Evolution and modulation of Ag filament dynamics within memristive devices based on necklace-like Ag@TiO₂ nanowire networks

Abstract

Random nanowire networks (NWNs) are regarded as promising memristive materials for applications in information storage, selectors, and neuromorphic computing. The further insight to understand their resistive switching properties and conduction mechanisms is crucial to realize the full potential of random NWNs. Here, a novel planar memristive device based on necklace-like structure Ag@TiO2 NWN is reported, in which a strategy only using water to tailor the TiO2 shell on Ag core for necklace-like core-shell structure is developed to achieve uniform topology connectivity. With analyzing the influence of compliance current on resistive switching characteristics and further tracing evolution trends of resistance state during the repetitive switching cycles, two distinctive evolution trends of low resistance state failure and high resistance state failure are revealed, which bear resemblance to memory loss and consolidation in biological systems. The underlying conduction mechanisms are related to the modulation of the Ag accumulation dynamics inside the filaments at cross-point junctions within conductive paths of NWNs. An optimizing principle is then proposed to design reproducible and reliable threshold switching devices by tuning the NWN density and electrical stimulation. The optimized threshold switching devices have a high ON/OFF ratio of ~107 with threshold voltage as low as 0.35 V. This work will provide insights into engineering random NWNs for diverse functions by modulating external excitation and optimizing NWN parameters to satisfy specific applications, transforming from neuromorphic systems to threshold switching devices as selectors.

Self-Assembled Monolayer and Nanoparticles Coenhanced Fragmented Silver Nanowire Network Memristor

“…30,31 The variation in threshold voltages, high-resistance state (HRS) failure, or switching failure can be ascribed to the above phenomenon. 21 At smaller compliance currents, the fracture of slim Ag CFs at junctions is dominated by surface atom self-diffusion. 29 However, surface Ag atoms tend to diffuse to the junctions due to the Gibbs−Thomson effect.…”

“…31,32 When the accumulated atoms coarsen the CFs to some extent, nonvolatile switching or ohmic contact is triggered. 21 Moreover, it is difficult to reset the CFs by an inverse voltage due to the symmetrical structure of the NWstacked junction. As a consequence of the above issues, large variations in threshold voltage, switching failure, and poor cycling durability occur, which may account for the restricted developments of integrated neuron and synapse memristors based on AgNW networks.…”

“…Therefore, Ag core-insulative shell NWs are generally used to fabricate random AgNW networks with high-density MIM junctions. Endeavors have been devoted to interface engineering of AgNWs, mainly producing core–shell NWs of AgNW-AgO x , AgNW-TiO 2 , AgNW-TiO 2 NPs, Ag-NiO, AgNW-PVP, , etc. Threshold switching (TS) in resistance with ON–OFF ratios of 10 2 –10 7 has been demonstrated in these core–shell NWs under external electrical bias, which arises from the formation/rupture of conductive filaments at cross-point junctions.…”

“…However, such formation and fracture of CFs are unstable. At large compliance currents to induce nonvolatile switching, local enhanced Joule heating and electromigration are generated at the nanoscale cross-points and heterogeneous network, resulting in welded junctions or NW fragmentations. , The variation in threshold voltages, high-resistance state (HRS) failure, or switching failure can be ascribed to the above phenomenon . At smaller compliance currents, the fracture of slim Ag CFs at junctions is dominated by surface atom self-diffusion .…”

“…The endurance performance of the AgNS-NP/SAM: (f) retention measurements of the device with a reading voltage of 0.1 V, and the sampling interval is 10 5 s; pulse measurements results of (g) AgNS-NP and (h) AgNS-NP/SAM. (i) Comparison of the memory window and cycle of the AgNS-NP/SAM and previously reported AgNW memristors, including AgNW/AgOx core−shell (CS)15 , Ag/NiO core−shell,21 AgNW@AgO X ,18 AgNW@PVP,22 AgNW-PVDF,26 and PI/AgNWs/TiO 2 /PI 19.…”