Magnetic Sensor Reference Layer Stack for High Spin Polarization
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Solution Overview
Problem
As recording density increases, the need for reduced spacing between shields in magnetic read sensors to maintain signal-to-noise performance is critical, but existing reference layers are inadequate, particularly due to issues with narrower track widths and decreased shield spacing.
Innovation Solution
A reference layer stack comprising a first ferromagnetic layer, a magnetic coupling layer, and a boron-free third ferromagnetic layer is introduced, with specific thicknesses and materials like CoFe, Ta, and MgO, to enhance spin polarization and sensor sensitivity, avoiding plasma treatment that can reduce performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If recording density is increased, then more data can be written in the same space, but signal-to-noise performance deteriorates due to narrower track widths and decreased shield spacing
Solution Approach 1:
The patent changes the material composition and thickness parameters of the reference layer stack. Specifically, it uses a CoFe alloy layer (3-5 nm thick) followed by a CoFeB alloy layer (1.5-3 nm thick), optimizing the thickness and material parameters to maintain high spin polarization despite reduced shield spacing and narrower track widths associated with higher recording densities.
Solution Approach 2:
The patent employs a composite reference layer structure consisting of multiple ferromagnetic layers with different material compositions (CoFe and CoFeB alloys) and distinct magnetic properties. This composite structure enables the system to maintain measurement precision by combining layers with complementary characteristics, achieving high spin polarization that compensates for the deteriorating signal-to-noise ratio at higher recording densities.
2Measurement precision
If shield spacing is reduced to maintain signal-to-noise performance at higher densities, then device dimensions are constrained, but manufacturing precision becomes more difficult to achieve
Solution Approach 1:
The patent optimizes the thickness parameters of the reference layer components (CoFe layer: 3-5 nm, CoFeB layer: 1.5-3 nm) to achieve the desired magnetic properties. By carefully controlling these nanoscale thickness parameters, the invention maintains signal-to-noise performance without requiring extremely tight shield spacing control, thereby reducing manufacturing precision requirements.
Solution Approach 2:
The patent performs preliminary magnetic layer deposition with specific thicknesses and compositions before final assembly. The reference layer stack is pre-configured with optimized CoFe and CoFeB layer thicknesses to establish the desired magnetic properties in advance, which compensates for variations in shield spacing and reduces the need for post-manufacturing adjustments.
3Strength
If plasma treatment is applied to the reference layer, then adhesion is improved, but spin polarization is reduced leading to decreased sensor sensitivity
Solution Approach 1:
The patent extracts or removes the plasma treatment step from the manufacturing process. By eliminating plasma treatment, the invention preserves the spin polarization of the CoFe and CoFeB reference layers, thereby maintaining high sensor sensitivity. The decision to omit plasma treatment, despite potential adhesion benefits, prioritizes the magnetic properties critical for sensor performance.
Solution Approach 2:
The patent accepts potential adhesion issues as a temporary or acceptable compromise rather than applying plasma treatment. The reference layer structure is designed to function effectively without plasma treatment, treating the adhesion challenge as a secondary issue that can be addressed through alternative means if necessary, rather than risking the loss of spin polarization through plasma processing.
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 improved reference layer stack provides high spin polarization and increased sensor sensitivity, effectively maintaining signal-to-noise performance even with narrower track widths and reduced shield spacing.
Implementation Method 1
The improved reference layer stack provides high spin polarization and increased sensor sensitivity
Data Source
AI summary
A magnetic sensor configured to reside in proximity to a recording medium during use having a high spin polarization reference layer stack above AFM layers. The reference layer stack comprises a first boron-free ferromagnetic layer above the AFM coupling layer; a magnetic coupling layer on and in contact with the first boron-free ferromagnetic layer; a second ferromagnetic layer comprising boron deposited on and contact with the magnetic coupling layer; and a boron-free third ferromagnetic layer on and in contact the second ferromagnetic layer. A barrier layer is deposited on and in contact with the boron-free third ferromagnetic layer. In one aspect of the invention, the magnetic coupling layer may comprise at least one of Ta, Ti, or Hf. A process for providing the magnetic sensor is also provided.