2D Magnetic Sensor Sense Layer Structure for Reduced Hysteresis
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Solution Overview
Problem
Conventional magnetoresistive elements exhibit hysteresis in their response to varying external magnetic fields due to local magnetic stray fields, which are challenging to minimize without compromising sensitivity or signal-to-noise ratio.
Innovation Solution
A magnetoresistive element with a sense layer comprising a synthetic antiferromagnetic structure, where the sense layer has a ferromagnetic first sense sublayer and a second sense sublayer separated by a non-magnetic spacer, with a sense magnetic ratio between 0.1 and 0.25, reducing the net stray field and minimizing hysteresis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sense magnetization is saturated to improve sensitivity, then the sensitivity to external magnetic field is improved, but the local magnetic stray field increases causing hysteresis
Solution Approach 1:
The sense layer is divided into two separate ferromagnetic sublayers (first and second sense sublayers) that are antiferromagnetically coupled through a non-magnetic spacer layer. This segmentation allows each sublayer to contribute differently to the net magnetic moment, enabling reduced stray field while maintaining sensitivity.
Solution Approach 2:
The two sense sublayers are designed with different magnetic properties - the first sense sublayer has higher spontaneous magnetization and the second sense sublayer has lower spontaneous magnetization. This local quality difference creates an unbalanced structure where the net magnetic moment is reduced, thereby decreasing the stray field and hysteresis while preserving the sense layer's ability to respond to external fields.
2Object-generated harmful factors
If the thickness of the sense layer is decreased to reduce the stray field, then the hysteresis is reduced, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The sense layer employs an asymmetric structure with two sublayers of different thicknesses and different spontaneous magnetizations. The first sense sublayer is thinner with higher magnetization, while the second sense sublayer is thicker with lower magnetization. This asymmetric design creates a net magnetic moment that is reduced compared to a uniform layer of equivalent total thickness, thereby reducing stray field without sacrificing signal strength.
Solution Approach 2:
The invention changes the magnetic parameters of the sense layer by creating an unbalanced magnetic structure where the net magnetic moment is optimized. By adjusting the thickness and magnetization of each sublayer, the patent achieves a parameter configuration that reduces stray field (and thus hysteresis) while maintaining adequate signal-to-noise ratio for sensitive magnetic field detection.
3Device complexity
If conventional sense layer structures are used to maintain simplicity, then the device complexity is low, but hysteresis response occurs
Solution Approach 1:
The sense layer is segmented into two ferromagnetic sublayers separated by a non-magnetic spacer layer, creating a synthetic antiferromagnetic structure. This segmentation is implemented using standard thin-film deposition techniques, maintaining manufacturing simplicity while effectively reducing the net magnetic moment and associated hysteresis.
Solution Approach 2:
The sense layer is constructed as a composite structure combining ferromagnetic materials with a non-magnetic spacer layer. This composite approach uses materials that are compatible with existing tunnel magnetoresistive technology, allowing the hysteresis reduction to be achieved without significantly increasing device complexity or manufacturing difficulty.
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 results in reduced hysteresis, improved sensitivity, and enhanced signal-to-noise ratio, along with increased sensor lifetime and stability.
Implementation Method 1
a first sense sublayer (231) in contact with the tunnel barrier layer (22) and separated from a second sense sublayer (232) by a first non-magnetic spacer layer (233) such that the first sense sublayer (231) is antiferromagnetically coupled to the second sense sublayer (232)
Implementation Method 2
A magnetoresistive element (10) comprises a tunnel barrier layer (22) included between a reference layer (21) having a reference magnetization (210) and a sense layer (23) having a sense magnetization (230)
Implementation Method 3
the sense magnetization (230) is saturated. However, the saturated sense magnetization (230) induces a local magnetic stray field, shown by numeral 55 in FIG. 1, coupling with the reference layer (21) in a closed magnetic flux configuration
Implementation Method 4
the reference magnetization (210) is pinned by a pinning layer (24), such as an antiferromagnetic layer, by exchange coupling
Data Source
AI summary
A magnetoresistive element for a 2D magnetic sensor, the magnetoresistive element including a tunnel barrier layer included between a reference layer having a reference magnetization and a sense layer having a sense magnetization. The sense layer includes a sense synthetic antiferromagnetic structure including a first sense sublayer in contact with the tunnel barrier layer and separated from a second sense sublayer by a first non-magnetic spacer layer such that the first sense sublayer is antiferromagnetically coupled to the second sense sublayer. The sense layer is configured such that a sense magnetic ratio ΔM defined as:ΔM=MsFM2tFM2-MsFM1tFM1MsFM2tFM2+MsFM1tFM1wherein MSFM1 and MSFM2 are the spontaneous magnetizations of the first and second sense sublayers and tFM1 and tFM2 are the thicknesses of the first and second sense sublayers; and wherein the sense magnetic ratio is between 0.1 and 0.25.