Magnetic Sensor Hysteresis Reduction via Reflux Field
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Solution Overview
Problem
Magnetic sensors used in electric and hybrid cars face challenges in accurately measuring currents due to high hysteresis in magnetoresistive effect elements, which affects measurement accuracy and linearity.
Innovation Solution
A magnetic sensor structure is developed with a ferromagnetic layer (hysteresis cancel layer) laminated opposite to the antiferromagnetic layer to apply a reflux magnetic field, reducing remnant orthogonal components and hysteresis, and functioning as a temperature compensation mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetoresistive effect element with a free magnetic layer is used to detect magnetic fields, then the magnetization direction can be changed by external magnetic fields for detection, but hysteresis occurs due to remnant magnetization components orthogonal to the initial magnetization direction
Solution Approach 1:
An antiferromagnetic layer is introduced as an intermediary between the fixed magnetic layer and the free magnetic layer. This antiferromagnetic layer generates exchange coupling bias that aligns the magnetization direction of the free magnetic layer, reducing remnant orthogonal components and hysteresis while maintaining the ability to detect external magnetic fields.
Solution Approach 2:
The invention changes the magnetic parameters by applying a bias magnetic field during the formation of the antiferromagnetic layer, controlling the exchange coupling bias strength and direction. This parameter adjustment optimizes the alignment of the free magnetic layer's magnetization direction, minimizing hysteresis effects.
2Measurement precision
If a hard bias layer formed of a permanent magnet is provided to apply bias magnetic field, then the magnetization direction can be aligned, but the device complexity increases
Solution Approach 1:
The invention extracts the bias magnetic field generation function from a separate hard bias layer (permanent magnet) and integrates it into the antiferromagnetic layer itself through exchange coupling. This eliminates the need for an additional hard bias layer structure, reducing device complexity while maintaining magnetization alignment capability.
Solution Approach 2:
The antiferromagnetic layer is merged with multiple functions: it provides exchange coupling bias to align the free magnetic layer, generates the necessary magnetic field alignment, and reduces hysteresis. This consolidation of functions into a single layer reduces overall device complexity compared to using separate hard bias layers.
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 solution effectively reduces hysteresis and improves measurement accuracy and linearity of the magnetic sensor, enabling more precise current detection in electric and hybrid cars.
Implementation Method 1
an antiferromagnetic layer which is able to generate an exchange coupling bias with the free magnetic layer and which is able to align the magnetization direction of the free magnetic layer in a predetermined direction
Implementation Method 2
a ferromagnetic layer which generates an exchange coupling bias with the antiferromagnetic layer and which is able to align the magnetization direction thereof in a predetermined direction
Implementation Method 3
the ferromagnetic layer is able to impart a reflux magnetic field having a component in a direction along the sensitivity axis to the free magnetic layer
Implementation Method 4
a magnetoresistive effect element having a sensitivity axis in a specific direction; the magnetoresistive effect element has a laminate structure in which a fixed magnetic layer and a free magnetic layer are laminated to each other
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A magnetic sensor (1) is provided which includes: a magnetoresistive effect element (11) in which a fixed magnetic layer (21) and a free magnetic layer (23) are laminated to each other with a nonmagnetic material layer (23) provided therebetween; at a side of the free magnetic layer opposite to the side thereof facing the nonmagnetic material layer, an antiferromagnetic layer (24) which generates an exchange coupling bias with the free magnetic layer and which aligns the magnetization direction of the free magnetic layer in a predetermined direction in a magnetization changeable state; and at a side of the antiferromagnetic layer opposite to the side thereof facing the free magnetic layer, a ferromagnetic layer (25) which generates an exchange coupling bias with the antiferromagnetic layer and which aligns the magnetization direction thereof in a predetermined direction in a magnetization changeable state. The magnetization direction based on the exchange coupling bias generated in the free magnetic layer is the same direction as the magnetization direction based on the exchange coupling bias generated in the ferromagnetic layer, and the ferromagnetic layer is able to impart a reflux magnetic field having a component in a direction along a sensitivity axis (D2) to the free magnetic layer.