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

Abstract

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 online adjustment of the tradeoff 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.