• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1081-1084
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• 1995

Internal voids located within an insulation will arise partial discharge that causes local breakdown and even the entire insulation breakdown. For HV apparatuses, it is usual case that several voids are formed within non-uniform electric field condition rather than single void within uniform field, which can be solved analitically. The purpose of this work is to study partial discharge and breakdown characteristics of an insulation according to the distribution pattern of two disc-type voids that are located within non-uniform field. The results from numerical field analysis and experiments show that the electric field within the voids decreases as they are arranged more serially, which accordingly results in the increase of partial discharge inception field(PDIF) much higher than that of single void model. With parallel arranged voids, PDIF is almost the same as that of single void model. On the other hand, AC breakdown strength decreases as voids are arranged more serially, which is a natural result considering the reduction of effective insulation thickness. For parallel voids, this effect cannot he noticed where as they show different pattern compared with single void and serial void models in $\Phi$-Q-N analysis. Considering these results may leads us to the conclusion that, in the evaluation of insulating products through PD test, it is not sufficient to determine only PDIV or existence of PD at predetermined voltage level. We could evaluate more accurately by considering all the available data such as PDIV, PD magnitude, PD occurring phase, number of PD pulses, and etc.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.413-413
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• 2012

Lead sulfide (PbS) Colloidal quantum dots (CQDs) are promising material for the photovoltaic device due to its various outstanding properties such as tunable band-gap, solution processability, and infrared absorption. More importantly, PbS CQDs have large exciton Bohr radius of 20 nm due to the uniquely large dielectric constants that result in the strong quantum confinement. To exploit desirable properties in photovoltaic device, it is essential to fabricate a device exhibiting stable performance. Unfortunately, the performance of PbS NQDs based Schottky solar cell is considerably degraded according to the exposure in the air. The air-exposed degradation originates on the oxidation of interface between PbS NQDS layer and metal electrode. Therefore, it is necessary to enhance the stability of Schottky junction device by inserting a passivation layer. We investigate the effect of insertion of passivation layer on the performance of Schottky junction solar cells using PbS NQDs with band-gap of 1.3 eV. Schottky solar cell is the simple photovoltaic device with junction between semiconducting layer and metal electrode which a significant built-in-potential is established due to the workfunction difference between two materials. Although the device without passivation layer significantly degraded in several hours, considerable enhancement of stability can be obtained by inserting the very thin LiF layer (<1 nm) as a passivation layer. In this study, LiF layer is inserted between PbS NQDs layer and metal as an interface passivation layer. From the results, we can conclude that employment of very thin LiF layer is effective to enhance the stability of Schottky junction solar cells. We believe that this passivation layer is applicable not only to the PbS NQDs based solar cell, but also the various NQDs materials in order to enhance the stability of the device.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.141-141
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• 2012

The electronic and optical properties of Indium Zinc Tin Oxide (IZTO) thin films using gas environment were investigated by X-ray photoelectron spectroscopy (XPS) and reflection electron energy loss spectroscopy (REELS). REELS spectra revealed that the band gaps of IZTO thin films are 3.26, 3.07, and 3.46 eV for water mixed with oxygen, argon mixed with oxygen, and air environments, respectively. The measured band gaps by REELS are consistent with the optical band gaps obtained by UV-Spectrometer. The optical properties represented by the dielectric function $\mathfrak{m}$, the refractive index n, the extinction coefficient k, and the transmission coefficient T of the IZTO thin films with different gas environments were determined from a quantitative analysis of REELS spectra. The calculated transmission from quantitative analysis of REELS spectra shows good agreement with transmission measured by UV-spectrometer. The transmission values of 89% and low electrical resistivity of $3.55{\times}10^{-3}{\Omega}{\cdot}cm$ have been achieved for argon mixed with oxygen which indicates that the gas enviroment plays an important role in improving the electronic and optical properties of films.

• Journal of the Korean Ceramic Society
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• v.49 no.3
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• pp.266-271
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• 2012

The effect of $Bi(Mg_{1/2}Sn_{1/2})O_3$ (BMS) modification on the crystal structure, ferroelectric and piezoelectric properties of $Bi_{1/2}(Na_{0.8}K_{0.2})_{1/2}TiO_3$ (BNKT) ceramics has been investigated. The BMS-substitution induced a transition from a ferroelectric (FE) tetragonal to a nonpolar pseudocubic phase, leading to degradations in the remnant polarization, coercive field, and piezoelectric coefficient $d_{33}$. However, the electric-field-induced strain was significantly enhanced by the BMS substitution-induced phase transition and reached a highest value of $S_{max}/E_{max}$ = 633 pm/V under an applied electric field of 6 kV/mm when the BMS content reached 6 mol%. The abnormal enhancement in strain was attributed to the field-induced transition of the pseudocubic symmetry to other asymmetrical structure, which was not clarified in this work.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.20-22
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• 1999

The effect of dopant and stoichiometry on the physical and optical properties of $LiNbO_{3}$ were studied. We prepared three samples, undoped, MgO doped $LiNbO_{3}$ with congruent composition and near-stoichiometric $LiNbO_{3}$. Dielectric constant and transmittance in UV/VIS/IR light range were measured. The results showed that the features for high [Li]/[Nb] were similar to those for low [Li]/[Nb] but with high [Mg].

• Journal of Sensor Science and Technology
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• v.6 no.3
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• pp.200-206
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• 1997

Using $SiCl_{2}H_{2}$, $NH_{3}$ and $N_{2}O$, we have fabricated silicon oxynitride ($Si_{x}O_{y}N_{z}$) layers on thermally oxidized silicon wafer by low pressure chemical vapor deposition. Three different compositions were achieved by controlling gas flow ratios($NH_{3}/N_{2}O$)) to 0.2, 0.5 and 2 with fixed gas flow of $SiCl_{2}H_{2}$. Ellipsometry and high frequency capacitance-voltage(HFCV) measurements were adapted to investigate the difference of the refractive index, dielectric constant, and composition, respectively. Regardless of nitride content, silicon oxynitrides had similar stability to silicon nitrides. The relative standing of alkali ion sensitivity in silicon oxynitride layers was influenced by nitride content. The better alkali ion-sensitivity was achieved by increasing oxide content in bulk of silicon oxynitrides.

• Electrical & Electronic Materials
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• v.16 no.9
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• pp.64.1-64
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• 2003

A metal-ferroelectric [SrBi$_2$Ta$_2$O$\_$9/ (SBT)-high-k-insulator(PrOx)-semiconductor(Si) structure has been fabricated and evaluated as a key part of metal-ferroelectric-insulator-semiconductor-field-effect-transistor MFIS-FET memory, aiming to improve the memory retention characteristics by increasing the dielectric constant in the insulator layer and suppressing the depolarization field in the SBT layer. A 20-nm PrOx film grown on Si(100) showed both a high of about 12 and a low leakage current density of less than 1${\times}$ 10e-8 A/$\textrm{cm}^2$ at 105 MV/cm. A 400-nm SBT film prepared on PrOx/Si shows a preferentially oriented (105) crystalline structure, grain size of about 130 nm and subface roughness of 3.2 nm. A capacitance-voltage hysteresis is confirmed on the Pt/SBT/PrOx/Si diode with a memory window of 0.3V at a sweep voltage width of 12 V. The memory retention time was about 1 104s, comparable to the conventional Pt/SBT/SiO$\_$x/N$\_$y/(SiO$\_$N/)/Si. The gradual change of the capacitance indicates that some memory degradation mechanism is different from that in the Pt/SBT/SiON/Si structure.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.8
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• pp.404-410
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• 2006

Toward the practical applications, on operation of conduction-cooled HTS SMES at temperatures well below 40[K] should be investigated, in order to take advantage of a greater critical current density of HTS and considerably reduce the size and weight of the system. In order to take advantage of a greater critical current density of high temperature superconducting (HTS) and considerably reduce the size and weight of the system, conduction-cooled HTS superconducting magnetic energy storage (SMES) at temperatures well below 40[K] should be investigated. This work focuses on the breakdown and flashover phenomenology of dielectrics exposed in air and/or vacuum for temperatures ranging from room temperature to cryogenic temperature. Firstly, we summarize the insulation factors of the magnet for the conduction cooled HTS SMES. And Secondly a surface flashover as well as volume breakdown in air and/or vacuum with two kind insulators has been investigated. Finally, we will discuss applications for the HTS SMES including aging studies on model coils exposed in vacuum at cryogenic temperature. The commercial application of many conduction-cooled HTS magnets, however, requires refrigeration at temperatures below 40[K], in order to take advantage of a greater critical current density of HTS and reduce considerably the size and weight of the system. The magnet is driven in vacuum condition. The need to reduce the size and weight of the system has led to the consideration of the vacuum as insulating media. We are studying on the insulation factors of the magnet for HTS SMES. And we experiment the spacer configure effect in the dielectric flashover characteristics. From the results, we confirm that our research established basic information in the insulation design of the magnet.

• 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.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.3 s.32
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• pp.77-82
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• 2004

In this paper, warpages of heterogeneous LTCC substrates comprised of high K/low K hi-layered structure were investigated. The effect of glass content in high K LTCC layer on the warpage of substrate during co-firing process was examined. Shrinkage and dielectric properties of high K and low K green sheets were measured. In-situ camber observation by hot stage microscopy showed different camber development of heterogeneous LTCC substrates according to glass content in high K green sheet. High K green sheet containing $50\%$ glass was matched to low K green sheet in the shrinkage. Therefore, LTCC substrate of Low K/High K+$50\%$ glass structure showed flat surface after sintering.