Novel MTJ-Based Sensing Inverter Variation Tolerant Nonvolatile Flip-Flop in the Near-Threshold Voltage Region

In recent years, the low power design of Internet of Things devices has become increasingly important. The most basic method to implement a low power design is to reduce static power consumption. In this regard, a spin-transfer-torque magnetic-tunnel-junction-based nonvolatile flip-flop (NVFF) is a promising candidate for storing the computing data while the power is off. However, as the technology node scales down, the process variation increases, leading to a restoration failure in previous NVFFs, especially in the near-threshold voltage (NTV) region. For better energy efficiency when operating the NVFF in the NTV region, this article presents a novel NVFF that guarantees a target restore yield of 4σ and a target read disturbance margin of 6σ in the NTV region (0.6 V supply voltage), along with auto-zeroing and dynamic reference voltage (DRV) techniques, using only a single capacitor to improve the NVFF's restore yield. The Monte Carlo HSPICE simulation results using industry-compatible 28-nm model parameters show that the proposed NVFF satisfies both the target restore yield and the read disturbance margin, saving 44% restoration time compared with the current state-of-the-art NVFF, which does not satisfy the target restore yield despite having offset cancellation characteristic.