Reversible migration of silver on memorized pathways in Ag-Ge40S60 films

Abstract

Reversible and reproducible formation and dissolution of silver conductive filaments are studied in Ag-photodoped thin-film Ge 40 S 60 subjected to electric fields. A tip-planar geometry is employed, where a conductive-atomic-force microscopy tip is the tip electrode and a silver patch is the planar electrode. We highlight an inherent "memory" effect in the amorphous chalcogenide solid-state electrolyte, in which particular silver-ion migration pathways are preserved "memorized" during writing and erasing cycles. The "memorized" pathways reflect structural changes in the photodoped chalcogenide film. Structural changes due to silver photodoping, and electrically-induced structural changes arising from silver migration, are elucidated using Raman spectroscopy. Conductive filament formation, dissolution, and electron (reduction) efficiency in a lateral device geometry are related to operation of the nano-ionic Programmable Metallization Cell memory and to newly emerging chalcogenide-based lateral geometry MEMS technologies. The methods in this work can also be used for qualitative multi-parameter sampling of metal/amorphous-chalcogenide combinations, characterizing the growth/dissolution rates, retention and endurance of fractal conductive filaments, with the aim of optimizing devices. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Conductive bridging random access memory—materials, devices and applications

“…More significantly, E o in equation (7) must be less than 0.1 eV following conditioning to attain sub-20 ns switching. We believe this reduction in E o occurs along the region where the filament forms because the initial filament growth permanently 'opens-up' the electrolyte structure in this volume, thereby reducing the strain term and facilitating preferential regrowth along the same pathway in subsequent cycles [104]. E o in the surrounding material will not be affected and so other locations in the electrolyte will not be favored for filament formation during repeated programming.…”

“…This type of modeling is critical for expanding use of CBRAM in circuit applications, from NVM to neuromorphic systems. Although Monte Carlo methods have been shown to effectively model particular aspects of metal transport and filament formation [88,104], these statistical models are not easily mapped into the compact models necessary for circuit design. Compact models are built from closed form analytical functions that are best derived from device physics.…”

Communication—Impact of Filament Instability in an Ag2S-Based Conductive-Bridge RAM for Cross-Point Selector Applications

“…As a result, the dendritic shaped conductive filament mainly composed of Ag atoms forms inside the Ag 2 S material, as depicted in the right panel of Figure 1. 11 When a negative bias is applied to the TE, the formed conductive filament begins to rupture because of oxidation of the Ag atoms (Ag → Ag + + e − ). Based on this principle, the amount of Ag atoms used to compose the filament in the Ag 2 S material could be modulated by I comp during the SET process (HRS to LRS).…”

Preferred location for conducting filament formation in thin-film nano-ionic electrolyte: study of microstructure by atom-probe tomography

“…The nanocolumns become relatively Ag-rich during the photodoping, grow through the a-Ch thin film; in this case the Ag + ions migrate towards the cathode, enabling the metallic CF to grow from the cathode towards the anode. The CFs are estimated to be some tens of nanometers wide and are often in the form of a cone based on the cathode [2], unlike the dendritic shape observed for CF growth on samples with lateral geometry [8]. Erasing occurs by dissolution of the CF on reversing the polarity, leading to the high-resistance OFF state.…”