Key factors to enhance the switching characteristics in submicron MRAM cells

The dependence of the switching field distribution of magnetic random access memory cells on film roughness, saturation magnetization, film thickness, and cell aspect ratio is discussed. We found that a flat interface between the tunnel oxide and the magnetic film is very important in suppressing switching field variation. For free-layer materials, NiFe, CoNiFe, CoFeB, and lamellar structures are examined. By trying various compositions of these materials, we have improved switching characteristics with small saturation magnetization and small thickness. Good results with lamellar structures suggest that the suppression of the grain growth in the ferromagnetic layer is another effective way to get enhanced switching characteristics.