Area dependence of thermal stability factor in perpendicular STT-MRAM analyzed by bi-directional data flipping model

We report a statistical analysis of the thermal stability factor (Δ) for the top-pinned perpendicular magnetic tunnel junction (p-MTJ). By using a bi-directional data flipping model, the data retention characteristics of the “0” and “1” states can be fitted separately, including the saturation of failure probability. With the help of a resistance evaluation for the 16-kbit MTJ array, it became clear that the Δ of the “1” state increased as the device area increased, whereas the Δ of the “0” state remains constant regardless of the size. Moreover, we found that the p-MTJ exhibited a much smaller variation of Δ (9.6 ~ 14.3%) compared with the in-plane MTJ. Variations of Δ in both states decreased as the area increased. In combination with an intense magnetic measurement for the discrete monitor devices, the key parameter to increase the Δ and suppress its variation was investigated.