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

Abstract

Magnetoresistive random access memory (MRAM) suffers from low magnetoresistance ratio and serious variations in both low-resistance state (R P ) and high-resistance state (R AP ). The resulting narrow resistance window between R P and R AP 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 R P and R AP 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 R P and R AP cells. Thus, a larger or smaller reference current can be obtained for the read of R AP or R P 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.