• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.476-480
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• 2003

Polyethylene used as insulating material of power cable is nonpolar and low dielectric loss polymer. But it has defects of tree generation and accumulation of space charge by an applied voltage resulting in the decreased life and performance. To solve these problems, mixed films with LLDPE and EVA that is similar to LLDPE at physical properties in case of low VA contents were made and tested due to the blend ratios of 80:20, 70:30, 60:40 and 50:50[wt%] respectively. We investigated AC electrical treeing characteristics to acquire the best mixture ratio and effect of the tip radius of needle electrode to develop excellent treeproof materials. The degree of crystallity calculated with XRD pattern is higher for pure LLDPE, 50:50 and 70:30. For DSC analysis, it is confirmed that the melting points of mixed specimens are lower than that of pure LLDPE and higher than pure EVA's. The shape of tree propagation showed that pure EVA was electrical tree shape of the branch type, pure LLDPE and blended specimens was able to confirm tree shape of the bush type. As the tip radius go up in the blend ratio 70:30 specimen, the tree inception voltage rise. Probably the reason is the relaxation of electric field in the specimen with bigger tip ratio. As the 6 specimens were applied AC 5[KV],7.5[KV],10[KV] respectively, tree growth length is far shorter in the specimen with blend ratio 70:30, 50:50 than in pure EVA and pure LLDPE specimen. Conclusively, it is confirmed that specimens of which blend ratio are 70:30 and 50:50 are good in electrical tree retardant characteristics, especially, 70:30 has lower dielectric loss than 50:50 and its mixture ratio is the best.

• Macromolecular Research
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• v.12 no.1
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• pp.78-84
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• 2004

Advanced epoxy molding compounds (EMCs) should be considered to alleviate the thermal stress problems caused by low thermal conductivity and high elastic modulus of an EMC and by the mismatch of the coefficient of thermal expansion (CTE) between an EMC and the Si-wafer. Though A1N has some advantages, such as high thermal conductivity and mechanical strength, an A1N-filled EMC could not be applied to commercial products because of its low fluidity and high modules. To solve this problem, we used 2-$\mu\textrm{m}$ fused silica, which has low porosity and spherical shape, as a small size filler in the binary mixture of fillers. When the composition of the silica in the binary filler system reached 0.3, the fluidity of EMC was improved more than twofold and the mechanical strength was improved 1.5 times, relative to the 23-$\mu\textrm{m}$ A1N-filled EMC. In addition, the values of the elastic modules and the dielectric constant were reduced to 90％, although the thermal conductivity of EMC was reduced from 4.3 to 2.5 W/m-K, when compared with the 23-$\mu\textrm{m}$ A1N-filled EMC. Thus, the A1N/silica (7/3)-filled EMC effectively meets the requirements of an advanced electronic packaging material for commercial products, such as high thermal conductivity (more than 2 W/m-K), high fluidity, low elastic modules, low dielectric constant, and low CTE.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05a
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• pp.113-116
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• 2004

The materials showing high structure dispersion with functional properties were developed on the quartz base and those were obtained by mechano-chemical reaction technology. Depending on the processing conditions and subsequent applications the materials produced by mechano-chemical reaction show concurrently magnetic, dielectric and electrical properties. The obtained magnetic-electrical powders classified by aggregate complex of their features as segnetomagnetics, containing a dielectric material as a carrying nucleus, particularly the quartz on that surface one or more layers of different compounds were synthesized having thickness up to 10~50 nm showing magnetic, electrical properties and others. The similarity of the structure of surface layers of quartz particles subjected to mechano-chemical processing and nano-structure cluspol (clusters in a polymer matrics) material was also confirmed by the fact that the characteristics of ferromagnetic quartz of insulating nano-composite powder were changed with time, after its preparing process was completed. The magnetic permeability of the sample was decreasing within first two months down by 15~20 %. Then, the magnetic characteristics were almost stabilized steadily and continuously. The observed changes were related with defective structure of the particles, elastic stress relief, and changes of electron density and magnetic moment in deformation zones. This process of stabilization of the investigated properties could be intensified by the thermal annealing heat treatment in short time period of the nano-composite quartz powders at the temperature ranges of 100~15$0^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.31-32
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• 2010

In our previous reports [1-3], electron transport for the switching and memory devices using alkyl thiol-tethered Ru-terpyridine complex compounds with metal-insulator-metal crossbar structure has been presented. On the other hand, among organic memory devices, a memory based on the OFET is attractive because of its nondestructive readout and single transistor applications. Several attempts at nonvolatile organic memories involve electrets, which are chargeable dielectrics. However, these devices still do not sufficiently satisfy the criteria demanded in order to compete with other types of memory devices, and the electrets are generally limited to polymer materials. Until now, there is no report on nonvolatile organic electrets using nano-interfaced organic monomer layer as a dielectric material even though the use of organic monomer materials become important for the development of molecularly interfaced memory and logic elements. Furthermore, to increase a retention time for the nonvolatile organic memory device as well as to understand an intrinsic memory property, a molecular design of the organic materials is also getting important issue. In this presentation, we report on the OFET memory device built on a silicon wafer and based on films of pentacene and a SiO2 gate insulator that are separated by organic molecules which act as a gate dielectric. We proposed push-pull organic molecules (PPOM) containing triarylamine asan electron donating group (EDG), thiophene as a spacer, and malononitrile as an electron withdrawing group (EWG). The PPOM were designed to control charge transport by differences of the dihedral angles induced by a steric hindrance effect of side chainswithin the molecules. Therefore, we expect that these PPOM with potential energy barrier can save the charges which are transported to the nano-interface between the semiconductor and organic molecules used as the dielectrics. Finally, we also expect that the charges can be contributed to the memory capacity of the memory OFET device.[4]

• Polymer(Korea)
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• v.24 no.6
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• pp.737-743
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• 2000

Polyquinonediimines (PQDI) which have stable structure on heat and contains mono-azobenzene in the side chain were synthesized by means of condensation polymerization under TiCl$_4$. The synthesized monomers and polymers were identified by FT-IR, $^1$H-NMR, and elementary analysis. Especially, PQDI was comfirmed by the double-bonding peak of >C=N appeared near 1625 $cm^{-1}$ / by means of FT-IR spectrum. PQDI containing mono-azobenzene group in both side chains wat not soluble in non-polar solvents at all but partially soluble in the polar solvents having small dielectric constant, and dissolved in the strong acid such as sulfuric acid and $CH_3$SO$_3$H. Molecular weight distribution of PQDI measured by GPC showed 1.74. It was confirmed through X-ray diffraction analysis that the polymer was partially crystalline at the low angle region, but amorphous after heat treatment at 1$25^{\circ}C$. The glass transition temperature (T$_{g}$ ) of synthesized polymer was measured as 1$25^{\circ}C$ by differential scanning calorimetry. The SHG value for $\chi$$^{(2)}$ after poling at 1$25^{\circ}C$ was 8.6 pm/V (λ=1.542 ${\mu}{\textrm}{m}$). The SHG value slowly decreased with time from the start but appeared temporal stability after 100 hours.

• Applied Chemistry for Engineering
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• v.17 no.2
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• pp.217-222
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• 2006

Polyimides have been investigated extensively and used widely over the past three decades because of their high performance properties such as excellent thermal, mechanical, and electrical properties. Polyimides are difficult to be processed because of the aromatic moieties, imide group, and insoluble nature in most organic solvents. The soluble polyimides were synthesized from 2,2,-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BAPAF) and 3,3,-diamino-4,4-dihydroxybyphenyl (HAB) as aromatic diamines and 4,4-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), pyromellitic dianhydride (PMDA), 4,4-oxydiphthalic dianhydride (OPDA), 3,3,4,4-benzophenone tetracarboxylic dianhydride (BTDA) and 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride (DSDA) as aromatic dianhydrides. The polyimides were characterized by NMR, FR-IR, TGA and the dielectric constant of the obtained polyimides was calculated from storage of electro-capacity. A novel photosensitive polyimide was synthesized by the reaction of polyimide, containing hydroxyl group and methacryloyl chloride using triethylamine. The good micro-pattern was obtained with photosensitive polyimide from the photolithographic technique.

• The Korean Journal of Rheology
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• v.11 no.1
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• pp.9-17
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• 1999

Viscoelastic characteristics of cured phenolic resin/carbon fiber composite materials were investigated through glass transition and degradation reaction processes in the high temperature region up to $400^{\circ}C$. A typical glass transition of the cross-linked thermoset polymer was followed by irreversible degradation reactions, which were exhibited by the increasing storage modulus and loss modulus peak. A degradation master curve was constructed by using the vertical and horizontal shift factors, both of which complied well with the Arrhenius equation in light of the kinetic expression of degradation rate constants. Using an analogy to the Havriliak-Negami equation in dielectric relaxation phenomena, a viscoelastic modeling methodology was developed to characterize the frequency- and temperature-dependent complex moduli of the degrading thermoset polymer composite systems. The temperature-dependent relaxation time of the degrading composites was determined in a continuous fashion and showed a minimum relaxation time between the glass transition and degradation reaction regions. The capability of the developed modeling methodology was demonstrated by describing the complex behavior of the viscoelastic complex moduli of reacting phenolic resin composite systems.

• Journal of the Korean Magnetics Society
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• v.20 no.4
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• pp.143-148
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• 2010

This study examined the effects of sheet thickness on electromagnetic wave absorption characteristics and internal microstructure in 92.6%Fe-6.5%Si-0.9%Cr (wt%) alloy flakes/polymer composite sheets available for quasi-microwave band. The composite sheets with the thickness of 0.3, 0.4 and 0.5 mm were prepared by tape casting. A significant decrease in transmission parameter $S_{21}$ and a large increase in power loss were observed for the thick composite sheet in the frequency range of 1~5 GHz. However the permeability properties were not affected by thickness variation, while the imaginary part of complex permittivity increased with the increase of sheet thickness at 1~5 GHz. The enhanced electromagnetic wave absorption characteristics in the thicker composite sheets was attributed to the changed microstructure and the higher dielectric loss.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.371-380
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• 2006

We design and fabricate a novel tunable wavelength filter, which utilizes long-range surface plasmon-polaritons excited along nm-thick-metal strips. A gold metal strip, with $\sim$ cm length, 20 nm thickness, and $\sim$ 5$\mu$m width, is embedded in thick thermo-optic Polymer films supported by a silicon wafer. A dielectric Bragg grating structure is Placed on the metal strip, so that transmission signals at telecom wavelength are selected by thermal effect of the thermo-optic polymer. High extinction ratio of 25 dB and total insertion loss of $\sim$25 dB/cm can be measured by single-mode coupling of optical fibers. We also verify that wavelength tuning of the long-range surface plasmon-polariton filters can be achieved by electric current directly applied to the metal-strip waveguides.

• Applied Chemistry for Engineering
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• v.2 no.3
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• pp.253-261
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• 1991

Polyamic acids, precursor polymers of polyimides have been obtained by the solution polycondensation of benzophenone tetracarboxylic dianhydride (BTDA) with 4, 4'-diamino diphenyl methane (MDA) and/or 3, 3'-dimethyl benzidine (OTB). The reaction was carried in two solvent systems such as m-cresol and m-cresol/xylene mixture. The results of TGA analysis showed that the polyimide films had good thermal stability with the initial decomposition temperature ranging from $540^{\circ}$ to $590^{\circ}$. According to DSC analysis of polymers, the glass transition temperature was over $340^{\circ}$. Polyimide film samples, showed good mechanical and electrical properties, had over $16Kg/mm^2$ of tensile strength and about 200 KV/mm of dielectric breakdown voltage. The properties of the copolymer from MAD/OTB were better than those of the homopolymer from MDA. And the polymer synthesized in m-cresol had lower properties than that obtained in m-cresol/xylene.