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▼ [15a-3A-1] Pulse width dependence of a spin-orbit torque induced magnetization switching
Keywords:Spintronics,Spin Orbit torque,3-terminal MTJ
Recently, three-terminal spintronics devices that utilize torque originating from the spin-orbit interaction (spin-orbit torque: SOT) have attracted great attention. In addition to the two conventional structures, which have the easy axis perpendicular to the film plane (type Z) or in-plane and orthogonal to the long axis of channel (type Y), we proposed in the last meeting a new structure with the easy axis being parallel to the channel (Type X) and demonstrated the basic operation using dc current. Here, we study, using the type X and type Y, the current pulse width tp dependence of the SOT switching from dc to sub-ns region. Note that tp dependence of SOT switching has been highly controversial; a theory predicted that the threshold current is less sensitive to tp for type Z (and type X) than type Y , whereas an experimental study showed that the results of type Z was well described by a conventional spin-transfer torque switching model that holds true for type Y .
The film with a stack of Ta/CoFeB/MgO/CoFeB/Co/Ru/Co is deposited on Si wafer by dc/rf magnetron sputtering. The deposited film is processed into three-terminal SOT devices with an elliptic magnetic tunnel junction on a Ta channel by electron beam lithography and Ar ion milling. Type-X and type-Y devices are fabricated on the same wafer. Current pulses with various tp are supplied from a pulse generator. The threshold voltage Vth for switching (average of 10-times measurement) is plotted as a function of tp for both types X and Y. Vth of type Y steeply increases as tp decreases below 100 ns. In case of tp = 2 ns, switching is observed only three times in 10-times trials, where voltage pulses up to 2.6 V are applied. In contrast, Vth of type X gradually increases with decreasing tp. We observe 50-times switching for 50-times trials even in tp < 500 ps (not shown). These results suggest that type-X structure is promising for high-speed applications.
The film with a stack of Ta/CoFeB/MgO/CoFeB/Co/Ru/Co is deposited on Si wafer by dc/rf magnetron sputtering. The deposited film is processed into three-terminal SOT devices with an elliptic magnetic tunnel junction on a Ta channel by electron beam lithography and Ar ion milling. Type-X and type-Y devices are fabricated on the same wafer. Current pulses with various tp are supplied from a pulse generator. The threshold voltage Vth for switching (average of 10-times measurement) is plotted as a function of tp for both types X and Y. Vth of type Y steeply increases as tp decreases below 100 ns. In case of tp = 2 ns, switching is observed only three times in 10-times trials, where voltage pulses up to 2.6 V are applied. In contrast, Vth of type X gradually increases with decreasing tp. We observe 50-times switching for 50-times trials even in tp < 500 ps (not shown). These results suggest that type-X structure is promising for high-speed applications.