Dual-Layer Free Layer TMR Element Magnetostriction Control
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Solution Overview
Problem
Designing Tunneling Magnetoresistance (TMR) read elements that achieve high TMR values while maintaining controlled magnetostriction, as excessive magnetostriction can destabilize the sensor and reduce sensitivity, and existing free layers like CoFe or CoFeB offer high TMR but poor magnetic stability.
Innovation Solution
A dual-layer free layer structure in TMR elements, comprising a first ferromagnetic amorphous or polycrystalline layer optimized for TMR and a second layer optimized for magnetostriction, with the second layer exposed to oxygen to reduce magnetostriction, ensuring both high TMR and stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-layer ferromagnetic free layer (e.g., CoFe or CoFeB) is used in TMR elements, then high TMR values are achieved, but magnetostriction becomes excessive causing magnetic instability and reduced sensitivity
Solution Approach 1:
The free layer is divided into two distinct ferromagnetic layers: a first layer (CoFeB or CoFe) optimized for high TMR, and a second layer (NiFe or CoFe) optimized for controlled magnetostriction. This segmentation allows each layer to independently contribute its specialized function, resolving the contradiction between achieving high TMR and maintaining magnetic stability.
Solution Approach 2:
The patent employs a composite free layer structure combining two different ferromagnetic materials with complementary properties. The first layer provides high spin polarization for TMR, while the second layer provides controlled magnetostriction, creating a composite structure that achieves both high TMR and magnetic stability simultaneously.
2Force
If the magnetostriction of the free layer is increased to enhance magnetic moment, then the magnetic moment is strengthened, but the sensor becomes destabilized and sensitivity is reduced
Solution Approach 1:
The magnetic moment function is segmented from the stability function into two separate layers. The first ferromagnetic layer is optimized to provide strong magnetic moment for signal detection, while the second ferromagnetic layer is optimized to provide controlled, reduced magnetostriction for stability. This functional segmentation resolves the contradiction between magnetic moment strength and sensor reliability.
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 dual-layer structure achieves high TMR values with reduced magnetostriction, enhancing the magnetic stability and sensitivity of the TMR elements, thereby optimizing their performance.
Implementation Method 1
TMR read elements differ from GMR elements in that a thin, electrically insulating, tunnel barrier layer (e.g., aluminum oxide or magnesium oxide) is used between the ferromagnetic pinned layer and the ferromagnetic free layer
Implementation Method 2
The composition and configuration of the ferromagnetic free layer of TMR read elements may vary depending on desired implementations... it is desirable to have both high TMR and controlled magnetostriction
Implementation Method 3
the second layer exposed to oxygen to reduce magnetostriction
Data Source
AI summary
Tunneling magnetoresistive (TMR) elements and associated methods of fabrication are disclosed. In one embodiment, the TMR element includes a ferromagnetic pinned layer structure, a tunnel barrier layer, and a free layer having a dual-layer structure. In one embodiment, the free layer includes a first amorphous free layer and a second amorphous free layer. In another embodiment, the free layer includes a first polycrystalline free layer and a second amorphous free layer. The compositions of the first free layer and the second free layer of the dual layer structure differ to provide improved TMR performance and controlled magnetostriction. In one example, the first free layer may have a composition optimized for TMR while the second free layer may have a composition optimized for magnetostriction.