Magnetic Sensor Self-Pinned Layer for AMR Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing magnetic sensors in electric vehicles face instability due to anisotropic magnetoresistance (AMR) effects caused by external magnetic fields, which complicates obtaining stable output characteristics, especially when ambient temperatures change.
Innovation Solution
A magnetic sensor configuration using a self-pinned type ferromagnetic fixed layer with an Ru antiparallel coupling film of specific thickness and equal Curie temperatures for the ferromagnetic films, along with a magnetic balance type current sensor that includes a feedback coil and magnetic shield to cancel induction magnetic fields, reduces AMR effects and enhances stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an Ru film with thickness of 0.75 nm to 0.95 nm (second peak) is used for antiparallel coupling, then the structure is easier to manufacture, but the AMR effect increases and output stability deteriorates
Solution Approach 1:
The patent changes the Ru film thickness parameter from the conventional second peak range (0.75-0.95 nm) to the first peak range (0.2-0.4 nm). This parameter change reduces the AMR effect while maintaining manufacturability, as the first peak thickness is easier to control within a narrower range and achieves better magnetic coupling characteristics.
Solution Approach 2:
The patent applies different Ru film thicknesses to different regions of the magnetic sensor structure. Specifically, the Ru film thickness is optimized locally at the interface between the ferromagnetic layer and the Ru film to be in the first peak range (0.2-0.4 nm), while other portions may have different thicknesses. This local optimization reduces the AMR effect at critical interfaces.
2Ease of manufacture
If the magnetization amount of ferromagnetic films is not equal, then the manufacturing process is simpler, but the AMR effect occurs and measurement precision deteriorates
Solution Approach 1:
The patent uses asymmetric ferromagnetic film structures with different thicknesses (first ferromagnetic layer: 1-5 nm, second ferromagnetic layer: 3-10 nm) but equal magnetization amounts. This asymmetric design with controlled magnetization equality reduces the AMR effect while maintaining manufacturing feasibility through adjusted thickness ratios.
Solution Approach 2:
The patent changes the magnetization amount parameter of the ferromagnetic films to be equal, achieved by adjusting film thicknesses and material compositions. This parameter change eliminates the AMR effect and improves measurement precision while keeping the manufacturing process within reasonable complexity.
3Device complexity
If a conventional fixed resistance element structure is used, then the device complexity is lower, but the output characteristic stability under temperature change is insufficient
Solution Approach 1:
The patent uses a composite structure for the fixed resistance element comprising multiple ferromagnetic layers (CoFeB, CoFe) with different magnetic properties coupled through Ru films. This composite structure achieves temperature-stable resistance characteristics by balancing the magnetic properties of different materials, improving reliability without excessive complexity increase.
Solution Approach 2:
The patent implements a feedback mechanism where the magnetic properties of the ferromagnetic layers are designed to compensate for temperature-induced resistance changes. The equal magnetization amounts and antiparallel coupling create a feedback effect that stabilizes the output characteristic across temperature variations.
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 effectively suppresses AMR effects, ensuring a stable output characteristic across varying temperatures and improves the sensitivity and accuracy of current measurement in electric vehicles.
Implementation Method 1
a magnetoresistance effect element whose resistance value changes owing to application of an induction magnetic field from a current to be measured
Implementation Method 2
a self-pinned type ferromagnetic fixed layer configured to be formed by causing a first ferromagnetic film and a second ferromagnetic film to be antiferromagnetically coupled to each other via an antiparallel coupling film
Data Source
AI summary
A magnetism sensor comprises a magnetoresistive element, the resistance of which changes due to the application of an induced magnetic field from the current being measured, and a fixed-resistance element. The fixed-resistance element has a self-pinned ferromagnetic fixed layer comprising a first ferromagnetic film and a second ferromagnetic film coupled antiferromagnetically with an antiparallel coupling film interposed therebetween. The antiparallel coupling film is a ruthenium film that exhibits an antiferromagnetic coupling effect with a first peak thickness. The difference between the degrees of magnetization of the first ferromagnetic film and the second ferromagnetic film is effectively zero.