SAF Reference Layer Structure for Low-Stray-Field STT-MRAM
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Solution Overview
Problem
In Magnetoresistive Random Access Memory (MRAM) devices, the stray magnetic field from the reference layer disrupts the thermal stability of the free layer, making it challenging to maintain a robust magnetic switching margin and high packing density, especially as device sizes decrease.
Innovation Solution
A synthetic antiferromagnetic (SAF) structure with intrinsic perpendicular magnetic anisotropy (PMA) is implemented, using a laminated AP2/Ru/CoFeB configuration, where the thickness of the AP2 and CoFeB layers is minimized to reduce the stray field, and antiferromagnetic coupling is enhanced to induce PMA in the CoFeB layer, thereby reducing the net stray field and maintaining high coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional reference layer is used in MRAM devices, then the reference layer provides stable magnetization direction, but the stray magnetic field from the reference layer disrupts the thermal stability of the free layer
Solution Approach 1:
The reference layer is segmented into two separate ferromagnetic layers (AP1 and AP2) with opposite magnetization directions, separated by a nonmagnetic spacer. This segmentation allows the stray fields from each layer to partially cancel each other out, reducing the net stray field affecting the free layer while maintaining stable reference magnetization.
Solution Approach 2:
The synthetic antiferromagnetic structure uses two reference layers with equal and opposite magnetization directions that act as counterweights to each other's stray fields. The opposing magnetic moments create compensating stray fields that reduce the overall harmful magnetic field affecting the free layer's thermal stability.
2Reliability
If the reference layer thickness is increased to enhance magnetic stability, then the reference layer provides stronger magnetization, but the stray field on the free layer increases
Solution Approach 1:
By dividing the reference layer into two thinner layers (AP1 and AP2) with opposite magnetization, each layer generates a smaller stray field individually. The segmentation allows maintaining sufficient reference magnetization stability while reducing the peak stray field magnitude that would affect the free layer.
Solution Approach 2:
The invention changes the magnetic parameters of the reference layer by introducing opposite magnetization directions in two separate layers. This parameter change transforms the stray field distribution, reducing the net harmful field while preserving the reference layer's ability to provide stable magnetization direction.
3Quantity of substance
If device size is reduced to increase packing density, then higher packing density is achieved, but the stray field disruption to thermal stability becomes more significant
Solution Approach 1:
The segmented synthetic antiferromagnetic reference layer structure reduces the stray field footprint, allowing smaller device dimensions without proportionally increasing stray field impact. This enables higher packing density while maintaining adequate thermal stability margins in scaled devices.
Solution Approach 2:
The counterbalancing stray fields from the dual reference layers reduce the net magnetic field disruption, enabling smaller device sizes where stray field effects would normally be more pronounced. This allows achieving higher packing density without sacrificing thermal stability.
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 solution effectively minimizes the stray field on the free layer, enhancing thermal stability and TMR ratio while allowing for higher packing density and scalability in MRAM devices.
Implementation Method 1
antiferromagnetic coupling between a layer with intrinsic perpendicular magnetic anisotropy (PMA) and a CoFeB layer to establish PMA in the latter
Implementation Method 2
The tunnel barrier layer is thin enough that a current through it can be established by quantum mechanical tunneling of conduction electrons
Implementation Method 3
the spin angular moment of electrons incident on a ferromagnetic layer interacts with magnetic moments of the ferromagnetic layer near the interface between the ferromagnetic and non-magnetic spacer. Through this interaction, the electrons transfer a portion of their angular momentum to the ferromagnetic layer
Implementation Method 4
based on the integration of silicon CMOS with MTJ technology, is a major emerging technology that is highly competitive with existing semiconductor memories such as SRAM, DRAM, and Flash
Data Source
AI summary
A synthetic antiferromagnetic structure for a spintronic device is disclosed and has an FL2/Co or Co alloy/antiferromagnetic coupling/Co or Co alloy/CoFeB configuration where FL2 is a ferromagnetic free layer with intrinsic PMA. Antiferromagnetic coupling is improved by inserting a Co or Co alloy dusting layer on top and bottom surfaces of the antiferromagnetic coupling layer. The FL2 layer may be a L10 ordered alloy, a rare earth-transition metal alloy, or an (A1/A2)n laminate where A1 is one of Co, CoFe, or an alloy thereof, and A2 is one of Pt, Pd, Rh, Ru, Ir, Mg, Mo, Os, Si, V, Ni, NiCo, and NiFe, or A1 is Fe and A2 is V. A method is also provided for forming the synthetic antiferromagnetic structure.