TMR Sensor Composite Free Layer for High MR Ratio
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Solution Overview
Problem
TMR sensors face a challenge in maintaining a high MR ratio while keeping the areal resistance (R.A) low, as reducing AlOx thickness to achieve lower R.A results in a decreased MR ratio, and existing solutions struggle to improve this ratio while maintaining magnetic softness and acceptable magnetostriction.
Innovation Solution
Replacing the conventional free layer with a laminate comprising an iron-rich layer, such as Fe-rich FeNi, in combination with other magnetic layers like Permalloy, to enhance the MR ratio while maintaining magnetic softness and suitable magnetostriction, and using a process compatible with existing TMR device manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If AlOx thickness is reduced to achieve lower areal resistance, then areal resistance decreases, but MR ratio drops
Solution Approach 1:
The patent applies composite materials by creating a free layer composed of multiple magnetic sublayers (CoFeB, CoFe, and NiFe layers) with specific thickness ratios. This composite structure enables the system to achieve both low areal resistance and high MR ratio simultaneously, resolving the contradiction between these two parameters that cannot be achieved with single-material layers.
Solution Approach 2:
The patent utilizes parameter changes by precisely controlling the thickness parameters of each sublayer in the composite free layer. By optimizing the thickness ratios of CoFeB, CoFe, and NiFe layers, the patent achieves the desired balance between areal resistance and MR ratio, demonstrating how parameter optimization can resolve technical contradictions.
2Measurement precision
If conventional free layer structure is used, then manufacturing is simple, but MR ratio cannot be improved while maintaining magnetic softness
Solution Approach 1:
The patent employs composite materials by constructing the free layer from multiple magnetic sublayers (CoFeB, CoFe, NiFe) rather than using a conventional single-layer structure. This composite approach enables improved MR ratio and magnetic softness while the patent maintains compatibility with existing manufacturing processes, thus managing the complexity increase.
Solution Approach 2:
The patent applies segmentation by dividing the free layer into multiple functional sublayers, each with specific magnetic properties. The CoFeB layer provides high spin polarization, the CoFe layer provides magnetic coupling, and the NiFe layer provides magnetic softness. This segmentation allows independent optimization of each sublayer's properties to achieve the overall performance goals.
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 new composite free layer structure significantly enhances the MR ratio while keeping the areal resistance low, allowing for adjustable magnetic softness and magnetostriction, as demonstrated by comparison with reference samples, with no change in the manufacturing process flow.
Implementation Method 1
A related effect to the GMR phenomenon described above is tunneling magnetic resistance (TMR) in which the layer that separates the free and pinned layers is a non-magnetic insulator, such as alumina or silica.
Implementation Method 2
The latter is a synthetic antiferromagnet formed by sandwiching antiferromagnetic coupling layer 14 between two antiparallel ferromagnetic layers 13 (AP2) and 15 (AP1).
Implementation Method 3
The change of resistivity of certain materials in the presence of a magnetic field (magneto-resistance or MR). Magneto-resistance can be significantly increased by means of a structure known as a spin valve where the resistance increase (known as Giant Magneto-Resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel
Data Source
AI summary
The conventional free layer in a TMR read head has been replaced by a composite of two or more magnetic layers, one of which is iron rich The result is an improved device that has a higher MR ratio than prior art devices, while still maintaining free layer softness and acceptable magnetostriction. A process for manufacturing the device is also described.