Gradient Glassing Agent Free Layer for MTJ Thermal Stability
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Solution Overview
Problem
Current magnetic tunnel junction (MTJ) devices face challenges in achieving high thermal stability and reducing critical current density for spin-transfer torque magnetic random access memory (STT-MRAM) while maintaining perpendicular magnetic anisotropy, as crystalline anisotropy plays a detrimental role in thermal stability and is difficult to control.
Innovation Solution
The MTJ structure incorporates a free layer with a gradient of glassing agents, maintaining an amorphous character in the middle region and selectively crystallizing regions at interfaces, enhancing perpendicular magnetic anisotropy and thermal stability through the use of materials like Si, Ta, and CoFeB layers, with a perpendicular Hk enhancing layer to dominate the anisotropy field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a crystalline magnetic layer is used to provide perpendicular magnetic anisotropy, then the magnetic anisotropy is enhanced, but the thermal stability deteriorates due to crystalline anisotropy
Solution Approach 1:
The patent applies local quality by creating a gradient distribution of glassing agents within the magnetic layer. The middle region contains higher concentration of glassing agents to maintain amorphous character and reduce crystalline anisotropy, while interface regions have lower concentration to allow crystallization and enhance perpendicular anisotropy. This spatial variation in material composition resolves the contradiction between thermal stability and magnetic anisotropy.
Solution Approach 2:
The patent uses composite materials by combining ferromagnetic materials (such as CoFeB) with glassing agents (such as Si, Ta, W, Mo, Hf) in specific concentrations. This composite approach allows the magnetic layer to simultaneously exhibit amorphous regions for thermal stability and crystalline regions for perpendicular anisotropy, resolving the fundamental contradiction between these two properties.
2Stability of the object's composition
If the magnetic layer is made amorphous to reduce crystalline anisotropy, then thermal stability is improved, but perpendicular magnetic anisotropy decreases
Solution Approach 1:
The patent applies local quality by creating a gradient distribution of glassing agents within the magnetic layer. The middle region contains higher concentration of glassing agents to maintain amorphous character and reduce crystalline anisotropy, while interface regions have lower concentration to allow crystallization and enhance perpendicular anisotropy. This spatial variation in material composition resolves the contradiction between thermal stability and magnetic anisotropy.
Solution Approach 2:
The patent segments the magnetic layer into functionally distinct regions: an amorphous middle region for thermal stability and crystalline interface regions for perpendicular anisotropy. This segmentation allows each region to optimize its local properties without compromising the overall device performance.
3Stability of the object's composition
If glassing agents are added to maintain amorphous character, then thermal stability is improved, but the device complexity increases
Solution Approach 1:
The patent applies parameter changes by controlling the concentration of glassing agents as a continuous gradient from the middle region to the interface regions. This parameter variation allows precise control over the amorphous-crystalline transition, achieving the desired thermal stability and magnetic anisotropy balance through compositional tuning rather than complex structural design.
Solution Approach 2:
The patent utilizes the controlled crystallization process where glassing agents are strategically positioned to prevent crystallization in the middle region while allowing it at the interfaces. This selective discarding of amorphous character at interfaces and recovery in the middle region optimizes both thermal stability and magnetic anisotropy without adding significant device complexity.
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 configuration achieves higher thermal stability and lower critical current density, enhancing the magnetic tunnel junction's performance by maintaining amorphous character and increasing perpendicular anisotropy, making it suitable for high-density STT-MRAM and other spintronic devices.
Implementation Method 1
the ferromagnetic layer is doped with a glassing agent to retain an amorphous character in a center region thereof and thereby reduce crystalline anisotropy
Implementation Method 2
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 layer and non-magnetic spacer. Through this interaction, the electrons transfer a portion of their angular momentum to the ferromagnetic free layer
Implementation Method 3
exhibiting perpendicular magnetic anisotropy (PMA) wherein the ferromagnetic layer is doped with a glassing agent to retain an amorphous character in a center region thereof and thereby reduce crystalline anisotropy and provide a higher PMA for a given magnetic moment along with higher thermal stability for the device
Data Source
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AI summary
A magnetic element is disclosed wherein first and second interfaces of a free layer with a perpendicular Hk enhancing layer and tunnel barrier, respectively, produce enhanced surface perpendicular anisotropy to increase thermal stability in a magnetic tunnel junction (MTJ). The free layer may be a single layer or a composite and is comprised of one or more glassing agents that have a first concentration in a middle portion thereof and a second concentration less than the first concentration in regions near first and second interfaces. As a result, a CoFeB free layer, for example, selectively crystallizes along first and second interfaces but maintains an amorphous character in a middle region containing a glass agent providing the annealing temperature is less than the crystallization temperature of the middle region. The magnetic element may be part of a spintronic device or serve as a propagation medium in a domain wall motion device.