A High-reliability Reading Scheme for STT-MRAM with a Symmetric Dual-reference Sensing Amplifier

Spin transfer torque magnetic random access memory (STT-MRAM) is one of the most promising new type of non-volatile memory. A lot of research has been made to push it to be the universal memory for its prominent advantages. Although great improvements have been made in reading scheme of STT-MRAM, read reliability is still a tough problem mainly because of low tunnel magnetoresistance ratio (TMR) and resistance variation of MTJ. Conventional sensing amplifier with only one reference cell fails to distinguish the stored data when resistance difference between data cell and reference cell is small. Therefore, a high-reliability reading scheme for STT-MRAM with a symmetric dual-reference sensing amplifier has been proposed in this paper. Two reference cells adopted in the proposed circuit guarantee a sufficient sensing margin to achieve a high-reliability read operation. Monte Carlo simulation results show that sensing node at data cell varies from 440.3mV to 514.5mV when MTJ is in low state and from 270.9mV to 396.3mV when MTJ is in high state. Results also indicate that zero-error rate has been achieved.