SOT concept


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Spin Orbit Torque Magnetic Random Access Memory (SOT-MRAM) is the latest generation of MRAM. Unlike its predecessor Spin Transfer Torque (STT) MRAM though, SOT-MRAM does not require passing of a high current through the magnetic device during the Write operation, with the Writing done by a current flowing through an adjacent metal line.

STT
SOT

The absence of high-voltage stress on the device allows for practically infinite SOT-MRAM endurance even at the fastest, sub-ns write speeds. Furthermore, SOT-switching does not need to rely on thermal activation to initiate switching, which makes reliable sub-ns switching with no incubation delays inherently feasible. As a result, SOT-MRAM may be used as DRAM- or SRAM-like working memory, which is nearly impossible with STT-MRAM.

SOT switching is based on the electron Spin-Orbit interaction, which is a relativistic effect of a charge (electron) moving at high speed through an electric field from the crystalline lattice. Due to Lorentz transformation, the electrons experience an effective magnetic field, which splits the trajectories of electrons with opposite spins.

Lorentz transform

This results in the generation of a spin current flowing perpendicular to the charge current, which may switch the magnetization direction of an adjacent (storage) ferromagnetic layer. When the direction of the charge current is reversed, the spin current polarization (e.g. spin orientation) is reversed, and the magnetization is switched to the opposite state.

SOT