SOT Magnetic Memory Layout for Dense MRAM With Stable Switching
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Solution Overview
Problem
The challenge of achieving high integration density in magnetic random access memory (MRAM) is hindered by the decrease in magnetization stability of TMR elements when made compact, leading to data rewriting issues and increased current requirements, which affect operating life and integration rate.
Innovation Solution
A magnetic memory design incorporating spin-orbit torque (SOT) wiring lines intersecting with magnetoresistance effect elements, utilizing a novel control element configuration to reduce reversal current and increase integration density, with specific arrangements and orientations of ferromagnetic layers and control elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TMR elements are made more compact to achieve high integration density, then integration density is improved, but magnetization stability decreases
Solution Approach 1:
The patent introduces a shape anisotropy factor through specific geometric configuration of the ferromagnetic layer (elongated shape with defined long axis orientation). This changes the magnetic anisotropy parameters to provide directional stability, allowing compact elements to maintain magnetization stability through shape-dependent anisotropy rather than relying solely on volume
Solution Approach 2:
The ferromagnetic layer is designed with asymmetric elongated geometry where the long axis is oriented in a specific direction (first direction) perpendicular to the stacking direction. This asymmetric shape creates shape anisotropy that stabilizes magnetization along the long axis, enabling compact design while maintaining stability
2Reliability
If the volume of ferromagnetic layers is increased to raise magnetization stability, then magnetization stability is improved, but integration density decreases
Solution Approach 1:
The patent changes the magnetic anisotropy parameters by introducing shape anisotropy through elongated geometry. This allows the magnetization stability to be maintained through directional constraints rather than increased volume, enabling compact high-density integration
Solution Approach 2:
The patent transitions from relying on volumetric stability to shape-based stability by introducing geometric dimensions (elongated shape with specific long axis orientation). This dimensional approach allows compact volume while maintaining stability through shape constraints
3Ease of operation
If current density is increased to reverse magnetization by STT, then magnetization reversal is achieved, but element operating life decreases
Solution Approach 1:
The patent changes the magnetic anisotropy parameters to create shape anisotropy with a preferred magnetization direction along the long axis. This reduces the current density required for magnetization reversal by providing a defined easy axis, thereby achieving magnetization reversal with lower currents that preserve element operating life
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 design effectively lowers reversal current and enhances integration density by optimizing current flow and reducing leak currents, while maintaining data stability and reducing the number of control elements required per element.
Implementation Method 1
a method in which a spin transfer torque (STT) generated by passing an electric current through the stacking direction of a magnetoresistance effect element is used to perform writing (magnetization reversal)
Implementation Method 2
tunnel magnetoresistance (TMR) elements which use insulating layers (tunnel barrier layers, barrier layers) for the non-magnetic layers
Data Source
AI summary
A magnetic memory including a plurality of magnetoresistance effect elements that hold information, each including a first ferromagnetic metal layer with a fixed magnetization direction, a second ferromagnetic metal layer with a varying magnetization direction, and a non-magnetic layer sandwiched between the first and second ferromagnetic metal layers; a plurality of first control elements that control reading of the information, wherein each of the plurality of first ferromagnetic metal layers is connected to a first control element, a plurality of spin-orbit torque wiring lines that extend in a second direction intersecting with a first direction which is a stacking direction of the magnetoresistance effect elements, wherein each of the second ferromagnetic metal layers is joined to one spin-orbit torque wiring line; a plurality of second control elements that control electric current flowing through the spin-orbit torque wiring lines.