MR Signal Path Compensation Using Layout-Matched Reference Elements
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Solution Overview
Problem
Magnetic field sensors, particularly magnetoresistance (MR) elements, face challenges in compensating for non-ideal effects such as temperature variation, stress variation, and non-linearity, which are difficult to measure directly and require separate sensors that may not match the primary sensing element, and laser pinning is constrained by area and spacing requirements.
Innovation Solution
The implementation of secondary MR elements, layout-matched to the primary signal path, which are immune to the applied magnetic field, are used to directly measure temperature and stress, with a layout that includes anti-pinned MR arrays in parallel or series, and a bridge configuration with quadrilateral symmetry for enhanced laser pinning and routing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate sensors (e.g., bipolar junction transistors) are used to measure temperature and stress for compensation, then temperature and stress can be measured, but the sensors may not completely match the primary TMR/GMR sensing element, resulting in compensation error
Solution Approach 1:
The patent uses identical TMR/GMR sensing elements for both primary sensing and temperature/stress compensation. These secondary sensing elements are layout-matched to the primary elements, ensuring they experience the same temperature, stress, and environmental conditions. This homogeneity in sensor type and layout ensures that the compensation data accurately reflects the conditions of the primary sensing element, eliminating the mismatch error that would occur with different sensor types.
Solution Approach 2:
The patent creates copies of the primary TMR/GMR sensing elements as secondary sensing elements. These copies are identical in structure and material composition to the primary elements and are positioned to experience the same environmental conditions. By using these copied elements to measure temperature and stress, the system obtains accurate compensation data that directly corresponds to the primary element's conditions.
2Ease of operation
If laser pinning is used to pin MR elements, then the direction of magnetic field sensitivity can be set, but minimum area and minimum spacing to neighboring devices are required, making it difficult to optimize MR area usage
Solution Approach 1:
The patent combines primary and secondary sensing elements into a single integrated structure that shares common magnetic layers and pinning regions. By merging the functionality of multiple elements into one compact unit, the patent eliminates the need for separate laser pinning areas and spacing requirements that would be needed if the elements were implemented separately. This integration achieves both precise magnetic field direction control and optimized area usage.
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 approach allows for accurate compensation of MR elements by directly measuring temperature and stress, optimizing area usage and minimizing metal layers, thereby enhancing the sensitivity and accuracy of magnetic field sensing.
Implementation Method 1
Magnetic field sensors include magnetoresistance (MR) elements. These elements have an electrical resistance that changes in the presence of an external magnetic field.
Implementation Method 2
The resistance of the spin valve changes as a function of the magnetic alignment of the reference and free layers. The magnetic alignment of the free layer moves in response to external magnetic fields.
Implementation Method 3
The bias may be generated by one or more magnetic layers (bias layers) that are magnetically coupled to the free layer. In the absence of an external magnetic field, the bias layers may cause the magnetic alignment of the free layer to default to a predetermined alignment.
Implementation Method 4
MR elements can be locally heated with a laser for laser pinning.
Data Source
AI summary
Methods and apparatus for a magnetic field sensor having a first set of MR elements configured to change in resistance due to an applied magnetic field having an orientation in a sensitive axis of the first set of MR elements and a second set of MR elements that are immune to the applied magnetic field. The second set of MR elements is configured to change in resistance due to temperature. A processor can compensate for the response of the first set of MR elements based on the temperature information from the second set of MR elements.