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Memrisys 2017


  • InterContinental Athenaeum Athens 93 Leof. Andrea Siggrou Athina, 117 45 Greece (map)

The MemoCIS EU cost action organized the International Conference on Memristive Materials, Devices & Systems (MEMRISYS) in the city of Athens, Greece, from 3-6 April 2017. 

MEMRISYS 2017 aims providing a timely discussion on Memristor Technologies presenting the latest developments across a wide range of fields: from materials to devices, circuits, systems and applications. The impact of this topic is showcased by the ever-increasing number of publications in topical journals and conference proceedings as well as the numerous targeted workshops and symposia organised. The need for more transdisciplinary interactions is however acknowledged for further progressing the state-of-art. MEMRISYS 2017  addressed this need by consolidating the underlying research communities in materials science, electron devices, circuits and systems, computation and neuromorphic engineering in a single international conference that will bring a new holistic view of developments in the field.

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Several authors of Neuromimetics network presented some of their recent results in this thematic conference.

Jordi Suñé from UAB neuromorphic presented some results on RRAM characterization in collaboration with CEA-LETI (Grenoble, France) in the framework of the PANACHE project (ENIAC JU) and results on volume switching in complex oxides, in collaboration with the Institute of Materials Science of Barcelona (ICMAB) .

Volume Resistive Switching in a Three-Terminal CeO2-x/La0.8Sr0.2MnO3 device

J. Suñé1*, R. Ortega-Hernández1,2, M.Coll2, J. C. González-Rosillo2, A. Palau2, X. Obradors2, E.Miranda1, and T. Puig2

1Department d’Enginyeria Electrònica, Universistat Autonoma de Barcelona, 08193-Bellaterra, SPAIN

2Institut de Ciència de Materials de Barcelona, CSIC, Campus UAB, 08193-Bellaterra, SPAIN

*Corresponding author Email: Jordi.Sune{at}uab{dot}cat

Abstract
An Ag/CeO 2-x / La 0.8 Sr 0.2 Mn O3 /CeO 2-x /Ag structure showing bipolar Resistive Switching (RS), see Fig. 1, has been used to change the resistance of a La 0.8 Sr 0.2 MnO 3 (LSMO) conductive track in a non-volatile, tunable manner, as shown in Fig. 2. LSMO volume RS effects due to Metal to Insulator Transition (MIT) were demonstrated with conductive- Atomic Force Microscopy (c-AFM) 1 and with micrometer-scale metallic probes2. However, building useful electron devices, with deposited or sputtered metallic electrodes, requires a cap layer of an oxygen-scavenging material. CeO 2-x , that easily exchanges oxygen ions with LSMO, allows inducing the direct and reverse MIT during the set/reset transitions, respectively 2 . Our results demonstrate that RS in these devices is due to a homogeneous phenomenon extended over the 40nm LSMO layer thickness and it is not produced by localized conducting filaments (CFs). This conclusion is supported by previous volume RS effects reported in thin (10nm) La 0.7 Sr 0.3 MnO 3 layers using c-AFM 1 . To demonstrate this, we report the fabrication of a three terminal (3T) gate-controlled device in which the current conduction along the LSMO track connected by two electrodes is modulated by inducing non-volatile RS in a finite portion of the track using a gate electrode. We have also found similar results in other perovskites such as YBa 2 Cu 3 O7-δ (YBCO) and NdNiO 3 (NNO), which behave as mixed electronic-ionic conductors and show MIT. Our results demonstrate a new class of RS (volume switching as opposed to interface or filamentary switching) and opens the possibility of fabricating 3T memristive devices with enhanced potentiality. 3

Characterization and modelling of HfO2-based devices showing

J. Suñé1, A. Rodriguez-Fernandez1, C. Cagli2, L. Perniola2, and E. Miranda1

1Departament d’Enginyeria Electrònica, Universitat Autònoma de Barcelona, 08193-Bellaterra, SPAIN

2CEA, LETI,MINATEC Campus, Grenoble, France

*Corresponding author Email: Jordi.Sune{at}uab{dot}cat

Abstract
A complete characterization of Resistive Switching (RS) Ti/HfO 2 (10nm)/TiN devices fabricated at LETI was performed with the final goal of extracting the parameters of a new behavioral model aimed at SPICE simulation. To prevent irreversible cell breakdown and to control the low resistance state (LRS) resistance, a N-MOS transistor is used in series with the ReRAM device, embodying a 1T1R cell. Devices exhibit the typical bipolar resistive switching behavior with SET/RESET depending logarithmically with voltage ramp rate in quasistatic stress conditions. The compliance current, on-resistance and reset current are successfully adjusted by changing the transistor gate voltage VG (see Fig.1). Off-resistance controllable multiple states can be achieved by changing the maximum reset voltage. Constant voltage experiments reveal exponential dependence on pulse voltage amplitude, consistent with dielectric breakdown dependence. Resistance ratio can be adjusted during pulse measurements by changing pulse amplitude (Fig.2) and pulse time duration (results not shown). Endurance depends on stress conditions, >100 Mcycles were demonstrated with V PULSE =1.25V and t RESET =t SET =10µs. Second order memristive effects 1,2 are also found, mainly represented by the fact that the R OFF /R ON ratio depends on stress history (Fig.2). The behavioral model for the conduction characteristic of bipolar RRAM devices is based on a diode-like structure with hysteretic properties introduced via a logistic hysteron relying on the Krasnoselskii-Pokrovskii operator. When implemented in LT-SPICE, the model is able to deal with arbitrary input signals and the simulations include a physics-based model for statistical variations. The model is successfully applied to the case of 1T1R structures with the parameters extracted for the LETI technology.