Active Shield MR Sensor Pinning Layer
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Solution Overview
Problem
Fabricating metallic CPP MR sensors with a thickness less than 300 Å while maintaining adequate read signal performance is challenging, as large sensor thicknesses are required for optimal performance but hinder higher density recording, and TMR-based sensors face similar issues at smaller spacings.
Innovation Solution
One of the shields in the MR sensor is used as an active portion, orthogonally coupled to the pinned layer through a thin AFM material layer, eliminating the need for a conventional AFM pinning layer and reducing the overall sensor thickness, thereby enabling higher density recording and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional AFM pinning layer is used in the MR sensor, then the pinned layer magnetic moment is fixed perpendicular to the ABS, but the sensor thickness increases beyond 300 Å, preventing higher density recording
Solution Approach 1:
The shield and pinning layer are merged into a single integrated structure. The shield layers (first shield 401 and second shield 402) directly provide the pinning function through orthogonal coupling to the pinned layer, eliminating the need for a separate AFM pinning layer. This merging reduces the sensor thickness to below 300 Å while maintaining the necessary magnetic pinning function for reliable read signal performance.
Solution Approach 2:
The shield layers perform multiple functions: they provide magnetic shielding to absorb stray fields from neighboring transitions, and simultaneously serve as the pinning layer through orthogonal coupling to fix the pinned layer magnetic moment. This multi-functionality eliminates the need for dedicated AFM pinning layers while maintaining both shielding and pinning requirements for adequate read signal performance.
2Productivity
If the sensor thickness is reduced to enable higher density recording, then the spacing between shields decreases, but the read signal amplitude decreases
Solution Approach 1:
The shield magnetic moments are made dynamic rather than fixed. The first shield 401 and second shield 402 are orthogonally coupled to the pinned layer and free layer respectively, allowing their magnetic moments to rotate in response to transitions on the magnetic disk. This dynamic response amplifies the read signal amplitude even at reduced sensor thicknesses, enabling higher density recording while maintaining signal quality.
Solution Approach 2:
The patent uses a composite structure where the shield layers are made of ferromagnetic material (such as CoFe) rather than conventional non-magnetic spacer materials. This composite approach combines the shielding function with the pinning function and adds dynamic response capability, achieving both reduced thickness and maintained signal amplitude.
3Manufacturing precision
If a thin AFM coupling layer is used to orthogonally couple the shield to the pinned layer, then the sensor thickness is reduced, but the coupling strength may be insufficient
Solution Approach 1:
The patent optimizes the parameters of the AFM coupling layer (such as thickness and material composition) to achieve sufficient orthogonal coupling strength. By carefully controlling the coupling layer parameters and the orthogonal coupling angle between the shield and pinned layer, strong enough coupling is achieved to fix the pinned layer magnetic moment while keeping the overall sensor thickness below 300 Å.
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 approach allows for reduced MR sensor thickness, enabling higher density recording and improved signal-to-noise ratio by using the shield as a pinning layer, which is not fixed, allowing the magnetic moment to rotate similarly to the free layer, resulting in a high-amplitude net read signal.
Implementation Method 1
The shield is orthogonally coupled to the pinned layer through an orthogonal coupling layer, such as a thin layer (i.e., 20 Å) of AFM material. Through this structure, the magnetic moment of the shield pins the magnetic moment of the pinned layer transverse to the ABS of the read element
Implementation Method 2
The second pinned (reference) layer is antiparallel coupled with the first pinned (keeper) layer across the antiparallel coupling layer. Accordingly, the magnetization of the second pinned (reference) layer is oriented in a second direction that is antiparallel to the direction of the magnetization of the first pinned (keeper) layer
Implementation Method 3
As the read element passes over the transitions, the magnetic fields of the transitions modulate the resistance of the read element. The change in resistance of the read element is detected by passing a sense current through the read element, and then measuring the change in bias voltage across the read element to generate a read signal
Implementation Method 4
When the transition passes under the MR sensor, the magnetic fields of the transition will rotate the magnetic moment of the free layer, which in turn changes the resistance of the MR sensor
Data Source
AI summary
Read elements and associated methods of fabrication are disclosed. A read element as described herein includes a magnetoresistance (MR) sensor sandwiched between first and second shields. The read element uses the first shield as an active portion of the MR sensor. Instead of implementing an AFM pinning layer in the MR sensor, the first shield takes the place of the AFM pinning layer. The first shield is orthogonally coupled to the pinned layer through an orthogonal coupling layer, such as a thin layer of AFM material. Through this structure, the magnetic moment of the first shield pins the magnetic moment of the pinned layer transverse to the ABS of the read element, and an AFM pinning layer is not needed.