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Faraday Discussions

Ruomeng Huang, Gabriela P Kissling, Reza Kashtiban, Yasir J Noori, Katarina Cicvarić, Wenjian Zhang, Andrew L Hector, Richard Beanland, David C Smith, Gillian Reid, Philip N Bartlett, C H Kees de Groot
We have recently reported a new method for the electrodeposition of thin film and nanostructured phase change memory (PCM) devices from a single, highly tuneable, non-aqueous electrolyte. The quality of the material was confirmed by phase cycling via electrical pulsed switching of both 100 nm nano-cells and thin film devices. This method potentially allows deposition into extremely small confined cells down to less than 5 nm, 3D lay-outs that require non-line-of-sight techniques, and seamless integration of selector devices...
November 9, 2018: Faraday Discussions
Benedikt Kersting, Martin Salinga
The market launch of Intel's 3D XPoint™ proves phase change technology has grown mature. Besides storing information in a fast and non-volatile way, phase change memories (PCMs) may facilitate neuromorphic and in-memory computing. In order to establish PCM as a lasting element of the electronics ecosystem, scalability to future technology nodes needs to be assured. Continued miniaturization of PCM devices is not only prescribed in order to achieve memories with higher data density and neuromorphic hardware capable of processing larger amounts of information...
November 7, 2018: Faraday Discussions
Silvia Gabardi, Gabriele G Sosso, Joerg Behler, Marco Bernasconi
Strategies to reduce the incubation time for crystal nucleation and thus the stochasticity of the set process are of relevance for the operation of phase change memories in ultra-scaled geometries. With these premises, in this work we investigate the crystallization kinetics of the phase change compound GeTe. We have performed large scale molecular dynamics simulations using an interatomic potential, generated previously from a neural network fitting of a database of ab initio energies. We have addressed the crystallization of models of amorphous GeTe annealed at different temperatures above the glass transition...
October 31, 2018: Faraday Discussions
Nobuki Inoue, Hisao Nakamura
We investigated the resistive switching mechanism between the high-resistance state (HRS) and the low-resistance state (LRS) of the GeTe-Sb2Te3 (GST) superlattice. First-principles calculations were performed to identify the structural transition pathway and to evaluate the current-voltage (I-V) characteristics of the GST device cell. After determining the atomistic structures of the stable structural phases of the GST superlattice, we found the structural transition pathways and the transition states of possible elementary processes in the device, which consisted of a thin film of GST superlattice and semi-infinite electrodes...
October 31, 2018: Faraday Discussions
Yusuke Hiruma, Kai Yoshikawa, Masa-Aki Haga
A new type of memristor inspired by bio-membranes is presented, based on the proton movement resulting from proton-coupled electron transfer (PCET) processes in dinuclear Ru complexes, whereby a two-terminal device based on said Ru complexes and a proton-conducting polymer was constructed as a proof-of-concept. Two ITO electrodes were modified separately with dinuclear Ru complexes that bear tetraphosphonic acid linkers at both ends and a 2,6,2',6'-tetrakis(benzimidazol-2-yl)-4,4'-bipyridine (RuNH-OH) or 1,3,1',3'-tetrakis(benzimidazol-2-yl)-5,5'-biphenyl (RuCH-OH) bridging ligand, and both ITO electrodes exhibit PCET processes with different Ru(ii/iii) redox potentials and pKa values...
October 30, 2018: Faraday Discussions
Anthony J Kenyon, Manveer Singh Munde, Wing H Ng, Mark Buckwell, Dovydas Joksas, Adnan Mehonic
We report a study of the relationship between oxide microstructure at the scale of tens of nanometres and resistance switching behaviour in silicon oxide. In the case of sputtered amorphous oxides, the presence of columnar structure enables efficient resistance switching by providing an initial structured distribution of defects that can act as precursors for the formation of chains of conductive oxygen vacancies under the application of appropriate electrical bias. Increasing electrode interface roughness decreases electroforming voltages and reduces the distribution of switching voltages...
October 29, 2018: Faraday Discussions
Hongchu Du, Chun-Lin Jia, Joachim Mayer
Recently, extended mixed dislocations were observed at a [001]/(100) low-angle tilt grain boundary of a SrTiO3 bicrystal because of a slight twist between the two crystal parts. The b = a[201]/(100) mixed dislocations at the grain boundary dissociate into three dislocations with Burgers vector b of a/2[101], a[100], and a/2[101], respectively. A structure model has been proposed in particular for the dislocation cores of the two partials with b = a/2[101] based on the high-angle annular dark-field (HAADF) images acquired by scanning transmission electron microscopy (STEM)...
October 29, 2018: Faraday Discussions
Elia Ambrosi, Alessandro Bricalli, Mario Laudato, Daniele Ielmini
Resistive switching random-access memory (ReRAM) is one of the most promising technologies for non-volatile memories. Thanks to the low power and high speed operation, the high density CMOS-compatible integration, and the high cycling endurance, the ReRAM technology is becoming a strong candidate for high-density storage arrays and novel in-memory computing systems. However, ReRAM suffers from cycle-to-cycle switching variability and noise-induced resistance fluctuations, leading to insufficient read margin between the programmed resistive states...
October 26, 2018: Faraday Discussions
Christoph Baeumer, Thomas Heisig, Benedikt Arndt, Katharina Skaja, Francesco Borgatti, Francesco Offi, Federico Motti, Giancarlo Panaccione, Rainer Waser, Stephan Menzel, Regina Dittmann
Resistive switching oxides are highly attractive candidates to emulate synaptic behaviour in artificial neural networks. Whilst the most widely employed systems exhibit filamentary resistive switching, interface-type switching systems based on a tunable tunnel barrier are of increasing interest, since their gradual SET and RESET processes provide an analogue-type of switching required to take over synaptic functionality. Interface-type switching devices often consist of bilayers of one highly mixed-conductive oxide layer and one highly insulating tunnel oxide layer...
October 26, 2018: Faraday Discussions
Dirk J Wouters, Stephan Menzel, Jonathan A J Rupp, Tyler Hennen, Rainer Waser
The I-V switching curves of bipolar switching non-volatile ReRAM devices show peculiar characteristics, such as an abrupt ON switching and the existence of a universal switching voltage. This switching behavior has been explained by the presence of a filamentary process, in which the width of a conductive filament changes during switching resulting in different resistance states. Vice versa, similar (ON) switching behavior, e.g. that of volatile switching Cr-doped V2O3 devices, has been interpreted as an indication of the presence of similar filamentary switching...
October 26, 2018: Faraday Discussions
Konstantin Z Rushchanskii, Stefan Blügel, Marjana LeŽaić
We present phase diagrams of binary oxides, Hf-O, Zr-O and Y-O, obtained by ab initio evolutionary simulations, in order to explore possible metastable crystalline suboxide structures which could be quenched during the electroforming processes within the conductive filaments in stoichiometric HfO2, ZrO2 and Y2O3 host materials, in resistive switching devices. We find that, in the range MO-MO2 (where M = Hf, Zr, Y), the most energetically favourable atomic configurations have properties which facilitate the ionic conduction of oxygen...
October 26, 2018: Faraday Discussions
W Wang, G Pedretti, V Milo, R Carboni, A Calderoni, N Ramaswamy, A S Spinelli, D Ielmini
Resistive switching random-access memory (ReRAM) is a two-terminal device based on ion migration to induce resistance switching between a high resistance state (HRS) and a low resistance state (LRS). ReRAM is considered one of the most promising technologies for artificial synapses in brain-inspired neuromorphic computing systems. However, there is still a lack of general understanding about how to develop such a gestalt system to imitate and compete with the brain's functionality and efficiency. Spiking neural networks (SNNs) are well suited to describe the complex spatiotemporal processing inside the brain, where the energy efficiency of computation mostly relies on the spike carrying information about both space (which neuron fires) and time (when a neuron fires)...
October 26, 2018: Faraday Discussions
Melika Payvand, Manu V Nair, Lorenz K Müller, Giacomo Indiveri
Memristive devices represent a promising technology for building neuromorphic electronic systems. In addition to their compactness and non-volatility, they are characterized by their computationally relevant physical properties, such as their state-dependence, non-linear conductance changes, and intrinsic variability in both their switching threshold and conductance values, that make them ideal devices for emulating the bio-physics of real synapses. In this paper we present a spiking neural network architecture that supports the use of memristive devices as synaptic elements and propose mixed-signal analog-digital interfacing circuits that mitigate the effect of variability in their conductance values and exploit their variability in the switching threshold for implementing stochastic learning...
October 25, 2018: Faraday Discussions
Stephan Menzel, Moritz von Witzleben, Viktor Havel, Ulrich Böttger
In contrast to classical charge-based memories, the binary information in redox-based resistive switching devices is decoded by a change of the atomic configuration rather than changing the amount of stored electrons. This offers in principle a higher scaling potential as ions are not prone to tunneling and the information is not lost by tunneling. The switching speed, however, is potentially smaller since the ionic mass is much higher than the electron mass. In this work, the ultimate switching speed limit of redox-based resistive switching devices is discussed...
October 25, 2018: Faraday Discussions
A Zaffora, F Di Quarto, H Habazaki, I Valov, M Santamaria
Redox-based resistive switching memories (ReRAMs) are the strongest candidates for next generation nonvolatile memories. These devices are commonly composed of metal/solid electrolyte/metal junctions, where the solid electrolyte is usually an oxide layer. A key aspect in the ReRAMs development is the solid electrolyte engineering, since it is crucial to tailor the material properties for obtaining excellent switching properties (e.g. retention, endurance, etc.). Here we present an anodizing process as a non vacuum and low temperature electrochemical technique for growing oxides with tailored structural and electronic properties...
October 25, 2018: Faraday Discussions
Keqin Liu, Liang Qin, Xiaoxian Zhang, Jiadi Zhu, Xinhao Sun, Ke Yang, Yimao Cai, Yuchao Yang, Ru Huang
Memristive devices based on electrochemical processes are promising candidates for next-generation memory and neuromorphic applications. The redox processes happening at the interfaces are crucial steps for the ionization as well as generation of counter charges, and are thus indispensable for successful resistive switching, but their detailed mechanism has not been fully clarified. Here, we study the interfacial redox reactions in the forming process of memristive devices based on valence change and electrochemical metallization, using high-resolution electron microscopy and electrostatic force microscopy observations...
October 24, 2018: Faraday Discussions
Wataru Hiraya, Nozomi Mishima, Takaaki Shima, Seishiro Tai, Tohru Tsuruoka, Ilia Valov, Tsuyoshi Hasegawa
Doping impurity atoms into semiconductor materials changes the resistance of the material. Selecting the atomic species of a dopant and the precise control of the number of dopant atoms in a unit volume can control the resistance to a desired value. The number of dopant atoms is usually controlled when the materials are synthesized. It can also be controlled after synthesizing by injecting dopant atoms using an ion implantation technique. This physical method has now enabled atom by atom implantation at the desired position...
October 24, 2018: Faraday Discussions
Itır Köymen, Pınar Aydoğan Göktürk, Coşkun Kocabaş, Şefik Süzer
The memristor has been the topic of heated research activity since the Pt/TiO2/TiOx/Pt structure was reported by Hewlett-Packard Labs. The characteristics of memristors such as the pinched hysteresis loops and time and input signal-dependent memristance are due to the drift of positively charged oxygen vacancies in the TiOx layer. While different modes of switching behaviour have been characterized, observing the switching as it happens with in situ measurements using X-ray photoelectron spectroscopy (XPS) can allow a better understanding of the device operation...
October 24, 2018: Faraday Discussions
S K Bose, S Shirai, J B Mallinson, S A Brown
We report a detailed study of neuromorphic switching behaviour in inherently complex percolating networks of self-assembled metal nanoparticles. We show that variation of the strength and duration of the electric field applied to this network of synapse-like atomic switches allows us to control the switching dynamics. Switching is observed for voltages above a well-defined threshold, with higher voltages leading to increased switching rates. We demonstrate two behavioral archetypes and show how the switching dynamics change as a function of duration and amplitude of the voltage stimulus...
October 24, 2018: Faraday Discussions
Louis P Romero, Stefano Ambrogio, Massimo Giordano, Giorgio Cristiano, Martina Bodini, Pritish Narayanan, Hsinyu Tsai, Robert M Shelby, Geoffrey W Burr
Hardware accelerators based on two-terminal non-volatile memories (NVMs) can potentially provide competitive speed and accuracy for the training of fully connected deep neural networks (FC-DNNs), with respect to GPUs and other digital accelerators. We recently proposed [S. Ambrogio et al., Nature, 2018] novel neuromorphic crossbar arrays, consisting of a pair of phase-change memory (PCM) devices combined with a pair of 3-Transistor 1-Capacitor (3T1C) circuit elements, so that each weight was implemented using multiple conductances of varying significance, and then showed that this weight element can train FC-DNNs to software-equivalent accuracies...
October 24, 2018: Faraday Discussions
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