Charge-Recycling-Based Redundant Write Prevention Technique for Low-Power SOT-MRAM

In spin-orbit torque magnetic random access memory (SOT-MRAM), as write energy is much larger than read energy, writing data to memory only when the new data is different from the stored data can lead to considerable write energy savings. In this paper, we propose three low-power techniques that can significantly reduce write energy in the read-compare-write process. In the proposed approaches, redundant charge in read operation has been efficiently reused to generate a negative voltage for write assistance, which leads to short write time. A selective precharging technique is also proposed to minimize the voltage swings between read and write operations. In addition, asymmetric write current due to source degeneration of write transistor can be resolved with the write voltage suppression scheme. Our circuit simulations with 65-nm CMOS technology show that when the stored data and new data are the same, up to 61% of write energy savings have been achieved compared with the conventional 2T-1MTJ cell. When the proposed SOT-MRAM is used as L3 caches of X86 processor, the gem5 simulations also show that average 48.2% of write energy savings can be achieved in various workloads of SPEC2006.