Hybrid SAF Layer for Perpendicular MTJ Thermal Stability
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Solution Overview
Problem
Conventional magnetic tunnel junction (MTJ) devices in MRAMs face challenges in achieving high magnetic anisotropy, thermal stability, and low damping constants, which are essential for improved device performance, particularly when using cobalt/platinum (Co/Pt) or cobalt/nickel (Co/Ni) multilayer stacks.
Innovation Solution
A hybrid structure is introduced, where a fixed layer in the MTJ comprises a first synthetic antiferromagnetic (SAF) multilayer with high perpendicular magnetic anisotropy and damping constant, coupled with a second SAF multilayer having lower damping constant, along with an SAF coupling layer, formed from a cobalt platinum (Co/Pt) multilayer stack coupled with a cobalt nickel (Co/Ni) multilayer stack, to enhance magnetic anisotropy and thermal stability while reducing the damping constant.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single Co/Pt or Co/Ni multilayer stack is used in the fixed layer, then the device structure is simple, but the magnetic anisotropy is insufficient and thermal stability is poor
Solution Approach 1:
The fixed layer is constructed as a composite structure combining two different SAF multilayer stacks (Co/Pt and Co/Ni) with distinct magnetic properties. The first SAF multilayer provides high perpendicular magnetic anisotropy while the second SAF multilayer contributes low damping constant, achieving superior overall performance that neither single-material stack could provide alone.
Solution Approach 2:
The fixed layer is divided into multiple functional segments - specifically two separate SAF multilayer stacks with different material compositions and magnetic characteristics. This segmentation allows each segment to contribute its unique strength (one for high anisotropy, one for low damping) while working together through the SAF coupling layer to achieve the desired combined performance.
2Reliability
If a single SAF multilayer is used in the fixed layer, then the damping constant is reduced, but the thermal stability is insufficient
Solution Approach 1:
The fixed layer employs a composite structure of two SAF multilayer stacks with different material systems (Co/Pt and Co/Ni). The first stack provides high perpendicular magnetic anisotropy for thermal stability, while the second stack contributes low damping constant, achieving a balance that neither single-material stack could achieve alone.
Solution Approach 2:
Different regions of the fixed layer are assigned different material properties optimized for specific functions: the first SAF multilayer is optimized for high perpendicular magnetic anisotropy to ensure thermal stability, while the second SAF multilayer is optimized for low damping constant to facilitate magnetization switching. Each local region contributes its specialized property to the overall device performance.
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 hybrid structure achieves high magnetic anisotropy, good thermal stability, and a lower damping constant, resulting in improved performance of perpendicular magnetic tunnel junction (pMTJ) devices, addressing the limitations of single Co/Pt or Co/Ni multilayer stacks.
Implementation Method 1
The fixed layer also includes an SAF coupling layer between the first and the second SAF multilayers
Implementation Method 2
The first SAF multilayer has a first perpendicular magnetic anisotropy (PMA) and a first damping constant. The second SAF multilayer has a second perpendicular magnetic anisotropy (PMA) and a second damping constant
Data Source
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AI summary
A magnetic tunnel junction (MTJ) device includes a free layer. The MTJ also includes a barrier layer coupled to the free layer. The MTJ also has a fixed layer, coupled to the barrier layer. The fixed layer includes a first synthetic antiferromagnetic (SAF) multilayer having a first perpendicular magnetic anisotropy (PMA) and a first damping constant. The fixed layer also includes a second SAF multilayer having a second perpendicular magnetic anisotropy (PMA) and a second damping constant lower than the first damping constant. The first SAF multilayer is closer to the barrier layer than the second SAF multilayer. The fixed layer also includes a SAF coupling layer between the first and the second SAF multilayers.