Hybrid, organic and bio-materialsS
Memristor materials, mechanisms and devices for unconventional computing
Growing area of unconventional computing aims to develop bio-inspired systems, capable to parallel processing, learning and decision making. Memristive devices are new electronic elements with synapse-like characteristics. The symposium will cover materials aspects for unconventional computers.
The scope of the symposium is to exchange recent results and ideas in the field of realization of single memristive devices, their deterministic and stochastic networks, and in adjacent branches of unconventional computing based on chemical reactions and use of biological samples. A complete variety of materials, used currently for these purposes, will be overviewed by leading experts and discussed during presentations and round table. The material aspects will concern the composition (organic, inorganic, biological) and experimental methods of the realization of both single elements and neuromorphic networks. Additional attention will be dedicated to the theoretical aspects of the description and prediction of properties of the elements and networks. These models must form a basis for the future development of new systems with improved properties. The involvement of the industrial participants (chairing round tables) will underline necessary actions helping the realization of commercial prototypes of the devices and systems. Concerning that the topic is very young (the breaking increase of the activity in the field started only after 2008) and there were no conferences dedicated to the material aspects of the problem, we expect that the symposium can be a real forum in this field that will allow a breakthrough in the improvement of the elements and networks composition, as well as methods of their realization. The symposium will provide wide opportunities for young scientists to improve their educational level in this very new field. Additionally, we expect the formation of new international teams who will be able to propose and successfully execute new project at European and International levels.
Hot topics to be covered by the symposium:
- The symposium will be divided in sessions, dedicated to special topics:
- Inorganic (metal oxide) memristive devices.
- Alternative memristive devices and networks (including organic systems).
- Chemical computing.
- Bio-neuro-inspired computing.
- Theoretical aspects of devices and network functioning.
At the end of the symposium we plan to organize a round table with the invitation of industry representatives for the discussion of theory-experiment relations and feedback, as well as perspectives of the industrial realization of prototypes, discussed during the symposium.
- Metal oxide memristive devices.
- Alternative memristive devices and networks Iincluding organic systems).
- Theoretical aspects of devices and networks.
- Novel computing substrates.
In addition, it is under the discussion the organization of joint session with I and Q symposia, dedicated to the research in Japan.
- L.O. Chua, University of California, Berkeley, USA
- Y. Pershin, University of S. Carolina, USA
- G. Wendin, Chalmers University of Technology, Sweden
- W. Lu, University of Michigan, USA
- D. Querlioz, IEF Orsay University, France
- M. Salinga, RWTH Aachen, Department of Physics, Germany
- T. Hasegawa, Nims MANA, Tsukuba, Japan
- H. Kim, Chonbuk National University, Korea
- M. Frasca, University of Catania, Italy
- A. Thomas, Bielefeld University, Germany
- V. Privman, Clarkson University, USA
- F. Peper, National Institute of Information and Communications Technology, Advanced ICT Research Institute, Japan
Confirmed invited speakers:
- D. Strukov, University of California, Santa Barbara, USA
- M. Di Ventra, University of California, San Diego, USA
- S. Iannotta, CNR-IMEM, Italy
- R. Waser, RWTH Aachen University, Germany
- D. Vuillaume, IEMN-CNRS, France
- C.S. Hwang, Seoul National University, Korea
Proceedings of the papers, accepted for the symposium will be published in Physica Status Solidi C. In addition, selected papers, after double review procedure, will be published in special issue of Physica Status Solidi A or B.
Department of Physics
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Authors : Adnan Mehonic, Mark Buckwell, Luca Montesi Manveer Munde, Anthony Kenyon
Affiliations : Department of Electronic & Electrical Engineering - University College London
Resume : We demonstrate a redox-based resistive switch exploiting the formation of conductive filaments in bulk silicon-rich silicon oxide. Our devices exhibit multi-level switching and analogue modulation of resistance as well as standard two-level switching. We demonstrate different operational modes (bipolar and unipolar switching modes) that make it possible to dynamically adjust device properties, in particular two highly desirable properties: non-linearity and self-rectification. Scanning tunnelling microscopy (STM), atomic force microscopy (AFM), and conductive atomic force microscopy (C-AFM) measurements provide a more detailed insight into both the location and the dimensions of the conductive filaments. We discuss aspects of conduction and switching mechanisms and propose a physical model of resistive switching. We demonstrate room temperature quantisation of conductance in silicon oxide resistive switches, implying ballistic transport of electrons through a quantum constriction, associated with an individual silicon filament in the SiOx bulk.
Authors : Mark Buckwell, Adnan Mehonic, Luca Montesi Manveer Munde, Anthony Kenyon
Affiliations : Department of Electronic & Electrical Engineering - University College London
Resume : We make use of atomic force microscopy (AFM), conductive atomic force microscopy (C-AFM) and x‑ray photoelectron spectroscopy (XPS) to characterise the physical processes occurring in the formation of conducting filaments in silicon-rich silicon oxide (SiOx) resistive switches. Surface analyses of the SiOx layer and top contacts of our devices are employed to establish the chemical nature of filament formation and the structural properties of the oxide layer. Investigation of oxide breakdown is also used to further understand the changes occurring in the SiOx which enable switching behaviour. Thus a conduction mechanism which enables our devices to function as redox-based resistive switches is proposed.
Authors : S. Hoffmann-Eifert; N. Aslam; V. Longo*; F. Roozeboom*; W.M.M. Kessels*; and R. Waser
Affiliations : Peter Gruenberg Institute (PGI-7) and JARA-FIT, Forschungszentrum Juelich, Germany; *Department of Applied Physics, Eindhoven University of Technology, The Netherlands
Resume : Metal-oxide-metal devices are considered as strong candidates for modern non-volatile ReRAM. The resistive switching (RS) mechanism in SrTiO3 (STO) has been extensively studied for single crystals and PLD grown heteroepitaxial thin films. A dominant filamentary nature of the RS behavior was reported while under certain conditions also area-dependent interface-type switching was observed. This study is related to the effect of Sr/Ti composition in ultrathin nanocrystalline STO films on the RS properties of Pt/STO/TiN devices. The films were grown by atomic layer deposition (ALD) while the cation composition was adjusted by the Sr to Ti cycle ratio. A post annealing at 600°C for 5-10 min in N2 was performed prior to the top electrode deposition. STO thin films of different thicknesses between 8 and 15 nm and of three different compositions x=[Sr]/([Sr]+[Ti]), i.e. x=0.50, 0.57, and 0.46 were studied. The sizes of the cross bar junctions were varied from 1 µm2 to 0.0016 µm2. The electroforming and RS behaviors of the devices are discussed with respect to thin film growth induced effects like composition, thickness, and morphology and also in regard to the device and operation controlled parameters like pad size, electroforming procedure, and operational currents and voltages. The obtained RS characteristics are comprised in a statistical manner and controlling parameters are discussed. This work was funded in part by FP7 under grant ENHANCE-238409.
Systems and modelling : M. Frasca
Authors : M. Di Ventra and Y. Pershin
Affiliations : Department of Physics, UCSD
Resume : I will discuss a novel computing paradigm we named memcomputing  inspired by the operation of our own brain. Memcomputing computing using memory circuit elements or memelements  satisfies important physical requirements: (i) it is intrinsically massively parallel, (ii) its information-storing and computing units are physically the same, and (iii) it does not rely on active elements as the main tools of operation. I will discuss the various possibilities offered by memcomputing, the criteria that need to be satisfied to realize this paradigm, provide several examples showing the massively-parallel solution of optimization problems, and a practical CMOS-compatible realization using memcapacitors .  M. Di Ventra and Y.V. Pershin, Nature Physics, 9, 200 (2013).  M. Di Ventra, Y.V. Pershin, and L.O. Chua, Proc. IEEE, 97, 1717 (2009).  F. L. Traversa, F. Bonani, Y.V. Pershin and M. Di Ventra, Dynamic Computing Random Access Memory, submitted for publication. Preprint on arXiv:1306.6133
Authors : M. Klimo, E.Linn, M. Fratrik, P. Jancovic, O. Such, K. Frohlich
Affiliations : University of Zilina, Slovakia;RWTH Aachen, Germany; University of Zilina, Slovakia; IEE SAS, Slovakia; MI SAS, Slovakia; IEE SAS, Slovakia
Resume : Klimo and Such argued theoretically that anti-serially connected memristors compute MIN and MAX functions. This allows one to implement fuzzy logic with passive circuits, representing variables by voltages. In that work authors used a linear model of the memristor. The actual behaviour of memristors is however more complex as demonstrated by our experiments. Much experimental insight into behaviour of the anti serial configuration has been shed by E. Linn et al in their work on complementary resistive switching. In that context one uses voltage pulses for setting the device into a known state. In the context of fuzzy computation (MIN and MAX) one uses a full voltage range and the previous state of the computational gate may override the input magnitudes, creating non-action windows, where the memory property of anti-serial connection predetermines the outcome of computation. Material dependence also plays a key role. Metal oxide devices exhibit strongly nonlinear OFF states. Even when MIN or MAX gate is operated outside of a non-action window, beyond a certain range of inputs the output diverges from minimum towards a linear combination of inputs. This behaviour contrasts ECM devices that closely reproduce MIN and MAX functions. In our contribution we analyze experimental behaviour of tantalum and hafnium oxide based memristive devices. We show that depending on individual properties of the constituent devices, the output I-V of the MIN gate can be non-symmetric.
Authors : G.A. Patterson, F.N. Sangiuliano Jimka, P.I. Fierens, D.F. Grosz
Affiliations : Instituto Tecnologico de Buenos Aires; Instituto Tecnologico de Buenos Aires; Instituto Tecnologico de Buenos Aires, Consejo Nacional de Investigaciones Cientificas y Tecnicas (Arg.); Instituto Tecnologico de Buenos Aires, Consejo Nacional de Investigaciones Cientificas y Tecnicas (Arg.)
Resume : Stotland and Di Ventra  presented simulations of a memristor system which took into account the interaction of internal (inherent to the sample) noise with the system nonlinearity. In particular, they studied the effect of additive white Gaussian noise, that can be associated with thermal fluctuations. They showed that there is an optimal noise intensity for which the contrast between low- and high-resistance values is maximized. Recently, experiments on manganite samples have shown that the addition of an optimal amount of noise also improves the contrast between resistance states . Furthermore, general characteristics of the governing equations which lead to the observed improvement were validated by simulations. In this work we experimentally study the interplay between temperature and electrical noise and we characterize the memory performance of a manganite. In particular, we find memory enhancement due to noise at temperatures from 30 to 80 C and signal-to-noise ratios as low as 0 dB. These results might be of relevance in the area of memory devices and other circuits involving memristors where the large scale of integration leads to higher working temperatures and lower signal-to-noise ratios.  A. Stotland and M. Di Ventra. Phys. Rev. E 85, 011116 (2012).  G.A. Patterson, P.I. Fierens and D.F. Grosz. Appl. Phys. Lett. 87, 074102 (2013).
Authors : Qurat-ul-ann (Anna) Mirza, Yogesh N. Joglekar
Affiliations : Indiana University Purdue University Indianapolis (IUPUI)
Resume : Since 2008, thin-film memristive systems have attracted tremendous attention. Similarities between their I-V characteristics and those of ion channels in an axon have spurred interest in semiconductor neurons - nanoscale circuits with action-potential-like threshold response. A minimal model of the biological neuron is best obtained via dynamical-systems approach and shows that two types of memristors, namely sodium and potassium channels, are required for the action potential. This action potential is characterized by a periodic, spiking (voltage) response to a steady state, dc (current) stimulus. In this work, we search for a corresponding minimal model with thin-film memristor circuits. We theoretically and numerically investigate I-V characteristics of circuits with mem-elements and their traditional counterparts in the ac and dc regimes. For a sinusoidal ac voltage, we show that memristor saturation is signaled by generation of higher harmonics with maximum weight in the current. By using phase-space analysis, we show that an ac (current) response in the presence of a dc (voltage) stimulus a key characteristic of a neuron requires a memristor with multiple, coupled internal state variables, or at least two distinct memristors, each with a single state variable. Our results provide a detailed theoretical understanding of excitable memristor circuits.
Bio-inspired systems : V. Privman
Authors : D. Vuillaume
Affiliations : IEMN, CNRS & Univ. of Lille, Villeneuve d'Ascq, France.
Resume : We have recently demonstrated how to design a hybrid (nanoparticule/molecule) SYNAPSTOR (synapse transistor) mimicking the dynamic plasticity of a biological synapse. This device (memristor-like) mimics short-term plasticity (STP) , STDP (spike-timing dependent plasticity) , two "functions" of learning processes. We demonstrated an associative memory, which can be trained to present a pavlovian response . Here we report on a detailed understanding of the dynamic electrical behavior of these synapstors, and how to optimize them to work at low voltage (∼ 1V). We also develop an electrolyte-gated version of this device for biocompatible applications . We report on a detailed understanding of the electrical behavior of these synapstors in physiologically relevant conditions. We discuss why these last results represent major improvements towards the use of these organic/NPs synapstor in biocompatible application e.g. as synapse prosthesis.  F. Alibart et al., Adv. Func. Mater. 20, 330 (2010).  F. Alibart et al., Adv. Func. Mater. 22, 609-16 (2012).  O. Bichler et al., IEEE Trans. Electron. Dev. 57(11), 3115-3122 (2010).  O. Bichler et al., Neural Computation 25(2), 549-566 (2013).  S. Desbief et al., European Conference on Molecular Electronics (ECME), 2013. This work was financially supported by the EU FP7-NMP (grant n° 280772), project "I‐ONE, FP7-FET (grant n° 318597), project "SYMONE" and ANR (project SYNAPTOR).
Authors : Tatiana Berzina
Affiliations : CNR-IMEM (National Council of the Researches Institute of Materials for Electronics and Magnetism), Parco Area delle Scienze 37A, 43124, Parma, Italy
Resume : The hardware realization of adaptive networks requires the fabrication of special electronic devices possessing a number of specific characteristics: they must have a memory, and, more specifically, their conductivity must increase with the frequency of their involvement into the signal propagation processes, allowing, therefore, a Hebbian  or so-called synaptic type of learning. We present the data on fabrication methods and properties of an electrochemically controlled conducting polymeric device (organic memristive device) which can be used as a key element of complex adaptive networks, mimicking biosystems in their information processing. Working principle of the device is based on very high ratio in the conductivity of polyaniline in its reduced and oxidized forms . In particular, the following aspects will be illustrated: -construction and composition of the discrete element; -operating principles of an individual organic memristor- a polymeric hetero-junction electrochemical device; -fabrication and properties of a 3D stochastic network of organic memristive devices; -properties of organic memristor - living systems (Physarum Polycephalum) interfaces in terms of integration of the single cell living system into the electronic circuits for the utilization of its adaptive abilities for the information processing. 1. D.O. Hebb, The origin of behavior. A Neurophsychological theory, NY: Wiley, 1961. 2. V. Erokhin, T. Berzina, M.P. Fontana, J. Appl. Phys., 97, 2005, 064501.
Poster 1 : C.S. Hwang
Authors : Panagiotis Bousoulas, Irini Michelakaki, Dimitris Tsoukalas
Affiliations : Department of Applied Physics, National Technical University of Athens, Iroon Polytechniou 9 Zografou, 15780 Athens, Greece
Resume : In this work we demonstrate that TiO2-x based Resistive Random Access Memories (ReRAM) devices can function without an initial electroforming process and a wide range of switching ratios could be achieved by controlling the oxygen content, the sweep bias amplitude and the width of the voltage pulse applied on the memory cell. The influence of deposition ambient during thin film sputtering at room temperature to the resistive properties of titanium oxide will be presented. Thus, we investigate how we can improve and stabilize the switching effect of TiO2-x based resistive devices by tailoring the oxygen flow during deposition of the film, suggesting that there is a direct connection between the fabrication procedure and switching phenomenon. By controlling the density of oxygen vacancies into the dielectric matrix we can also improve the repeatability and the operation of the device, in terms of distribution of the SET/RESET voltages. We propose that ultra high density of vacancies deteriorate the switching phenomenon, whereas high vacancy density results in better switching behavior. Switching speed, endurance and retention performance reveals the excellent functionality of our device as a non-volatile memory element and conduction mechanism analysis demonstrates the manifestation of Poole-Frenkel emission in conjunction with trap-assisted tunneling, which is also deployed in order to interpret the gradual increase of current during SET process.
Authors : M. A. Vieira1,2, M. Vieira1,2,3,V. Silva1,2, P. Louro1,2, M. Barata 1,2
Affiliations : 1Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Em?dio Navarro, 1949-014 Lisboa, Portugal Tel: 351 21 8317290, Fax: 351 21 8317114, email@example.com ; 2 CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal
Resume : In this paper we exploit the nonlinear property of the SiC multilayer devices under near- ultraviolet (350 nm) irradiation to design an optical processor for error detection and correction that enable reliable spectral data delivery of four-wave mixing over unreliable communication channels. The SiC optical processor is realized by using double pin/pin a-SiC:H photodetector with front and back biased optical gating elements. Red, green, blue and violet digital signals are transmitted together at different bit sequences. The combined optical signal is analyzed by reading out the photocurrent under at different background intensities. Boolean operations such as exclusive OR (EXOR) and three bit addition are optically demonstrated in the visible range. The combination of such switching devices show that when one or all of the inputs are present the system will behave as an XOR gate representing the SUM. When two or three inputs are on, the system acts as AND gate indicating the present of the CARRY bit. Other arithmetic operations are performed by addition together with some logic operations. In this paper we investigate additional parity logic operations performed by use of the four incoming pulsed communication channels that are transmitted and checked for errors together. As a simple example of this approach, we describe an all optical processor for error detection and correction and then provide the experimental demonstration of this idea.
Authors : G. Giusti (a), T. Toccoli (a), G. Baldi (b), L. Aversa (a), R. Tatti (a), R. Verucchi (a), S. Iannotta (b)
Affiliations : a) Istituto dei Materiali per lElettronica e il Magnetismo, IMEMCNR, Sede di Trento, Via alla Cascata 56/C 38123 Povo (TN), Italy b) Istituto dei Materiali per lElettronica e il Magnetismo, IMEMCNR, Parma, Viale Usberti 37/A, 43124 Parma (Italy)
Resume : A pulsed, supersonic, cluster-beam source based on microplasma ablation has been used to realize a TiO2 thin films for memristive applications. This technique, changing the working parameter permit easily to change the stoichiometry of the film giving rise to oxygen vacancy or sovra-stoichiometry ( Detto et al. doi: 10.1039/c2cp40120g). The crystalline phase could be also controlled. All these parameters could be used to control in detail the growth process and obtain film suitable for memresistive applications. Here we report about the characterization both by chemical and by morphological analyzes of the thin films in order to understand the roles of the several variables of coating process. Some preliminary result about the possibility of using these films as memristor could be also presented.
Authors : Mahyar Shahsavari, M. Faisal Nadeem, S. Arash Ostadzadeh, Philippe Devienne, Pierre Boulet,
Affiliations : University of Lille, LIFL, CNRS Delft University of Technology
Resume : Memristor is a two-terminal nanodevice that has recently attracted the attention of many researchers. Its simple structure, non-volatility behavior, high-density integration, and low-power consumption make the memristor a promising candidate to act as a switch in digital gates for future high- performance and low-power nanocomputing applications. In this paper, we model the behavior of memristor by using Verilog- A. To investigate its characteristics in a circuit, we use the HSPICE simulator. Furthermore, a library of digital gates are provided by using two approaches to make digital gates:the first one is based on material implication, and the second one is based on crossbar arrays. Finally, we perform a comparison and evaluation between two methods.
Authors : Alice Dimonte, Tatiana Berzina, Victor Erokhin
Affiliations : CNR-IMEM (National Council of the Researches Institute of Materials for Electronics and Magnetism), Parco Area delle Scienze 37A, 43124, Parma, Italy
Resume : Physarum Polycephalum slime mold is an eukaryotic organism, a single cell made by a myriad of nuclei dispersed in the cytoplasm. In this study Physarum has been loaded with BaFe12O19 magnetic particles. It was observed that particles are biocompatible; they are engulfed and transported inside Physarums body (this event has been proven thanks to SEM and EDX analysis). This opens huge possibilities and research development in the field of unconventional computing. It is fundamental the presence of a tool, that can be defined as DEFLECTOR, by which controlling the variation of the attraction/repulsion growth, in a certain direction. As the magnetic-particles-loaded-mold system is sensitive to magnetic field, combining loading of Physarum with functional nanoparticles and simultaneous routing of its active zones, could be a new way to design hybrid devices: DEFLECTOR. By orienting the external magnetic field it is possible to direct the deflection, while, acting on the intensity of the field will change the strength of the deflection itself. Magnetic particles can also be exploited to record information of the applied field; in this respect, the system can be considered as an amorphous biological processor with integrated memory properties. Targeting the growth with external actions provides new capabilities for the realization of bio-inspired computational or robotic systems, based on Physarum polycephalum.
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Authors : V.A. Demin (1,2), P.K. Kashkarov (1,2,3), M.V. Kovalchuk (1,2,3)
Affiliations : (1) National Research Center "Kurchatov Institute", 123182 Moscow, Russia (2) Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region, 141700, Russia (3) Lomonosov Moscow State University, GSP-1, Lelinskie Gory, Moscow 119991, Russia
Resume : The electrochemical organic memristor with polyaniline active layer is a stand-along device, designed and realized for the reproduction of some synapse properties in electronic circuits. It was demonstrated the advantageous possibilities of networks built of such organic memristors in tasks of supervised and unsupervised learning. Nevertheless, for practical usage and reproducibility of memristor adaptive networks it is needed to control or predict its properties during the preparation and functioning under different conditions. It was experimentally shown that working principles of the single memristor are based on the drift of lithium ions between the working conducting polymer channel and solid electrolyte. But so far there is no theoretical description of the memristor in action from the point of view of physical and chemical laws. In this work a new theoretical model of the polyaniline memristor device is presented. The developed model of the organic memristor functioning was based on the detailed consideration of possible electrochemical processes occuring in the active zone of this device. Results of the calculation have demonstrated not only the qualitative explanation of the characteristics, observed in the experiment, but also quantitative similarities of the resultant current values. It is shown how the memristor could behave at zero potential difference relative to reference electrode. This improved model can establish a basis for the design and prediction of properties of more complicated circuits and systems (including stochastic ones) based on the organic memristive devices.
Authors : Giuseppe Tarabella, Angelica Cifarelli, Alice Dimonte, Tatiana Berzina, Salvatore Iannotta, Pasquale DAngelo
Affiliations : Giuseppe Tarabella, Salvatore Iannotta, Pasquale DAngelo. Institute of Materials for Electronics and Magnetism (IMEM) - National Research Council (CNR) Viale Usberti 37A, Parco Area delle Scienze 43124, Parma (Italy); Angelica Cifarelli, Alice Dimonte, Tatiana Berzina. Department of Physics, University of Parma, Viale Usberti 37A, Parco Area delle Scienze 43124, Parma (Italy).
Resume : The slime mould Physarum Polychephalum (PP) is an eukaryote cell which growing interest by the scientific community is due to its properties of intelligence, creativity and capacity of learning. Recent progresses in PP show how it can be employed as main material in non-conventional-computing, robot-physarum and PP-based network circuits. Here the mould has been investigated with a conventional electrochemical cell by using PEDOT:PSS as reference electrode. A 2-terminat device in a memristor-like configuration has been used to investigate the current flowing in the mould/PEDOT:PSS/electrode system by cyclic current-voltage measurements implementing a Cyclic Voltammetry-like analysis. The effect of the counter electrode on the current response has been analysed. We characterized the mould with three different electrodes, Platinum, Silver and Gold, used as working electrodes, acquiring I-V curves upon a symmetric voltage scan sweep. The I-V curve of the Pt-electrode shows a pair of redox peaks at about -3V and +2.2V vs. PEDOT:PSS, at -2.8/+1.6V for Au, and -2.5/+0.6V for Ag. The area of I-V curves is lower for the Ag-gate, it increases for Au and becomes the highest for the Pt, that is ascribed to the different regimes of operation obtained using different electrodes. The 2-terminal device shows a resistive bi-stable state, it can be considered as a basic-logic unit for computing. The building of logic elements with living cells realizes an effective living technology platform.
Authors : HEHE ZHANG, NABEEL ASLAM, and SUSANNE HOFFMANN-EIFERT
Affiliations : Forschungszentrum Juelich, PGI-7, and JARA-FIT, 52425 Juelich, Germany
Resume : Resistive switching memory (ReRAM) requires high off/on resistance ratio, high endurance at low operation current and low switching voltage. One of the most studied resistive switching (RS) oxides, TiOx fits to these requirements, but suffers from high leakage current through sneak paths. To reduce the total leakage in TiOx based ReRAM devices, a bilayer stack of TiOx and a highly insulating layer like Al2O3 is one of the choices. For very small devices, deposition techniques guaranteeing high thin film quality are needed, therefore atomic layer deposition (ALD) was chosen. A systematic study on TiOx/Al2O3 bilayer structures integrated into cross point TiN/bilayer/Pt devices was carried out for ReRAM application. ALD was used for the deposition of Al2O3 and TiOx thin films, along with the optimization of growth parameters for amorphous Al2O3 films of about 3 to 10 nm thickness. With AFM, XPS and SEM the high qualities of Al2O3 thin layers were verified through low surface roughness, stoichiometric composition and sharp interface. In this contribution, we will discuss the influence of the thicknesses of the Al2O3 and TiOx films on the RS behavior of the bilayer stacks. We found that the variation of TiOx thickness has a significant effect on the HRS/LRS ratio during switching, whereas the change of Al2O3 thickness mainly affects the forming and reset voltage. Bilayer cells with about 3 to 4 nm Al2O3 and 5 to 10 nm TiOx exhibited stable bipolar type RS with resistance ratios of about 10E4 to 10E5. This and other dependencies will be discussed. This work was supported in part by the Deutsche Forschungsgemeinschaft (SFB917), and by the Global Research Laboratory program (2012040157) through the National Research Foundation (NRF) of Korea.
Authors : Fabien Alibart*, Selina La Barbera, Dominique Vuillaume, Marie Minvielle, Guillaume Saint-Girons, Romain Bachelet, Catherine Dubourdieu
Affiliations : Fabien Alibart*; Selina La Barbera; Dominique Vuillaume; IEMN-CNRS, Boulevard Poincarre, Villeneuve dAscq, France Marie Minvielle; Guillaume Saint-Girons; Romain Bachelet; Catherine Dubourdieu; Institut des Nanotechnologies de Lyon, UMR CNRS 5270, Ecole Centrale Lyon, Ecully, France
Resume : These past years, the development of neuromorphic computing has been strongly boosted by the large amount of nanoscale memory components that demonstrated the ability to realize the synaptic operation . If each technology presents different pros and cons for the implementation of synaptic functions, a common goal in order to succeed in the hardware realization of neuromorphic systems, will be their integration into high density crossbar and interfacing with a CMOS platform for neuron operation. In this work, we investigate two promising candidates for synapse implementation, namely TiO2 and HfO2 resistive switches, and study engineering solutions for their integration into crossbar. Depending on the stack of layers configuration of the device (i.e. nature, composition and thickness), different switching mechanisms can be realized, from interface switching to filamentary switching, leading to different memory performances that could benefit to synaptic operation (i.e. analog controllability, retention, ). Practically, we show how engineering solutions are a simple tool to tune the forming voltage and to make each technology suitable for crossbar integration.  F. Alibart, E. Zamanidoost, D. B. Strukov, Nature Communication, 2072, 4, 2013
Authors : Yong Tae Kim1, Minho Choi2
Affiliations : 1Semiconductor Materials and Device Lab., Korea Inst. of Sci. and Tech., Seoul, Korea: 2Department of Materials Sci. and Eng., Hanyang University, Seoul, Korea
Resume : InSbTe alloys are a promising candidate for optical and multi-level cell (MLC) phase change memory device. Among InSbTe alloys, In3SbTe2 (IST) shows multi step switching operation and excellent thermal stability. However, it is tradeoff between higher thermal stability and switching speed because for the thermally stable materials phase transformation needs higher activation energy, which may relate to switching speed. But, there is no report about the switching speed of IST. Then, switching speed test shows that the IST has serious drawback in the set/reset speeds that are slower than those of the GeSbTe (GST) by 1.5~1.7 times. To improve the set/reset switching speed of the IST, Bi atoms are doped into the IST within the maximum range of 5.5 at.%. As a result, the set switching speed of Bi doped IST is 2.6 times as fast as that of the un-doped IST, and the reset speed also shows the same trend. Effect of Bi atoms in the IST raises question that the fast phase transformation is related with the Bi atoms and optical reflectivity. Atomic lattice images are thoroughly investigated and it is found that lattice distortion is generated by the Bi atoms, which increases vacancy concentration although the crystal structure of Bi doped IST is similar to the un-doped IST that is confirmed with x-ray diffractions and Laue patterns. Microscopic analysis of Bi doped IST reveals that inter-planar distance and directions of  and [1-1-2] zone axes are changed with the concentration of Bi atoms. In this work, we will discuss the relationship among the vacancy, the activation energy, the reflectivity and the switching speed of Bi-doped IST MLC-phase change memory devices.
Authors : F. Zeng, S.Z. Li, J. Yang, H. Y. Liu, G. S. Tang and F. Pan
Affiliations : Key laboratory of Advanced Materials (MOE), School of Materials Science, Tsinghua University, 100084 Beijing, China
Resume : Mimicking synaptic functions using memristor will contribute significantly to the development of bio-inspired computing system. It is very competitive in device technique, computing method and power consumption, etc., for simply using a memristor node to replace a complex circuit having the equivalent functions. This prompts us to realize synaptic functions as many as possible using one memristor and resolve the problems met in integrating memristor arrays. We report our recent works may provide helpful ideas for constructing artificial synapse. We utilized the compounds naturally formed in the metallic electrode/polymer interfaces in these works. In the memristor structure of Ag/PEDOT:PSS/Ta, the Ag filaments formed by the bias induced the synaptic modification, while the interface compound at the PEDOT:PSS/Ta interface constructed p-n junction with PEDOT:PSS. This memristor structure enhanced the resistivity effectively, which is favorable for the memristor integration. We have successfully mimicked spike-rate-dependent-plasticity, spike-time-dependent-plasticity and learning model of stock of contacts. In the memristor structure of Ti/PEDOT:PSS/Ti, the Ti compound at the interface has contrast switching direction with PEDOT:PSS. The former has lower switching threshold. Thus, the synaptic weight increased with the stimulations under the low strength, but decreased due to the de-doping of PEDOT:PSS under the greatly culminated stimulation strength. These contrast mechanisms prevented the system from losing stability. Moreover, this structure can be expanded to the memristor systems having negative differential resistivity and resolve the competing problem in the memristor integration.
Authors : Fabrizio Cleri (1), Sergio Carrillo (1,2), Cristophe Krzeminski (2)
Affiliations : (1) IEMN, University of Lille I, 59652 Villeneuve d'Ascq, France; (2) IEMN, Departement ISEN, Blvd. Vauban, 59100 Lille, France
Resume : Recently, self-assembled networks of functionalized nano particles (NPSAN) were proposed as a prototype of innovative devices , with switchable NP-NP links. Thanks to the chemical properties of the surface molecules, these would ultimately show memristive behaviour, as building blocks of a logical computing architecture . Inspired by the experiments in [1,2], we describe the atomic structure of large (50 nm) Au NP, coated by a dense monolayer of azobenzene-bithiophene (AzBT) derivatives. We use atomic-scale simulations to address the multi scale problem of computing the electrical response of the NP-NP contact, under different biasing conditions and different switching states of the AzBT molecules. We run Molecular Dynamics simulations, with AzBT molecules linked to the surface of rigid NP, and interdigitated as a function of the NP-NP distance and molecule density. We then can compute the local conductivity of such realistic interacting configurations, by a localised tight-binding decimation method. Finally, simulating the aggregate logic response of such model NP structures is also considered. We outline a divide-and-conquer technique, to calculate the response of multiterminal networks, by recursive Green functions .  G. Wendin, et al. Int. J. Unconv. Comp., 8, 325-332 (2012)  V. Beiu et al., Procs. of ICNAAM 2012, AIP Conf. Proc. Vol. 1479, pp. 1875-1879 (2012)  C. White and A. P. Horsfield, paper I.11 Symp. I, E-MRS 2012 Fall Meeting, Warsaw
Authors : P. Bousoulas1, I. Giannopoulos1, K. Giannakopoulos2, P. Dimitrakis2, D. Tsoukalas1
Affiliations : 1Department of Applied Physics, National Technical University of Athens, Iroon Polytechniou 9 Zografou, 15780 Athens, Greece 2Institute of Microelectronics, NCSR Demokritos, Aghia Paraskevi, 15310 Athens, Greece
Resume : Resistive Random Access Memory (ReRAM) with a structure Au/TiO2-x/Au demonstrated a clear bipolar resistive switching behavior without the necessity of an initial electroforming process. The titanium oxide (TiO2-x) thin film was deposited by reactive RF magnetron sputtering at room temperature in a controlled oxygen/argon ambient1. The high density of oxygen vacancies within the film (induced by the low oxygen content) is essential component for the formation of conducting filaments and demonstration of DC or nanosecond pulsed resistance switching. Conductive Atomic Force Microscopy (C-AFM) on structures without the Au top electrode was then employed in order to investigate the nanoscale electrical properties of the device. In situ current distribution during the SET process revealed possible formation of conducting filaments while DC sweeping bias voltage revealed an OFF/ON switching ratio of about 200. We have also demonstrated that by using C-AFM both a low resistance state and a high resistance state can be written by bipolar voltage application imaged by corresponding patterns on the TiO2-x film, suggesting that oxygen ions movement at the Au coated tip/TiO2-x interface plays a critical role in the rupture of conducting filaments and thus correlating the macroscopic characteristics of our device1 with microscopic origins. Conduction mechanism analysis divulged that trap assisted tunneling governs the conduction behavior of the high resistance state, whereas as Ohms interpret well the electrical behavior of low resistance state. 1 P. Bousoulas, I. Michelakaki, and D. Tsoukalas, Influence of oxygen content of room temperature TiO2-x deposited films for enhanced resistive switching memory performance, J. Appl. Phys. 115, Article in press, (2014)
Authors : Sang-Soo Lee, Kiwon Oh, Woojin Jeon
Affiliations : Korea Institute of Science and Technology
Resume : Recently, resistance switching (RS) phenomena in a bulk polymer nanocomposite using Ag nanowires have been reported. However, the RS behavior seems to be unstable, reversible, or irreversible by cases. In this study, in order to solve the aforementioned problems, we propose a RRAM material of novel concept, which is made up of the one-dimensional resistance-switchable fillers in a polymer matrix. A nanocomposite capable of showing a resistance-switching behavior is prepared using novel resistance-switchable fillers embedded in a polymer matrix. The filler in this study employs a conformal passivation layer of highly crystalline TiO2 on surfaces of conductive Ag nanowires to effectively gate electron flows delivered through the conductive core, resulting in an excellent resistance-switching performance. A nanocomposite prepared by controlled mixing of the resistance-switchable nanowires with a polymer matrix successfully exhibited a resistance-switching behavior of highly enhanced reliability and a resistance on/off ratio, along with flexibility due to the presence of nanowires of a tiny amount. The advantages of our approach include a simple and low-cost fabrication procedure along with sustainable performances suitable for a resistance switching random-access-memory application.
Authors : G.I. Tselikov, A.V. Emelyanov, I.M. Antropov, V.A. Demin, P. K. Kashkarov
Affiliations : National Research Centre Kurchatov Institute, "Moscow Institute of Physics and Technology (State University)"; National Research Centre Kurchatov Institute; National Research Centre Kurchatov Institute; National Research Centre Kurchatov Institute, "Moscow Institute of Physics and Technology (State University)"; National Research Centre Kurchatov Institute, "Moscow Institute of Physics and Technology (State University)", Lomonosov Moscow State University.
Resume : Currently, much attention is being devoted to memory circuit elements (memristors). One of the most promise compounds for applications in memristor devices is TiOx (x≤2). In our work we investigated the electrophysical properties of Pt/TiOx/TiO2/Pt memristor elements. This structure was obtained with the use of pulsed laser deposition technique. The thickness of both TiOx and TiO2 layers was varied in the range from 10 nm to 60 nm. During the measurements we calculated the resistance of structure in low and highly conductive state (Roff and Ron respectively). It was found that the value Roff/Ron of the investigated structure nonmonotonically depends on the thickness of TiOx/TiO2 structure. It must be noted that maximum value Roff/Ron is obtained when the thickness of both TiOx and TiO2 layers equals 30 nm. It was suggested that a broad distribution of stoichiometry index inside the TiOx/TiO2 layers is responsible for observed nonmonotonic dependence. This hypothesis was further provided by the results of Auger spectrometry measurements.
Authors : Sébastien Le Beux1, Fabien Alibart2, Dominique Vuillaume2, Catherine Dubourdieu1, Ian OConnor1
Affiliations : 1. Institut des Nanotechnologies de Lyon, UMR CNRS 5270, Ecole Centrale Lyon, Ecully, France; 2. IEMN-CNRS, Boulevard Poincarre, Villeneuve dAscq, France
Resume : Among the key issues the semiconductor industry is facing are the power consumption and the die size of the interconnect in modern nanoelectronics. Crossbars of memristive devices based on resistive switching oxides are currently considered as a replacement solution for reconfigurable interconnects in Field Programmable Gate Array (FPGA)-like architectures. Nevertheless, crossbar architectures of memristive devices have significant drawbacks inherent to the large fan-in/fan-out such as power supply limitation and cross-talk between devices when one particular component needs to be addressed. In this work, we propose to evaluate the case of a matrix-based interconnect using oxide-based memristive devices. Such architecture requires smaller connectivity with respect to crossbar, thus potentially leading to a reduced complexity for memristive device operation. The set of required connections in the memristive-devices-based interconnect is defined according to the considered network topology,. e.g. butterfly. The resulting interconnect structure can be configured according to application-specific connectivity requirements.
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Authors : J. Samà 1, S. Shumovitch 2 ,O. Casals 1, J. D. Prades 1, J. Salzman 2, A. Romano-Rodríguez 1
Affiliations : 1 MIND-IN2UB-Dept. Electronics, Universitat de Barcelona (UB), Martí i Franquès 1, 08028, Barcelona, Spain; 2 Department of Electrical Engineering Technion, Israel Institute of Technology Technion City, Haifa 32000, Israel
Resume : Non volatile memories based on switchable resistance cells have emerged in the last years as an alternative to conventional technologies like Si-based flash memories. One of the most promising resistive switching devices is metal-insulator-metal (MIM) structures formed by metal oxides like TiO2 and HfO2. The switching mechanism of these devices depends on both metal electrodes and insulator. In configurations like cross-bar structures, these devices can work together as a high density non volatile memory with a low power consumption compared to current technologies. The switching resistance performance of Pt/HfO2 /Ti atomic-layer deposited (ALD) MIM devices in a cross-bar structure has been characterized. Bipolar resistive switching and non volatile memory effects have been observed. High endurance and reliability, working at low currents current (1µA) and moderate voltages (3V maximum) provides excellent features to act as a non volatile memory. Devices show a high-to-low resistance ratio larger than 103, proving the excellent quality of the device. The formation of an oxygen vacancies channel in the dielectric thanks to an inert cathode (Pt) and an oxidizable anode (Ti) can explain the reversible resistance change of the HfO2 layer, as has been reported. To complete the electrical study, impedance spectroscopy analysis has been carried out, together with physical and chemical characterization of the devices, in agreement with previously reported operation mechanisms.
Authors : F. Messerschmitt, M. Kubicek, M. Ezbiri, J. Fompeyrine, C, Marchiori, J.L.M. Rupp
Affiliations : Electrochemical Materials, ETH Zurich; Advanced Functional Materials, IBM Zurich Research Laboratory, Zurich, Switzerland
Resume : Recent advances in metal oxide-based ReRAMs revealed their powerful alternative to replace classic transistor based memories due to their fast non-volatile ns-switching and scalability. Despite the promises, a full understanding of the switching mechanism and kinetics is still missing. In this context, we discuss the carrier contribution (ionic vs. electronic) towards resistive switching on the model material Sr(Ti,Fe)O3 for which the band gap can be altered by Δ1.5eV. For this study, cross-bar memory arrays of Pt|Sr(Tix,Fe1-x)O3|Pt were fabricated and classically analyzed by cyclic & pulsed experiments with respect to oxide doping. Importantly, these classic experiments are limited to understand equilibrium vs. non-equilibrium transport since always a metastable state remains; carrier diffusion kinetics can hardly be determined. Hence, chronoamperometry measurements to analyze kinetics and the required minimum switching voltages are suggested to compare and investigate different metal oxides. Exemplarily, time constants of 200-400s (till stable currents establish) at 1-3V are measured. Through an extension of the Cottrell equation we determine bias-dependent diffusion constants of 2x10-19-9x10-20m2/s for 6-2MV/m at ambient. Further, we discuss the influence of fabrication methods by comparing epitaxial SrTiO3 thin films grown by MBE on silicon wafers to polycrystalline samples; larger HRS/LRS ratios and smaller switching voltages for decreased defect densities are observed.
Authors : Adnan Younis, Dewei Chu and Sean Li
Affiliations : School of Materials Science and Engineering, University of New South Wales, Sydney, 2052, NSW, Australia
Resume : Abstract We report various ceria based nanostructures such as; nanorods, nano-dots and nanocubes to demonstrate excellent bipolar resistive switching characteristics. Bottom up approaches, such as electrochemical deposition and solvothermal techniques have been deployed to fabricate these nanostructures. In the first approach, the vertically aligned ZnO (NR) arrays were grown on transparent conductive glass by electrochemical deposition while CeO2 quantum dots (QDs)/ nano-dots were prepared by a solvothermal method. Subsequently, the as-prepared CeO2 QDs were embedded into ZnO NRs array by dip-coating to obtain CeO2-ZnO nano-composite. Interestingly, such a device exhibits excellent resistive switching properties with much higher ON/OFF ratios, better uniformity and stability over the pure ZnO and CeO2 thin films. In a different approach, self-assembled CeO2 nanocubes based resistance switching devices were fabricated by hydrothermal process. The devices were proven to exhibit even more excellent resistive switching performance. The origin of switching behaviour on the basis of filament model and inter cube junctions was presented. Furthermore, indium (In) and Gadolinium (Gd) doped CeO2 nanocubes were also prepared to expand these nanostructures for memristive applications. The present studies demonstrate that ceria nanostructures have the potential for next generation non-volatile memory applications. Biography Mr Adnan Younis received his M.Phil in Physics from Quaid-i-Azam University Islamabad-Pakistan in 2009, where he researched high temperature superconductors in the Material Science laboratory of Dr. Nawazish Ali Khan. He is currently a PhD candidate with Prof. Sean Li and Dr. Dewei Chu in the laboratory of advanced multifunctional and energy materials at school of Material Science and Engineering, University of New South Wales Australia. His research interests involve development of metal oxides with their applications in next generation non-volatile memory devices such as resistive random access memories (RRAM).
Authors : ARITA Masashi, KUDO Masaki, OHNO Yuuki, MURAKAMI Yosuke, TAKAHASHI Yasuo
Affiliations : Hokkaido Univ., IST
Resume : Because of a possibility used as analog memories, resistive RAMs (ReRAMs) are energetically studied. Recently, they are investigated as synapses of artificial neural networks. The stacked film composed of a solid electrolyte and Cu (or Ag) is one of ReRAMs, which are believed to operate by formation and rupture of conductive filament formed in the electrolytes. However, details of the analog operation are still obscure. The combination of Cu/MoOx studied in this work is in this category. To understand some details, the switching operation was investigated dynamically by means of the TEM/STM in-situ observation. Typical results of Cu/MoOx/TiN showed the cyclic bi-polar ReRAM switching inside the TEM instrument. In the Set process, a region with dark contrast grew from the interface between MoOx and TiN. The EDX results indicated that this region contained more Cu than other regions in the MoOx layer. This region was small when the resistance changed suddenly to the low resistance state, and it grew along the Cu top electrode (TE) during subsequent current flow. Just after the weak Reset, no drastic change was recognized in the TEM image. Afterwards, it shrunk to the Cu (TE) layer. The Cu conductive filament contributes to the ReRAM switching, but it does not need to be recognizably thick. The filament became large with high compliance current. The filament position connecting TE and BE was not fixed.
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