Development of magnetic tunnel junction for toggle-MRAM

MRAM using 'toggle' switching mode is tested and characterized with respect to the free layer material and thickness combinations of SAF (synthetic antiferromagnet) structure. The tested MTJ cell size is 0.4 /spl times/ 0.8 /spl mu/m/sup 2/ with elliptical shape. The switching characteristics of toggle-MRAM depend strongly on Hk (crystal anisotropy field) and Hex (exchange coupling field). To get small switching field, the main effort should be focused on reducing Hk, since Hk mainly affects the spin-flop field (Hsf) while Hex mainly affects the saturation field (Hsat). Comparing several materials as free layer, it is found that Hk of NiFe is smaller than that of CoFeB. A smaller switching field in MTJ stacks can be obtained with NiFe SAF free layer.