Dynamic Data-Dependent Reference to Improve Sense Margin and Speed of Magnetoresistive Random Access Memory

摘要

Magnetoresistive random access memory (MRAM) suffers from low magnetoresistance ratio and serious variations in both low-resistance state (RP) and high-resistance state (RAP). The resulting narrow resistance window between RP and RAP makes it difficult to acquire a sufficient sense margin for accurate read operation. In this brief, a novel read circuit for MRAM is proposed with dynamic data-dependent reference current to improve the sense margin. Instead of using the average of read currents of a pair of dummy RP and RAP cells as reference, our reference current is generated in a data-dependent manner by subtracting the read current of the selected cell from the sum of read currents of a pair of dummy RP and RAP cells. Thus, a larger or smaller reference current can be obtained for the read of RAP or RP cell, respectively, helping in expanding the sense margins. The larger sense margin can further improve the sense speed and the read yield. Evaluation shows that 2× increase in typical sense margin, 60% reduction in sense time, and remarkable reduction in bit error rate are achieved compared with the conventional averaging reference scheme. The accompanying cost in power consumption is acceptable.