Mitigating BTI-Induced Degradation in STT-MRAM Sensing Schemes

Spin-transfer torque magnetic RAM (STT-MRAM), which uses a magnetic tunnel junction to store binary data, is a promising memory technology. With many benefits, such as low leakage power, high density, high endurance, and nonvolatility, it has been explored as an SRAM replacement for cache design or a DRAM replacement for main memory. Meanwhile, along with the continuous shrinking of CMOS process technology, the bias temperature instability (BTI) effect has become a major reliability issue. Prior work has investigated the influence of the BTI effect on the SRAM sense amplifier, but no investigation has been done for the STT-MRAM sense amplifier. Therefore, this paper investigates the BTI effect on STT-MRAM sense amplifiers. We propose a majority-based technique and an alternative sensing technique to reduce circuit degradation. To further improve sensing delay, we propose using forward body bias (FBB) on an access transistor with a positive voltage. Extensive simulation results are done to show the effectiveness of the proposed techniques. The sensing delay for reading zeros and ones can be reduced by 10.61% and 4.35%, respectively, on average, with the majority-based technique. The sensing delay for reading zeros and ones can be reduced by 4.42% and 1.83%, respectively, on average, using the alternative sensing technique. The sensing delay for reading zeros and ones can be reduced by 15.37% and 6.25%, respectively, on average, by using both techniques simultaneously. When using the majority-based and alternative sensing techniques with the FBB technique, the sensing delay for reading zeros and ones can be improved by 29.93% and 57.67%, respectively, on average. We also analyze the BTI-induced degradation of a high-performance sense amplifier and a low power sense amplifier with the proposed techniques. The simulation results show that our proposed technique and simulation flow can be easily extended to other sense amplifiers.