CPP MR Sensor Shield with Antiparallel Structure
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Solution Overview
Problem
Current CPP-MR sensors experience noise during read operations due to stray magnetic fields from adjacent data bits and tracks, which affects the spatial resolution and accuracy of magnetic recording disk drives as data density increases.
Innovation Solution
The implementation of an antiparallel structure (APS) with a nonmagnetic antiparallel coupling film between two ferromagnetic films in the top and optionally bottom magnetic shields, along with a nonmagnetic decoupling layer to prevent domain wall movement and reduce noise, results in a shield structure that minimizes hysteresis in transfer curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional magnetic shields are used in CPP-MR sensors, then the shields can absorb stray magnetic fields from adjacent bits and tracks, but domain wall movement in the shield layers causes noise during read operations
Solution Approach 1:
The shield is segmented into multiple functional layers: an electroplated shield layer for absorbing stray magnetic fields, a nonmagnetic decoupling layer to prevent domain wall coupling, and an antiparallel structure with two ferromagnetic films for providing a stable magnetic reference. This segmentation allows each layer to perform its specific function without interfering with others, reducing noise while maintaining shielding effectiveness.
Solution Approach 2:
A nonmagnetic decoupling layer is introduced as an intermediary between the electroplated shield layer and the antiparallel structure. This intermediary layer prevents the transfer of domain wall movements from the electroplated layer to the ferromagnetic layers, thereby eliminating the noise mechanism while preserving the magnetic shielding function of the overall structure.
2Measurement precision
If the sense current is directed perpendicularly through the sensor stack, then the sensor achieves higher sensitivity, but the structure becomes more complex with multiple ferromagnetic and nonmagnetic layers
Solution Approach 1:
The antiparallel structure serves multiple functions simultaneously: it provides magnetic shielding, establishes a stable reference magnetization direction, and reduces noise through domain wall decoupling. The electroplated shield layer also serves dual purposes as both a magnetic shield and an electrical contact. This multi-functionality reduces the need for additional components, offsetting the complexity of the CPP structure.
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 proposed shield structure significantly reduces noise and hysteresis in CPP-MR sensors, ensuring accurate and reliable data reading by decoupling the electroplated shield layer from the ferromagnetic layers, leading to improved magnetic shielding and reduced noise during read operations.
Implementation Method 1
The APC film induces antiferromagnetic (AF) coupling between the two ferromagnetic films so that they have their respective magnetizations oriented antiparallel
Implementation Method 2
the shields ensure that the sensor reads only the information from the bit stored directly beneath it on a specific track of the disk by absorbing any stray magnetic fields emanating from adjacent bits and adjacent tracks
Implementation Method 3
The nonmagnetic decoupling layer is preferably Ru or a NiCr alloy, but may be any nonmagnetic material with a thickness sufficient to magnetically decouple the electroplated shield layer from the APS so that domain wall movement in the electroplated shield layer does not transfer to the ferromagnetic layers in the APS
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... With a sense current applied to the sensor, the rotation of the free-layer magnetization relative to the reference-layer magnetization due to the presence of an external magnetic field is detectable as a change in electrical resistance
Data Source
AI summary
A current-perpendicular-to-the-plane magnetoresistive sensor structure includes at least an improved top shield structure and optionally also a similar bottom shield structure. The top shield structure includes an antiparallel structure (APS) of two ferromagnetic films and a nonmagnetic antiparallel coupling (APC) film between them. The APC film induces antiferromagnetic (AF) coupling between the two ferromagnetic films so that they have their respective magnetizations oriented antiparallel. An important aspect of the APS is that there is no antiferromagnetic layer adjacent the upper ferromagnetic film, so that the upper ferromagnetic film does not have its magnetization pinned by an antiferromagnetic layer. An electroplated shield layer is formed above the APS. A nonmagnetic decoupling layer is located between the APS and the electroplated shield layer to prevent domain wall movement in the electroplated shield from transferring to the ferromagnetic layers in the APS and thus possibly induce noise in the sensor.