Emerging Sensing Techniques for Emerging Memories

Among all emerging memories, Spin-Transfer Torque Random Access Memory (STT-RAM) has shown many promising features such as fast access speed, nonvolatility, compatibility to CMOS process and excellent scalability. However, large process variations of both magnetic tunneling junction (MTJ) and MOS transistor severely limit the yield of STT-RAM chips. In this work, we present a recently proposed sensing technique called nondestructive self-reference read scheme (NSRS) to overcome the bit-to-bit variations in STT-RAM by leveraging the different dependencies of the high-resistance state of MTJs on the sensing current biases. Additionally, a few enhancement techniques including R-I curve skewing, yield-driven sensing current selection, and ratio matching are introduced to further improve the robustness of NSRS. The measurements of a 16Kb STT-RAM test chip shows that NSRS can significantly improve the chip yield by reducing sensing failures with high sense margin and low power consumptions.