Fig. 1. (Color online) SOT device structure and the SOT-MTJs process flow. (a) Three-dimensional schematic pictures of SOT device. (b) Cross-section TEM images cutting along the SOT track (x-direction). (c) Substrate treatment for low roughness. (d) SOT track, MTJ film stack deposition and magnetic anneal. (e) MTJ patterning and encapsulation. (f) Top electrode process.

Fig. 2. (Color online) Detailed microstructure of the MTJ film stack and the resistivity of W. (a) TEM diagram of the MTJ film stack. (b) Nano-beam diffraction analysis of W captured from the red box in (a). EDS mappings of (c) W, (d) Mg, (e) Co and (f) Fe. (g) The XRD curve for a simplified film structure of W/CoFeB/MgO/Ta. (h) The resistivities of W with various thicknesses. The resistivity of 5 nm W is highlighted by red circle. The orange color gradient indicate the W phase transition.

Fig. 3. (Color online) The typical electrical and magnetic properties of the SOT device. The wafer level distribution of theR_SOT, MR,J_SW, R_AP andR_P. (a) TypicalR–H hysteresis loops of the SOT-MTJs. (b) TypicalR–J hysteresis loops of the SOT MTJs obtained from the same sample in (a). The wafer-level electrical distribution of (c)R_SOT, (d) MR, (e)J_SW. (f–h) The corresponding CDF plots. (i) The bit-cell resistance distributions of SOT MTJs for both P and AP states.

Fig. 4. Normalized (a)I_SW, (b)I_FL, (c)I_SOT, and (d)I_FL/I_SW as functions of MTJ long axisb. The data are normalized by the average value of MTJ withb = 2100 nm.

Fig. 5. (Color online) The switching probability (P_SW) as a function of applied voltage when pulse widths were varied from 50µs down to 100 ns for both (a) P-to-AP and (b) AP-to-P directions. (c) The extractedJ_C at different pulse width for both P-to-AP and AP-to-P directions whenP_SW = 50%.

Fig. 6. (Color online) (a)R_SOT,R_P,R_AP measured after the corresponding cycling current pulses for a typical SOT-MTJ device. (b) The MR loops were recorded multiple times at each power of 10 pulses up to 10¹⁰. (c) The extractedJ_SW from (b) multiple times at each power of 10 pulses.

Fig. 7. (Color online) (a) The extracted switching probabilities as a function of the external magnetic field and the corresponding fitting curve. (b) Diamond plots of∆ for the MTJs with various MTJ long axisb. (c) The failure-bit rates of different bake time, i.e., 12, 24, 48 h at 200 °C, respectively.