4.7 A 65nm ReRAM-enabled nonvolatile processor with 6× reduction in restore time and 4× higher clock frequency using adaptive data retention and self-write-termination nonvolatile logic

With the rising importance of energy efficiency, zero leakage power and instant-on capability are highly desired features in energy harvesting sensors, as well as “normally off” high performance processors. However, intermittent power in such systems requires nonvolatile memory (NVM) to hold intermediate data and avoid rollbacks. Previous work has adopted FeRAM and STT-MRAM to achieve zero-standby power and fast-restore nonvolatile processors (NVPs) [1–3]. Previous NVPs, however, suffer from several drawbacks: 1) Various power interrupt periods are not considered; 2) the 2-macro memory architecture slows access speed; 3) worst-case store/restore operations are always performed. We present a 65nm fully-CMOS-logic-compatible ReRAM-based NVP achieving time/space-adaptive data retention. A 1-macro nvSRAM with self-write-termination (SWT) is integrated to boost clock frequency and reduce store energy. The adaptive retention and SWT strategy relieve the ReRAM write endurance challenge (106–1012), making it sufficient for most applications. The NVP operates at 100MHz with 20ns/0.45nJ restore time (TRESTORE)/energy (ERESTORE), realizing 6× reduction in TRESTORE, >6000× reduction in ERESTORE and 4× higher clock frequency compared with existing designs.