Study of intermediate magnetization states in deep submicrometer MRAM cells

Using experimental and micromagnetic modeling, the intermediate magnetization states in deep submicrometer MRAM cells, their effects on the switching behavior and designs to eliminate them, are presented. The elliptical MRAM cell with varied aspect ratio and minor axis length is built using synthetic pinned layer-AlO_x-free layer structure. At-field and remnant R-H curves are collected for various design and process parameters: free layer thickness, cell aspect ratio, different free layer material NiFe, CoFe, CoFeB and combinations of them. For not well optimized designs, the at-field R-H curves are not desirable squares with significant amount of irregularities or kinks that can be separated into two types: type V and type H. From micro-magnetic modeling, the magnetization of the type V kink state is identified as vortex configuration. For the type H, the magnetization state has a horseshoe configuration.