Memory Devices Based on Solid Electrolytes

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0997-I05-01

Memory Devices Based on Solid Electrolytes Michael N Kozicki Center for Applied Nanoionics, Arizona State University, Box 876206, Tempe, AZ, 85287-6206

ABSTRACT 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. INTRODUCTION The semiconductor industry has acknowledged that it faces ever-increasing difficulty in attaining the goals set forth in the International Technology Roadmap for Semiconductors [1]. The Roadmap states that the problems associated with physical and operational scaling are particularly acute for solid state memory, where current mainstream charge storage technologies have a very doubtful existence in anything like their current form as we move beyond the 32 nm node. The scaling quandary has led to an avalanche of alternative memory technologies and particularly of those that rely on resistance change mechanisms. A wide variety of efforts has been highlighted in the technical literature but even though investment has been significant in the most promising cases, no new technology has been universally adopted by the industry, mostly due to non-scalable operational characteristics. This has kept the door open for new contenders. One such new technology is resistance change memory based on solid electrolytes. A number of semiconductor companies and research institutions are developing resistance change devices that utilize a variety of solid electrolytes and mobile ions. The lowering of the resistance is attained by the reduction of ions in the 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 (or in some cases a high-current forward bias) that results in the breaking of the metallic