Area-Efficient Nonvolatile Flip-Flop Based on Spin Hall Effect

Systems that rely on energy harvested from ambient sources are gaining increased attention due to their possible usage in low-power applications. Owing to the unreliable nature of such ambient energy sources, these systems suffer from supply voltage degradation and power interruptions. Therefore, the computational scheme for such energy-harvesting systems is divided into small incremental steps along with nonvolatile memory elements that conserve the data between subsequent power interruptions. Toward that end, we propose a new nonvolatile flip-flop (NVFF) that exhibits better energy efficiency and denser area compared to previous designs. The NVFF utilizes a single spin Hall effect-based magnetic tunnel junction (SHE-MTJ) because of its favorable device characteristics, like high spin injection efficiency and decoupled read-write paths. We also propose a new restore mechanism, wherein a CMOS inverter is used as a gain element to attain reliable restore operation with single SHE-MTJ per NVFF. A detailed device-circuit simulation, including variational analysis, proves the reliability of the proposed NVFF.