Spin-Orbit Torque Wiring for Low-Current Magnetization Reversal
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Solution Overview
Problem
Magnetization reversal in TMR and GMR elements requires high current densities, which affects durability and energy efficiency, particularly when writing information, and existing methods using spin transfer torque (STT) do not adequately address these issues.
Innovation Solution
A spin current magnetization reversal element utilizing a pure spin current generated by spin-orbit interaction, combined with a spin-orbit torque wiring that includes a low-resistance portion and a pure spin current generator, allows for magnetization reversal without net charge flow, thereby reducing current density and improving element longevity.
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 introduces a spin-orbit torque wiring as an intermediary component that generates pure spin current through spin-orbit interaction. This pure spin current acts as a mediator to transfer angular momentum to the ferromagnetic layer for magnetization reversal, while the charge current flows only in the spin-orbit torque wiring and not through the magnetoresistance element, thereby protecting the element from high current stress and improving its lifetime
Solution Approach 2:
The patent replaces the conventional spin transfer torque (STT) method where charge current flows directly through the magnetoresistance element with a spin-orbit torque (SOT) method where pure spin current is generated externally. This substitution eliminates the need for charge current to pass through the element, reducing electrical stress and improving reliability
2Reliability
If pure spin current is generated by spin-orbit interaction, then the current flowing in the magnetoresistance element is reduced to zero, but additional wiring structure complexity is introduced
Solution Approach 1:
The patent modifies the electrical resistance parameter of the spin-orbit torque wiring by introducing a low-resistance portion with different material composition or structure. This parameter change reduces Joule heat generation in the wiring while maintaining the spin-orbit interaction functionality, balancing the trade-off between improved reliability and structural complexity
Solution Approach 2:
The spin-orbit torque wiring is constructed as a composite structure with different portions having different resistance characteristics. The low-resistance portion uses materials or structures optimized for current conduction, while other portions maintain the spin-orbit interaction properties, creating a functionally optimized composite wiring system
3Loss of energy
If low-resistance portion is added to the spin-orbit torque wiring, then Joule heat generation is reduced, but the device structure becomes more complex
Solution Approach 1:
The spin-orbit torque wiring is segmented into functionally distinct portions: a spin-orbit interaction portion that generates pure spin current and a low-resistance portion that efficiently conducts current with minimal Joule heating. This segmentation allows each portion to be optimized for its specific function, reducing overall energy loss while maintaining manufacturability
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 proposed solution enables magnetization reversal with reduced current density, enhancing the durability and energy efficiency of magnetoresistance effect elements by leveraging pure spin current and spin-orbit torque, while minimizing Joule heat generation.
Implementation Method 1
an applicable method using magnetization reversal using pure spin current generated by a spin-orbit interaction has been proposed
Implementation Method 2
The pure spin current generated by the spin-orbit interaction causes a spin-orbit torque (SOT), and magnetization reversal can be caused by a magnitude of the SOT
Implementation Method 3
The pure spin current is generated by the same number of upward spin electrons and downward spin electrons flowing in opposite directions. Here, since the flow of electric charges is canceled, the current is zero in a direction in which the pure spin current flows
Implementation Method 4
a low-resistance portion which is connected to both ends of the generator in the second direction and is formed of a material having a smaller electrical resistivity than the generator
Data Source
AI summary
A spin current magnetization reversal element includes: a first ferromagnetic metal layer with a changeable magnetization direction, and a spin-orbit torque wiring, wherein a first direction is defined as a direction perpendicular to a surface of the first ferromagnetic metal layer, the wiring extends in a second direction intersecting the first and is bonded to a first surface of the first ferromagnetic metal layer, wherein the wiring includes a pure spin current generator which is bonded to the metal layer, and a low-resistance portion which is connected to both ends of the generator in the second direction and is formed of a material having a smaller electrical resistivity than the generator, and the generator is formed so that an area of a cross-section orthogonal to the first direction continuously and/or stepwisely increases as it recedes from a bonding surface bonded to the first ferromagnetic metal layer in the first direction.