Laminated Free Layer for Magnetic Read Transducer Corrosion
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Solution Overview
Problem
Conventional magnetic recording read transducers with CoFe/CoB bilayer free layers are prone to corrosion and residual stress during fabrication, which can lead to peeling or cracking, and have high electron corrosion potential, limiting their performance and durability.
Innovation Solution
A laminated free layer structure is introduced, comprising ferromagnetic layers interleaved with additional corrosion-resistant layers such as NiFe, Ru, or MgO, which reduces corrosion potential and enhances resistance to defects like delamination and lateral corrosion propagation, thereby improving the transducer's performance and manufacturability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a CoFe/CoB bilayer free layer is used to achieve higher moment and lower magnetostriction, then the magnetic performance is improved, but the corrosion resistance deteriorates and residual stress increases
Solution Approach 1:
The patent applies composite materials by creating a laminated free layer structure that combines CoFeB layers with corrosion-resistant barrier layers (such as Ru, Rh, Ir, or their alloys). This composite structure integrates the high magnetic moment properties of CoFeB with the corrosion resistance of the barrier layers, resolving the contradiction between magnetic performance and corrosion resistance. The alternating layers allow each material to contribute its advantageous properties while mitigating its disadvantages.
Solution Approach 2:
The patent segments the free layer into multiple thin layers (CoFeB layers and barrier layers) rather than using a single thick CoFe/CoB bilayer. This segmentation reduces the overall corrosion potential by distributing the vulnerable magnetic layers among protective barrier layers, while maintaining the necessary magnetic moment through the cumulative effect of multiple CoFeB segments. It also helps manage residual stress by distributing it across multiple thin interfaces.
2Strength
If a CoFe/CoB bilayer free layer is used to achieve higher moment and lower magnetostriction, then the magnetic performance is improved, but residual stress increases causing peeling or cracking
Solution Approach 1:
The patent segments the free layer into multiple thin CoFeB layers separated by barrier layers. This segmentation reduces residual stress by distributing it across multiple thin interfaces rather than concentrating it in a single thick layer. Each thin CoFeB layer experiences less cumulative stress, and the barrier layers act as stress buffers, preventing peeling and cracking while maintaining the necessary magnetic moment through the cumulative magnetic contribution of all CoFeB segments.
Solution Approach 2:
The patent applies local quality by placing corrosion-resistant barrier layers specifically at strategic positions within the free layer structure, adjacent to the CoFeB magnetic layers. This localized placement of protective materials provides stress management and corrosion protection exactly where needed at the interfaces, while the CoFeB layers maintain their magnetic functionality. Each local region has optimized properties: CoFeB for magnetic moment and barrier layers for stress management and corrosion resistance.
3Strength
If a CoFe/CoB bilayer free layer is used, then the magnetic performance is improved, but the electron corrosion potential increases making the sensor more susceptible to corrosion during fabrication
Solution Approach 1:
The patent applies composite materials by creating a laminated free layer structure that combines CoFeB layers with corrosion-resistant barrier layers (such as Ru, Rh, Ir, or their alloys). This composite structure integrates the high magnetic moment properties of CoFeB with the corrosion resistance of the barrier layers, resolving the contradiction between magnetic performance and corrosion resistance. The alternating layers allow each material to contribute its advantageous properties while mitigating its disadvantages.
Solution Approach 2:
The patent uses barrier layers (Ru, Rh, Ir, or their alloys) as intermediary materials between the CoFeB magnetic layers and the external environment. These intermediary barrier layers have low electron corrosion potential and act as protective mediators, preventing direct exposure of the CoFeB layers to corrosive chemicals during fabrication. The barrier layers transmit magnetic fields while blocking corrosive effects, thus protecting the magnetic layers without compromising their functionality.
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 laminated free layer structure significantly reduces corrosion and residual stress, leading to improved performance and manufacturability of magnetic recording read transducers, enhancing their capability to resist corrosion and maintain structural integrity.
Implementation Method 1
Each of the additional layer(s) has a higher corrosion resistance than all of the ferromagnetic layers. The laminated free layer structure significantly reduces corrosion and residual stress
Implementation Method 2
The free layer 15 may also be subject to residual stress. Residual stress may be induced during the deposition and post anneal of the CoB portion of the free layer 15
Implementation Method 3
The read sensor 14 is typically a giant magnetoresistive (GMR) sensor or tunneling magnetoresistive (TMR) sensor. The free layer 15 has a magnetization sensitive to an external magnetic field
Implementation Method 4
Residual stress may be induced during the deposition and post anneal of the CoB portion of the free layer 15
Data Source
AI summary
A method and system provide a magnetic transducer including a first shield, a read sensor, and a second shield. The read sensor is between the first shield and the second shield. The read sensor has a free layer including a plurality of ferromagnetic layers interleaved with and sandwiching at least one additional layer. Each of the ferromagnetic layers includes at least one of Fe, Co and B and has a first corrosion resistance. The additional layer(s) have a second corrosion resistance greater than the first corrosion resistance.