Abstract
Nanometer-scale resistive switching devices operated in the metallic conductance regime offer ultimately scalable and widely reconfigurable hardware elements for novel in-memory and neuromorphic computing architectures. Moreover, they exhibit high operation speed at low power arising from the ease of the electric-field-driven redistribution of only a small amount of highly mobile ionic species upon resistive switching. We investigate the memristive behavior of a so-far less explored representative of this class, the Ag/AgI material system in a point contact arrangement established by the conducting PtIr tip of a scanning probe microscope. We demonstrate stable resistive switching duty cycles and investigate the dynamical aspects of non-volatile operation in detail. The high-speed switching capabilities are explored by a custom-designed microwave setup that enables time-resolved studies of subsequent set and reset transitions upon biasing the Ag/AgI/PtIr nanojunctions with sub-nanosecond voltage pulses. Our results demonstrate the potential of Ag-based filamentary memristive nanodevices to serve as the hardware elements in high-speed neuromorphic circuits.
Highlights
Large crossbar arrays of transition-metal-oxide-based filamentary RRAM devices operated in the metallic conductance regime of 102–104Ω have been successfully utilized recently to perform various linear operations relying on hardware-implemented vector–matrix multiplication [10,11,12]
In this paper we explore the dynamical properties of room-temperature resistive switching established in metallic Ag/AgI/PtIr nanojunctions
Memristive nanojunctions were created by approaching a mechanically sharpened PtIr tip of a custom-built scanning tunneling microscope (STM) to the AgI-coated thin film structure schematically illustrated in the lower inset of Figure 1a
Summary
The half a century long increase of the computational capacity of von Neumann architectures built on ever-shrinking complementary metal-oxide semiconductor (CMOS)-based hardware units is facing its technological, economical and fundamental barriers: (i) Further miniaturization of the CMOS transistors below 10 nm channel length is technologically extremely demanding and cost-inefficient. (ii) Their digital operation is not sustainable below the scale of the Fermi wavelength, which is typically ca 10 nm in layered semiconductors. (iii) the so-called von Neumann bottleneck, i.e., the bandwidthlimited and power-hungry permanent data transfer between the physically separated processing, memory and permanent storage units prevents the large-scale establishment of autonomous, energy-efficient “internet of things (IoT)” hardware solutions [1].Two-terminal, non-volatile resistance-change memory devices (RRAMs) [2,3,4], the operation of which relies on controllable, electric-field-induced structural changes in an electronically insulating ionic conductor medium, offer a viable alternative to intrinsically overcome the above limitations: (i) Due to their self-assembled, filamentary nature, the macroscopically observable conductance features of the devices are determined by lithographically inaccessible, metallic volumes close to the atomic scale. (ii) The Fermi wavelength in these filaments falls in the regime of the interatomic distances granting metallic conductance in this ultimate scaling limit. (iii) The device conductance is largely determined by the rearrangement of only a few atoms in this narrowest cross section, which can take place at a very large bandwidth and unprecedentedly low energy cost [5,6,7,8,9]. In order to challenge device operation in AgI-based nanoswitches down to sub-nanosecond timescales for the first time, a special purpose pulsed microwave setup was developed and successfully utilized to fire 500 ps long set/reset voltage pulses and acquire the resulting resistive switching at 1 GHz bandwidth.
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