Development of magnetic tunnel junction for toggle MRAM

Toggle switching mode MRAM is tested and characterized with respect to the free- and pinned-layer material,and thickness. With magnetization curves, we were able to find the optimum thickness combinations of free-layer and spacer materials. For CoFeB where the intrinsic anisotropy field (Hi) is about 20-30 Oe, one needs to have a reasonably high exchange coupling field (Hex) to ensure large switching margin. In case of an NiFe/Ru/NiFe free-layer, Hi is usually much smaller than Hex, so that further decrease of Hex between two magnetic layers is needed. The pinned-layer roughness and thickness are other factors to be optimized to reduce the toggle switching field. High cell aspect ratio >= 3.0 helps to minimize the switching distribution and enhance the switching stability.