Scaling Properties of Step-Etch Perpendicular Magnetic Tunnel Junction with Dual-CoFeB/MgO Interfaces

We built and studied the size scaling effect of perpendicular magnetic tunnel junctions (p-MTJs) with step-etch structure and dual-MgO/CoFeB interfaces. The step-etch structure yields symmetrical R-H loop, while dual-MgO/CoFeB interfaces raises cell anisotropy, thus the data retention time. The p-MTJ of 45-nm diameter shows spin-transfer torque switching voltage V-sw with tight temporal sigma (sigma(V-sw) <3.7%). The thermal stability factor is 60. Although the critical switching current (I-c0) reduces with MTJ area, its density (J(c0)) increases. One plausible explanation of this observation is that the magnetization reversal of small MTJ follows the single-domain macrospin model, while that of the larger MTJ may be affected by the nucleation of domain during the magnetization reversal, and the wall motion leads to J(c0) lowering; the other may be due to process-induced film damage. Fortunately, the switching efficiency (E-b/vertical bar I-c0 vertical bar) is higher for smaller p-MTJ.