Energy-Efficient Nonvolatile Flip-Flop With Subnanosecond Data Backup Time for Fine-Grain Power Gating

A nonvolatile flip-flop (NVFF) is proposed, where magnetic tunnel junctions (MTJs) are incorporated into a CMOS flip-flop (FF) to enable nonvolatility. The voltage-controlled magnetic anisotropy (VCMA) effect is utilized to back up the latched data into MTJs before the power supply is turned off. Switching an MTJ through the VCMA effect does not require a dedicated write circuit for data backup, resulting in reduced area as compared with NVFFs exploiting the spin transfer torque (STT) switching mechanism. In a VCMA-based NVFF, the MTJs are coherently switched, enabling ultra-energy efficient data backup with subnanosecond backup time. Simulation results exhibit more than a 342× (33.7×) improvement in data backup energy per bit, and more than 35.5× (7.7×) improvement in data backup delay per bit as compared with the most efficient STT-based NVFFs (spin Hall effect-based NVFF). The energy efficiency of the VCMA-based NVFF results in sufficiently short breakeven times, enabling effective fine-grain power gating.