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▲ [16a-C41-9] Electric-field induced magnetization switching in CoFeB/MgO magnetic tunnel junction with thick MgO barrier
Keywords:Spintronics, magnetic tunnel junction, CoFeB/MgO
Magnetization switching energy is expected to be reduced by the electric-field induced scheme, because charging/discharging energy of the capacitor is a few orders smaller than the Joule heating consumed by the conventional current-induced scheme for magnetic tunnel junctions (MTJs). So far, we used the CoFeB/MgO/CoFeB MTJ as a pseudo-capacitor [1,2], in which, even for the electric-field switching, the energy was governed by the Joule heating resulted from tunnel current. In this work, to reduce the Joule heating, we use a CoFeB/MgO with high junction resistance R by increasing MgO barrier thickness.
We fabricate a MTJ with a diameter of 60 nm from a stack of Ta(5)/Pt(5)/[Co(0.34)/Pt(0.4)]x6/Co(0.4)/ Ru(0.42)/[Co(0.34)/Pt(0.4)]x2/Co(0.34)/Ta(0.3)/Co20Fe60B20(1)/MgO(2.8)/Co18.75Fe56.25B25(1.8)/Ta(5)/Ru(5) (numbers in parentheses are nominal thickness in nm) deposited on a sapphire substrate. The device resistance-are product RA is 176000 Ohm micrometer2 at zero bias, which is several-order larger than those for the current-induced switching devices. The product of switching probabilities (PPtoAPPAPtoP) from parallel (P) to anti-parallel (AP) and from AP to P by the application of an electric-field pulse of 0.78 V/nm as a function of pulse duration tpulse of almost unity is obtained at tpulse ~ 1.25 ns, at which the switching energy is evaluated to be 6.3 fJ/bit. While this is one or two-order smaller switching energy than those reported so far [3], the energy is still dominated by the Joule heating. This is due to stronger bias dependence of R for MTJs with thicker MgO, neglected in the previous report on MTJs with high R [4]. In order to suppress the Joule heating, one needs search ways to reduce the bias dependence of R as well as the threshold electric field for the switching.
[1] S. Kanai et al., Appl. Phys. Lett. 101, 12403 (2012).
[2] F. Matsukura et al., Nat. Nanotech. 10, 209 (2015).
[3] S. Kanai et al., Appl. Phys .Lett. 108, 192406 (2016).
[4] C. Grezes et al., Appl. Phys. Lett. 108, 012403 (2016).
We fabricate a MTJ with a diameter of 60 nm from a stack of Ta(5)/Pt(5)/[Co(0.34)/Pt(0.4)]x6/Co(0.4)/ Ru(0.42)/[Co(0.34)/Pt(0.4)]x2/Co(0.34)/Ta(0.3)/Co20Fe60B20(1)/MgO(2.8)/Co18.75Fe56.25B25(1.8)/Ta(5)/Ru(5) (numbers in parentheses are nominal thickness in nm) deposited on a sapphire substrate. The device resistance-are product RA is 176000 Ohm micrometer2 at zero bias, which is several-order larger than those for the current-induced switching devices. The product of switching probabilities (PPtoAPPAPtoP) from parallel (P) to anti-parallel (AP) and from AP to P by the application of an electric-field pulse of 0.78 V/nm as a function of pulse duration tpulse of almost unity is obtained at tpulse ~ 1.25 ns, at which the switching energy is evaluated to be 6.3 fJ/bit. While this is one or two-order smaller switching energy than those reported so far [3], the energy is still dominated by the Joule heating. This is due to stronger bias dependence of R for MTJs with thicker MgO, neglected in the previous report on MTJs with high R [4]. In order to suppress the Joule heating, one needs search ways to reduce the bias dependence of R as well as the threshold electric field for the switching.
[1] S. Kanai et al., Appl. Phys. Lett. 101, 12403 (2012).
[2] F. Matsukura et al., Nat. Nanotech. 10, 209 (2015).
[3] S. Kanai et al., Appl. Phys .Lett. 108, 192406 (2016).
[4] C. Grezes et al., Appl. Phys. Lett. 108, 012403 (2016).