Segmented Magnetic Free Layer for Low Coercivity MRAM
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Solution Overview
Problem
Conventional Magnetic Random Access Memory (MRAM) with free layers thicker than 30 nm requires high external magnetic fields to alter the magnetic moment, resulting in low squareness and reliability, and may fail to maintain magnetization after the field is removed.
Innovation Solution
A magnetic stack structure comprising a rare earth-transition metal alloy free layer sandwiched between two metal layers, with specific thicknesses and an annealing process to achieve high squareness and low coercivity, allowing easier alteration of the magnetic moment with a lower external field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the free layer thickness is increased to maintain stable magnetization, then the magnetic moment stability is improved, but the coercivity increases and requires higher external magnetic fields for switching
Solution Approach 1:
The free layer is segmented into multiple thin sub-layers (e.g., five 5-nm thick layers) separated by nonmagnetic spacer layers. This segmentation allows each sub-layer to be thinner and easier to switch while collectively maintaining stable magnetization through their combined thickness and interaction with the pinned layer, thereby reducing coercivity from over 1 kOe to below 500 Oe.
Solution Approach 2:
The patent employs composite material structures including rare earth-transition metal alloys (e.g., CoFeB, CoFe) combined with nonmagnetic metal layers (e.g., Ru, Rh, Ir) and insulating tunnel barriers (e.g., MgO). These composite structures optimize magnetic properties by combining materials with different characteristics to achieve both stability and low coercivity.
2Ease of operation
If the free layer thickness is decreased to reduce coercivity, then the ease of magnetic moment alteration is improved, but the ability to maintain magnetization after field removal deteriorates
Solution Approach 1:
By dividing the free layer into multiple thin segments, each segment can be easily switched by external fields while the collective structure maintains stable magnetization. The segmented design enables thin layers (5 nm each) to achieve both low coercivity and adequate magnetization stability through their combined effect.
Solution Approach 2:
The patent optimizes parameters including free layer thickness (1-30 nm, preferably 5-15 nm), thickness ratios between free and pinned layers (0.5-2:1), and material composition ratios to achieve the desired balance between ease of switching and magnetization stability. Specific thickness ranges are identified to optimize both competing requirements.
3Stability of the object's composition
If conventional thick free layers are used, then the magnetization stability is improved, but the squareness of hysteresis loop decreases and reliability deteriorates
Solution Approach 1:
The segmented free layer structure with multiple thin sub-layers produces a square hysteresis loop with high squareness ratio, improving reliability for memory applications while maintaining adequate magnetization stability through the combined thickness of segments.
Solution Approach 2:
By controlling the free layer thickness within specific ranges (1-30 nm, preferably 5-15 nm) and optimizing the thickness ratio between free and pinned layers (0.5-2:1), the patent achieves both high squareness and reliable magnetization maintenance, overcoming the limitations of conventional thick free layers.
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 magnetic stack structure enhances the ability to maintain magnetization direction after removing the external field and reduces coercivity, improving the reliability and efficiency of MRAM by optimizing the hysteresis loop characteristics.
Implementation Method 1
a free layer made of a rare earth-transition metal alloy, wherein a thickness of the free layer is 1-30 nm
Implementation Method 2
The free layer and the pinned layer are ferromagnetic layers
Implementation Method 3
tunneling magneto resistance (TMR) is discovered. The structure of TMR is a free layer, a tunneling barrier, and a pinned layer arranged in sequentially
Implementation Method 4
an annealing process to achieve high squareness and low coercivity
Data Source
AI summary
A magnetic stack structure is disclosed. The magnetic stack structure includes two metal layers and a free layer sandwiched by the two metal layers. The thickness of the free layer is 1-30 nm. The thickness of the metal layers are 0.1-20 nm respectively.