[Zurück]

M. Bendra, S. Fiorentini, J. Ender, R. Orio, T. Hadámek, W.J. Loch, N. Jørstad, S. Selberherr, W. Goes, V. Sverdlov:
"Spin Transfer Torques in Ultra-Scaled MRAM Cells";
Vortrag: MIPRO 2022, Opatija, Croatia; 23.05.2022 - 27.05.2022; in: "2022 45th Jubilee International Convention on Information, Communication and Electronic Technology (MIPRO)", (2022), ISBN: 978-953-233-103-5; S. 129 - 132.

Modern magnetoresistive random access memory
(MRAM) cells with single-digit nanometer diameters,
utilize a combination of perpendicular interface-induced and
shape-driven out-of-plane anisotropy in a free layer (FL)
consisting of several ferromagnetic parts separated by tunnel
barriers and/or nonmagnetic spacers. To accurately evaluate
the torques acting in such a structure, we generalized the
coupled spin and charge drift-diffusion transport approach
to account for a number of tunnel barriers (TB) or spacers
separating the elongated ferromagnetic pieces. The inclusion
of the tunneling magnetoresistance effect is achieved by
modeling the TB as a poor conductor with a conductivity
locally dependent on the relative magnetization orientation
of the ferromagnetic layers. The TB parameters are calibrated
to reproduce the expected torque magnitudes in
magnetic tunnel junctions (MTJ). To reproduce the spin
transfer torques acting on a FL in a MTJs with several
TBs and spacers, a special treatment of the spin current is
proposed. In elongated FLs, position-dependent torques are
present in the ferromagnetic pieces due to non-homogeneous
magnetization. We show that, with the proposed approach,
composite FLs with several TBs are treated on equal footing.
Our simulations of the magnetization dynamics in composite
elongated FLs agree well with recent experimental demonstrations
of switching of ultra-scaled MRAM cells.

Spin Transfer Torques, Ultra-Scaled MRAM Cells, LLG, perpendicular magnetic anisotropy