Ultra-Low Write Energy Composite Free Layer Spin-Orbit Torque MRAM

A highly efficient exchange-coupled free-layer spin-orbit torque (SOT) magnetic random access memory cell is proposed for ultra-high-density memory. By exploiting typically unrealized benefits of SOT-in particular, its compatibility with low-damping magnetic insulators and the energy efficiencies associated with exchange coupling of hard/soft composite structures-a write energy of 18 aJ/bit for 1 ns switching is achieved. Furthermore, high magnetocrystalline anisotropy materials such as L1 0 -FePt or L1 0 -FePd are employed not only to facilitate achievement of ultra-high-density memory but also to allow for reduction of heavy metal layer volume and a reduction in write energy not seen in previous CoFeB-based cells. This energy is within a factor 72 of the theoretical limit of 60~k_{B}T . It also represents a factor of >500 improvement relative to state-of-the-art DDR4 DRAM cells.