High-Endurance Bipolar ReRAM-Based Non-Volatile Flip-Flops with Run-Time Tunable Resistive States

ReRAM technologies feature desired properties, e.g. fast switching and high read margin, that make them attractive candidates to be used in non-volatile flip-flops (NVFFs). However, they suffer from limited endurance. Therefore, cell degradation considerations are a necessity for practical deployment in non-volatile processors (NVPs). In this paper, we present two bipolar ReRAM-based NVFFs, Hypnos and Morpheus, with enhanced endurance and energy efficiency. Hypnos reduces the ReRAM electrical stress during set operation while keeping the imposed NVFF area overhead at a minimum. In Morpheus, a write-termination circuit is used to further enhance the ReRAM endurance and energy efficiency at the cost of an affordable area overhead. Moreover, both NVFFs feature run-time tunable resistive states to enable on-line adjustment of the trade-off among endurance, retention, energy consumption, and restore success rate (in case of approximate computing). Experimental results demonstrate that Hypnos reduces the ReRAM set degradation by 91%, on average. Moreover, the write-termination mechanism in Morpheus further reduces the remaining degradation by 93%/97% in set/reset operation, on average. The results also demonstrate enhanced energy efficiency in both NVFFs.