Perpendicular Magnetized Magnetic Random-Access Memory Cells Utilizing the Precessional Spin-Current Structure: Benefits for Modern Memory Applications

Abstract

The various memory applications such as embedded nonvolatile memory, embedded static random-access memory, and standalone dynamic random-access memory have different requirements for the performance of the perpendicular magnetic tunnel junction (pMTJ). However, in conventional pMTJ structures, the write current and stability of the free layer are directly coupled, leading to undesirable tradeoffs in performance specifications such as endurance and data retention. With the introduction of the precessional spin-current (PSC) structure, we demonstrate a significant gain in the spin transfer torque (STT) efficiency. The PSC structure shows similar critical current values as the conventional pMTJ structure. But we observe a significant increase in thermal stability, which is largely responsible for the enhancement in the STT efficiency. Smaller device dimensions show higher efficiency increase. We confirm the higher data retention time in a thermally activated switching experiment at 180 °C. The PSC structure exhibits more than two decades lower thermal decay rates within 100 h of wait over the conventional pMTJ. These results demonstrate that it is possible to achieve the necessary retention times at high-temperature operation without increasing the power consumption or higher current in normal operation. Furthermore, we demonstrate that even for short write pulsewidth, the switching currents of the PSC structure remain similar to the pMTJ structure while still having better retention.