New power-gating architectures using nonvolatile retention: Comparative study of nonvolatile power-gating (NVPG) and normally-off architectures for SRAM

Power-gating (PG) architectures employing nonvolatile state/data retention are expected to be a highly efficient energy reduction technique for high-performance CMOS logic systems. Recently, two types of PG architectures using nonvolatile retention have been proposed: One architecture is nonvolatile PG (NVPG) using nonvolatile bistable circuits such as nonvolatile SRAM (NV-SRAM) and nonvolatile flip-flop (NV-FF), in which nonvolatile retention is not utilized during the normal SRAM/FF operation mode and it is used only when there exist energetically meaningful shutdown periods given by break-even time (BET). In contrast, the other architecture employs nonvolatile retention during the normal SRAM/FF operation mode. In this type of architecture, an even short standby period can be replaced by a shutdown period, and thus this architecture is also called normally-off (NOF) rather than PG. In this paper, these two PG architectures for a FinFET-based high-performance NV-SRAM cell employing spintronics-based nonvolatile retention were systematically analyzed using HSPICE with a magnetoresistive-device macromodel. The NVPG architecture shows effective reduction of energy dissipation without performance degradation, whereas the NOF architecture causes severe performance degradation and the energy efficiency of the NOF architecture cannot be superior to that of the NVPG architecture.