and assisted the growth of nanoplatelets up to 100nm in diameters. The addition of a small amount of h-BN enhanced the thermal conductivity of the $Al_2O_3-based$ polymer composites, from 1.45W/mK to 2.33 W/mK.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.3
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• pp.276-282
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• 2016

The effects of conductive additives in a $La_{0.8}Sr_{0.2}MnO_3$ perovskite bifunctional electrode for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were investigated in an alkaline solution. Highly porous carbon black (CB) and Ni powder were added to the bifunctional electrodes as conductive additives. The surface morphologies of electrodes containing CB and Ni were observed by scanning electron microscopy (SEM). The current densities for both ORR and OER were changed by the addition of CB. The conductive additive changed physical properties of bifunctional electrodes such as the sheet conductance, gas permeability and contact angle. It was observed that the air permeability of electrode was most effective to enhance the currents for ORR and OER.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.376-379
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• 2004

The aim of this study is to prepare mixed Ni/Mg/Al/Cu/Ti powder in epoxy matrix with carbon fiber (NCF, MCF, ACF, CCF, TCF) conductive composite possessing eletromagnetic interference(EMI) shilding effectiveness(SE). A series if NCF/MCF/ACF/CCF/TCF composite were prepared by the hand lay up method. The various compositions of NCF/MCF/ACF/CCF/TCF were 10, 25, 50 percent by weight. The best EMI shilding effectiveness of all NCF/MCF/ACF is doout 40dB.

• Proceedings of the Korean Printing Society Conference
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• 2007.11a
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• pp.59-64
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• 2007

We have manufactured low-curable silver pastes for gravure printing out of roll to roll printing process. When printing, the pastes be used different silver powder shape because of the printing characteristics. The pastes were prepared with silver powder by silver powder shape, polyester resin, solvent and homogenized on a standard three-roller mill. And the pastes exhibited a shear-thinning flow at viscosity profile. Moreover the adhesive strength and resistivity of silver film had good characteristics. With the manufactured paste in this study, RFID antenna circuit had flexible is manufactured and it had $10^{-4}{\sim}10^{-5}{\Omega}{\cdot}cm$.

• Applied Chemistry for Engineering
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• v.21 no.2
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• pp.224-229
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• 2010

Transparent conductive oxide films have been widely used in the field of flat panel display (FPD). Transparent conductive Indium Zinc Oxide (IZO) thin films with excellent chemical stability have attracted much attention as an alternative material for Indium Tin Oxide (ITO) films. In this study, using $In_2O_3$ and ZnO powder mixture with a ratio of 90 : 10 wt% as a target, IZO films are prepared on polynorbornene (PNB) substrates by electron beam evaporation. The effect of thickness and $O_2$ introduction flow rate on the optical, electrical, structural properties and surface composition of deposited IZO films were investigated by UV/Visible spectrophotometer, 4-point probe method, SEM, XRD and XPS.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1322-1325
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• 2005

The main objectives of this research work are to develop conductive glass fiber woven roving and carbon fiber unidirectional fabric composite materials and to determine their electromagnetic shielding effectiveness(EMSE). Epoxy is the matrix phase and glass, carbon fiber are the reinforcement phase of the composite material. Carbon black are incorporated as conductive fillers to provide the electromagnetic shielding properties of the composite material. The amount of carbon black in the composite material is varied by changing the carbon black composition, woven roving and unidirectional (fabric) structure. The EMSE of various fabric composites is measured in the frequency range from 300MHz to 800MHz. The variations of EMSE of woven roving and unidirectional composites with fabric structure, metal powder composite are described. Suitability of conductive fabric composites for electromagnetic shielding applications is also discussed.

• Korean Journal of Materials Research
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• v.10 no.5
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• pp.364-368
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• 2000

SiC fiber reinforced $Si_3N_4$ matrix composites combined with electrical conductive phases of carbon fiber and WC powder fabricated by hot pressing at 1773K. The ability to predict fracture in the ceramic matrix composites was evaluated by measuring simultaneous load-deflection and electrical resistanc difference-deflection curves in four point bending tests. The changes in electrical resistance differences closely corresponded to the fracture behavior of the composites. Different electrical conductive phases are suited to predicting different stages and rates of fracture. These obsevations how that it is possible to perform "in situ" fracture detection in ceramic composites.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.8
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• pp.651-656
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• 2012

A study on capacitive characteristics of stylus pen for touch panel are progressed in this paper. Also the main factors for capacitive sensitivity are studied. Namely, highly sensitive stylus pen which can be applied to capacitive touch panel are studied based on the analysis of materials and process conditions regardless of pattern shapes. Stylus pen was made of PDMS(Poly-Di-Methyl-Siloxane) and conductive metal powders which does not damage the touch panel surface. We tried to get the advantages of both the properties of soft PDMS and conductive metal powders. We found that potential difference of capacitance change with conductivity of the composite materials(PDMS + metal powders) it implies that during touch process, large voltage difference can be caused by the high conductive materials of stylus pen. Stylus pen made by PDMS with mixed with Ag powders which has large conductivity shows more capacitance change of 1 pF than PDMS with other materials of Ni or C powders.

• Composites Research
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• v.17 no.5
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• pp.68-77
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• 2004

The electromagnetic (EM) absorption or shielding characteristics of a material is an important issue not only for military purpose but also for commercial purposes such as radar, electric or telecommunication devices. In order to design the effective electromagnetic wave absorber, the electromagnetic characteristics of the constituents of the material should be available in target frequency band. Also, it must be possible to predict the electromagnetic properties of absorbers with respect to the content of lossy ingredients. In this study, the dielectric properties of unsaturated polyester resins containing nano-size conductive carbon black powder were measured with a free space method in the X-band frequency range and analyzed with respect to the content of carbon black. Finally, the method for estimating the dielectric properties of polymeric resin containing conductive carbon black with respect to the EM frequency was developed and verified.