MTJ Sensor Domain Stable Free Layer Segmentation
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Solution Overview
Problem
Conventional magnetic field sensors using MTJ or GMR devices require longitudinal bias magnetization to maintain free layer stability, which increases costs and reduces sensitivity due to potential hysteresis caused by large external magnetic fields.
Innovation Solution
Subdividing the free layer into multiple elements with an aspect ratio of at least 1.2, ensuring they are smaller than the Néel wall width, making them domain stable without the need for longitudinal bias, thus eliminating the requirement for bias magnets and enhancing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If longitudinal bias magnetization is used to maintain free layer stability, then the free layer remains stable under external magnetic fields, but the device sensitivity is reduced and manufacturing cost increases
Solution Approach 1:
The free layer is divided into multiple segments (first free layer and second free layer) with different magnetization directions. Each segment responds differently to external magnetic fields, and their combined effect provides stability without requiring longitudinal bias magnets, thereby maintaining sensitivity.
Solution Approach 2:
Different regions of the free layer are given different magnetic properties through selective magnetization directions. The first free layer has magnetization in a first direction while the second free layer has magnetization in a second direction, creating local quality variations that enable stable operation without bias magnets.
2Stability of the object's composition
If longitudinal bias magnets are added to prevent multi-domain states, then the free layer remains single-domain, but the device complexity and manufacturing cost increase
Solution Approach 1:
The bias magnets are extracted and removed from the device structure. Instead of using external bias magnets, the patent achieves single-domain stability through the intrinsic properties of the segmented free layer structure itself, eliminating the need for additional bias magnet components.
Solution Approach 2:
The free layer structure serves its own stabilization function without requiring external bias magnets. The segmented design with different magnetization directions creates self-stabilizing effects that maintain single-domain states under external magnetic fields, making the device self-sufficient.
3Measurement precision
If the free layer is made larger to improve signal strength, then the sensing capability increases, but the free layer becomes susceptible to multi-domain states under external fields
Solution Approach 1:
The free layer is segmented into multiple smaller regions (first and second free layers) that can be larger in overall area for improved signal strength, while each segment remains small enough to maintain single-domain stability. The segmentation allows the structure to achieve both large total area and small local dimensions.
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 allows for a more compact, cost-effective magnetic field sensor that remains stable under large external magnetic fields, reducing hysteresis and improving sensitivity, while being impervious to local temperature fluctuations and external field variations.
Implementation Method 1
magnetic field detection by MTJ or GMR devices
Implementation Method 2
GMR (Giant Magneto Resistance) bearing stripes
Implementation Method 3
giving the free layer magnetization shape anisotropy in the longitudinal direction
Data Source
AI summary
By subdividing the free layer of a GMR/TMR device into multiple sub-elements that share common top and bottom electrodes, a magnetic detector is produced that is domain stable in the presence of large stray fields, thereby eliminating the need for longitudinal bias magnets. Said detector may be used to measure electric currents without being affected by local temperature fluctuations and/or stray fields.