A multi-level-cell spin-transfer torque memory with series-stacked magnetotunnel junctions

We first report a multi-level-cell (MLC) spin-transfer torque memory (SPRAM) with series-connected magnetotunnel junctions (MTJs). The series MTJs (with different areas) show multi-level resistances by a combination of their magnetization directions. A four-level operation by spin-transfer-torque writing was experimentally demonstrated. A scheme for the write/read operation of the MLC SPRAM was also presented.