• Title/Summary/Keyword: 결함밀도

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Study on the optimization of additive manufacturing process parameters to fabricate high density STS316L alloy and its tensile properties (고밀도 STS316L 합금 적층 성형체의 제조공정 최적화 및 인장 특성 연구)

  • Yeonghwan Song
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.33 no.6
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    • pp.288-293
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    • 2023
  • To optimize the process parameters of laser powder bed fusion process to fabricate the high density STS316L alloy, the effect of laser power, scanning speed and hatching distance on the relative density was studied. Tensile properties of additively manufactured STS316L alloy using optimized parameters was also evaluated according to the build direction. As a result of additive manufacturing process under the energy density of 55.6 J/mm3, 83.3 J/mm3 and 111.1 J/mm3, high density STS316L specimens was suitably fabricated when the energy density, power and scan speed were 83.3 J/mm3, 225 W and 1000 mm/s, respectively. The yield strength, ultimate tensile strength, and elongation of STS316L specimens in direction perpendicular to the build direction, show the most competitive values. Anisotropic shape of the pores and the lack of fusion defects probably caused strain localization which result in deterioration of tensile properties.

A Study of the Acoustic Microscope System by Large Aperture Probe (대구경 탐촉자를 이용한 초음파 현미경 시스템 연구)

  • Cho, Yong-Sang;Kim, Jae-Hoon
    • Journal of the Korean Society for Nondestructive Testing
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    • v.23 no.5
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    • pp.475-479
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    • 2003
  • Traditional ultrasonic evaluation to detect micro/small surface cracks is the pulse-echo technique using the normal immersion transducer with high frequency, or the angle beam transducer with surface wave. It is difficult to make the automatic ultrasonic system that is to detect micro and small surface crack and position on the large structure like steel and ceramic rolls, because of the huge data of inspection and the ambiguous position data of transducer. The aim of this study using the high precision scanning acoustic microscope with 10MHz large aperture transducer was to display the real time A, B, C-scan for the automatic ultrasonic system in order to detect the existence and position of surface crack. The ultrasonic method with large aperture transducer was improved the scanning time and speed over 10times faster than traditional methods.

Synthesis of BaTiO3 Thin Film on Ti Electrode by the Current Pulse Waveform (펄스전류파형을 이용한 Ti 전극위에서 BaTiO3박막의 합성)

  • Kang, Jinwook;Tak, Yongsug
    • Applied Chemistry for Engineering
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    • v.9 no.7
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    • pp.998-1003
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    • 1998
  • $BaTiO_3$ thin film was electrochemically deposited on Ti electrode in a 0.4 M $Ba(OH)_2$ solution of $85^{\circ}C$ using a current pulse waveform. Both $BaTiO_3$ crystallinity and faradaic efficiency for the film formation were enhanced with the increase of cathodic current density and pulse time. Based on the surface analysis and electrochemical studies, it was suggested that, during cathodic pulsed, the surface pH increase due to the reduction of $H_2O$ accelerates the structural changes of Ti oxides which were formed during anodic cycle. Prior to experiments, Ti oxides were intentionally grown in 0.1 M $H_2SO_4$ solution and the effect of initial oxide film thickness on the $BaTiO_3$ film formation was investigated. The migration of $Ti^{+4}$ ions through the oxide film was retarded with the increase of film thickness and it was observed that the crystallization of $BaTiO_3$ was only limited to the defect area of surface oxides.

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Electromigratoin and thermal fatigue in Cu mentallization for ULSI (고집적용 구리배선의 electromigration 및 thermal fatigue 연구)

  • Kim Y.H.;Park Y.B;Monig R.;Volkert C.A.;Joo Y.C
    • Journal of the Microelectronics and Packaging Society
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    • v.12 no.1 s.34
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    • pp.53-58
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    • 2005
  • We researched damage formation and failure mechanism under DC(direct current) and AC(alternative current) in order to estimate reliability of Cu interconnects in ULSI. Higher current density and temperature induces more short TTF(time to failure) during interconnects carry DC. Measurement reveals that Cu electromigration has activation energy of 0.96eV and current density exponent value of 4. Thermal fatigue is occurred under DC, and higher frequency and ${\Delta}$T value gives more severe damage during interconnects carry AC Through failure morphology analysis with respect to texture, we observed that damages had grown widely and facetted grains had appeared in (100)grain but damages in (111) had grown thickness direction of line and had induced a failure rapidly.

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The TDDB Characteristics of Thin $SiO_2$ with Stress Voltage Polarity (스트레스전압 극성에 따른 얇은 산화막의 TDDB 특성)

  • Kim, Cheon-Soo;Yi, Kyoung-Soo;Nam, Kee-Soo;Lee, Jin-Hyo
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.26 no.5
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    • pp.52-59
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    • 1989
  • The reliability of the thin thermal oxide was investigated by using constant current stress method. Polysilicon gate MOS capacitors with oxide thickness range of 20-25nm were used in this experiment. Automatic measurement and statistical data analysis which were essential in reliability evaluation of VLSI process preformed by HP 9000 computer. Based on TDDB results, defect density, breakdown charge (Qbd) and lifetime of oxide film were evaluated. According to the polarity of the stress, some different characteristics were shown. Defect density was 62/$cm^2$ at negative gate injection. The value of Qbd was about 30C/$cm^2$ at positive gate injection, and about 21C/$cm^2$ at negative. The current density acceleration factor was 1.43$cm^2$/A for negative gate injection, and 1.25$cm^2$/A for positive gate injection.

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Formation of Aluminum Etch Tunnel Pits with Uniform Distribution Using UV-curable Epoxy Mask (UV-감응형 에폭시 마스크를 사용한 균일한 분포의 터널형 알루미늄 에치 피트 형성 연구)

  • Park, Changhyun;Yoo, Hyeonseok;Lee, Junsu;Kim, Kyungmin;Kim, Youngmin;Choi, Jinsub;Tak, Yongsug
    • Applied Chemistry for Engineering
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    • v.24 no.5
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    • pp.562-565
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    • 2013
  • The high purity Al foil, which has an enlarged surface area by electrochemical etching process, has been used as an anode for an aluminum electrolytic capacitor. Etch pits are randomly distributed on the surface because of the existence of surface irregularities such as impurity and random nucleation of pits. Even though a large surface area was formed on the tunnel-etched Al, its applications to various fields were limited due to non-uniform tunnel morphologies. In this work, the selective electrochemical etching of aluminum was carried out by using a patterned mask fabricated by photolithographic method. The formation of etch pits with uniform distribution has been demonstrated by the optimization of experimental conditions such as current density and etching solution temperature.

Properties and defects of Mn-Zn Ferrite single crystals grown by the modified process (연속 성장법으로 성장된 Mn-Zn Ferrite 단결정 특성 및 결함)

  • 정재우;오근호
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.1 no.2
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    • pp.23-33
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    • 1991
  • Mn - Zn Ferrite has the natural characteristics of incongruent melting and the zinc oxide evaporation while the crystal is being grown. As a result of these, it comes into existence to be a non-uniform distribution of cations along the crystal growth axis and also Pt particles are usually precipitated into the crystals in Bridgman method since the melt zone is maintained for a long time in the crucible. These have bad effects on the magnetic properties of ferrites. But, to overcome these faults and then acquire the better single crystals. new modified growth method was developed and the growth factors were investigated as following: melt height in the crucible, surface tension and density of melt, the behavior of melt at interface, the shapes of crucible and solid -liquid interface, powder feeding rate, and the crystal growing speed. In additon, when we analyzed the compositional fluctuations of grown crystals, they were supressed within 1.5 mol% $Fe_20_3$, 2 mol% MnO, ZnO respectively with comparing to initial composition of crystal and the microstructures of crystals on the(110) plane were observed by optical microscope through the chemical etching technique and the magnetic properties were determined.

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Electrical characteristics of 4H-SiC MIS Capacitors With Ni/CNT/SiO2 Structure (Ni/CNT/SiO2 구조의 4H-SiC MIS 캐패시터의 전기적 특성)

  • Lee, Taeseop;Koo, Sang-Mo
    • Journal of IKEEE
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    • v.18 no.4
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    • pp.620-624
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    • 2014
  • In this study, the electrical characteristics of Ni/CNT/$SiO_2$ structures were investigated in order to analyze the mechanism of carbon nanotubes in 4H-SiC MIS device structures. We fabricated 4H-SiC MIS capacitors with or without carbon nanotubes. Carbon nanotubes were dispersed by isopropyl alcohol. The capacitance-voltage (C-V) is characterized at 300 to 500K. The experimental flat-band voltage ($V_{FB}$) shift was positive. Near-interface trapped charge density and oxide trapped charge density values of Ni/CNT/$SiO_2$ structure were less than values of reference samples. With increasing temperature, the flat-band voltage was negative. It has been found that its oxide quality is related to charge carriers or defect states in the interface of 4H-SiC MIS capacitors. Gate characteristics of 4H-SiC MIS capacitors can be controlled by carbon nanotubes between Ni and $SiO_2$.

Passivation properties of SiNx and SiO2 thin films for the application of crystalline Si solar cells (결정질 실리콘 태양전지 응용을 위한 SiNx 및 SiO2 박막의 패시베이션 특성 연구)

  • Jeong, Myung-Il;Choi, Chel-Jong
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.24 no.1
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    • pp.41-45
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    • 2014
  • We have investigated the passivation property of $SiN_x$ and $SiO_2$ thin films formed using various process conditions for the application of crystalline Si solar cells. An increase in the thickness of $SiN_x$ deposited using plasma enhanced chemical vapor deposition (PECVD) led to the improvement of passivation quality. This could be associated with the passivation of Si dangling bonds by hydrogen atoms which were supplied during PECVD deposition. The $SiO_2$ thin films grown using dry oxidation process exhibited better passivation behavior than those using wet oxidation process, implying the dry oxidation process was more effective in the formation of high quality $SiO_2$ thin films. The relative effective life time gradually decreased with increasing dry oxidation temperature. Such a degradation of passivation behavior could be attributed to the increase in interface trap density caused by thermal damages.

Single Crystal Growth of GaAs by Single Temperature Zone horizontal Bridgman(1-T HB) Method (단일 온도대역 수평 Bridgman(1-T HB) 법에 의한 GaAs 단결정 성장)

  • 오명환;주승기
    • Korean Journal of Crystallography
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    • v.7 no.1
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    • pp.73-80
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    • 1996
  • The single crystal growth has been carried out with the newly designed 1-T HB(single temperature zone horizontal Bridgman) system for GaAs crystals of 2 inch diameter doped with Si, Zn or undoped. With this method, incidence probability of single crystallinity was shown to be 0.73. Lattice defects evaluated from EPD(etch pit density) measurement were in the range of 5,000-20,000/cm2, dependent upon the doping condition. For the undoped GaAs crystals, carrier concentrations from the Hall measurement were ∼1×1016/cm3 at the seed part, which were less than half the concentrations of double of triple temperature zone(2-T, 3-T) HB grown crystals. By the 1-T HB method, therefore, GaAs crystals can be grown successfully with better yield and higher purity.

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