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Abstract: Theoretical impedance relationships in a limiting process with non-steady-state surface diffusion were derived based on the interfacial conductivity concept at the interface between an oxygen ion conductor and a metallic electrode. While the non-steady-state surface diffusion of adsorbed neutral oxygen on the metallic electrode could be described by Fick's second law, approximated and equivalent equations to the Warburg impedance and Gerischer impedance were derived according to the boundary conditions and occurrence of dissipation by the chemical reaction. The diffusion related to the electrochemical impedance signal is not the diffusion of the oxygen ions. In addition, it is not necessary to assume an electrochemical potential gradient or profile of the free electrons in the metallic electrode. The relationships obtained in this paper indicate that electrochemical potential measured by an instrument is clearly defined by the electrochemical potential of free electrons at the triple phase boundary. The meaning of the equivalent electrical circuits corresponding to the impedance spectra is reconsidered from the view points of the interfacial conductivity concept. [Copyright &y& Elsevier]

Bipolar resistance switching (BRS) behavior and the effects of atmosphere (air, vacuum, O2 gas, or N2 gas) on BRS behavior occurred in the top and bottom interfaces in the M(top electrode)/WO3-x/Pt(bottom electrode) (M = Pt, Au) devices were investigated. Stable BRS only can be obtained in the interface with Pt electrode. And, the top Pt/WO3-x interface exhibited stable BRS only in an oxygen-rich atmosphere (air and O2 gas). In contrast, the bottom WO3-x/Pt interface showed stable BRS under any atmosphere. Based on the x-ray photoelectron spectroscopy measurement on Pt, Au/WO3-x interfaces, it is identified that the oxygen migration process during resistance switching mainly occurs between the Pt/WO3-x interface and Pt electrode. [ABSTRACT FROM AUTHOR]

Atomic switches are nanoionic devices that control the diffusion of metal cations and their reduction/oxidation processes in the switching operation to form/annihilate a metal atomic bridge, which is a conductive path between two electrodes in the on-state. In contrast to conventional semiconductor devices, atomic switches can provide a highly conductive channel even if their size is of nanometer order. In addition to their small size and low on-resistance, their nonvolatility has enabled the development of new types of programmable devices, which may achieve all the required functions on a single chip. Three-terminal atomic switches have also been developed, in which the formation and annihilation of a metal atomic bridge between a source electrode and a drain electrode are controlled by a third (gate) electrode. Three-terminal atomic switches are expected to enhance the development of new types of logic circuits, such as nonvolatile logic. The recent development of atomic switches that use a metal oxide as the ionic conductive material has enabled the integration of atomic switches with complementary metal-oxide-semiconductor (CMOS) devices, which will facilitate the commercialization of atomic switches. The novel characteristics of atomic switches, such as their learning and photosensing abilities, are also introduced in the latter part of this review. [ABSTRACT FROM AUTHOR]

Atomic switch, operating by forming and dissolving a metal-protrusion in a nanogap, shows an exponentially large bias dependence and a faster switching with increasing temperature and decreasing off-resistance. These major characteristics are explained with a simple model where the electrochemical potential at the subsurface of solid-electrolyte electrode determines the precipitation rate of metal atoms and the electric-field in the nanogap strongly affects the formation of metal-protrusion. Theoretically calculated switching time, based on this model, well reproduced the measured properties of a Cu2S-based atomic switch as a function of bias, temperature and off-resistance, providing a significant physical insight into the mechanism. [ABSTRACT FROM AUTHOR]

Quantized conductance was observed in a cation-migration-based resistive switching memory cell with a simple metal–insulator–metal (MIM) structure using a thin Ta2O5 layer. The observed conductance changes are attributed to the formation and dissolution of a metal filament with an atomic point contact of different integer multiples in the Ta2O5 layer. The results demonstrate that atomic point contacts can be realized in an oxide-based MIM structure that functions as a nanogap-based atomic switch (Terabe et al 2005 Nature433 47). By applying consecutive voltage pulses at periodic intervals of different times, we also observed an effect analogous to the long-term potentiation of biological synapses, which shows that the oxide-based atomic switch has potential for use as an essential building block of neural computing systems. [ABSTRACT FROM AUTHOR]