Composite SOT-MTJ Memory for Ultra-Fast Low-Power Switching

The patent introduces a spin Hall channel layer as an intermediary component between the current path and the magnetic tunnel junction. The charge current flows through the spin Hall channel which converts it to a transverse spin current via the spin Hall effect, which then acts on the recording layer. This intermediary mechanism allows writing without applying high voltage directly across the tunnel barrier, thus preventing breakdown while achieving magnetization switching.

The patent replaces the direct spin-transfer torque mechanism (which requires high voltage across the MTJ) with a spin-orbit torque mechanism utilizing the spin Hall effect. Instead of injecting spin-polarized current vertically through the tunnel barrier, a charge current is applied laterally through the spin Hall channel, generating spin current transverse to the current direction through the spin Hall effect. This substitution eliminates the high voltage requirement across the tunnel barrier.

The patent segments the read and write current paths. The write operation uses lateral current through the spin Hall channel, while the read operation uses vertical current through the MTJ stack. This segmentation allows independent optimization of read and write operations, enabling accurate readout without risking unintended magnetization switching that would occur with high voltage applied directly across the MTJ.

The spin Hall channel acts as an intermediary for write operations only, while read operations directly measure the MTJ resistance. This separation ensures that read currents, which are relatively low, do not trigger switching, while write currents are channeled through the spin Hall effect mechanism that is insensitive to the same stability constraints.

The patent introduces a magnetic flux guiding layer with high magnetic permeability underneath the spin Hall channel, creating an asymmetric magnetic structure. This asymmetric configuration, combined with canted annealing or oval-shaped patterning of the recording layer, generates a uniaxial magnetic anisotropy that provides the necessary symmetry breaking for deterministic switching without external magnetic fields. The asymmetric structure guides magnetic flux preferentially in one direction, enabling field-free switching.

The patent changes the magnetic anisotropy parameters through canted annealing processes or geometric shaping (oval patterns) of the recording layer. By controlling the annealing temperature, magnetic field angle, or aspect ratio of the pattern, the magnetic energy landscape is modified to create a uniaxial anisotropy with an easy axis at a specific angle. This parameter change eliminates the need for external magnetic fields during operation, as the anisotropy itself provides the switching direction.

The patent applies local quality enhancement by introducing a magnetic flux guiding layer with high permeability in specific regions underneath the spin Hall channel. This localized structure concentrates and guides magnetic flux precisely where needed, enhancing the spin-orbit torque efficiency at the recording layer interface. The improved local magnetic field concentration allows for more effective magnetization switching with lower currents, enabling smaller recording layer volumes without sacrificing thermal stability.

The patent employs composite material structures including the spin Hall channel made of high-Z materials (Pt, β-Ta, β-W, doped Cu) with large spin Hall angles, combined with the recording layer and magnetic flux guiding layer. This composite structure leverages the high spin Hall angle material to generate stronger spin currents from the same charge current, improving switching efficiency and allowing reduced recording layer volume while maintaining thermal stability through the enhanced spin-orbit coupling.