TMR Sensor Reference Layer Structure for Low High-Field Angular Error
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Solution Overview
Problem
Magnetoresistive sensor elements face challenges in maintaining low angular error at high magnetic fields, as reducing the thickness of ferromagnetic layers to increase stiffness detrimental to magneto-transport properties and results in low TMR response.
Innovation Solution
A magnetoresistive element with a ferromagnetic reference layer, a sense layer, and a tunnel barrier layer, where the reference layer includes a reference coupling layer between a pinned and coupled layer, with a thin Ta insert layer for ferromagnetic exchange coupling, and thermally treated under a magnetic field, maintaining high saturation field and TMR response without decreasing layer thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the thickness of the first and second ferromagnetic reference layers is decreased to increase the stiffness of the SAF structure, then the saturation field and magnetization stability at high applied magnetic fields is improved, but the magneto-transport properties deteriorate and the TMR response becomes very low
Solution Approach 1:
The patent applies local quality by creating a gradient in boron concentration within the ferromagnetic reference layers. The first ferromagnetic reference layer has a boron concentration gradient ranging from 0% at the interface with the antiferromagnetic layer to 20% at the interface with the tunnel barrier layer. This spatial variation in composition allows different regions of the same layer to have different magnetic properties, enabling the structure to maintain both high stiffness and good magneto-transport properties.
Solution Approach 2:
The patent uses composite materials by combining ferromagnetic layers with different boron concentrations in a single continuous layer structure. The first ferromagnetic reference layer is composed of a CoFeB alloy with a graded boron concentration, creating a composite structure that integrates regions with different magnetic characteristics. This composite approach allows the layer to simultaneously provide the stiffness needed for high-field stability and the magneto-transport properties needed for strong TMR response.
2Force
If the thickness of the ferromagnetic reference layers is decreased down to 1.0 nm to increase SAF structure stiffness, then the saturation field increases and magnetization becomes more rigid, but the pinning with the AF layer is lost
Solution Approach 1:
The patent applies local quality by creating a gradient in boron concentration within the ferromagnetic reference layers. The first ferromagnetic reference layer has a boron concentration gradient ranging from 0% at the interface with the antiferromagnetic layer to 20% at the interface with the tunnel barrier layer. This spatial variation in composition allows different regions of the same layer to have different magnetic properties, enabling the structure to maintain both high stiffness and good magneto-transport properties.
Solution Approach 2:
The patent uses composite materials by combining ferromagnetic layers with different boron concentrations in a single continuous layer structure. The first ferromagnetic reference layer is composed of a CoFeB alloy with a graded boron concentration, creating a composite structure that integrates regions with different magnetic characteristics. This composite approach allows the layer to simultaneously provide the stiffness needed for high-field stability and the magneto-transport properties needed for strong TMR response.
3Measurement precision
If the thickness of the ferromagnetic reference layers is decreased to increase stiffness, then the angular error at high magnetic fields is reduced, but the TMR response becomes very low
Solution Approach 1:
The patent applies local quality by creating a gradient in boron concentration within the ferromagnetic reference layers. The first ferromagnetic reference layer has a boron concentration gradient ranging from 0% at the interface with the antiferromagnetic layer to 20% at the interface with the tunnel barrier layer. This spatial variation in composition allows different regions of the same layer to have different magnetic properties, enabling the structure to maintain both high stiffness and good magneto-transport properties.
Solution Approach 2:
The patent uses composite materials by combining ferromagnetic layers with different boron concentrations in a single continuous layer structure. The first ferromagnetic reference layer is composed of a CoFeB alloy with a graded boron concentration, creating a composite structure that integrates regions with different magnetic characteristics. This composite approach allows the layer to simultaneously provide the stiffness needed for high-field stability and the magneto-transport properties needed for strong TMR response.
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 achieves high stiffness and thermal stability with reduced angular error at high magnetic fields, improving accuracy and TMR response, while preserving magnetic layer thickness.
Implementation Method 1
A magnetic sensor element based on the tunnel magnetoresistance (TMR) effect can be used for 2D magnetic field detection
Implementation Method 2
a pinned first ferromagnetic reference layer in contact with an antiferromagnetic layer
Implementation Method 3
thermally treating the magnetoresistive element at 310°C during 90 min under an applied magnetic field of about 1T
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A magnetoresistive element (2) for a two-dimensional magnetic field sensor, comprising: a ferromagnetic reference layer (21) having a fixed reference magnetization (210), a ferromagnetic sense layer (23) having a sense magnetization (230) that can be freely oriented relative to the reference magnetization (210) in the presence of an external magnetic field, and a tunnel barrier layer (22) between the reference and sense ferromagnetic layers (21, 23); the reference layer (21) comprising a reference coupling layer (213) between a reference pinned layer (211) and a reference coupled layer (212); the reference coupled layer (212) comprising a first coupled sublayer (214) in contact with the reference coupling layer (213), a second coupled sublayer (215), a third coupled sublayer (217) and a insert layer (216) between the second and third coupled sublayers (215, 217); the insert layer (216) comprising a transition metal and has a thickness between about 0.1 and about 0.5 nm, and the thickness of the reference coupled layer (212) is between about 1 nm and about 5 nm.