Multiple-Cell Reference Scheme for Narrow Reference Resistance Distribution in Deep Submicrometer STT-RAM

Abstract— Spin-transfer-torque random access memory (STT-RAM) has attracted much research interest because of its characteristics of nonvolatility (i.e., zero standby power) and small cell size (i.e., high density and high performance). As the technology node is scaled down, however, the sensing margin of the STT-RAM is degraded because of the increased process variation and reduced supply voltage. To improve the sensing margin, this brief focuses on a reference scheme design capable of reducing the reference resistance distribution. A multiple-cell
reference (MCR) scheme is proposed that achieves the narrow reference resistance distribution. Moreover, the MCR scheme does not exhibit parasitic mismatch, regularity problem, read disturbance, and write current degradation, and it also has small area overhead. As increasing battery lifetime and decreasing device size have become the main objectives of low-power VLSI circuit designs, spin-transfer-torque random access memory (STT-RAM) having the
characteristics of nonvolatility and small cell size has been widely researched < final year projects >