TMR Sensor Vortex Stack for Improved Transfer-Curve Linearity
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Solution Overview
Problem
Magnetic field sensors, particularly those using TMR elements, suffer from non-linear transfer curves and sensitivity errors due to the uncontrolled alignment of the free layer's magnetic vortex, leading to inaccuracies in sensing applications.
Innovation Solution
Incorporating a bias layer, such as an antiferromagnetic layer, to offset the magnetic vortex in the free layer of TMR elements, enhancing linearity and reducing errors by shifting the transfer curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a TMR element with a vortex free layer is used, then the sensing capability is improved, but the transfer curve becomes non-linear causing sensitivity errors
Solution Approach 1:
The patent introduces a bias layer with asymmetric magnetic properties (coercive field Hc) that applies a unidirectional offset field to the vortex free layer. This asymmetric magnetic field shifts the transfer curve horizontally, transforming the non-linear response into a linear one within the operating range, thereby resolving the contradiction between sensing capability and linearity.
Solution Approach 2:
The patent changes the magnetic field parameter by introducing a bias field from the bias layer. This parameter change (adding a constant offset field) modifies the operating point of the TMR element, shifting the transfer curve to achieve linearity while preserving the vortex-induced sensing capability.
2Measurement precision
If the vortex in the free layer is used for sensing, then magnetic field detection is enhanced, but sensitivity errors increase due to uncontrolled vortex alignment
Solution Approach 1:
The bias layer acts as an intermediary between the vortex free layer and the external magnetic field. It provides a controlled offset field that stabilizes the vortex alignment and compensates for manufacturing variations, thereby reducing sensitivity errors without requiring precise control of the vortex itself.
Solution Approach 2:
The bias layer pre-establishes a controlled magnetic offset field before the sensing operation begins. This preliminary action (applying the bias field) prepares the vortex free layer in a known state, compensating for any uncontrolled alignment issues that would otherwise cause sensitivity errors.
3Reliability
If a bias layer is added to offset the vortex, then linearity is improved, but device complexity increases
Solution Approach 1:
The bias layer serves multiple functions simultaneously: it provides the offset field for linearity correction, stabilizes the vortex alignment, and can be integrated into existing TMR stack fabrication processes. This multi-functionality justifies the added layer by delivering multiple benefits from a single structural addition.
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 improved linearity and reduced sensitivity errors in TMR sensors, resulting in more accurate magnetic field sensing.
Implementation Method 1
a bias layer to offset the vortex by magnetic bias
Implementation Method 2
the vortex layer is configured for exchange bias
Implementation Method 3
These elements have an electrical resistance that changes in the presence of an external magnetic field
Implementation Method 4
Spin valves are a type of magnetoresistance element formed from two or more magnetic materials or layers
Implementation Method 5
the vortex layer is configured for RKKY coupling with the bias layer
Data Source
AI summary
Methods and apparatus for devices including TMR elements with a free layer having a vortex layer to provide a magnetic vortex, a spacer layer, a reference layer, and a bias layer to offset the vortex by magnetic exchange bias. Sensor embodiments increase linearity for enhancing sensor performance.