• 한국초전도학회:학술대회논문집
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• v.9
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• pp.260-260
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• 1999

We compared c-axis tunneling characteristics of small stacked intrinsic Josephson junctions prepared on the surface of pristine, I-, and HgI$_2$-intercalated Bi$_2Sr_2CaCu_2O_{8+x}$ (Bi2212) single crystals. The R(T) curves are almost metallic in I-Bi2212 specimens, but semiconducting in HgI$_2$-Bi2212 ones.· The transition temperatures were 82.0 K, 73.0 K, and 76.8 K for pristine Bi2212, I-Bi2212, and HgI2-Bi2212 specimens, respectively, consistent with p-T$_c$ phase diagram. Current-voltage (IV) characteristics of both kinds of specimens show multiple quasiparticle branches with well developed gap features, indicating Josephson coupling is established between neighboring CuO$_2$ planes. The critical current I$_c$ of I-Bi2212 is almost the same as of that of pristine crystals, but I$_c$ is much reduced in Hgl$_2$-Bi2212. In spite of expanded interlayer distances, the interlayer coupling is not significantly affected in I-Bi2212due to holes generated by iodine atoms. The coupling in HgI$_2$-Bi2212 is, however, weakened due to inertness of HgI$_2$ molecules and the expansion of interlayer distance. Relation between the superconducting transition temperature T$_c$ and the critical current I$_c$ seems to contradict Anderson's interlayer-pair-tunneling theory but agree with a modified version of it.

• Korean Journal of Materials Research
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• v.23 no.8
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• pp.430-434
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• 2013

Quantum dots(QDs) with their tunable luminescence properties are uniquely suited for use as lumophores in light emitting device. We investigate the microstructural effect on the electroluminescence(EL). Here we report the use of inorganic semiconductors as robust charge transport layers, and demonstrate devices with light emission. We chose mechanically smooth and compositionally amorphous films to prevent electrical shorts. We grew semiconducting oxide films with low free-carrier concentrations to minimize quenching of the QD EL. The hole transport layer(HTL) and electron transport layer(ETL) were chosen to have carrier concentrations and energy-band offsets similar to the QDs so that electron and hole injection into the QD layer was balanced. For the ETL and the HTL, we selected a 40-nm-thick $ZnSnO_x$ with a resistivity of $10{\Omega}{\cdot}cm$, which show bright and uniform emission at a 10 V applied bias. Light emitting uniformity was improved by reducing the rpm of QD spin coating.At a QD concentration of 15.0 mg/mL, we observed bright and uniform electroluminescence at a 12 V applied bias. The significant decrease in QD luminescence can be attributed to the non-uniform QD layers. This suggests that we should control the interface between QD layers and charge transport layers to improve the electroluminescence.

• Proceedings of the Korean Vacuum Society Conference
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• 1994.02a
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• pp.50-50
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• 1994

Half-metallic Heusler alloys (NiMnSb, ppdMnSb, pptMnSb) have attracted much attention due to their unique electronic and magnetic structures. Sppin-ppolarized band structure calculation ppredicts metallic behavior for the majority sppin states and semiconductor behavior for the minority sppin states. We have studied the electronic structures of these half-metallic Heusler alloys by core-level pphotoemission sppectroscoppy of Mn 2pp and 3s XppS sppectra. We found large intensities of Mn 2pp satellites and 3s exchange spplitting comppared with other metal Mn-alloys. These satellite structure can be understood by applying Anderson imppurity model. This fact supports the calculated sppin pprojected ppartial density of states which suggests that the valence electrons be highly sppin ppolarized near Fermi level and that the electrons involved with charge-transfer be mainly minority sppin ones which have semiconducting band structure. The trend of charge transfer energies Δ from ligands (Sb 5pp) to Mn 3d, obtained from our model fitting, is consistent with that calculated from sppin pprojected ppartial density of state. Also the trend of d-d electron correlation energies U calculated from Mn Auger line L3 VV by Mg $K\alpha$ source is comppatible with that resulted from our model fitting. We fitted the Mn 3s curve in the same way as for insulating Mn comppounds by using the same pparameters calculated from Mn 2pp curve fitting exceppt for the Coulomb interaction energy Q between core hole and d-electrons. The 3s sppectra were analyzed by combing the charge transfer model and a simpple model taking into account the configuration mixing effect due to the intra-shell correlation. We found that the exchange interaction between 3s hole and 3d electrons is mainly respponsible for the satellite of Mn 3s sppectra. This is consistent with the neutron scattering data, which suggests local 3d magnetic moment. We find that the XppS analysis results of Mn 2pp and 3s satellite structures of half-metallic Heusler alloys are very similar to those of insulating transition metal comppounds.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.93-96
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• 2005

The arc melting was employed to prepare undoped $CoSb_3$ compounds and their thermoelectric properties were investigated. Specimen annealed at $400^{\circ}C$ for 24 hrs showed sound microstructure. However, considerable voids and cracks were found after annealing at above $500^{\circ}C$. It seems to be attributed to the phase dissociation and thermal expansion due to phase transitions during annealing and cooling. Single phase $\delta-CoSb_3$ was successfully obtained by annealing at $400^{\circ}C$ for 24 hrs. In the case of increasing annealing temperature, phase decompositions occurred. Undoped $CoSb_3$ showed p-type conduction and intrinsic semiconducting behavior at all temperatures examined. Thermoelectric properties were remarkably improved by annealing and they were closely related to phase transitions.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.4
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• pp.31-34
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• 2016

System In Package (SiP) is getting popular and momentum for the recent wearable, IoT and connectivity application apart from mobile phone. This is driven by market demands of cost competitive, lighter and smaller/thinner and higher performance. As one of many semiconducting assembly products, Leadframe product has been widely used for low cost solution, light/ small and thin form factor. But It has not been applied for SiP although Leadframe product has many advantages in cost, size and reliability performance. SiP is mostly based on laminate substrate and technically difficult on Leadframe substrate because of a limitation in SMT performance. In this paper, Leadframe based SiP product has been evaluated about key technical challenges in SMT performance and electrical shield technology. Mostly Leadframe is considered not available to apply EMI shield because of tie-bar around package edge. In order to overcome two major challenges, connection bars were deployed properly for SMT pad to pad and additional back-side etching was implemented after molding process to achieve electrical isolation from outer shield coating. This product was confirmed assembly workability as well as reliability.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.12
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• pp.89-100
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• 1997

This paper investigated a new type of low voltage threshold switch (LVTS). As distinguished from the many other types of electronic threshold switches, the LvTS is ; voltage controlled, occurs at low voltages ($V_{2}$ $O_{5}$lV devices. The average low threshold voltage < $V_{LVT}$>=218 mV (standard deviation =24mV~kT/q, where T=300K), and was independent of the device area (x100) and amorphous oxide occurred in an ~22.angs. thick interphase of the V/amorphous- $V_{2}$ $O_{5}$ contacts. At $V_{LVT}$ there was a transition from an initially low conductance (OFF) state into a succession of quantized states of higher conductance (ON). The OFF state was spatically homogeneous and dominated by tunneling into the interphase. The ON state conductances were consistent with the quantized conductances of ballistic transport through a one dimensional, quantum point contact. The temeprature dependence of $V_{LVT}$, and fit of the material parameters (dielectric function, barrier energy, conductivity) to the data, showed that transport in the OFF and ON states occurred in an interphase with the characteristics of, respectively, semiconducting and metallic V $O_{2}$. The experimental results suggest that the LVTS is likely to be observed in interphases produced by a critical event associated with an inelastic transfer of energy.rgy.y.rgy.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2245-2250
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• 2014

A new accepter unit, 6,7-difluoro-2,3-dihexylquinoxaline, was prepared and utilized for the synthesis of the conjugated polymers containing electron donor-acceptor pair for OPVs. New series of copolymers with dioctyloxybenzodithiophene as the electron rich unit and 6,7-difluoro-2,3-dihexylquinoxaline as the electron deficient unit are synthesized. The solid films of poly[2,6-(4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene)-alt-5,8-(6,7-difluoro-2,3-dihexylquinoxaline)] (PBQxF) and poly[2,6-(4,8-bis(2-ethylhexyloxy) benzo[1,2-b:4,5-b']dithiophene)-alt-5,8-(6,7-difluoro-2,3-dihexyl-5,8-di(thiophen-2-yl) quinoxaline)] (PBDTQxF) show absorption bands with maximum peaks at about 599 and 551 nm and the absorption onsets at 692 and 713 nm, corresponding to band gaps of 1.79 and 1.74 eV, respectively. The devices comprising PBQxF with $PC_{71}BM$ (1:2) showed open-circuit voltage ($V_{OC}$) of 0.64 V, short-circuit current density ($J_{SC}$) of $1.58mA/cm^2$, and fill factor (FF) of 0.39, giving power conversion efficiency (PCE) of 0.39%. To obtain absorption in the longer wavelength region, thiophene units without any alkyl group are incorporated as one of the monomers in PBDTQxF, which may result in low solubility of the polymers to lead lower efficiency.

• Journal of the Korean Magnetics Society
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• v.15 no.3
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• pp.181-185
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• 2005

We have investigated the effects of Al codoping on the structural, electrical transport, and magnetic properties of oxide diluted magnetic semiconductor $Zn_{1-x}Cr_xO$ thin films prepared by reactive sputtering. Nondoped $Zn_{0.99}Cr_{0.01}O$ thin films show semiconducting transport behavior and weak ferromagnetic characteristic. The Al doping increases the carrier concentration and results in an decrease of resistivity and metal-insulator transition behavior. With increasing carrier concentration, the magnetic properties drastically change, exhibiting a remarkable increase of the saturation magnetization. These results show carrier-enhanced ferromagnetic order in Cr-doped ZnO.

• Journal of Sensor Science and Technology
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• v.23 no.1
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• pp.15-18
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• 2014

We present gas sensing performance based on $2{\times}2$ sensor array with four different elements ($TiO_2$, $SnO_2$, $WO_3$ and $In_2O_3$ thin films) fabricated by rf sputter. Each thin film was deposited onto the selected $SiO_2$/Si substrate with Pt interdigitated electrodes (IDEs) of $5{\mu}m$ spacing which were fabricated on a $SiO_2$/Si substrate using photolithography and dry etching. For 5 ppm $NO_2$ and 50 ppm CO, each thin film sensor has a different response to offers the distinguishable response pattern for different gas molecules. Compared with the conventional micro-fabrication technology, $2{\times}2$ sensor array with such remarkable response pattern will be open a new foundation for monolithic integration of high-performance chemoresistive sensors with simplicity in fabrication, low cost, high reliablity, and multifunctional smart sensors for environmental monitoring.

• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.53-61
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• 1986

A gas sensor which has been made by wet process had fabricated by coating each of the mixture on alumina tube and firing at 85$0^{\circ}C$ for 3hrs. A gas concentration such $H_2$, CO, $C_3H_8$, $C_2H_2$ and $CH_4$ vs its detection voltage characteristics has been in-vestigated on $SnO_2-In_2O_3-MgO$ system doped with PdO, $La_2O_3$, $ThO_2$, NiO and $Nb_2O_5$ The optimum sensitivity composition for various gases were 90w/o $SnO_2$-9w/o $In_2O_3$-1w/o MgO for $H_2$, $C_2H_2$ CO and $C_3H_8$ and 95w/o $SnO_2$-4w/o $In_2O_3$-1w/o MgO for $CH_4$. The sample which has been made by wet process than dry process had predominated sensitivity for each gases and particle size of the sample coprecipitated with PH=9 was 0.1${\mu}{\textrm}{m}$ The $SnO_2$-In2_O_3-MgO$ system doped with 2w/o $Nb_2O_5$ and NiO was the most sensitive for $H_2$ and $C_2H_2$ gas. In $SnO_2$-In2_O_3-MgO$ system doped with $ThO_2$ the sensitivity of $H_2$ gas was decreased but CO gas was in-creased when dopant con was increased.