Collective capacitive and memristive responses in random nanowire networks: Emergence of critical connectivity pathways

PUBLISHED ; Random nanowire networks (NWNs) are promising synthetic architectures for non-volatile memory devices and hardware-based neuromorphic applications due to their history-dependent re- sponses, recurrent connectivity, and neurosynaptic-like behaviours. Such brain-like functions occur due to emergent resistive switching phenomena taking place in the interwire junctions which are viewed as memristive systems; they operate as smart analogue switches whose resistance depends on the history of the input voltage/current. We successfully demonstrated that NWNs made with a particular class of memristive junctions can exhibit a highly-selective conduction mechanism which uses the lowest-energy connectivity path in the network identified as the ?winner-takes-all? state. The complex and adaptive behaviour of these junctions lead the system to channel the current through a single conductive path that spans the source-drain electrodes sandwiching the NWN. But these complex networks do not always behave in the same fashion; in the limit of sufficiently low input currents (preceding this selective conduction regime), the system behaves as a leakage capacitive network and its electrical activation is driven by cascades of breakdown-based switch- ing events involving binary capacitive transitions. Understanding these two regimes is crucial to establish the potential of these materials for neuromorphics and for this we present two computa- tional modelling schemes designed to describe the capacitive and memristive responses of NWNs interrogated adiabatically by voltage/current sources. In particular, our capacitive network model is regarded as a parallel RC circuit, with a leakage current term, to simulate their non-ideal ca- pacitive properties. Our findings reveal the fault-tolerant aspect in the slow-switching dynamics of memristive networks in contrast with the abrupt activation response obtained in the fast-switching process of binary capacitive networks. Our results are corroborated by experimental evidence that ...