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Lee, Sangheon,Woo, Jiyong,Lee, Daeseok,Cha, Euijun,Hwang, Hyunsang Springer 2014 Nanoscale research letters Vol.9 No.1
<P>In this research, we analyzed the multi-functional role of a tunnel barrier that can be integrated in devices. This tunnel barrier, acting as an internal resistor, changes its resistance with applied bias. Therefore, the current flow in the devices can be controlled by a tunneling mechanism that modifies the tunnel barrier thickness for non-linearity and switching uniformity of devices. When a device is in a low-resistance state, the tunnel barrier controls the current behavior of the device because most of the bias is applied to the tunnel barrier owing to its higher resistance. Furthermore, the tunnel barrier induces uniform filament formation during set operation with the tunnel barrier controlling the current flow.</P>
Lee, Myoung-Jae,Park, Gyeong-Su,Seo, David H.,Kwon, Sung Min,Lee, Hyeon-Jun,Kim, June-Seo,Jung, MinKyung,You, Chun-Yeol,Lee, Hyangsook,Kim, Hee-Goo,Pang, Su-Been,Seo, Sunae,Hwang, Hyunsang,Park, Sung American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.35
<P>Transition metal oxide-based memristors have widely been proposed for applications toward artificial synapses. In general, memristors have two or more electrically switchable stable resistance states that device researchers see as an analogue to the ion channels found in biological synapses. The mechanism behind resistive switching in metal oxides has been divided into electrochemical metallization models and valence change models. The stability of the resistance states in the memristor vary widely depending on: oxide material, electrode material, deposition conditions, film thickness, and programming conditions. So far, it has been extremely challenging to obtain reliable memristors with more than two stable multivalued states along with endurances greater than ∼1000 cycles for each of those states. Using an oxygen plasma-assisted sputter deposition method of noble metal electrodes, we found that the metal-oxide interface could be deposited with substantially lower interface roughness observable at the nanometer scale. This markedly improved device reliability and function, allowing for a demonstration of memristors with four completely distinct levels from ∼6 × 10<SUP>-6</SUP> to ∼4 × 10<SUP>-8</SUP> S that were tested up to 10<SUP>4</SUP> cycles per level. Furthermore through a unique in situ transmission electron microscopy study, we were able to verify a redox reaction-type model to be dominant in our samples, leading to the higher degree of electrical state controllability. For solid-state synapse applications, the improvements to electrical properties will lead to simple device structures, with an overall power and area reduction of at least 1000 times when compared to SRAM.</P> [FIG OMISSION]</BR>
Lee, Daeseok,Woo, Jiyong,Park, Sangsu,Cha, Euijun,Lee, Sangheon,Hwang, Hyunsang Institute of Pure and Applied Physics 2014 Japanese Journal of Applied Physics Vol. No.
<P>As semiconductor devices are being increasingly scaled down, complex and high-aspect-ratio (AR) structures become necessary. The spin-on-glass (SOG) method has been considered to be effective for filling high-AR (>50) structures, because it enables low-cost fabrication and it has greater amenability to such structures. However, this method requires high temperatures (>600 degrees C) that can lead to degradation (i.e., oxidation) of adjoining active regions, and additional processes to restore these regions are necessary. We propose a low process temperature (similar to 400 degrees C) SOG method involving high-pressure annealing, for the filling of high-AR structures without the creation of voids. (C) 2014 The Japan Society of Applied Physics</P>
Lee, Wootae,Park, Jubong,Kim, Seonghyun,Woo, Jiyong,Shin, Jungho,Choi, Godeuni,Park, Sangsu,Lee, Daeseok,Cha, Euijun,Lee, Byoung Hun,Hwang, Hyunsang American Chemical Society 2012 ACS NANO Vol.6 No.9
<P>We demonstrate a high-performance selection device by utilizing the concept of crested oxide barrier to suppress the sneak current in bipolar resistive memory arrays. Using a TaO(x)/TiO(2)/TaO(x) structure, high current density over 10(7) A cm(-2) and excellent nonlinear characteristics up to 10(4) were successfully demonstrated. On the basis of the defect chemistry and SIMS depth profile result, we found that some Ta atoms gradually diffused into TiO(2) film, and consequently, the energy band of the TiO(2) film was symmetrically bent at the top and bottom TaO(x)/TiO(2) interfaces and modified as a crested oxide barrier. Furthermore, the one selector-one resistor device exhibited significant suppression of the leakage current, indicating excellent selector characteristics.</P>
Lee, Joonmyoung,Bourim, El Mostafa,Shin, Dongku,Lee, Jong-Sook,Seong, Dong-jun,Park, Jubong,Lee, Wootae,Chang, Man,Jung, Seungjae,Shin, Jungho,Hwang, Hyunsang Elsevier 2010 CURRENT APPLIED PHYSICS Vol.10 No.1
<P><B>Abstract</B></P><P>To analyze the switching mechanism of Nb doped SrTiO<SUB>3</SUB> (Nb:STO) single crystal in a high resistive state (HRS) and low resistive state (LRS), we performed a complex impedance spectroscopy in the frequency domain. We demonstrated the domination of the oxygen vacancies to the resistive switching. Based on the impedance spectroscopy in the HRS and LRS, we concluded that the origin of resistive switching is due to the combination of Schottky junction and a generation of conduction electron from oxygen vacancies. The calculation of activation energies in each resistance state has been performed comparatively, which proposed that a first ionization of oxygen vacancies is responsible for the switching.</P>
A Correlation Between Crack Growth and Abrasion for Selected Rubber Compounds
( Hyunsang Lee ),( Wonseok Wang ),( Beomsu Shin ),( Seong Lak Kang ),( Kailash Chandra Gupta ),( Changwoon Nah ) 한국고무학회 2019 엘라스토머 및 콤포지트 Vol.54 No.4
A typical wear pattern was reported to resemble the fatigue crack growth behavior considering its mechanism, especially for amorphous rubbers such as styrene-butadiene rubber (SBR). In this study, the wear and crack growth rates were correlated using two separate experiments for carbon black and silica-reinforced selected rubber compounds. The wear rate was determined using a blade-type abrasion tester, where the frictional energy input during wearing was measured. The crack propagation rate was determined under different tearing energy inputs using a home-made fatigue tester, with a pureshear test specimen containing pre-cracks. The rates of abrasion and crack propagation were plotted on a log-log scale as a function of frictional and tearing energies, respectively. Reasonable agreement was observed, indicating that the major mechanism of the abrasion pattern involved repeated crack propagation.
A Correlation Between Crack Growth and Abrasion for Selected Rubber Compounds
Lee, Hyunsang,Wang, Wonseok,Shin, Beomsu,Kang, Seong Lak,Gupta, Kailash Chandra,Nah, Changwoon The Rubber Society of Korea 2019 ELASTOMERS AND COMPOSITES Vol.54 No.4
A typical wear pattern was reported to resemble the fatigue crack growth behavior considering its mechanism, especially for amorphous rubbers such as styrene-butadiene rubber (SBR). In this study, the wear and crack growth rates were correlated using two separate experiments for carbon black and silica-reinforced selected rubber compounds. The wear rate was determined using a blade-type abrasion tester, where the frictional energy input during wearing was measured. The crack propagation rate was determined under different tearing energy inputs using a home-made fatigue tester, with a pure-shear test specimen containing pre-cracks. The rates of abrasion and crack propagation were plotted on a log-log scale as a function of frictional and tearing energies, respectively. Reasonable agreement was observed, indicating that the major mechanism of the abrasion pattern involved repeated crack propagation.
한현상(Hyunsang Han),이동규(Dongkyu Lee),이종화(Jonghwa Lee),박진일(Jinill Park),박경석(Kyungseok Park) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_1
Fuel economy in a commercial vehicle is different from a passenger car. Therefore, in this paper differences between the two vehicles are described. Specially, it handles about measurement of the accessory traction force, engine friction and injected fuel. Energy consumption on each accessory is calculated quantitatively by measuring energy flow during traveling under practical road. In order to confirm energy flow measurement, engine frictions from engine dynamometer test is compared with measured data. Calculated engine friction using cylinder pressure from engine dynamometer test is equal to measured engine friction that is obtained by subtracting accessory traction force from engine total friction. With the measurement, Energy consumption of every fuel economy factors in a commercial vehicle are measured and analyzed during traveling in certain section of road.