A ReRAM-Based Nonvolatile Flip-Flop With Self-Write-Termination Scheme for Frequent-OFF Fast-Wake-Up Nonvolatile Processors

Nonvolatile flip-flops (nvFFs) enable frequent-off processors to achieve fast power-off and wake-up time while maintaining critical local computing states through parallel data movement between volatile FFs and local nonvolatile memory (NVM) devices. However, current nvFFs face challenges in large store energy ( $\text{E}_{\mathrm {S}}$ ) and long voltage stress time on the device ( $\text{T}_{\mathrm {STRESS}}$ ), due to wide distribution in the write time of NVM device as well as unnecessary writes. Moreover, heavy parasitic load on the power rail cause long wake-up time for restoring data from NVM to FFs. This paper proposes the resistive RAM (ReRAM)-based nvFF with self-write termination (SWT) and reduced loading on power rail to: 1) reduce 93+% waste of $\text{E}_{\mathrm {S}}$ from fast switching or matched cells; 2) suppress endurance and reliability degradation resulted from overprogramming and long $\text{T}_{\mathrm {STRESS}}$ ; and 3) achieve reliable and 26+ times faster restore operation compared with previous nvFFs. We have fabricated a nonvolatile processor and a test chip with SWT-nvFFs using logic-process ReRAM in a 65-nm CMOS process. Measured results show sub-2-ns termination response time and sub-20-ns chip-level restore time.