Dual Free Layer Sensor with Positive Ferromagnetic Coupling
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Solution Overview
Problem
The performance of dual free layer read sensors in magnetic hard disk drives depends on the coupling between the free layers, their composition, and internal structure, necessitating improved free layer compositions and structures to enhance sensitivity and efficiency.
Innovation Solution
The implementation of novel laminates and sub-layer compositions for the ferromagnetic free layers, including cobalt iron and amorphous cobalt boron sub-layers, with a non-magnetic spacer or barrier layer to achieve positive ferromagnetic coupling, optimizing the magnetoresistive ratio and scissor mode operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dual free layers are separated by a non-magnetic spacer or barrier layer to enable scissor mode operation, then sensitivity is improved, but coupling between free layers becomes difficult to control
Solution Approach 1:
The patent applies parameter changes by modifying the composition and thickness of ferromagnetic sub-layers (CoFe, CoB, CoFeB) to control the coupling between free layers. By adjusting parameters such as boron content (10-30 atomic percentage), layer thickness (5-100 Angstroms), and material composition, the invention achieves desired positive ferromagnetic coupling while maintaining scissor mode operation and high sensitivity.
Solution Approach 2:
The patent employs composite materials by creating multi-layer ferromagnetic structures with different material compositions. The free layers consist of composite sub-layers including cobalt iron (CoFe), amorphous cobalt boron (CoB), and cobalt iron boron (CoFeB), which work together to achieve both strong coupling and high sensitivity through the composite magnetic properties of these materials.
2Reliability
If free layer composition and structure are optimized to improve coupling, then magnetoresistive ratio is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing each free layer into multiple functional sub-layers with specific compositions and thicknesses. The free layers are segmented into CoFe, CoB, and CoFeB sub-layers, each performing specific functions related to magnetization control and coupling, which simplifies the manufacturing process by allowing independent optimization of each sub-layer.
Solution Approach 2:
The patent uses parameter changes to optimize manufacturing by establishing specific ranges for composition (e.g., boron content of 10-30 atomic percentage) and thickness (5-100 Angstroms) of each sub-layer. These parameter specifications provide clear manufacturing targets that balance performance requirements with fabrication feasibility.
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 enhances the coupling between the free layers, improving the sensitivity and performance of dual free layer read sensors by aligning magnetization directions and skewing them orthogonally, thereby effectively responding to external magnetic fields.
Implementation Method 1
disposed between the first and second ferromagnetic free layers. The first and second ferromagnetic free layers are positively (ferromagnetically) coupled through the non-magnetic spacer or insulative barrier layer
Implementation Method 2
Contemporary read heads typically include a read sensor (e.g. a tunneling magnetoresistive or so-called 'giant' magnetoresistive read sensor)
Data Source
AI summary
A magnetic sensor includes first and second ferromagnetic free layers that are not magnetically pinned, and a non-magnetic spacer layer disposed between them. The first ferromagnetic free layer comprises a first plurality of ferromagnetic sub-layers that includes a first cobalt iron sub-layer that is in contact with the non-magnetic spacer layer, and a first amorphous cobalt boron sub-layer that is not in contact with the non-magnetic spacer layer. The second ferromagnetic free layer comprises a second plurality of ferromagnetic sub-layers that includes a second cobalt iron sub-layer that is in contact with the non-magnetic spacer layer, and a second amorphous cobalt boron sub-layer that is not in contact with the non-magnetic spacer layer. Each of the first and second cobalt iron sub-layers has a composition Co(100−x)Fe(x) with x being in the range of 10 to 90 atomic percentage.