Thermal atomic layer deposition of ternary Ge-S-Se alloy for advanced ovonic threshold switch selectors in three-dimensional cross-point memory array

Abstract

Two-terminal ovonic threshold switch (OTS) selectors based on chalcogenide alloys have attracted significant attention as alternatives to conventional silicon-based transistors. These selectors offer outstanding features that enable the mass production of three-dimensional cross-point arrays for advanced memory technologies. In this study, we developed a thermal atomic layer deposition (ALD) process for ternary Ge-S-Se alloys. By utilizing ALD super-cycles of Ge-Se and Ge-S, a broad range of film compositions can be achieved. We investigated the electrical characteristics and film properties of the deposited films, with a focus on their smooth surfaces and excellent conformality, which are indispensable characteristics for future vertical cross-point structures. By incorporating S into the Ge-Se film via an ALD super-cycle, we achieved a significant reduction in off-current of Ge0.50S0.15Se0.35 to approximately 35 nA. Additionally, the thermal stability of Ge0.50S0.15Se0.35 film is enhanced up to 420 ℃ due to the higher bandgap and shorter bonding length of S, exhibiting a cyclic endurance of more than 5 × 107. This research not only provides insight into the control of the film composition to improve and modify device characteristics but also constructs a foundation of ALD-based OTS research on ternary Ge-S-Se for a future X-point memory application.