Multilayered MR Free Layer Structure for Low-Hysteresis Sensing
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Solution Overview
Problem
Magnetic field sensors, particularly TMR and GMR elements, suffer from hysteresis issues that lead to inaccuracies in angular accuracy and sensing, especially at low fields, which are not adequately addressed by existing technologies.
Innovation Solution
A multilayered free layer structure is introduced in magnetoresistance elements, comprising alternating CoFeB layers and spacer layers, with a thin first CoFeB layer in contact with the barrier layer to reduce hysteresis and increase output amplitude, thereby enhancing angular accuracy and linear response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional single-layer free layer is used in TMR/GMR elements, then the device structure is simple, but hysteresis is large leading to low angular accuracy
Solution Approach 1:
The free layer is segmented into multiple alternating CoFeB and spacer layers instead of using a single continuous layer. This segmentation allows different regions to contribute differently to the magnetic response, reducing hysteresis while maintaining structural complexity at an acceptable level.
Solution Approach 2:
The free layer uses a composite structure combining CoFeB (a soft magnetic material with high spin polarization) and spacer layers (non-magnetic materials). This composite approach leverages the advantageous properties of each material to achieve low hysteresis and high output amplitude simultaneously.
2Measurement precision
If the free layer is made to track the external field perfectly, then angular sensitivity is high, but hysteresis impairs this tracking leading to error
Solution Approach 1:
The magnetic parameters of the free layer are changed by using multiple layers with different thicknesses and compositions. The alternating CoFeB and spacer layers create a cumulative magnetic moment that responds linearly to external fields, improving both tracking accuracy and response linearity.
Solution Approach 2:
Different regions of the multilayered free layer have different local magnetic properties. The CoFeB layers provide high spin polarization while the spacer layers provide magnetic decoupling, creating local quality variations that collectively reduce hysteresis and improve response linearity.
3Measurement precision
If a thin CoFeB layer is used at the barrier interface, then hysteresis is reduced, but the total magnetic moment may be insufficient
Solution Approach 1:
Multiple CoFeB layers are merged in series with spacer layers in between. Each CoFeB layer contributes to the total magnetic moment, and their combined effect accumulates to provide sufficient overall magnetic moment while the thin individual layers at interfaces minimize hysteresis.
Solution Approach 2:
Spacer layers act as intermediaries between CoFeB layers, providing magnetic decoupling that allows each CoFeB layer to contribute independently to the total magnetic moment. This mediator structure enables the system to achieve high total moment without increasing hysteresis.
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 multilayered structure significantly reduces hysteresis and increases output amplitude, leading to improved angular accuracy and more accurate magnetic field sensing.
Implementation Method 1
giant magnetoresistance (GMR) element
Implementation Method 2
Hysteresis is the relative difference between a forward and a reverse angular (or field) sweep at a given field (or angle)
Data Source
AI summary
According to one aspect of the present disclosure, a magnetic field sensor includes a magnetoresistance (MR) element. In some embodiments, the MR element includes a reference layer, a free layer, and a barrier layer. In some embodiments the free layer includes two or more cobalt iron boron (CoFeB) layers, wherein a first one of the CoFeB layers is in contact with the barrier layer, and two or more spacer layers. In some embodiments, the CoFeB layers and the spacer layers alternate to form a multilayered free layer structure. In some embodiments, the magnetic field sensor comprises an angle sensor or a current sensor. In some embodiments, the contact between the first one of the CoFeB layers and the barrier layer is configured to reduce hysteresis in the MR element. In some embodiments, the alternating CoFeB layers and spacer layers are configured to increase output amplitude of the MR element.