Spin-Orbit Torque Wiring Layout for Low-Current Magnetization Reversal
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Solution Overview
Problem
Magnetization reversal in TMR and GMR elements requires high current densities, which can lead to reduced durability and energy inefficiency, and existing methods like STT and SOT do not adequately address these issues.
Innovation Solution
A spin current magnetization rotational element with a spin-orbit torque wiring that includes a narrow portion to generate a pure spin current, reducing current density and enabling efficient magnetization reversal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high current density is applied to achieve magnetization reversal in TMR/GMR elements, then the magnetization reversal is achieved, but the durability and lifetime of the element deteriorates
Solution Approach 1:
The patent segments the current path by introducing a separate spin-orbit torque wiring layer adjacent to the magnetoresistance element. The write current flows through this dedicated wiring layer rather than through the magnetoresistance element itself, separating the write and read current paths. This segmentation allows the element to undergo magnetization reversal without direct current stress, improving durability while maintaining the ability to switch magnetization states.
Solution Approach 2:
The spin-orbit torque wiring layer acts as an intermediary that converts charge current into spin current via the spin Hall effect. Instead of applying high current density directly to the magnetoresistance element, the patent uses this intermediate layer to generate the necessary spin torque remotely. The intermediary wiring layer protects the sensitive magnetoresistance element from direct current damage while still achieving the desired magnetization reversal through spin transfer torque.
2Reliability
If a spin-orbit torque wiring layer is added to generate pure spin current, then the current density through the magnetoresistance element is reduced, but the device complexity increases
Solution Approach 1:
The patent merges the spin-orbit torque wiring layer with the existing magnetoresistance element stack in a vertically integrated structure. The wiring layer is positioned adjacent to and bonded with the magnetoresistance element, combining the write current path and the magnetoresistance function into a single compact device. This merging approach reduces the need for separate external wiring and simplifies the overall device architecture while still providing the protective benefits of spin-orbit torque.
Solution Approach 2:
The patent transitions from a planar current path through the magnetoresistance element to a three-dimensional configuration where the spin-orbit torque wiring layer is positioned in an adjacent vertical dimension. This dimensional change allows the write current to flow parallel to rather than through the element stack, reducing complexity by utilizing spatial arrangement rather than adding numerous interlayer connections.
3Area of moving object
If the element size is decreased to improve integration density, then the scaling is achieved, but the writing capability using magnetic field deteriorates
Solution Approach 1:
The patent replaces the magnetic field-based writing mechanism (which relies on current loops generating external fields) with a spin transfer torque mechanism. Instead of using mechanical/electromagnetic field generation from external wiring, the system uses quantum mechanical spin transfer effects that occur when spin-polarized current passes through the magnetic layers. This substitution enables effective magnetization reversal in miniaturized elements where external field generation becomes impractical.
Solution Approach 2:
The patent changes the fundamental writing mechanism parameter from magnetic field strength to spin current density. By utilizing spin transfer torque, the writing capability becomes dependent on the spin polarization and spin scattering properties of the materials rather than on the geometric configuration of current loops. This parameter change allows scaling to smaller dimensions because the effect is material-property-driven rather than geometry-driven, maintaining writing capability as element size decreases.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of a pure spin current for magnetization reversal reduces current density to less than 1×10^7 A/cm², enhancing the longevity and energy efficiency of magnetoresistance effect elements.
Implementation Method 1
a pure spin current generated in accordance with a spin orbit interaction could also be applied... A pure spin current that has undergone spin-orbit-interaction induces a spin orbit torque (SOT) and can cause magnetization reversal
Data Source
AI summary
A spin current magnetization rotational element according to the present disclosure includes a first ferromagnetic metal layer configured for a direction of magnetization to be changed and a spin-orbit torque wiring extending in a direction intersecting a lamination direction of the first ferromagnetic metal layer and bonded to the first ferromagnetic metal layer. The spin-orbit torque wiring includes a narrow portion, and at least a part of the narrow portion constitutes a junction to the first ferromagnetic metal layer.