GMR Current Sensor Segmented Hard Bias for Hysteresis Reduction
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Solution Overview
Problem
Current sensors with magnetoresistive elements face issues with hysteresis in output signals due to strong magnetization pinning at contact points with hard bias layers, leading to dead zones and reduced measurement accuracy.
Innovation Solution
A current sensor design with magnetoresistive elements featuring spaced-apart stripe-shaped portions and permanent magnet portions between them, where the permanent magnet portions include a hard bias layer and an electrode layer, reducing the contact area and applying a bias magnetic field to provide uniaxial anisotropy, thereby minimizing hysteresis and parasitic resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hard bias layers are formed at the ends and midpoint of GMR elements to apply bias magnetic field, then the linearity between electrical resistance value and external magnetic field intensity is improved, but the magnetization direction at contact portions is strongly pinned causing dead zones and hysteresis
Solution Approach 1:
The patent segments the hard bias layer into multiple smaller hard bias layers arranged in a matrix pattern (multiple rows and columns) across the GMR element. This segmentation distributes the bias magnetic field application across multiple contact points rather than having large continuous contact areas, thereby reducing the dead zone effect while maintaining the necessary bias field for linearity.
Solution Approach 2:
The patent applies hard bias layers selectively at specific locations (ends and midpoint of longitudinal direction, and ends and midpoint of width direction) rather than uniformly across the entire GMR element. This localized application provides bias magnetic field where needed for linearity while minimizing the total contact area that would cause magnetization pinning and dead zones.
2Reliability
If hard bias layers are used to initialize magnetization direction, then hysteresis is reduced, but contact portions become dead zones where magnetization direction cannot change
Solution Approach 1:
By dividing the hard bias layer into multiple smaller segments arranged in a matrix, the patent reduces the continuous contact area between the hard bias layer and the free magnetic layer. This segmentation allows the magnetization direction to change more freely in the regions between contact points, eliminating dead zones while maintaining hysteresis reduction through the distributed bias field application.
Solution Approach 2:
The patent introduces a non-magnetic intermediate layer between the hard bias layer and the free magnetic layer. This intermediary layer reduces the direct magnetic coupling and magnetization pinning effect at the contact interface, allowing the bias magnetic field to be applied without creating strong magnetization pinning that would cause dead zones.
3Device complexity
If GMR elements are disposed parallel to each other in longitudinal direction, then the structure is simplified, but parasitic resistance variations occur affecting measurement accuracy
Solution Approach 1:
The patent introduces asymmetric positioning of hard bias layers by placing them at specific locations (ends and midpoint) rather than uniformly distributing them. This asymmetric arrangement creates intentional variations in the magnetic field distribution that compensate for parasitic resistance variations, thereby improving measurement accuracy while maintaining relatively simple structural implementation.
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 reduces hysteresis and enhances measurement accuracy by minimizing dead zones and parasitic resistance variations, allowing for more precise current measurement.
Implementation Method 1
a hard bias layer that applies a bias magnetic field to the free magnetic layer
Implementation Method 2
applying a bias magnetic field to provide uniaxial anisotropy
Implementation Method 3
a giant magnetoresistive (GMR) element... the current value of a measurement current is detected using electrical resistance values of the GMR elements which are changed depending on the relationship between the magnetization direction
Implementation Method 4
has a magnetization direction that is pinned in a certain direction due to the exchange coupling magnetic field (Hex) which occurs between the antiferromagnetic layer and the ferromagnetic pinned layer
Implementation Method 5
an induction field caused by a measurement current... the free magnetic layer... has a magnetization direction which is changed due to the external magnetic field
Data Source
AI summary
A current sensor includes a magnetoresistive element that has a stripe shape and that has a sensing axis in a certain direction. The magnetoresistive element includes element portions that are disposed so as to be spaced apart from each other in a longitudinal direction of the stripe shape, and permanent magnet portions, each of which is disposed between adjacent ones of the element portions. Each element portion has a layered structure including a free magnetic layer whose magnetization direction is changed with respect to an external magnetic field, a non-magnetic intermediate layer, and a ferromagnetic pinned layer whose magnetization direction is pinned. The permanent magnet portion includes a hard bias layer, and an electrode layer that is disposed so as to cover the hard bias layer.