Spin-orbit torque nonvolatile flip-flop designs

Flip-flops (FFs) are basic units in electronic circuits. Recently, nonvolatile FFs (NVFFs) have attracted great interests for power-gating applications and a variety of NVFFs have been proposed by integrating nonvolatile memory devices. Among them, magnetic tunnel junction (MTJ) based NVFFs show considerable potential in terms of zero static power consumption and high endurance. Nevertheless, the mainstream spin transfer torque (STT) effect based MTJ switching approach for data storing still consumes much dynamic power and long delay, limiting the system performance and data reliability. The spin-orbit torque (SOT) effect provides an alternative approach for high-speed and low-power MTJ switching, therefore rather promising for NVFF design. In this work, we propose four NVFF designs based on the FF architectures (either DFF or SRFF) and perpendicular MTJ (pMTJ). The circuit structures and operations are investigated, and the performance is evaluated and compared at the 40 nm process technology node. Simulation results show that the proposed NVFFs can achieve high read speed (< 200 ps), low read power consumption (< 10 fJ) and area efficiency.