Variation-Tolerant Sensing Circuit for Ultralow-Voltage Operation of Spin-Torque Transfer Magnetic RAM

Abstract

Although promising as a future memory solution, the spin-torque transfer magnetic RAM has critical drawbacks due to the small operation margin in low supply voltage and large area of the sensing circuit. To overcome these disadvantages, we propose a novel sensing circuit that utilizes the data-dependent body-bias scheme with a single reference cell. Through Monte Carlo simulations using 45-nm process technology model parameters, the proposed circuit is verified to be highly robust to the variations in threshold voltage and cell resistance at ultralow supply voltages without sensing speed degradation. The proposed circuit has a read access pass yield of 96.5% for 16-Mb memory at $\mathbf{V}_{\mathbf{DD}} = 0.7 \mathbf{V}$ when the standard deviation of cell resistance is 10%. In addition, the area overhead is also reduced by 79% compared to the conventional sensing circuit.