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Memristors with diffusive dynamics as synaptic emulators for neuromorphic computing

Abstract

The accumulation and extrusion of Ca2+ in the pre- and postsynaptic compartments play a critical role in initiating plastic changes in biological synapses. To emulate this fundamental process in electronic devices, we developed diffusive Ag-in-oxide memristors with a temporal response during and after stimulation similar to that of the synaptic Ca2+ dynamics. In situ high-resolution transmission electron microscopy and nanoparticle dynamics simulations both demonstrate that Ag atoms disperse under electrical bias and regroup spontaneously under zero bias because of interfacial energy minimization, closely resembling synaptic influx and extrusion of Ca2+, respectively. The diffusive memristor and its dynamics enable a direct emulation of both short- and long-term plasticity of biological synapses, representing an advance in hardware implementation of neuromorphic functionalities.

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Figure 1: Highly nonlinear, fast and repeatable threshold switching behaviours of diffusive memristors.
Figure 2: In situ TEM observation of the threshold switching process suggesting the relaxation is a diffusion process driven by interfacial energy minimization.
Figure 3: Timing characteristics of SiOxNy:Ag diffusive memristor.
Figure 4: Simulated operation of a diffusive memristor device.
Figure 5: Schematic illustration of the analogy between Ca2+ and Ag dynamics, and short-term synaptic plasticity of the diffusive memristor.
Figure 6: Bio-realistic long-term plasticity.

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Acknowledgements

This work was supported in part by the US Air Force Research Laboratory (AFRL) (Grant No. FA8750-15-2-0044), the Intelligence Advanced Research Projects Activity (IARPA) (contract 2014-14080800008), US Air Force Office for Scientific Research (AFOSR) (Grant No. FA9550-12-1-0038), and the National Science Foundation (NSF) (ECCS-1253073). Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of AFRL. Part of the device fabrication was conducted in the clean room of the Center for Hierarchical Manufacturing (CHM), an NSF Nanoscale Science and Engineering Center (NSEC) located at the University of Massachusetts Amherst. The TEM work used resources of the Center for Functional Nanomaterials, which is a US DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704. The authors thank M. McLean for useful discussions on computing.

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J.J.Y. conceived the concept. J.J.Y., Q.X., Z.W. and S.J. designed the experiments. Z.W. fabricated the devices and S.J. performed electrical measurements. S.E.S. performed the simulation. H.L.X. carried out the in situ TEM characterizations. H.J., R.M., P.L., M.H., N.G., J.P.S., Z.L., Q.W., M.B., G.-L.L. and R.S.W. helped with experiments and data analysis. J.J.Y., Q.X., Z.W., S.J., S.E.S. and R.S.W. wrote the paper. All authors discussed the results and implications and commented on the manuscript at all stages.

Corresponding authors

Correspondence to Zhongrui Wang, Saumil Joshi or J. Joshua Yang.

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Wang, Z., Joshi, S., Savel’ev, S. et al. Memristors with diffusive dynamics as synaptic emulators for neuromorphic computing. Nature Mater 16, 101–108 (2017). https://doi.org/10.1038/nmat4756

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