Processes and Limitations during Filament Formation and Dissolution in GeSx-based ReRAM Memory Cells

摘要

The SET and RESET switching kinetics of Ag-GeSx-based ECM memory cells are experimentally investigated. The results were qualitatively and quantitatively reproduced by our simulation model, accounting for a tunneling gap between the tip of the growing filament and the active electrode. Key processes are the nucleation, the electron transfer at the interfaces, and ionic hopping in the electrolyte. Current-voltage sweeps and pulse measurements were used to study the switching kinetics with respect to variety of factors like voltage, current, resistance, time, electrolyte thickness, and stoichiometry. Multilevel operations through the adjustability of the ON resistance by current compliance and sweep rate were confirmed. The SET kinetics for low voltages was limited by the nucleation process. SET time and SET voltage strongly depend on the Ag-ion normalized concentration in the electrolyte. The RESET behavior was mostly independent of the current compliance and the ON resistance. However, lower ON resistances require higher RESET currents but at the same time the RESET time was independent of the ON resistance for nearly 2 orders of magnitude. By pulsed measurements of the RESET kinetics two voltage ranges in the RESET time versus RESET voltage behavior were identified for the first time. Limiting factors in these two ranges were found to be the electron transfer and the ion migration for low and high voltages, respectively.