A refresh operation method for solving thermal stability issues and improving endurance of ovonic threshold switching selectors

Abstract

An ovonic threshold switching (OTS) selector is indispensable for large-scale three-dimensional phase change memories (3D PCMs). To meet the requirement of compatibility with the back-end of line (BEOL) process over 400 °C, the trade-off between device performance and thermal stability is inevitable. For example, due to the diminished endurance at high temperatures, an OTS selector with a fast switching speed such as a Te system cannot be applied in the process. Besides, current practical OTS selectors with high thermal stability usually adopt material systems that possess overcomplicated composition or even toxic elements. To solve this problem, a refresh operation is proposed in this study to deal with the poor thermal stability issue of OTS selectors based on GeTe. It is found that the switching performance of GeTe selectors can be fully restored to the original level by the refresh operation after the devices fail. Meanwhile, the recovered selectors exhibit good consistency, indicating their capabilities to be applied in the BEOL process. Moreover, endurance of the device applying the refresh operation is further studied, and the results demonstrate an improvement of two orders of magnitude. Finally, the effectiveness of this refresh operation to improve the thermal stability of OTS devices based on another commonly used GeSe system is verified, which suggests that the proposed method can be widely applied to other OTS devices. This study provides a solution to overcome the high thermal stability requirement of OTS selectors and improve the working life of memory chips from a perspective of operation.