Memory devices based on solid electrolytes

Current mainstream memory technologies are unlikely to completely fulfill the solid state data storage requirements that will be imposed beyond the 32 nm node of the International Technology Roadmap for Semiconductors. One potential replacement technology is resistance change memory based on solid electrolytes and a number of significant research and development efforts are already underway. The lowering of the resistance is attained by the reduction of ions in a relatively high resistivity electrolyte to form a conducting bridge between the electrodes. The resistance is returned to the high value via the application of a reverse bias that results in the breaking of the conducting pathway. Germanium chalcogenides and Ag-Ge-S ternaries in particular possess good thermal processing characteristics while maintaining the necessary high ion mobility for rapid switching. Thermally diffused copper in deposited SiO₂ also is of interest, as thermal stability in excess of 600°C and commonly used constituents makes this material system compatible with the widest range of back-end-of-line processes. This paper details some of the developments in the understanding of the materials used in solid electrolyte resistance change devices and presents a short review of the electrical characteristics of devices based on Ag-Ge-S and Cu-Si-O electrolytes.