Observation and characterization of memristive silver filaments in amorphous zinc-tin-oxide
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Research Letter
Observation and characterization of memristive silver filaments in amorphous zinc-tin-oxide Hiep N. Tran, School of Engineering, RMIT University, GPO Box 2476V, Melbourne VIC 3001, Australia Thomas J. Raeber, School of Science, RMIT University, GPO Box 2476V, Melbourne VIC 3001, Australia Zijun C. Zhao, and David R. McKenzie, School of Physics, The University of Sydney, NSW 2006, Sydney, Australia Anthony S. Holland, School of Engineering, RMIT University, GPO Box 2476V, Melbourne VIC 3001, Australia Dougal G. McCulloch, Billy J. Murdoch, and Jim G. Partridge, School of Science, RMIT University, GPO Box 2476V, Melbourne VIC 3001, Australia Address all correspondence to Hiep N. Tran at [email protected] (Received 17 May 2018; accepted 27 July 2018)
Abstract Lateral memristors consisting of planar Ag electrodes (with sub-micrometer separation) supported on thin films of amorphous zinc-tin-oxide have been characterized. After an initial filament-forming process, each device exhibited volatile, resistive switching. In the low resistance state, the transport mechanism and conductance depended on prior activity and on the imposed current limit, mimicking biologic synaptic plasticity. Microscopic observations performed on each device revealed nanoscale filaments between the electrodes. These filaments were subject to Rayleigh instability and exhibited relaxation times determined by their effective radii. The relaxation times and on:off resistance ratios suggest suitability for threshold switching selector devices.
Introduction Amorphous oxide semiconductors (AOS) can be deposited over large areas with uniform structural and electrical properties.[1] These materials have received considerable research and industry attention, largely due to optical and electronic properties that make them suitable for transparent thin film transistors (TFTs), a building block for many types of display and interactive electronics.[1] Their flexibility and applicability to wearable electronics has also been demonstrated by numerous research groups.[1,2] The application of AOS in devices other than transistors, notably memristors and resistive random access memory, is gaining interest. For these devices, the oxide is typically inserted between metallic electrodes to form metal–insulator– metal structures, a two-terminal architecture well suited to implementation within three-dimensional arrays. Combining memristors and transistors for advanced neuromorphic circuits is an exciting prospect and self-programming capabilities have already been demonstrated using Si-based devices.[3] If these devices and circuits were based on AOS, then transparency, simplified fabrication, and/or flexibility would be added benefits. Indium-gallium-zinc-oxide (IGZO) is currently the dominant transparent AOS for TFTs but amorphous zinc-tin-oxide (a-ZTO) is a low-cost indium-free alternative. Thin films of a-ZTO have been deposited using numerous methods including chemical vapor deposition,[4] conventional physical vapor deposition (PVD),[5] and plas
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