Reduction of Writing Field Distribution in a Magnetic Random Access Memory With Toggle Switching

We have investigated the distribution of the flop field, which represents writing field in a toggle magnetic random access memory (MRAM). We analyzed the factors of the distribution by dividing them into the 45deg and f 35deg directions in (H_x, H_y) coordinates. We found that the distribution in the 135deg direction is mainly caused by stress-induced anisotropy and can be effectively suppressed by adopting materials that maintain low magnetostriction even after the fabrication process. On the other hand, we found that the distribution in the 45deg direction depends on the texture and atomic structure of the ferromagnetic layers, and that low distribution can be attained when the ferromagnetic layers are constructed from small crystalline grains or amorphous materials. We demonstrated a toggle MRAM with a distribution of the flop field only half that of the previously reported magnetic tunnel junction stack structure.