Faradaic currents and ion transfer numbers in electrochemical atomic switches

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The operating mechanism of the resistive switches, namely the formation and annihilation of a metal filament, is understood to be based on the oxidation and reduction of metal atoms (ions) in the solid-electrolyte materials. However, a variety of phenomena in the switching operation, such as migration of metal ions in materials, oxidation and reduction processes at interfaces between a solid-electrolyte and a metal electrode, are not yet revealed on the atomistic level. These fundamental understandings are essential for clarifying the ultimate physical limits of down-scaling of actual nanodevices. In addition, the physics of the resistive switches should be established prior to introducing these radically new devices into nowadays semiconductor circuits. Because the operating mechanism is much different from that of semiconductor devices, adequate analytical methods and models for calculations are also required to be newly developed.In the project, ionic transfer and oxidation/reduction of metal ions are studied with respect to materials used as ionic conductors and electrodes, to device structures, to forming and operating conditions, and so on. To reveal the main phenomena in the switching, i.e., diffusion and oxidation/reduction processes, the Faradaic transfer number is measured as a key parameter to understand the whole switching process.