Low-Temperature Performance of Nanoscale Perpendicular Magnetic Tunnel Junctions With Double MgO-Interface Free Layer

The temperature dependence of magnetoresistance and switching characterization based on spin transfer torque (STT) effect of perpendicular magnetic tunnel junctions (p-MTJs) with MgO/CoFeB/W/CoFeB/MgO double-interface free layer was studied. The tunneling magnetoresistance (TMR) ratio increases from 95% to 176% for both 84 and 64 nm-diameter p-MTJs, upon decreasing the temperature from 400 to 20 K. This change of TMR is dominated by a steady increase in the resistance of antiparallel state while the parallel state conductance remains almost constant. Switching behavior at various temperatures is investigated for pulse voltage-dependent STT measurements; resistance versus voltage loops for both the switching directions become more symmetric with decreasing temperature. Furthermore, low-temperature measurements of magnetic properties suggest that the effect of stray field for STT becomes weaker as the temperature decreases, which suggests the p-MTJs design for cryogenic memories.