High-Speed, Energy-Efficient Magnetic Nonvolatile Flip-Flop With Self-Adaptive Write Circuit Utilizing Voltage-Controlled Magnetic Anisotropy

Flip-flops (FFs) account for a very significant portion of the entire power consumption of VLSI circuits. Magnetic tunnel junctions (MTJs) can be combined with conventional FFs to achieve nonvolatility, almost unlimited write times, and higher energy efficiency. The mainstream MTJ switching mechanisms include spin-transfer torque (STT), spin-orbit torque (SOT), and voltage-controlled magnetic anisotropy (VCMA) effect, among them the first two mechanisms all facing the disadvantages of both large writing energy and writing latency. Instead, utilizing the VCMA effect to switch MTJ only needs a sub-nanosecond and has low energy consumption, which is more energy-efficient. In this article, first, a double-stage pre-charge sense amplifier (DPCSA) is proposed, reducing 53.9% of sensing delay compared with the conventional one. Second, based on DPCSA, a VCMA-MTJ-based multi-bit shared magnetic nonvolatile FF (MNV-FF) with a self-adaptive writing circuit is designed, achieving high speed and energy efficiency for backup and restore operations. Finally, by extending the MNV-FF, a magnetic nonvolatile register group (MNV-RG) with high area efficiency can be obtained. An SMIC 55 nm CMOS design kit and a VCMA-MTJ compact model described by Verilog-A language are used for hybrid simulation on the Cadence/Specter Platform. Simulation results in 0.7× and 1.3× of the improvements in data backup time and backup energy, respectively, compared with the efficient VCMA-MTJ-based MNV-FF. Two more improvements of 158.7× and 19.6× in data restore time and restore energy are also achieved in the same comparison.