Scaling Projections on Spin-Transfer Torque Magnetic Tunnel Junctions

We investigate scaling of technologically relevant magnetic tunnel junction devices in the trilayer and pentalayer configurations by varying the cross-sectional area along the transverse direction using the nonequilibrium Green's function spin transport formalism. We study the geometry dependence by considering square and circular cross sections. As the transverse dimension in each case reduces, we demonstrate that the transverse mode energy profile plays a major role in the resistance-area(RA) product. Both types of devices show constant tunnel magnetoresistance at larger cross-sectional areas but achieve ultrahigh magnetoresistance at small cross-sectional areas, while maintaining low RA products. We notice that although the critical switching voltage for switching the magnetization of the free-layer nanomagnet in the trilayer case remains constant at larger areas, it needs more energy to switch at smaller areas. In the pentalayer case, we observe an oscillatory behavior at smaller areas as a result of double barrier tunneling. We also describe how switching characteristics of both kinds of devices are affected by the scaling.