Spin-Orbit Torque Magnetic Memory Wiring Layout
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Solution Overview
Problem
Magnetization inversion in TMR and GMR elements using spin transfer torque (STT) faces challenges with high current density, which can reduce the lifespan of these elements, and integration of magnetoresistance effect elements using spin-orbit torque (SOT) generated by spin orbit interaction is not yet practical for production.
Innovation Solution
A magnetic memory design incorporating magnetoresistance effect elements with a first and second ferromagnetic metal layer, a nonmagnetic layer, spin-orbit torque wirings, control elements, and cell selection elements, where the spin-orbit torque wirings extend in a direction intersecting the lamination direction, allowing for efficient integration and reduced current density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spin transfer torque (STT) is used for magnetization inversion in TMR/GMR elements, then magnetization inversion efficiency is improved, but inversion current density becomes excessively high
Solution Approach 1:
The patent introduces a spin-orbit torque wiring layer made of heavy metal (such as Pt, Pd, Ir, Ta, or W) as an intermediary component. This layer generates spin-orbit torque through the spin Hall effect when current flows through it, which then acts on the ferromagnetic layer to induce magnetization inversion. The current flows through the spin-orbit torque wiring rather than directly through the magnetoresistance element, thus protecting the element from high current stress while still achieving efficient magnetization inversion.
2Reliability
If magnetoresistance effect elements are integrated using spin-orbit torque (SOT), then current density in elements is reduced, but integration practicality for production remains unproven
Solution Approach 1:
The patent segments the current path and functional layers into distinct components: a magnetoresistance effect element layer stack (including ferromagnetic layers, nonmagnetic layers, and tunnel barrier layers) and a separate spin-orbit torque wiring layer. This segmentation allows independent optimization of each component and simplifies the manufacturing process, as the spin-orbit torque wiring can be formed as a separate metal layer using standard semiconductor fabrication techniques.
Solution Approach 2:
The spin-orbit torque wiring layer serves multiple functions: it acts as both the current carrying path for generating spin-orbit torque and as part of the readout circuitry for detecting resistance changes in the magnetoresistance element. This multi-functionality reduces the number of separate components needed and simplifies the overall device structure, making it more suitable for practical integration.
3Productivity
If element size is reduced for better integration, then current required for STT writing decreases, but magnetic field writing becomes impossible due to current limits in thin wiring
Solution Approach 1:
The patent changes the fundamental parameter of how magnetization inversion is achieved - transitioning from magnetic field-based writing (which requires thick wiring to handle high currents) to spin-orbit torque-based writing (which uses spin-polarized current through heavy metal layers). This parameter change allows continued scaling to smaller element sizes while maintaining writing capability, as the spin-orbit torque mechanism is more efficient and does not suffer from the same current density limitations as magnetic field writing.
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
This design enables efficient integration of magnetoresistance effect elements using pure spin currents, reducing current density and enhancing the lifespan of TMR and GMR elements, while facilitating practical applications in magnetic memory technology.
Implementation Method 1
magnetization inversion using a pure spin current generated by spin orbit interaction has been studied
Implementation Method 2
A pure spin current generated by spin orbit interaction induces a spin-orbit torque (SOT) and magnetization inversion is caused by the SOT
Implementation Method 3
Giant magnetoresistance (GMR) elements and tunneling magnetoresistance (TMR) elements are known as magnetoresistance effect elements
Implementation Method 4
In TMR elements, an insulating layer (tunnel barrier layer, barrier layer) is used as a nonmagnetic layer
Data Source
AI summary
A magnetic memory includes magnetoresistance effect elements, each of which includes a first ferromagnetic metal layer in which a magnetization direction is fixed, a second ferromagnetic metal layer for a magnetization direction to be changed, and a nonmagnetic layer provided between the first ferromagnetic metal layer and the second ferromagnetic metal layer, a first wiring connected to the first ferromagnetic metal layer of at least one magnetoresistance effect element, spin-orbit torque wirings, each of which is connected to each of the second ferromagnetic metal layers of the magnetoresistance effect elements and extend in a direction intersecting a lamination direction of the magnetoresistance effect element, one first control element connected to the first wiring, one second control element connected to each of first connection points of the spin-orbit torque wirings, and first cell selection elements, each of which is connected to each of second connection points of the spin-orbit torque wirings.