CoFeB Insertion Layer for TDMR Center Shield Magnetization Alignment
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Solution Overview
Problem
In two-dimensional magnetic recording (TDMR) systems, the magnetization of the center shield is not fully reset to be parallel to the air-bearing surface (ABS) during the annealing process, affecting the stabilization of the lower sensor due to the lower temperature required for this step, which does not fully align the magnetization without disturbing the previously set magnetizations of the upper and lower sensors.
Innovation Solution
A laminated center shield with an antiparallel coupled magnetic structure, including a CoFeB alloy insertion layer below the antiparallel coupling layer, improves the smoothness and crystalline structure, allowing the magnetization of the center shield to be fully aligned parallel to the ABS after the second annealing step.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a second annealing step at lower temperature is performed to reset the magnetization of the center shield to be parallel to the ABS, then the magnetization of the upper and lower sensors is preserved, but the magnetization of the center shield is not fully reset
Solution Approach 1:
The patent introduces a CoFeB alloy insertion layer with specific compositional parameters (Co: 4-40 at%, Fe: 10-30 at%, B: 5-30 at%) to modify the magnetic properties of the center shield. This material composition change enables the center shield to achieve full magnetization alignment parallel to the ABS at the lower annealing temperature (150-250°C) without disturbing the previously set sensor magnetizations, thus resolving the contradiction between preserving sensor stability and achieving precise center shield alignment.
Solution Approach 2:
The patent creates a composite magnetic structure by inserting a CoFeB alloy layer between the antiparallel coupling layer and the soft magnetic layer in the center shield. This composite structure combines the exchange coupling properties of the antiparallel coupling layer with the specific magnetic anisotropy of the CoFeB alloy, enabling the center shield to be fully reset at lower temperatures while maintaining the stability of the sensor layers above it.
2Reliability
If a first annealing step at high temperature is performed to pin the magnetizations of the sensors orthogonal to the ABS, then the sensor magnetizations are stabilized, but the magnetization of the center shield is pinned orthogonal to the ABS and cannot be reset
Solution Approach 1:
The CoFeB alloy insertion layer is designed with specific compositional parameters that give it distinct magnetic properties compared to conventional soft magnetic materials. This parameter change in material composition allows the center shield to respond differently to thermal annealing, enabling full magnetization reset at lower temperatures that do not affect the already-pinned sensor layers, thus resolving the contradiction between maintaining pinning stability and enabling reset capability.
Solution Approach 2:
The CoFeB alloy insertion layer acts as an intermediary between the antiparallel coupling layer and the soft magnetic layer. This intermediate layer mediates the magnetic coupling and enables the center shield to be fully reset at lower temperatures, providing a pathway to resolve the conflict between the high-temperature pinning requirement and the low-temperature reset requirement.
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 solution enhances the stabilization of the lower sensor by ensuring the center shield's magnetization is correctly aligned, improving the signal-to-noise ratio and maintaining the stability of the upper and lower sensor magnetizations, thus improving the overall performance of the TDMR system.
Implementation Method 1
a second annealing step at lower temperature is required to reset the magnetization of the center shield to be parallel to the ABS
Implementation Method 2
the magnetization of the center shield is not fully reset to be parallel to the air-bearing surface (ABS) during the annealing process
Implementation Method 3
The first ferromagnetic layer is ferromagnetically exchange coupled to the side shields of the lower sensor to stabilize the magnetization of the lower sensor's free layer
Implementation Method 4
A GMR spin-valve sensor has a stack of layers that includes two ferromagnetic layers separated by a nonmagnetic electrically conductive spacer layer
Implementation Method 5
the rotation of the free-layer magnetization relative to the pinned-layer magnetization due to the presence of an external magnetic field is detectable as a change in electrical resistance
Implementation Method 6
In a CPP-TMR sensor the amount of tunneling current through the layers depends on the relative orientation of the magnetizations in the two ferromagnetic layers
Data Source
AI summary
A two-dimensional magnetic recording (TDMR) read head structure has the lower read sensor free layer magnetization biased by side shields of soft magnetic material. A center shield between the lower and upper sensors is an antiparallel coupled magnetic structure, i.e., first and second ferromagnetic layers separated by an antiparallel coupling (APC) layer. The first ferromagnetic layer is ferromagnetically exchange coupled to the side shields of the lower sensor to stabilize the magnetization of the lower sensor's free layer. The first ferromagnetic layer of the center shield is a multilayer of a lower NiFe layer and an upper CoFeB alloy layer inserted below the APC layer. The CoFeB alloy insertion layer increases the antiparallel coupling of the first and second ferromagnetic layers of the center shield after two orthogonal anneals so that the magnetization of the first ferromagnetic layer is aligned parallel to the air-bearing surface (ABS) of the TDMR structure.