• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.1
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• pp.1-7
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• 2016

RE : YAG ($RE=Nd^{3+}$, $Er^{3+}$) single crystals are laser diodes and generally grown by Czochralski method with controlling the various growth parameter. Since the defects occurred by temperature gradient or the rotation speed of solid-liquid growth interface act as the decline of crystal optical property during the growth procedure, crystalline quality improvement via defects analysis is necessary. The etch pit density (EPD) analysis was used to confirm the surface defect of grown RE : YAG single crystal and to select the area of transmission electron microscopy (TEM) analysis. Defects in the specimen produced by tripod polishing method such as buckling, rod shaped, bend contours by internal stress, segregation and others were observed by using 200 kV TEM and 300 kV FE-TEM.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.446-446
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• 2013

유기태양전지는 가벼운 무게와 우수한 유연성을 가져 플렉서블 태양전지 및 롤투롤(Roll-to-roll) 인쇄 공정에 대한 적용 가능성 때문에 많은 연구가 이루어지고 있다. 하지만 이종접합 유기태양전지를 상용화하기 위해서는 낮은 전력 변환 효율 (PCE)을 증진하는 연구가 필요하다. 본 연구에서는 간단한 용액공정을 통해 poly (3-hexylthiophene) (P3HT) 나노구조층을 사용하여 indium-tin-oxide 양극 전극/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) 정공수송층/P3HT 나노구조층/P3HT 복합체로 제작한 나노구조층/C60 전자수송층 /lithium quinolate 전자주입층/Al 음극 전극 구조의 유기태양전지를 제작하였다. 전류밀도-전압 곡선 결과는 P3HT 복합체 이용한 나노구조층를 가진 유기태양전지의 구조는 평면층을 가진 유기태양전지에 비해서 PCE가 향상됨이 관찰되었다. 유기태양전지는 짧은 엑시톤의 확산거리가 PCE 감소의 주요 원인이 된다. P3HT 복합체를 사용한 나노구조층을 가지는 유기태양전지는 광활성층과 전자수송층 사이의 계면이 넓어지는 효과를 가진다. 계면이 넓어지는 효과를 통해 생성된 엑시톤을 효율적으로 분리할 뿐만 아니라 더 많은 양의 전하를 생성할 수 있기 때문에 전하의 양이 증가되고 더 높은 전류를 생성하여 PCE를 효과적으로 높일 수 있다.

• Applied Chemistry for Engineering
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• v.27 no.5
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• pp.472-477
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• 2016

We studied the effects of anodic oxidation treatments of carbon fibers on interfacial adhesion of the carbon fibers-reinforced epoxy matrix composites with various current densities. The surface of treated carbon fibers was characterized by atomic force microscope (AFM), field emission-scanning electron microscope (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The interlaminar shear strength (ILSS) of the composites was determined by a short beam shear test. This result showed that both the roughness and oxygen group of the carbon fibers surface increased in proportion to the current density. After anodic-oxidation-treated, the ILSS also increased as a function of the current density. In addition, the proportional relationship between ILSS and phenolic hydroxyl group was confirmed. The ILSS of the CF-2.0 sample increased by 4% compared to that of the CF-AS sample, because the anodic oxidation treatment increased the oxygen group and roughness on the carbon fibers surface, which leading to the improvement of the interfacial adhesion of the carbon fibers-reinforced epoxy matrix composites. Among these, the phenolic hydroxyl group which has the proportional relationship with ILSS is found to be the most important factor for improving the interfacial adhesion of the carbon fibers-reinforced epoxy matrix composites.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1355-1357
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• 1998

TFT의 게이트 절연막으로 사용되는 절연체는 우수한 절연특성과 낮은 계면포획전하밀도($D_{it}$)를 요구한다. 이에 본 연구에서는 우수한 절연특성을 가지며, 격자상수가 Si과 유사한 $CaF_2$의 증착 특성을 연구하였다. 진공증착법을 이용하여 p형 Si(100) 기판위에 $CaF_2$의 기판온도, 두께를 변화시켜 전기적, 구조적 특성을 평가하였다. 또한 Si 기판에 방향에 따른 박막의 특성을 조사하였다. 구조적 특성분석으로부터 Si(100) 기판의 경우 $CaF_2$는 (200)방향으로 주도적인 성장을 하였으며 기판온도를 상승시킴에 따라 (220)방향으로도 성장을 하는 것으로 나타났다. 열처리 전후의 구조적 특성은 SEM을 통해서 확인 할 수 있었다. 열처리 전후의 특성 변화로부터 저온($100^{\circ}C$이하)에서는 기판과의 성장방향과 동일하였으며 고온($200^{\circ}C$이상)에서는 기판방향과는 다른 방향 성장 결과를 얻었다. 전기적 특성평가를 위하여 C-V 특성을 평가하였다. C-V 특성으로부터 Si(100) 기판의 온도가 $100^{\circ}C$, $1455\AA$ 두께로 증착한$CaF_2$ 박막의 $D_{it}$는 $1.8{\times}10^{11}cm^{-1}eV^{-1}$로 낮은 값을 가지 고 있었으며 0.1MV/cm에서 누설전류밀도가 $10^{-8}A/cm^2$ 이었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.225-225
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• 2008

PLZT 박막을 Pt/Ti/$SiO_2$/Si 기판 위에 RF-마그네트론 스퍼터링방법으로 형성할 때 기판온도에 따른 PLZT 박막의 결정성과 전기적 특성 및 강유전 특성에 미치는 영향에 관하여 연구하였다. 하부전극 Pt와 PLZT 박막 사이에는 완충층으로 $TiO_2$를 사용하여 계면에서의 상호확산을 제어하면서 우수한 물성의 PLZT 박막을 얻고자 하였으며, 여러 기판온도에서 PLZT 박막을 증착한 후, 박막의 결정화를 위해 급속열처리법으로 $700^{\circ}C$로 후열처리하였다. 그 결과 기판온도 $400^{\circ}C$에서 증착한 PLZT 박막이 가장 우수한 특성을 나타내었으며, 이때의 잔류분극과 누설전류밀도는 각각 15.8 ${\mu}C/cm^2$, $5.4\times10^{-9}A/cm^2$ 이였다. 그러나 $500^{\circ}C$에서는 결정립 조대화현상이 나타나면서 잔류분극과 누설전류밀도는 9 ${\mu}C/cm^2$, $3.09\times10^{-7}A/cm^2$로 특성이 저하되었다.

• Journal of IKEEE
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• v.27 no.3
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• pp.220-224
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• 2023

Row hammering is a phenomenon in which bit flips occur in adjacent rows when accessing a particular row continuously, causing data damage, security problems, and poor computing performance. This paper analyzes the cause and response method of row hammering through TCAD simulation in 2ynm DRAM. In the experiment, the row hammering is reproduced while changing the parameters of the trap and the device structure, and the trap density, temperature. It analyzes the relationship with Active Wisdom, etc. As a result, it was confirmed that changes in trap parameters and device structures directly affect ΔV_cap/pulse. This enables a fundamental understanding of low hammering and finding countermeasures, and can contribute to improving the stability and security of DRAM.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.7
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• pp.37-43
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• 2008

In this paper, the dependence of electrical characteristics of Silicon-$Al_2O_3$-Nitride-Oxide-Silicon (SANOS) memory cell transistors and program/erase (P/E) speed, reliability of memory device on interface trap between Si substrate and tunneling oxide and bulk trap in nitride layer were investigated using charge pumping method which has advantage of simple and versatile technique. We analyzed different SANOS memory devices that were fabricated by the identical processing in a single lot except the deposition method of the charge trapping layer, nitride. In the case of P/E speed, it was shown that P/E speed is slower in the SANOS cell transistors with larger capture cross section and interface trap density by charge blocking effect, which is confirmed by simulation results. However, the data retention characteristics show much less dependence on interface trap. The data retention was deteriorated as increasing P/E cycling number but not coincides with interface trap increasing tendency. This result once again confirmed that interface trap independence on data retention. And the result on different program method shows that HCI program method more degraded by locally trapping. So, we know as a result of experiment that analysis the SANOS Flash memory characteristic using charge pumping method reflect the device performance related to interface and bulk trap.

• Korean Journal of Materials Research
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• v.2 no.3
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• pp.172-179
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• 1992

$Al_2O_3/ZrO_2$ composites were fabricated by pressureless sintering from commercial powders and/or nano composite powder of $Al_2O_3/ZrO_2$. The Properties of the composites such as density, strength, hardness and fracture toughness were evaluated. Microstructures and fracture surfaces ware also examined. The flexural strength remains unchanged(~640 MPa) as long as the content of commercial powders is not extreamly high, and depends on microstructures of the composites. Fracture toughness(4.3-5.3 $Mpa{\cdot}m^{1/2}$) increases with increasing content of commercial powders. Fractography shows that failure-initiating sources are 1)surface flaws resulting from machining damage, 2)crack-shaped voids formed due to $ZrO_2$ agglomeration, and 3)surface separation caused by inhomogeneous blending and by sinterability difference between nato composite powder and commercial powders of $Al_2O_3/ZrO_2$. Failure mode of the composites was mainly transgranular.

• Korean Journal of Materials Research
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• v.9 no.11
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• pp.1112-1116
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• 1999

Thermoelectric effects on the temperature changes at the solid- and liquid-phase and its interface were studied by using the unidirectional solidification of $\textrm{Bi}_{2}\textrm{Te}_{3}$. Cooling or heating effects measured with current density. polarity and current passing time were quite different. By separating sole Peltier, Thomson and Joule heat theoretically and experimentally, the Peltier coefficient at the solid/liquid interface of $\textrm{Bi}_{2}\textrm{Te}_{3}$ was -1.10$\times\textrm{10}^{-1}$V, and the Thomson coefficients of solid- and liquid-phase were 7.31\times\textrm{10}^{-4}V/K, 5.77\times\textrm{10}^{-5}V/K, respectively. When D.C. passed from solid-phase to liquid-phase during the crystal growth of $\textrm{Bi}_{2}\textrm{Te}_{3}$ the crystal with more directionality was obtained owing to increase of the temperature gradient in liquid by the Peltier cooling. But in reverse current direction, the crystallinity was not changed significantly.

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.151-158
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• 2011

Bubbles within the foamed concrete manufactured by pre-foaming method is the main factor which affects the physical properties of foamed concrete such as density, strength, and porosity. Although many researches on foamed concrete have been continuously carried out, insufficient number of researches on the properties related to bubbles in the foamed concrete has been performed except for chemical application related researches. In order to make an optimal foamed concrete, study on the bubble properties must be pursued. In order to effectively implement bubbles in the manufacturing of foamed concrete, the bubble properties must be estimated. In this study, in order to determine the bubble properties, examination of the bubble properties according to types and foaming agent concentration was performed. An foaming agent used for this test were anionic surfactant, rosin, and protein system with the foaming agent concentration range of 0.05~13%. Test parameters considered in the study were foaming rate, foam volume, drainage solution volume, and bubble size. The study results showed that, regardless of foaming agent type, higher concentration of foaming agent showed an increase in the foaming rate. Also, the results showed that concentration of foaming agent affected bubble size, drainage solution volume change, and bubble distributions. With respect to the stability of the bubble, protein foaming agent was better than anion surfactant or rosin foaming agent. With respect to the bubble shape, anion surfactant and rosin formed bubbles had polygon shape where as protein formed bubbles had spherical shape.