SAF Magnetoresistive Stack for Zero-Field Sensor Sensitivity
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Solution Overview
Problem
Existing magnetoresistive stacks face challenges in achieving sensitivity independent of device size and minimizing radiated magnetic fields, which can induce coupling and noise in neighboring sensors.
Innovation Solution
The proposed magnetoresistive stack incorporates two synthetic antiferromagnetic (SAF) layers as both the reference and free layers, with carefully controlled antiferromagnetic RKKY coupling intensities to ensure zero total magnetic moment and independence from device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional spin valve with CoFe/NiFe or CoFeB/NiFe free layer is used, then the sensor can detect magnetic fields, but the magnetic moment of the free layer is quite important causing sensitivity to depend on device size and generating radiated magnetic fields
Solution Approach 1:
The free layer is divided into two separate magnetic layers (first free layer and second free layer) with opposite magnetization directions. Each layer contributes to the magnetic moment in opposite directions, causing cancellation of the total magnetic moment while maintaining the sensing capability through the relative magnetization change between the layers.
Solution Approach 2:
The patent uses two free layers with equal and opposite magnetization moments that act as counterweights to each other. The first free layer has magnetization in one direction while the second free layer has magnetization in the opposite direction, causing the total magnetic moment to be zero while still allowing the sensor to detect external magnetic fields through changes in the relative magnetization states.
2Measurement precision
If the free layer magnetic moment is increased to improve sensitivity, then the sensor becomes more sensitive to external fields, but the radiated magnetic field increases causing coupling with neighboring sensors
Solution Approach 1:
The free layer is segmented into two independent magnetic layers with opposite magnetization directions. This segmentation allows each layer to respond to external fields while their opposing moments cancel the radiated field, preventing coupling with neighboring sensors.
Solution Approach 2:
The patent converts the harmful radiated magnetic field into a beneficial configuration by arranging two free layers with opposite magnetization. The cancellation effect that eliminates radiated fields is achieved by designing the layers to have equal and opposite moments, turning what would be harmful radiation into a useful null effect.
3Volume of moving object
If the device size is reduced to improve integration, then the device becomes more compact, but the sensitivity decreases due to internal dipolar field effects
Solution Approach 1:
The free layer is segmented into two thin magnetic layers separated by a non-magnetic spacer. This segmentation allows the use of thinner layers that reduce dipolar field effects while maintaining the overall sensing functionality, enabling compact device design without sacrificing sensitivity.
Solution Approach 2:
The patent creates a composite structure with alternating magnetic and non-magnetic layers. The non-magnetic spacer between the two free layers prevents strong dipolar interactions while the composite structure maintains the magnetoresistive effect, allowing compact design with preserved sensitivity.
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 configuration results in a magnetoresistive stack with enhanced sensitivity that is not compromised by device size and eliminates radiated magnetic fields, thereby reducing noise and coupling with other sensors.
Implementation Method 1
a first non-magnetic spacer layer between the first magnetic layer and the second magnetic layer with a thickness enabling an antiferromagnetic RKKY coupling between the first magnetic layer and the second magnetic layer
Implementation Method 2
a second non-magnetic spacer layer between the third magnetic layer and the fourth magnetic layer with a thickness enabling an antiferromagnetic RKKY coupling between the third magnetic layer and the fourth magnetic layer
Implementation Method 3
A first antiferromagnetic layer in exchange coupling with the first magnetic layer
Data Source
AI summary
A magnetoresistive stack includes a reference layer including a magnetic layer, an antiferromagnetic layer in exchange coupling with the magnetic layer, a magnetic layer substantially of the same magnetisation as the magnetic layer, a spacer layer between the magnetic layers with a thickness for enabling an antiferromagnetic coupling between the magnetic layers of a first coupling intensity, a free layer having a coercivity of less than 10 microTesla, the free layer including a magnetic layer, an antiferromagnetic layer in exchange coupling with the magnetic layer, a magnetic layer substantially of the same magnetisation as the magnetic layer, a spacer layer between the magnetic layers with a thickness for enabling an antiferromagnetic coupling between the magnetic layers of a second coupling intensity lower than the first coupling intensity, a third spacer layer separating the reference and free layers.