  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 non-equilibrium
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 product. Both types of devices show
constant tunnel magnetoresistance at larger cross-sectional areas but achieve
ultra-high magnetoresistance at small cross-sectional areas, while maintaining
low resistance-area 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.
