T. Y. Lee

Chungnam National University, Daiden, Daejeon, South Korea

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Publications (59)68.74 Total impact

  • Eun Ho Kim, Tae Young Lee, Chee Won Chung
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    ABSTRACT: Etch characteristics of magnetic tunnel junction (MTJ) stacks masked with W/TiN films were investigated using an inductively coupled plasma reactive ion etching in a CH3OH/Ar gas. The effect of CH3OH concentration on the etch rate, etch selectivity and etch profile of MTJ stacks was examined. The high degree of anisotropy of etched MTJ stacks at high CH3OH concentrations resulted from the high etch selectivity of MTJ stacks to hard mask which was closely related with the high ratio of [H]/[Ar] peaks obtained by optical emission spectroscopy. The evolution of etch profile of MTJ stacks was examined to elucidate the etch mechanism in a CH3OH/Ar gas. Transmission electron microscopy of the etched MTJ stacks revealed the redeposition on the sidewall of MTJ stacks occurred during the early stage of etching and the gradual sputtering-off of the redeposited materials during further etching, resulting in a high degree of anisotropy. In addition, the redeposited materials turn out to be mainly Pt and Mn with low levels of Co and Fe by using energy dispersive X-ray spectroscopy
    Journal of The Electrochemical Society 01/2012; 159(3):H230-H234. DOI:10.1149/2.012203jes · 2.86 Impact Factor
  • Urology 09/2011; 78(3). DOI:10.1016/j.urology.2011.07.063 · 2.13 Impact Factor
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    ABSTRACT: A DC/DC converter is an electronic circuit which converts a source of direct current (DC) from one voltage level to another. Military applications require electronics that withstand low temperature and impact. This paper presents the low temperature evaluation of the commercial DC/DC converters, identification of the problem with them, suggestion of a method to overcome it, and the low temperature evaluation of the suggested DC/DC converter. From the experiment, the commercial DC/DC converters are sensitive to the operating temperature, especially 20 T: below zero. Based on this finding, a circuit is suggested, which replaces electrolyte capacitors to solid capacitors. It is observed that the DC/DC converter with solid capacitors works well at the temperature of 40 T: below zero. It is concluded that the DC/DC convert with solid capacitor can be used for military applications such as low temperature operation.
    01/2010; DOI:10.1109/TENCON.2010.5686353
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    ABSTRACT: A power management unit (PMU) chip supplying dual panel supply voltage, which has a low electro-magnetic interference (EMI) characteristic and is favorable for miniaturization, is designed. A two-phase charge pump circuit using external pumping capacitor increases its pumping current and works out the charge-loss problem by using bulk-potential biasing circuit. A low-power start-up circuit is also proposed to reduce the power consumption of the band-gap reference voltage generator. And the ring oscillator used in the ELVSS power circuit is designed with logic devices by supplying the logic power supply to reduce the layout area. The PMU chip is designed with MagnaChip’s 0.25 μm high-voltage process. The driving currents of ELVDD and ELVSS are more than 50 mA when a SPICE simulation is done.
    Journal of Central South University of Technology 08/2009; 16(4):621-628. DOI:10.1007/s11771-009-0103-6 · 0.36 Impact Factor
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    Y.H. Xia, Y.K. Jee, J. Yu, T.Y. Lee
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    ABSTRACT: Aluminum was added into Sn-3.0Ag (wt.%) solder to investigate the effect of aluminum concentration on the interfacial reaction of Sn-3.0Ag-xAl solders with copper or electroless nickel immersion gold (ENIG) metallizations. Four different Sn-3.0Ag-xAl solders (x=0wt.%, 0.1wt.%, 0.5wt.%, and 1.0wt.%) were used for comparison. It was found that the composition, morphology, and thickness of interfacial reaction products were strongly dependent on aluminum concentration. At low aluminum concentration (0.1wt.%), the typical Cu6Sn5 layer was formed at the interface. When the aluminum concentration was 0.5wt.%, a continuous CuAl2 layer spalled off from the interfacial Cu-Sn intermetallic compound (IMC) layer. Only a planar CuAl2 layer was observed at the interface when the aluminum concentration was increased to 1.0wt.%. In Sn-Ag-Al/ENIG reactions, Ni3Sn4 was formed and spallation occurred near the interface in the Sn-3.0Ag and Sn-3.0Ag-0.1Al solder joints. When the aluminum concentration was higher than 0.1wt.%, a thin planar AuAl compound formed at the interface. There was no P-rich phase formation that retarded the spalling phenomenon. The aluminum additive in Sn-Ag solder inhibited the growth of IMCs in the reaction with copper or ENIG metallizations, which was favorable for the reliability of solder joints.
    Journal of Electronic Materials 11/2008; 37(12):1858-1862. DOI:10.1007/s11664-008-0548-7 · 1.68 Impact Factor
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    ABSTRACT: Highly aligned, 2-3 wall carbon nanotube (CNT) arrays were used to examine the kinetics of CNT growth. A growth interruption method was used to determine the in situ growth rate. The growth interruption method with a water vapor treatment or acetylene treatment during the interruption enabled the production of CNT stacks with different morphologies. The catalytic activity was also monitored using this method. The lifetime of the catalyst was predicted and verified using the catalyst decay model. High temperature metal oxidation behavior using parabolic curve fitting is assigned to the decay process. Details of the analysis are presented.
    Applied Physics Letters 09/2008; 93(11):114101-114101-3. DOI:10.1063/1.2976328 · 3.52 Impact Factor
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    ABSTRACT: To investigate associations between gamma-glutamyltransferase (GGT) and components of metabolic syndrome (MS), insulin resistance and inflammatory markers in the Korean population. The 3508 subjects enrolled in this survey participated in the Korean Rural Genomic Cohort (KRGC) study. Written consent was obtained from the local ethical committee. Of these participants, 1437 were men (mean age 56.9 +/- 7.9 years) and 2071 were women (mean age 55.8 +/- 8.1 years). We measured GGT levels and various biochemical markers. To examine insulin resistance status, we used the homeostasis assessment method for insulin resistance (HOMA-IR). For inflammatory marker, we used C-reactive protein (CRP) levels. Serum GGT levels were significantly higher in the MS group compared to the healthy patient group [23 (5-1403) vs. 19 (5-1920) IU/l; P = 0.01]. The prevalence of MS and adjusted relative risk were both significantly increased from the lowest to highest GGT quartiles; these results persisted after adjustments for multiple confounders. Positive correlations were established between GGT and HOMA-IR or CRP. These results suggest that GGT levels may be a surrogate marker of insulin resistance, inflammation and MS.
    Diabetic Medicine 05/2008; 25(4):469-75. DOI:10.1111/j.1464-5491.2008.02415.x · 3.06 Impact Factor
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    ABSTRACT: Variation in the height of carbon nanotubes (CNTs) grown has been co-related to the type of multi-barrier-layer used. Initially, various types of barrier-layers such as Al, Al2O3, Al/SiO2, Al2O3/SiO2 were prepared onto a n-type Si (100) substrate. The thickness of SiO2 was ∼ 550 nm, where as, Al2O3 and Al were ∼ 15 nm thick. These samples were covered with ∼ 1 nm thick Fe catalyst layer. The coated samples were subjected to the thermal chemical vapor deposition (T-CVD) process. SEM analysis showed that, for Al2O3/SiO2 barrier layers, the average height of the CNTs was ∼ 10 μm, where as, for other types of samples it was less than ∼ 1 μm. To investigate this, multi-barrier layers were characterized by dynamic secondary ion mass spectrometry (D-SIMS). The observed variation in height of CNTs is attributed to the variation in diffusivity of Fe atoms into multi-barriers-layers. The results showed that, diffusion of Fe catalyst atoms could severally affect height of CNTs.
    Thin Solid Films 04/2008; 516(11):3646–3650. DOI:10.1016/j.tsf.2007.08.106 · 1.87 Impact Factor
  • Urology 09/2007; 70(3):279-280. DOI:10.1016/j.urology.2007.06.1011 · 2.13 Impact Factor
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    ABSTRACT: The performance of drop reliability was measured with Sn-3.5Ag-xZn solder joint on Cu and electroless Ni(P)/Au metallization after reflow and thermal aging (150degC, 500 hr). The content of Zn was 0, 1, 3 and 7 wt%. And interfacial reactions were investigated. The presence of Zn affected the type and morphology of IMC and showed the benefits on the drop reliability. In the case of Cu pad, Zn addition of more than 3 wt% suppressed growth of Cu<sub>6</sub>Sn<sub>5</sub> and introduced Ag<sub>5</sub>Zn<sub>8</sub>/Cu<sub>5</sub>Zn<sub>8</sub> layer, which increased drop resistance by about two times. During thermal aging, Cu<sub>6</sub>Sn<sub>5</sub> and Ag<sub>3</sub>Sn precipitated and grew in the interfacial IMC layer, which decreased the beneficial effect of Zn. In the case of Ni(P)/Au, Zn addition of 1 and 3 wt% transformed IMC from Ni<sub>3</sub>Sn<sub>4</sub> to Ni<sub>3</sub>Sn<sub>4</sub>/Ni<sub>5</sub>Zn<sub>21</sub>. Only Ni<sub>5</sub>Zn<sub>21</sub> were found for 7Zn specimen. The solder of 1 wt% Zn showed drop resistance about six times than that of Sn-3.5Ag. The improvement of drop resistance resulted from suppression of Ni<sub>3</sub>P and Ni<sub>3</sub>SnP growth. As the growth of Ni<sub>3</sub>P and Ni<sub>3</sub>SnP layer was effectively suppressed by zinc, the drop resistance increased substantially.
    Electronic Components and Technology Conference, 2007. ECTC '07. Proceedings. 57th; 07/2007
  • Journal- Korean Physical Society 05/2007; 50(95). DOI:10.3938/jkps.50.1372 · 0.43 Impact Factor
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    ABSTRACT: PAL-XFEL is the 4-th generation light source based on Self Amplified Spontaneous Emission (SASE) that Pohang Accelerator Laboratory is going to build. For the purpose, the linear accelerator, which is used for the injection to the PLS storage ring, will be upgraded and expanded to 3.7 GeV. In this paper, the overview of PAL-XFEL will be introduced including the physics design.
    01/2007; DOI:10.1063/1.2436049
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    ABSTRACT: We report the fabrication, characterization, and field emission properties of silicon oxide SiO x coated thin-multiwalled carbon nanotubes t-MWNTs. The coated t-MWNTs show improved field emission behavior. Initially, raw t-MWNTs diameter 5–8 nm were functionalized by acid treatment. Using spin on glass as a Si precursor, SiO x was coated on the nanotubes by routine chemical methods. The coated samples were characterized by high resolution transmission electron microscopy HRTEM, Fourier transform infrared FTIR spectroscopy, and thermogravimetric analysis TGA techniques. The HRTEM results show that the local thickness of the coating varies from 1 to 2 nm. The FTIR investigations show the formation of nanophases, such as Si–C, Si–O–C, and intercalated Si–O, at the coating/nanotube interface. The TGA reveals that the coating prevents the high-temperature oxidation and degradation of the nanotubes. The field emission characteristics of the coated, functionalized, and raw nanotubes show that the turn-on fields and current density are improved for the coated nanotubes. This improvement was attributed to the lowering of the work function and dielectric constant of the C / SiO x interface layer and the localization of the density of states close to the Fermi energy for the coated nanotubes. The analysis of the emission stability spectra shows that the coated nanotubes have a more favorable lifetime. The observed enhancement was attributed to the protection of the nanotubes from the reactive sputter etching during the field emission process. The details of the analysis are presented. © 2006 American Institute of Physics.
    Journal of Applied Physics 11/2006; 100(10). DOI:10.1063/1.2384795 · 2.19 Impact Factor
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    ABSTRACT: MWNT/nylon 6, 6 composite nanofibers were fabricated using an electrospinning method, and the electrical properties were examined as a function of the filler concentration. Initially, the pristine, purified MWNTs were treated with a 3:1 mixture of concentrated H2SO4/HNO3 to introduce carboxyl groups onto the MWNT surface. The carboxylated MWNTs were then treated with thionyl chloride and an ethylenediamine solution for amide functionalization. FT-IR spectroscopy was used to examine the functionalization of the MWNTs. Nylon 6, 6 is readily soluble in formic acid. Therefore, the amide functionalized MWNTs were dispersed in formic acid. The solution remained stable and uniform for more than 40 h. –NH2 termination of the MWNTs improved the dispersion stability of the MWNTs in formic acid. The MWNTs-suspended in a solution of nylon 6, 6 in formic acid was electrospun to obtain the nanofibers. The electrical properties of the nanofibers were examined as a function of the filler concentration. The results showed that the I–V properties of the nanofiber sheet improved with increasing filler concentration.
    Diamond and Related Materials 11/2006; 15(11):1839-1843. DOI:10.1016/j.diamond.2006.08.026 · 1.57 Impact Factor
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    ABSTRACT: The Pohang Accelerator Laboratory (PAL) is going to build a 4th generation light source, an X-ray free electron laser (XFEL) based on self-amplified spontaneous emission. For the purpose, the existing 2.5-GeV linear accelerator will be upgraded to 3.7 GeV and will include new features such as photo-cathode electron gun and bunch compressors. The other important parts of the PAL-XFEL are the long undulator and photon beamlines. In this paper, the design philosophy and the details of the PAL-XFEL will be presented along with the key physics issues.
    Journal- Korean Physical Society 05/2006; 4860(52). · 0.43 Impact Factor
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    ABSTRACT: Pohang Accelerator Laboratory has a plan to build an X-ray FEL machine. This new machine will utilize the exist-ing 2.5 GeV injection linac to the storage ring by upgrading its energy up to 3.7 GeV or more. The target wavelength will be 3-4. A and its third harmonic 1-1. A will also be used. The project will proceed in two stages: In the first stage, a VUV SASE machine with 320 MeV will be constructed and tested for the proof-of-principle. The full X-ray machine will be constructed in the next stage.
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    ABSTRACT: The growth of carbon nanotubes (CNTs) were evidently observed, at the channel ends of the mesoporous SAPO4-5 zeolites. The Fe-catalyst SAPO4-5 crystallites prepared by the sol–gel method were employed to the thermal CVD process, at a temperature ∼650 °C for 30 min, using the mixture of acetylene and ammonia gases. The recorded SEM images show the formation of well aligned MWNTs at the channel ends of the crystallites. The analysis of HRTEM shows that, the outer diameter of CNTs varies in the range of 25–27 nm, whereas, the inner diameter varies in the range of 14–17 nm. The diameter of the CNTs was found to be varied marginally as compared to that of the channel diameter of the SAPO4-5 crystallite. Furthermore, the observed formation of CNTs, along the ab-plane, could either be originated at a depth from the channels or at the channel ends of the crystallites. Although the former is attributed to the precipitation of the Fe-catalyst in the channels, the later is thought to be due to the out diffusion and clustering of Fe-atoms near the channel ends of the crystallites. The recorded micro-Raman spectrum showed the small ratio of, I(D)/I(G), which suggest that, the synthesized tubes are of high quality with less amount of defects.
    Diamond and Related Materials 11/2005; 14(11):1876-1881. DOI:10.1016/j.diamond.2005.08.016 · 1.57 Impact Factor
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    W. S. Lee, Jin Yu, T. Y. Lee
    Journal of Materials Science 10/2005; DOI:10.1007/s10855-005-4548-y · 2.31 Impact Factor
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    ABSTRACT: Single-walled nanotubes (SWNTs), thin multiwalled carbon nanotubes (t-MWNTs) and multiwalled carbon nanotubes (MWNTs) were treated with H2SO4–HNO3 acid solution, under different chemical conditions. The acid-treated CNTs were dispersed in DI water and in poly (3,4-ethylenedioxythiophene) (PEDOT) solution. Furthermore, the finely dispersed CNTs/PEDOT solutions were employed to a simple method of bar coating to obtain the transparent conductive films on the glass and polyethylene terephthalate (PET) film. A sheet resistance of 247 Ω/sq and a transmission of 84.7% were obtained at a concentration of the acid-treated CNTs of 0.01 wt.%.
    Diamond and Related Materials 09/2005; DOI:10.1016/j.diamond.2005.07.015 · 1.57 Impact Factor
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    J.S. Oh, T.Y. Lee, I.S. Ko, W. Namkung
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    ABSTRACT: The PAL XFEL will supply coherent radiations from VUV to X-rays. X-ray FEL for 0.3 nm lasing requires a minimum 3-GeV driver linac and a 60-m long in-vacuum undulator with a narrow variable gap. The linac should supply highly bright beams with emittance of 1.2 mm-mrad, a peak current of 3.5 kA, and a lower energy spread less than 0.03%. The beam quality is degraded along the undulator trajectory due to the energy loss, the wake field, and the magnetic field errors, etc. Especially the wake field effect is most sensitive parameter due to the narrow gap of the undulator. The preliminary design details of undulators for PAL-XFEL are presented with parametric analysis. The SASE performance is analyzed using simulation tool SIMPLEX [1].
    Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005

Publication Stats

448 Citations
68.74 Total Impact Points

Institutions

  • 2008–2010
    • Chungnam National University
      • • Department of Mechatronics Engineering
      • • College of Medicine
      Daiden, Daejeon, South Korea
  • 2009
    • Changwon National University
      • Department of Electronic Engineering
      Changnyeong, South Gyeongsang, South Korea
  • 2004–2008
    • Hanbat National University
      • Department of Material Sciences and Engineering
      Daiden, Daejeon, South Korea
  • 2002–2008
    • Sungkyunkwan University
      • School of Advanced Materials Science and Engineering (AMSE)
      Sŏul, Seoul, South Korea
  • 2006
    • Duke University
      Durham, North Carolina, United States
  • 2001–2006
    • Pohang University of Science and Technology
      • Pohang Accelerator Laboratory
      Andong, North Gyeongsang, South Korea
    • University of Suwon
      Tse-tsiu, Jeju, South Korea
  • 2005
    • Korea Advanced Institute of Science and Technology
      • Department of Materials Science and Engineering
      Seoul, Seoul, South Korea
  • 1998–2005
    • Pohang Accelerator Laboratory
      Urusan, Ulsan, South Korea
  • 2000
    • Hanyang University
      • College of Medicine
      Sŏul, Seoul, South Korea