Memristive devices based on single ZnO nanowires—from material synthesis to neuromorphic functionalities

Abstract

Memristive and resistive switching devices are considered promising building blocks for the realization of artificial neural networks and neuromorphic systems. Besides conventional top-down memristive devices based on thin films, resistive switching devices based on nanowires (NWs) have attracted great attention, not only for the possibility of going beyond current scaling limitations of the top-down approach, but also as model systems for the localization and investigation of the physical mechanism of switching. This work reports on the fabrication of memristive devices based on ZnO NWs, from NW synthesis to single NW-based memristive cell fabrication and characterization. The bottom-up synthesis of ZnO NWs was performed by low-pressure Chemical Vapor Deposition (LPCVD) according to a self-seeding Vapor-Solid (VS) mechanism on a Pt substrate over large scale (∼ cm2), without the requirement of previous seed deposition. The grown ZnO NWs are single crystalline with wurtzite crystal structure and are vertically aligned respect to the growth substrate. Single NWs were then contacted by means of asymmetric contacts, with an electrochemically active and an electrochemically inert electrode, to form NW-based electrochemical metallization memory (ECM) cells that show reproducible resistive switching behaviour and neuromorphic functionalities including short-term synaptic plasticity and Paired Pulse Facilitation (PPF). Besides representing building blocks for NW-based memristive and neuromorphic systems, these single crystalline devices can be exploited as model systems to study physicochemical processing underlaying memristive functionalities thanks to the high localization of switching events on the ZnO crystalline surface.

Experimental and Modeling Study of Metal–Insulator Interfaces to Control the Electronic Transport in Single Nanowire Memristive Devices

“…Single NW memristive cells were realized by contacting single-crystalline and hexagonal-shaped ZnO NWs (diameter of ∼100 nm) grown by low-pressure chemical vapor deposition (LP-CVD) with metal electrodes through a combined optical and electron beam lithography (EBL), as detailed in our previous works − (details of the ZnO NW synthesis and device fabrication can be found in the Experimental Section). Concerning device scalability, it is worth noticing that the ZnO NW diameter can be further reduced by exploiting peculiar growth strategies that allows the growth of ZnO NWs with diameters below 10 nm, as for example reported by Yin et al that exploited a catalyst-assisted growth technique.…”

“…A two-step electron beam lithography and metal deposition were performed to obtain asymmetrically contacted NW-based memrsitive cells. A detailed description of the synthesis of ZnO NWs and fabrication steps of single NW devices can be found in our previous work …”

“…A detailed description of the synthesis of ZnO NWs and fabrication steps of single NW devices can be found in our previous work. 46 Electrical Characterization. Electrical characterization was performed in two-terminal configuration by a Keithley 6430 subfemtometer sourcemeter with a remote preamplifier, a Keithley 2636A, and a probe station.…”

Recent advances in morphologically controlled synthesis of graphene oxide‐based nanocomposite as catalyst and fuel additive

“…[44] Milano et al has prepared the ZnO nanowires. [45] Various researcher and scientist have tried to fabricate the defined morphologies of ZnO by hydrothermal and solvothermal techniques but the fabricated product of ZnO mostly aggregates.…”

Simulating the filament morphology in electrochemical metallization cells

“…The CF can either short circuit both electrodes, or a nanometer wide gap remains between the CF and one of the electrodes, enabling the flow of electronic tunneling currents [6,12]. Formation of a quantum point contact is also possible [13][14][15]. The CF reduces the resistance of the device and therefore this effect is called SET.…”