Arsenic-free Ge-Te-based ovonic threshold switching material with reduced leakage current

There is growing interest in next-generation semiconductor memory that combines high speed, large capacity, and non-volatility. Many types of emerging memory technologies, such as PCRAM and MRAM, are being developed utilizing 3D crossbar array structures to achieve high integration. In this type of structure, selectors are essential for blocking sneak current that bypasses cells during read operations. Additionally, selectors have been applied for processing, such as neuromorphic computing. As selectors, ovonic threshold switching (OTS) materials with a large ON/OFF current ratio and high amorphous stability are required. Additionally, it is crucial to design OTS materials without using highly toxic substances such as arsenic. Herein, we demonstrate that an Ag-Ga-Ge-Te (AGGT) amorphous film exhibits threshold switching with a large ON/OFF current ratio, rendering it an effective switching material for non-volatile memory. Ga was found to reduce the leakage current in the OFF state because the enhancement of ionicity lowered carrier mobility. Ag improved amorphous stability, leading to high endurance. Moreover, we determined that the co-addition of Ag and Ga to Ge-Te modifies the conduction mechanism from bulk-dominated to interface-dominated conduction. Overall, our results suggest that stronger ionicity and enhanced amorphous stability are key for developing superior selector materials. These findings are completely different from those associated with reported selector materials in which high covalency is a critical factor. Therefore, we believe that AGGT amorphous films represent a completely new paradigm for designing OTS materials. Furthermore, they can contribute to improving the performance and practicality of next-generation semiconductor memory and processing.