p-MTJ Free Layer Boron Extraction for Higher Magnetic Moment
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Solution Overview
Problem
The presence of boron in the free layer of perpendicularly magnetized magnetic tunnel junctions (p-MTJs) leads to a lower magnetic moment and reduced perpendicular magnetic anisotropy, compromising thermal stability and data retention, especially during annealing processes.
Innovation Solution
A process involving low power plasma treatment and natural oxidation of the boron-containing free layer to segregate and remove boron, followed by an annealing step, which enhances boron segregation and forms a volatile boron oxide that can be removed, thereby maintaining the amorphous character and promoting lattice matching with the tunnel barrier and Hk enhancing layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If boron is included in the free layer to enable amorphous deposition and lattice matching, then lattice matching with tunnel barrier and Hk enhancing layers is improved, but magnetic moment and perpendicular magnetic anisotropy are reduced
Solution Approach 1:
The patent extracts boron from the free layer through selective oxidation and segregation processes. The free layer is oxidized to form boron oxide, which then segregates to interfaces or forms separate phases, effectively removing boron from the magnetic matrix while preserving the underlying FeCoB structure that provides high magnetic moment and PMA.
Solution Approach 2:
The patent changes the chemical state of boron from metallic/boride form in the as-deposited layer to oxidized form (boron oxide) through controlled oxidation processes. This parameter change enables boron to be selectively removed or segregated, resolving the contradiction between maintaining lattice matching benefits and eliminating magnetic moment degradation.
2Ease of manufacture
If boron is included in the free layer, then amorphous character is maintained during deposition, but thermal stability is reduced during annealing processes
Solution Approach 1:
The patent applies preliminary oxidation to the free layer before final annealing processes. This pre-oxidation converts boron to boron oxide, which then segregates during subsequent annealing, preventing boron from remaining in the free layer and compromising thermal stability while still allowing the layer to be deposited in an amorphous state initially.
3Stability of the object's composition
If a second metal oxide/free layer interface is introduced to enhance PMA and thermal stability, then thermal stability is improved, but device complexity increases
Solution Approach 1:
The patent makes the tunnel barrier layer and Hk enhancing layer serve dual functions: they provide their original roles (tunneling barrier and anisotropy enhancement) while also acting as interfaces that enhance PMA through the oxidized free layer structure. This multi-functionality improves thermal stability without adding separate dedicated layers, thus avoiding increased 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 approach maintains the magnetic properties and thermal stability of the p-MTJ, achieving a higher magnetic moment and perpendicular anisotropy, enabling improved data retention and read margin in memory applications.
Implementation Method 1
natural oxidation of the boron-containing free layer to segregate and remove boron, followed by an annealing step, which enhances boron segregation and forms a volatile boron oxide
Implementation Method 2
low power plasma treatment and natural oxidation of the boron-containing free layer
Implementation Method 3
followed by an annealing step, which enhances boron segregation and forms a volatile boron oxide that can be removed
Data Source
AI summary
A perpendicularly magnetized magnetic tunnel junction (p-MTJ) is disclosed wherein a boron containing free layer (FL) is subjected to a plasma treatment with inert gas, and a natural oxidation (NOX) process to form B2O3 before overlying layers are deposited. A metal layer such as Mg is deposited on the FL as a first step in forming a Hk enhancing layer that increases FL perpendicular magnetic anisotropy, or as a first step in forming a tunnel barrier layer on the FL. One or more anneal steps are essential in assisting B2O3 segregation from the free layer and thereby increasing the FL magnetic moment. A post-oxidation plasma treatment may also be used to partially remove B2O3 proximate to the FL top surface before the metal layer is deposited. Both plasma treatments use low power (<50 Watts) to remove a maximum of 2 Angstroms FL thickness.