Effect of dysprosium and lutetium metal buffer layers on the resistive switching characteristics of Cu–Sn alloy-based conductive-bridge random access memory

Vishwanath, Sujaya Kumar,Woo, Hyunsuk,Jeon, Sanghun IOP 2018 Nanotechnology Vol.29 No.38

<P>The conductive-bridge random access memory (CBRAM) has become one of the most suitable candidates for non-volatile memory in next-generation information and communication technology. The resistive switching (RS) mechanism of CBRAM depends on the formation/annihilation of the conductive filament (CF) between the active metal electrode and the inert electrode. However, excessive ion injection from the active electrode into the solid electrolyte reduces the uniformity and reliability of the RS devices. To solve this problem, we investigated the RS characteristics of a CuSn alloy active electrode with different compositions of Cu<SUB>x</SUB>–Sn<SUB>1–x</SUB> (0.13?<?X?<?0.55). The RS characteristics were further improved by inserting a dysprosium (Dy) or lutetium (Lu) buffer layer at the interface of Cu<SUB>x</SUB>–Sn<SUB>1–x</SUB>/Al<SUB>2</SUB>O<SUB>3</SUB>. Electrical analysis of the optimal Cu<SUB>0.4</SUB>–Sn<SUB>0.73</SUB>/Lu-based CBRAM exhibited stable RS behavior with low operation voltage (SET: 0.7 V and RESET: −0.3 V), a high on state/off state resistive ratio (10<SUP>6</SUP>), AC cyclic endurance (>10<SUP>4</SUP>), and stable retention (85 °C/10 years). To achieve these performance parameters, CFs were locally formed inside the electrolyte using a modified CuSn active electrode, and the amount of Cu-ion injection was reduced by inserting the Dy or Lu buffer layer between the CuSn active electrode and the electrolyte. In particular, conductive-atomic force microscopy results at the Dy or Lu/Al<SUB>2</SUB>O<SUB>3</SUB> interface directly showed and defined the diameter of the CF.</P>

Non-volatile resistive switching in CuBi-based conductive bridge random access memory device

Vishwanath, Sujaya Kumar,Woo, Hyunsuk,Jeon, Sanghun American Institute of Physics 2018 APPLIED PHYSICS LETTERS Vol.112 No.25

Resistive switching characteristics of all-solution-based Ag/TiO2/Mo-doped In2O3devices for non-volatile memory applications

Vishwanath, Sujaya Kumar,Kim, Jihoon The Royal Society of Chemistry 2016 Journal of Materials Chemistry C Vol.4 No.46

<P>In this paper, we demonstrate the fabrication of electrochemical-metallization-based resistive switching random access memory (ECM-based ReRAM) devices with an Ag/TiO2/Mo-doped In2O3configuration through a simple solution-based process. Both TiO2and Mo-doped In2O3layers in the memory device were spin-coated with polymer-assisted-solution inks formulated by coordinating the Ti-, Mo-, and In-complex with a water-soluble polymer. The Ag top electrode was inkjet-printed with Ag nanoparticle ink. The memory devices fabricated by all-solution processes demonstrated excellent bipolar switching behavior with a high resistive switching ratio of 10<SUP>3</SUP>, an excellent endurance of more than 1000 cycles, a stable retention time greater than 10<SUP>4</SUP>s at elevated temperatures, and a fast programming speed of 250 ns. The characterization results of the conduction mechanism in high and low resistive states indicate that the resistive switching is caused by the formation and rupture of nano-sized Ag conducting filaments in the TiO2layer. These results suggest the potential of all-solution-based ECM-based ReRAM for developing future nonvolatile memory devices at low cost.</P>

Enhancement of resistive switching properties in Al₂O₃ bilayer-based atomic switches: multilevel resistive switching

Vishwanath, Sujaya Kumar,Woo, Hyunsuk,Jeon, Sanghun IOP 2018 Nanotechnology Vol.29 No.23

<P>Atomic switches are considered to be building blocks for future non-volatile data storage and internet of things. However, obtaining device structures capable of ultrahigh density data storage, high endurance, and long data retention, and more importantly, understanding the switching mechanisms are still a challenge for atomic switches. Here, we achieved improved resistive switching performance in a bilayer structure containing aluminum oxide, with an oxygen-deficient oxide as the top switching layer and stoichiometric oxide as the bottom switching layer, using atomic layer deposition. This bilayer device showed a high on/off ratio (10<SUP>5</SUP>) with better endurance (∼2000 cycles) and longer data retention (10<SUP>4</SUP> s) than single-oxide layers. In addition, depending on the compliance current, the bilayer device could be operated in four different resistance states. Furthermore, the depth profiles of the hourglass-shaped conductive filament of the bilayer device was observed by conductive atomic force microscopy.</P>

Electromagnetic interference shielding effectiveness of invisible metal-mesh prepared by electrohydrodynamic jet printing

Vishwanath, Sujaya Kumar,Kim, Do-Geun,Kim, Jihoon IOP Publishing 2014 Japanese journal of applied physics Vol.53 No.5

<P>EMI shielding metal-mesh pattern was prepared on the plastic film by electrohydrodynamic (EHD) jet printing with Ag ink. The printed Ag line width in the mesh was 9.72 mu m which was small enough not to be distinctly detected by human eyes. The line-to-line spacing (pitch) in the mesh pattern was modulated in order to investigate the electrical and optical properties of the EHD jet-printed metal-mesh layers. The pitch of 300 mu m in the mesh led to the sheet resistance of 7 Omega/sq, the transmittance of 88.2%, and the haze less than 1%. Even though the decrease in the pitch resulted in the improvement on the electrical property of the metal-mesh layer, it was found that the decrease in the pitch simultaneously degraded the optical property such as transparency and haze. Electromagnetic interference shielding effectiveness (EMI SE) of the EHD jet-printed metal-mesh was investigated over the X-band frequency range (8-12 GHz). It turned out that the EHD jet-printed metal-mesh showed a high EMI SE of 20 dB which indicated that the mesh layer can be used in the various application of electronics for the EMI shielding purpose. (C) 2014 The Japan Society of Applied Physics</P>

The optoelectronic properties of tungsten-doped indium oxide thin films prepared by polymer-assisted solution processing for use in organic solar cells

Kumar Vishwanath, Sujaya,An, Taekyu,Jin, Won-Yong,Kang, Jae-Wook,Kim, Jihoon Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.39

<▼1><P>Tungsten-doped indium oxide transparent conducting thin films, to be applied to inverted organic solar cells, were prepared by a polymer-assisted solution process.</P></▼1><▼2><P>Tungsten-doped indium oxide (WIO) transparent conducting thin films, to be used in inverted organic solar cells (IOSCs), were prepared by a polymer-assisted solution (PAS) process. Tungsten has high Lewis acid strength and it is, therefore, a promising candidate dopant for formulating high-mobility transparent conducting oxides with high transmittance over a wide range of regions from visible to near-infrared. WIO–PAS was formulated by coordinating W- and In-anionic complexes with a water-soluble polymer, and subsequently spin-coated on glass substrates and heat-treated at elevated temperatures. The final WIO–PAS coating solution was prepared by adding W-PAS and In-PAS with W concentrations in solution ranging from 1 at% to 5 at%. The optimum W concentration resulting in the lowest resistivity of 7.38 × 10<SUP>−4</SUP> Ω cm was 3 at%. The optimum PAS-processed WIO (PAS–WIO) film, having a thickness of 230 nm, had a sheet resistance of 38 Ω sq<SUP>−1</SUP> and an optical transmittance greater than 85%. The potential of the optimum PAS–WIO films in IOSCs was also assessed. The IOSCs prepared with PAS–WIO films had a power conversion efficiency (PCE) of 5.6%, which is comparable to the PCE values of IOSCs with commercial tin-doped indium oxide (ITO) films. This suggests that the PAS–WIO films are a cost-effective alternative to the vacuum-based ITO films used for the fabrication of optoelectronic devices.</P></▼2>

Polymer-Assisted Solution Processing of TiO₂ Thin Films for Resistive-Switching Random Access Memory

Vishwanath, Sujaya Kumar,Jeon, Sanghun,Kim, Jihoon Electrochemical Society 2017 Journal of the Electrochemical Society Vol.164 No.2

<P>In this study, we present a polymer-assisted solution (PAS) process to prepare TiO2 electrolyte layers for resistive-switching random access memory (ReRAM). The PAS process utilizes the stability of metal-polymer complexes in the coating solution to form uniform and dense films. In addition, the viscosity of the PAS coating solution can easily be adapted for any currently used coating technique. The electrochemical-metallization-based (ECM-based) ReRAM devices were prepared by spin-coating the PAS coating solution on an indium tin oxide (ITO) glass substrate that is used as the bottom electrode. Cu was deposited on the PAS-TiO2 electrolyte as an electrochemically active metal electrode used as the top electrode. The ECM-based ReRAM with the PAS-TiO2 electrolyte layer demonstrated bipolar resistive-switching behavior with a memory window wider than 13, cycle endurance over 500 cycles, and retention time longer than 10(4) s. Analysis of the conduction mechanism in high and low resistive states indicates that the resistive switching is attributed to the formation and rupture of Cu conducting filaments (CFs) in the PAS-TiO2 electrolyte layer. (C) 2016 The Electrochemical Society. All rights reserved.</P>

Polymer-assisted solution processing of Mo-doped indium oxide thin films: high-mobility and carrier-scattering mechanisms

Vishwanath, Sujaya Kumar,Cho, Kuk Young,Kim, Jihoon IOP 2016 Journal of Physics. D, Applied Physics Vol.49 No.15

<P>Mo-doped indium oxide (MIO) transparent conducting films have been prepared by a polymer-assisted solution (PAS) process. Both Mo- and In-PASs have been formulated by coordinating Mo- and In-anionic complexes with polyethyleneimine. The final MIO-PAS coating solution was prepared by adding Mo-PAS and In-PAS with Mo concentration in solution ranging from 0 at% to 2.5 at%. The structural, optical and electrical properties of MIO films spin-coated on the glass substrates were characterized. The optimum Mo concentration leading to the best electrical and optical properties was 1.5 at%, showing a low resistivity of 3.9  ×  10<SUP>−3</SUP> Ω  ⋅  cm with high mobility of 43 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> and high transmittance from visible to near infrared regions. The carrier-transport mechanism in the PAS-processed MIO film was investigated by applying a theoretical scattering model (Brook–Herring–Dingle theory) to Hall mobility data. The scattering model confirms that the ionized and neutral impurities play important roles as dominant scattering centers in the PAS-processed MIO films.</P>

KNN based Machine Learning Approach for Text and Document Mining

Vishwanath Bijalwan,Vinay Kumar,Pinki Kumari,Jordan Pascual 보안공학연구지원센터 2014 International Journal of Database Theory and Appli Vol.7 No.1

Exploring the Potentiality of Novel Rhizospheric Bacterial Strains against the Rice Blast Fungus Magnaporthe oryzae

Amruta, Narayanappa,Kumar, M.K. Prasanna,Puneeth, M.E.,Sarika, Gowdiperu,Kandikattu, Hemanth Kumar,Vishwanath, K.,Narayanaswamy, Sonnappa The Korean Society of Plant Pathology 2018 Plant Pathology Journal Vol.34 No.2

Rice blast caused by Magnaporthe oryzae is a major disease. In the present study, we aimed to identify and evaluate the novel bacterial isolates from rice rhizosphere for biocontrol of M. oryzae pathogen. Sixty bacterial strains from the rice plant's rhizosphere were tested for their biocontrol activity against M. oryzae under in vitro and in vivo. Among them, B. amyloliquefaciens had significant high activity against the pathogen. The least disease severity and highest germination were recorded in seeds treated with B. amyloliquefaciens UASBR9 (0.96 and 98.00%) compared to untreated control (3.43 and 95.00%, respectively) under in vivo condition. These isolates had high activity of enzymes in relation to growth promoting activity upon challenge inoculation of the pathogen. The potential strains were identified based on 16S rRNA gene sequencing and dominance of these particular genes were associated in Bacillus strains. These strains were also confirmed for the presence of antimicrobial peptide biosynthetic genes viz., srfAA (surfactin), fenD (fengycin), spaS (subtilin), and ituC (iturin) related to secondary metabolite production (e.g., AMPs). Overall, the results suggested that application of potential bacterial strains like B. amyloliquefaciens UASBR9 not only helps in control of the biological suppression of one of the most devastating rice pathogens, M. grisea but also increases plant growth along with a reduction in application of toxic chemical pesticides.