RRAM-based 7T1R nonvolatile SRAM with 2x reduction in store energy and 94x reduction in restore energy for frequent-off instant-on applications

This study proposes a 7T1R nonvolatile SRAM (nvSRAM) to 1) reduce store energy by using a single NVM device, 2) suppress DC-short current during restore operations through the use of a pulsed-overwrite (POW) scheme, and 3) achieves high restore yield by using a differentially supplied initialization (DSI) scheme. This initialization-and-overwrite (IOW) 7T1R nvSRAM improves breakeven-time (BET) by 6+x, compared to previous nvSRAMs. We fabricated a 16Kb IOW-7T1R nvSRAM using HfOx RRAM and a 90nm process. This represents the first ever silicon verified single-NVM nvSRAM macro. Measurements obtained in test-mode confirm that the proposed nvSRAM reduces store energy by 2x and restore energy by 94x, compared to 2R-based nvSRAMs.