Magnetic Memory Using Spin-Orbit Interaction for Reliable Writing
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Solution Overview
Problem
Magnetic random access memories (MRAMs) face challenges in miniaturization due to the need for two transistors per memory cell and precise pulse width control for magnetization switching, and existing spintronics memories have narrower write and read windows due to voltage-controlled magnetic anisotropy (VCMA) requirements.
Innovation Solution
A magnetic memory design with a conductive nonmagnetic layer having a large spin-orbit interaction, where write currents are applied to the nonmagnetic layer to switch magnetization in MTJ elements, and potential differences are adjusted to reduce voltage variations across MTJ elements, allowing for collective writing and reading with reduced resistance variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage-controlled magnetic anisotropy (VCMA) is used for magnetization switching, then magnetization switching can be achieved, but the write window becomes narrower and pulse width control precision requirements increase
Solution Approach 1:
The patent changes the control parameter from voltage (VCMA) to current density applied to the nonmagnetic layer. By using spin-orbit interaction, the magnetization switching is achieved through current-induced spin torque rather than voltage-controlled anisotropy, thereby widening the write window and reducing pulse width control precision requirements
Solution Approach 2:
The patent introduces a nonmagnetic layer with large spin-orbit interaction as an intermediary between the current source and the magnetic layers. This nonmagnetic layer converts charge current into spin current through spin-orbit coupling, which then exerts torque on the storage layer to switch its magnetization, thereby solving the control precision issue
2Ease of operation
If write current is applied through the tunnel barrier in MTJ elements, then magnetization switching can be achieved, but tunnel barrier reliability decreases and read disturb increases
Solution Approach 1:
The patent segments the current path by introducing a separate nonmagnetic layer for write current. The write current flows through the nonmagnetic layer rather than the tunnel barrier, while the read current still flows through the MTJ element including the tunnel barrier. This segmentation allows independent optimization of write and read operations
Solution Approach 2:
The nonmagnetic layer with large spin-orbit interaction serves as an intermediary that enables magnetization switching without current passing through the tunnel barrier. The spin-orbit coupling in this layer generates spin torque that switches the storage layer magnetization, thereby protecting the tunnel barrier from write current damage
3Productivity
If MTJ elements are arranged on a nonmagnetic layer for collective writing, then productivity improves, but resistance variation across elements increases
Solution Approach 1:
The patent addresses resistance variation by carefully controlling the potential distribution across the nonmagnetic layer. By ensuring uniform current density distribution and appropriate contact positioning, the patent minimizes potential differences across different MTJ elements, thereby reducing resistance variation and improving manufacturing precision
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 magnetization switching and reading with reduced resistance variation across MTJ elements, improving miniaturization and operational reliability by maintaining consistent voltage and current paths.
Implementation Method 1
A magnetic memory design with a conductive nonmagnetic layer having a large spin-orbit interaction, where write currents are applied to the nonmagnetic layer to switch magnetization in MTJ elements
Implementation Method 2
The intermediate insulating layer is called the tunnel barrier, and is formed with an insulator that is very thin but can allow a tunneling current to flow
Implementation Method 3
When the magnetization directions of the storage layer and the reference layer are parallel to each other, the electrical resistance between the storage layer and the reference layer via the tunnel barrier is low, because of a magnetoresistive effect
Implementation Method 4
there also are known MRAMs in which voltage is applied to an MTJ element, and a magnetization switching is caused by virtue of a voltage-controlled magnetic anisotropy (VCMA) effect that changes the anisotropy energy of magnetization
Data Source
AI summary
A magnetic memory includes: a first and second terminals; a conductive layer including first to fourth regions, the first and fourth regions being electrically connected to the first and second terminals respectively; a first magnetoresistive element including: a first and second magnetic layers; a first nonmagnetic layer between the first and second magnetic layers; and a third terminal electrically connected to the first magnetic layer; a second magnetoresistive element including: a third and fourth magnetic layers; a second nonmagnetic layer between the third and fourth magnetic layers; and a fourth terminal electrically connected to the third magnetic layer; and a circuit configured to apply a write current between the first terminal and the second terminal and apply a first and second potentials to the third and fourth terminals respectively to write the first and second magnetoresistive elements, the first and second potentials being different from each other.