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Kim, Hyunjung,Park, Jingyu,Jeon, Heeyoung,Jang, Woochool,Jeon, Hyeongtag,Yuh, Junhan American Institute of Physics 2015 Journal of Vacuum Science & Technology. A Vol.33 No.5
<P>Diffusion barrier characteristics of tungsten-nitride-carbide (WNxCy) thin films interposed between Cu and SiO2 layers were studied. The WNxCy films were deposited by remote plasma atomic layer deposition (RPALD) using a metal organic source, (Cp-Me)W(CO)(2)(NO), and ammonia. Auger electron spectroscopy analysis indicated the WNxCy films consisted of tungsten, nitrogen, carbon, and oxygen. X-ray diffraction (XRD) analysis showed that the film deposited at 350 degrees C was nanocrystalline. The resistivity of WNxCy film deposited by RPALD was very low compared to that in previous research because of the lower nitrogen content and different crystal structures of the WNxCy. To verify the diffusion barrier characteristics of the WNxCy film, Cu films were deposited by physical vapor deposition after WNxCy film was formed by RPALD on Si substrate. The Cu/WNxCy/Si film stack was annealed in a vacuum by rapid thermal annealing at 500 degrees C. Cu diffusion through the barrier layer was verified by XRD. Stable film properties were observed up to 500 degrees C, confirming that WNxCy film is suitable as a Cu diffusion barrier in microelectronic circuits. VC 2015 American Vacuum Society.</P>
Resistive switching behaviors of Ti nano-layer embedded TaO<sub>x</sub>-based devices
Jeon, Heeyoung,Park, Jingyu,Jang, Woochool,Kim, Hyunjung,Lee, Kunyoung,Shin, Changhee,Lee, Jaemin,Jeon, Hyeongtag ELSEVIER 2017 CURRENT APPLIED PHYSICS Vol.17 No.2
<P>The role of a Ti nano-layer embedded in TaOx-based devices operating with conductive filaments consisting of oxygen vacancies was investigated. The Ti nano-layer was embedded in three different positions: the top interface (Au/TaOx), bottom interface (TaOx/TiN), and both interfaces. The embedded Ti nano-layer serves as not only an oxygen reservoir but also a tunneling barrier in the case of the top interface. The position of the Ti nano-layer and its thickness play important roles in the resistive switching behaviors. In addition, the effect of the current compliance on the resistive switching behaviors was evaluated. The different resistive switching behaviors were investigated using current voltage sweep measurements and X-ray photoelectron spectroscopy. The non-linear behavior of the low resistance state could be controlled by the top interface and current compliance. The current of the high resistance state could be controlled by the bottom interface. It is noteworthy that only 1.5-nm-thick Ti nano-layer can adjust the non-linear behavior of the low resistance state at top interface and the current of the high resistance state at bottom interface. (C) 2016 Elsevier B.V. All rights reserved.</P>
End to End ZigBee Home Network Security Solutions
Changguk Lee,Jaiyong Lee,Woochool Park,Mynghyun Yoon,Sunghyun Yang 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
ZigBee home network service is expected to fill every aspect of our lives and play increasingly important roles. ZigBee is designed to support low cost and battery powered applications. So ZigBee nodes have small memory and insufficient computation capability to support heavy data handling. In this paper, we presents a systematic analysis of the threats faced by IEEE 802.15.4 and the ZigBee Alliance. Attack scenarios are models and their impacts are evaluated. Some security problems within the current ZigBee security architecture are identified and remedies are suggests. And countermeasures of various attacks are also given. Most of the solutions are implemented in the Security Server. And ZigBee nodes have a few security handling capability.
Juhyun Lee,Seokyoon Shin,Sejin Kwon,Woochool Jang,Hyeongsu Choi,Hyunwoo Park,Namgue Lee,전형탁 한양대학교 세라믹연구소 2021 Journal of Ceramic Processing Research Vol.22 No.3
Among various thin film encapsulation (TFE) methods, thin films prepared by atomic layer deposition (ALD) have been shownto provide superior protection against the permeation of moisture and oxygen. This technique has numerous of advantagessuch as excellent uniformity, precise thickness control, and strong adhesion. Therefore, with ozone-based ALD, we conductedthe influence of the thickness of aluminum oxide (Al2O3) on moisture barrier properties. From the results of an electricalcalcium test, Al2O3 had two distinctly different permeation regimes. Between 10 and 25 nm of Al2O3 thickness, the water vaportransmission rate (WVTR) decreased exponentially from 6.3 × 10−3 to 1.0 × 10−4 g m−2 day−1 (1/60 times). In contrast, asthickness increased from 25 to 100 nm, the WVTR values decreased by only two-thirds, from 1.0 × 10−4 to 6.6 × 10−5 g·m−2·day−1. Tobetter understand the change from an exponential to a sub-exponential regime, defect density and refractive index of Al2O3were measured. The thickness dependence on defect density and refractive index was analogous with one of moisture barrierperformance. These results confirmed the existence of a critical thickness at which the WVTR decreased drastically.
Lee, Jaesang,Lee, Seung Jae,Han, Won Bae,Jeon, Heeyoung,Park, Jingyu,Jang, Woochool,Yoon, Chong Seung,Jeon, Hyeongtag WILEY‐VCH Verlag 2013 Physica status solidi. PSS. A, Applications and ma Vol.210 No.2
<P><B>Abstract</B></P><P>Titanium dioxide (TiO<SUB>2</SUB>) thin films were deposited by remote‐plasma atomic layer deposition (RPALD). The process window was determined in the range from 150 to 300 °C for atomic layer deposition of TiO<SUB>2</SUB> thin film. The crystal structure and grain size of the TiO<SUB>2</SUB> thin films deposited by RPALD was controlled via the variations of the deposition temperature and post‐deposition thermal annealing. The as‐deposited TiO<SUB>2</SUB> thin film grown at 150 °C was amorphous whereas the TiO<SUB>2</SUB> thin films grown above 200 °C were polycrystalline, consisting of anatase phase. As the deposition temperature increased, the grain size of the anatase phase progressively decreased. Meanwhile, when annealed at 900 °C, the amorphous TiO<SUB>2</SUB> thin film deposited at 150 °C crystallized into anatase structure. The film deposited at 200 °C retained the anatase structure up to 900 °C while incurring minimal grain growth. However, the post‐annealed TiO<SUB>2</SUB> thin films deposited at 250 and 300 °C partially transformed to the rutile structure, resulting in a mixture of anatase and rutile phases. It is speculated that the relatively large grain size of the films deposited below 200 °C likely suppressed the anatase → rutile transformation during annealing as the reduction of total fraction of grains boundaries, which acted as primary nucleation sites for the rutile transition, delayed the anatase → rutile transformation.</P>
Song, Hyoseok,Jeon, Heeyoung,Shin, Changhee,Shin, Seokyoon,Jang, Woochool,Park, Joohyun,Chang, Jaewan,Choi, Jae Hyoung,Kim, Younsoo,Lim, HanJin,Seo, Hyungtak,Jeon, Hyeongtag Elsevier S.A. 2016 Thin Solid Films Vol.619 No.-
<P><B>Abstract</B></P> <P>In this study, we report the effect of process conditions on the crystallinity and energy band structure of atomic layer deposition (ALD) ZrO<SUB>2</SUB> films deposited, using tris(dimethylamino) cyclopentadienyl zirconium as a precursor and ozone as a reactant. ZrO<SUB>2</SUB> films exhibited systematic changes in phase and energy band gap as a function of the ozone concentration. The crystal phase was transformed from the monoclinic phase to a tetragonal phase in the presence of higher ozone concentrations. In addition, spectroscopic ellipsometry measurements showed that the optical band gap and oxygen vacancy defects decreased with increasing ozone concentration. The valence band maximum also shifted closer to the Fermi energy level with increasing ozone concentration. The change in electronic structure driven by a high concentration of ozone led to reduced leakage current density and a high dielectric constant in the ZrO<SUB>2</SUB>-based metal-insulator-metal capacitors. These improvements were not observed for depositions performed using conventional ZrO<SUB>2</SUB> ALD with oxygen and water reactants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We report the effect of ozone concentration on the properties of ZrO<SUB>2</SUB> thin films. </LI> <LI> The ZrO<SUB>2</SUB> at higher O<SUB>3</SUB> transformed from a monoclinic phase to a tetragonal phase. </LI> <LI> The ZrO<SUB>2</SUB> at higher O<SUB>3</SUB> concentration showed the reduced leakage current. </LI> <LI> The ZrO<SUB>2</SUB> at higher O<SUB>3</SUB> concentration showed the higher dielectric constant. </LI> </UL> </P>