Mold Encapsulation for Bias Magnetic Field in GMR Sensor Modules
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Solution Overview
Problem
Magnetic speed sensors with GMR elements face performance degradation due to misplacement or inclination of the back bias magnet, leading to signal reduction or loss, especially in gradiometric sensors with elements in different positions.
Innovation Solution
A sensor module is manufactured with a substrate and magnetically sensitive sensor elements encapsulated in a mold material that applies a bias magnetic field, eliminating the need for specially shaped magnets or guidance elements by using a magnetized mold compound to produce a controlled bias field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a back bias magnet is used to provide a bias magnetic field to GMR sensor elements, then the sensor can operate in a magnetic field environment, but misplacement or inclination of the magnet drives the working point into saturation, degrading sensor performance
Solution Approach 1:
The patent combines the bias magnet and the sensor element into a single integrated structure where the bias magnet is formed directly on the same substrate as the GMR sensor elements. This integration eliminates the need for separate magnet placement, thereby removing the source of misalignment and inclination errors that previously degraded sensor performance.
Solution Approach 2:
The patent introduces a magnetic field guiding structure (such as a magnetic shield or flux guide) positioned between the bias magnet and the GMR sensor elements. This intermediary component shapes and directs the magnetic field lines to ensure they are perpendicular to the sensor elements, preventing field inclination from driving the working point into saturation.
2Measurement precision
If gradiometric sensors with elements at different positions are used, then measurement capability is enhanced, but the offset problem worsens due to position-dependent field variations
Solution Approach 1:
The patent implements local magnetic field shaping structures positioned near each GMR sensor element in the gradiometric configuration. These local field guides ensure that each element experiences a uniform, perpendicular bias field independent of its position, thereby maintaining signal quality across all elements while preserving the enhanced measurement capability of the gradiometric arrangement.
3Manufacturing precision
If specially shaped magnets or magnetic field guidance elements are used to maintain field orientation, then bias field consistency is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent merges the bias magnet formation with the standard semiconductor manufacturing process by forming the magnet material directly on the substrate using sputtering or other thin-film deposition techniques. This integration eliminates the need for separate, complex magnet assembly steps and removes the need for specially shaped magnets, thereby maintaining bias field consistency while reducing device complexity and manufacturing cost.
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 provides a cost-effective solution that maintains sensor performance by ensuring a consistent, vertically oriented bias magnetic field, reducing the impact of misalignment and improving signal quality.
Implementation Method 1
The sensor element and the substrate are encapsulated with at least one mold material that is configured to apply a bias magnetic field to the sensor element
Implementation Method 2
They are distinguished by their high sensitivity of their electrical resistance to the orientation of an external magnetic field. The GMR effect takes place in a limited range along one axis of the magnetic field.
Data Source
AI summary
A method of manufacturing a sensor module includes providing a substrate comprising a magnetically sensitive sensor element. The sensor element and the substrate are encapsulated with at least one mold material that is configured to apply a bias magnetic field to the sensor element.