Osan, South Korea
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Park Y.S.,Sungkyunkwan University | Sohn I.S.,Osan College | Bae D.H.,Sungkyunkwan University
International Journal of Automotive Technology | Year: 2014

This paper presents a method to assess of fatigue strength for resistance spot welded joints, which incorporates welding residual stress effects. To achieve this, first, a non-linear finite element analysis (FEA) was performed to simulate the spot-welding process. To validate the FEA results, the numerically calculated welding residual stresses of spot welds were then compared with experimental results measured by X-ray diffraction method. The residual stress distributions showed good agreement between calculations and experiments. To evaluate the effects of welding residual stress on the fatigue design criterion of resistance spot welded joints subjected to cross-tension load, the stress amplitude (σa-res) taking into account welding residual stress at a spot weld was proposed based on a modified Goodman equation incorporating the residual stress effect. Using the stress amplitude σa-res at the nugget edge of a spot weld, the ΔP - Nf relations obtained as the fatigue test results for spot welded joints were systematically rearranged to the σa-res - Nf relation. It was found that the proposed stress amplitude (σa-res) provides more reasonable and accurate fatigue design criterion of spot welded joints subjected to cross-tension load. © 2014 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.


Park S.,Korea University | Lee J.H.,Korea University | Kim H.-D.,Korea University | Hong S.M.,Korea University | And 3 more authors.
Physica Status Solidi - Rapid Research Letters | Year: 2013

The authors report the resistive switching characteristics of sol-gel based ZnO nanorods (NRs) fabricated on flexible substrates. A resistance ratio of 10, endurance of over 100 cycles, and narrower dispersion in the ON/OFF voltages and resistances compared to ZnO thin-film devices are demonstrated. Furthermore, the resistive switching characteristics on flexible substrates are maintained under severe substrate bending because of the ductile properties of the nanorods. Devices composed of the Au/sol-gel based NRs/Au structure have the potential for low-temperature flexible nonvolatile memory applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Song M.Y.,Korea University | Seo Y.,Korea University | Park S.,Korea University | Lee J.H.,Korea University | And 3 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2013

The authors report upon highly reproducible, unipolar resistive-switching random access memory with narrow voltage distributions using Au/ZnO nanorods/Au structures. The ZnO nanorods resistive switching layer was prepared by a simple spin-coating process on a sol-gel seed layer, and from its size confinement effect, this device showed narrow set/reset voltage distributions and low voltage operations compared with Au/ZnO thin film/Au structures. With this electrical uniformity, the device exhibited good reliabilities such as long retention (> 70000 sec) and high endurance (> 5000 cycles). © 2013 American Scientific Publishers.


Kim K.H.,Korea University | An H.-M.,Osan College | Kim H.-D.,Korea University | Kim T.G.,Korea University
Nanoscale Research Letters | Year: 2013

We propose a transparent conductive oxide electrode scheme of gallium oxide nanoparticle mixed with a single-walled carbon nanotube (Ga2O3 NP/SWNT) layer for deep ultraviolet light-emitting diodes using spin and dipping methods. We investigated the electrical, optical and morphological properties of the Ga2O3 NP/SWNT layers by increasing the thickness of SWNTs via multiple dipping processes. Compared with the undoped Ga2O3 films (current level 9.9 × 10-9 A @ 1 V, transmittance 68% @ 280 nm), the current level flowing in the Ga2O3 NP/SWNT increased by approximately 4 × 105 times and the transmittance improved by 9% after 15 times dip-coating (current level 4 × 10-4 A at 1 V; transmittance 77.0% at 280 nm). These improvements result from both native high transparency of Ga2O3 NPs and high conductivity and effective current spreading of SWNTs. © 2013 Kim et al.


Hong S.M.,Korea University | Kim H.-D.,Korea University | An H.-M.,Osan College | Kim T.G.,Korea University
IEEE Electron Device Letters | Year: 2013

In this letter, the effect of the work function difference between various top electrodes (TE-Ni, W, Ti, and Al) and the Pt bottom electrode, ΔΦM, on the resistive switching (RS) of SiN thin films was investigated. The cells with W and Ti TEs showed stable RS, but others failed to show RS. In particular, the Ti TE exhibited low operating currents (∼2μ A) and good retention properties (<∼ 104 s at 85° C). On the basis of the analysis of conduction mechanisms, it is found that stable RS of SiN films might be strongly related to the activation energy of traps induced by ΔΦM. Thus, the RS properties of the SiN films can be improved by engineering ΔΦM without additional processes. © 1980-2012 IEEE.


Yun M.J.,Korea University | Kim H.-D.,Korea University | Kim K.H.,Korea University | Sung H.J.,Korea University | And 4 more authors.
Thin Solid Films | Year: 2013

In this paper, we report a transparent conductive oxide electrode scheme working for ultraviolet light-emitting diodes based on indium tin oxide (ITO)-rod and a single walled carbon nanotube (SWCNT) layer. We prepared four samples with ITO-rod, SWCNT/ITO-rod, ITO-rod/SWCNT, and SWCNT/ITO-rod/SWCNT structures for comparison. As a result, the sample with SWCNT/ITO-rod/SWCNT structures showed the highest transmittance over 90% at 280 nm and the highest Ohmic behavior (with sheet resistance of 5.33 kΩ/□) in the current-voltage characteristic curves. © 2013 Elsevier B.V.


Kim H.-D.,Korea University | Kim H.-D.,Sejong University | Kim K.H.,Korea University | An H.-M.,Korea University | And 2 more authors.
Journal of Physics D: Applied Physics | Year: 2015

Charge-trap flash (CTF) memory using a zirconium nitride (ZrN)-based memristor switch (MRS) is demonstrated for next-generation nonvolatile memory. This device consists of a metal/MRS/nitride/oxide/silicon (M/MRS/N/O/S) structure so that electrical transport via the ZrN-based MRS layer can be utilized. Compared to previous oxide materials used as conduction paths, the proposed CTF device with a ZrN-based MRS exhibits a faster program/erase switching speed (20 ns/7 ns), along with comparable endurance and retention properties. © 2015 IOP Publishing Ltd.


Kim H.-D.,Korea University | Yun M.J.,Korea University | Hong S.M.,Korea University | An H.-M.,Korea University | And 2 more authors.
Physica Status Solidi - Rapid Research Letters | Year: 2013

The influence of the hydrogen annealing treatment on the reliability of Ti/HfOx /Pt capacitors is investigated by analyzing bias temperature instability (BTI). As compared to the N2-annealed sample, in the case of hydrogen-annealed samples, both the set/reset voltages and currents are reduced from 6.5 V/-1.6 V to 3.8 V/-1.2 V and from 4 mA/170 nA to 800 μA/30 nA at 0.1 V, respectively. Of particular interest is the dramatic reduction in the set voltage variation from 3.3 V to 1.8 V. In addition, in BTI experiments, the current shift at the high resistance state (HRS) is reduced from 1.5 μA to 40 nA under a bias stress of -1 V/1000 s and from 40 μA to 0.5 μA under a temperature stress of 120 °C/1000 s. These results show that the hydrogen annealing treatment is very effective in improving the reliability of RRAM cells because it reduces the leakage current under bias temperature stress. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


An I.-S.,Konkuk University | An S.,Konkuk University | Kwon K.J.,Konkuk University | Kim Y.J.,Osan College | Bae S.,Konkuk University
Oncology Reports | Year: 2013

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer insensitive to chemotherapy. Efforts are, therefore, directed toward understanding the molecular mechanisms of chemotherapy insensitivity and the development of new anticancer drugs. Ginsenoside Rh2, one of the components in ginseng saponin, has been shown to have antiproliferative effect on human NSCLC cells and is being studied as a therapeutic drug for NSCLC. microRNAs (miRNAs) are small, non-coding RNA molecules that play a key role in cancer progression and prevention. However, the miRNA portrait of ginsenoside Rh2-treated NSCLC cells has not yet been studied. In this study, we identified a unique set of changes in the miRNA expression profile in response to Rh2 treatment in the human NSCLC cell line A549. Using miRNA microarray analysis, we identified 44 and 24 miRNAs displaying changes in expression greater than 2-fold in Rh2-treated A549 cells. In addition, using an miRNA target prediction program, we discovered that these miRNAs are predicted to have several target genes related to angiogenesis, apoptosis, chromatic modification, cell proliferation and differentiation. Thus, these results may assist in the better understanding of the anticancer mechanism of Rh2 in NSCLC.


Jang K.-H.,Kwangwoon University | Oh S.-M.,Kwangwoon University | An H.-M.,Osan College | Cho W.-J.,Kwangwoon University
Current Applied Physics | Year: 2014

Resistive switching characteristics of solution-processed high-k thin films (HfOx and TaOx) were investigated for ReRAM applications. The thickness of solution-processed high-k thin films can be easily controlled by simple spin coating. We optimized the critical thickness of solution-processed HfOx and TaOx thin films, for reliable ReRAM operations. A similar bipolar resistive switching behavior was observed from both solution-processed and sputter-processed HfOx films. Furthermore, it was found that the solution-processed HfOx and TaOx films have a uniform resistive switching characteristic. The dominant conduction of these solution-processed films is described by Ohmic conduction in the low-resistance state. On the other hand, Ohmic conduction at low voltage and Poole-Frenkel emission at high voltage dominate in the high-resistance state. It was verified that the solution-processed HfO x and TaOx films have superior endurance and retention characteristics. Therefore, ReRAM devices based on solution-processed high-k materials are expected to be a promising candidate, for usage of resistive memory in glass substrate or flexible substrate based electronic devices. © 2013 Elsevier B.V. All rights reserved.

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