RRAM Endurance and Retention: Challenges, Opportunities and Implications on Reliable Design

We provide an overview of metal oxide RRAM design challenges and opportunities in terms of endurance, retention and variability and the implications on the reliability and security of memory designs. We revise multiple level cell programming, endurance enhancing mechanisms, short-term memory opportunities and variability-aware design methods. We study the restore yield of nonvolatile SRAM designs for different endurance enhancing memory windows and device variability ranges citing power, reliability, endurance, and store energy trade-offs taking into consideration program instability. A resistor window with a low high resistance state, which offers 100x enhanced endurance compared to a full range window, increases the restore power by around 2x while maintaining good yield in the absence of program instability. A resistor window with high low resistance state, which has 10x enhanced endurance, results in low restore power and store energy, and maintains good yield at low device process variations.