Controlling nanosecond spin-orbit torque switching of three terminal magnetic tunnel junctions with geometry

Recently we reported that a significant reduction of critical switching current I_c can be achieved in tungsten based three-terminal magnetic tunnel junctions with atomic Hf layer modification of the interfaces. This has stimulated additional work to further optimize these nanoscale structures to achieve still lower critical currents and higher speed switching for future cache memory applications. Here we report on a systematic study of the micromagnetic factors that determine both the intrinsic time scale of this nanosecond switching behavior and the degree of symmetry between the fast switching from parallel (P) to anti-parallel (AP) and the reverse. Using a modified geometry of the nanopillar magnetic tunnel junction structure we find that we are able to tune the relative speeds of reversal between two polarities. We have also designed a new spin Hall channel geometry to achieve a major reduction in channel resistance. This enables us to examine write error rates in the very high pulse current regime, I >> I_c . The results of these studies further demonstrate the feasibility of this type of three-terminal spin-orbit torque device as a high speed, energy efficient, non-volatile memory solution.