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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>
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>
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>
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>