Ashwin Rastogi

EECS Department, University of California, Berkeley

Technical Report No. UCB/EECS-2022-103

May 13, 2022

http://www2.eecs.berkeley.edu/Pubs/TechRpts/2022/EECS-2022-103.pdf

Spin-transfer torque (STT) has been used as the underlying physical mechanism in STT- RAM in industry to create fast and low-power spintronic memory devices. However, due to the geometry of STT devices, lower current densities and accordingly longer electrical pulse widths are necessary to achieve switching without device degradation. This in practice has limited STT devices to the nanosecond timescale. Spin-orbit torque (SOT) provides an alternative method of switching, i.e. writing bits, with spin currents without the limitation on current density. As a result, switching with current pulses as short as 200 ps (and 6 ps using photoconductive switches) has been demonstrated. In this work, the SOT switching mechanism on a metallic stack consisting of Cobalt magnetic thin film was simulated using the Landau-Lifshitz-Gilbert macrospin equation. The relationship between critical switching current density and other system parameters like in-plane field as well as the relationship between switching times and current density were simulated. The effects of ultrafast heating were incorporated into the simulation by solving the heat-diffusion equation and modeling saturation magnetization and anisotropy as functions of temperature. The results of the simulation are compared to experimental data and it was demonstrated that the simulation agrees well with the experiment. It is also shown that complete magnetization reversal is achievable in less than 200 ps as suggested by the simulation. These simulations enable engineers to see expected dynamics along with power consumption and response speed for a wide variety of ferromagnetic stacks without the direct need for fabrication and experimentation.

Advisors: Jeffrey Bokor

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BibTeX citation:

@mastersthesis{Rastogi:EECS-2022-103,
    Author= {Rastogi, Ashwin},
    Title= {Simulating Spin Orbit Torque Driven Switching with Ultrafast Thermal Effects},
    School= {EECS Department, University of California, Berkeley},
    Year= {2022},
    Month= {May},
    Url= {http://www2.eecs.berkeley.edu/Pubs/TechRpts/2022/EECS-2022-103.html},
    Number= {UCB/EECS-2022-103},
    Abstract= {Spin-transfer torque (STT) has been used as the underlying physical mechanism in STT- RAM in industry to create fast and low-power spintronic memory devices. However, due to the geometry of STT devices, lower current densities and accordingly longer electrical pulse widths are necessary to achieve switching without device degradation. This in practice has limited STT devices to the nanosecond timescale. Spin-orbit torque (SOT) provides an alternative method of switching, i.e. writing bits, with spin currents without the limitation on current density. As a result, switching with current pulses as short as 200 ps (and 6 ps using photoconductive switches) has been demonstrated. In this work, the SOT switching mechanism on a metallic stack consisting of Cobalt magnetic thin film was simulated using the Landau-Lifshitz-Gilbert macrospin equation. The relationship between critical switching current density and other system parameters like in-plane field as well as the relationship between switching times and current density were simulated. The effects of ultrafast heating were incorporated into the simulation by solving the heat-diffusion equation and modeling saturation magnetization and anisotropy as functions of temperature. The results of the simulation are compared to experimental data and it was demonstrated that the simulation agrees well with the experiment. It is also shown that complete magnetization reversal is achievable in less than 200 ps as suggested by the simulation. These simulations enable engineers to see expected dynamics along with power consumption and response speed for a wide variety of ferromagnetic stacks without the direct need for fabrication and experimentation.},
}

EndNote citation:

%0 Thesis
%A Rastogi, Ashwin 
%T Simulating Spin Orbit Torque Driven Switching with Ultrafast Thermal Effects
%I EECS Department, University of California, Berkeley
%D 2022
%8 May 13
%@ UCB/EECS-2022-103
%U http://www2.eecs.berkeley.edu/Pubs/TechRpts/2022/EECS-2022-103.html
%F Rastogi:EECS-2022-103