Magnetoresistive Sensor Stress Sensitivity Reduction

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Solution Overview

Problem

Magnetoresistive sensors face inaccuracies due to internal magnetic forces and mechanical stress/strain, which introduce angle errors and magnetoelastic behavior, affecting their performance over temperature and lifetime.

Innovation Solution

A magnetoresistive sensor design with a magnetic free bi-layer sandwiched between two non-magnetic layers, where the non-magnetic layers have atomic radii closely matched to the magnetic free layers to minimize lattice mismatch and reduce stress/strain sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional xMR sensor stacks are used, then the sensor can detect magnetic fields, but the sensor exhibits magnetoelastic behavior causing angle errors due to mechanical stress/strain

Engineering Contradiction:

Improveangle measurement accuracyVSAvoidsensor performance stability over temperature and lifetime

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

A non-magnetic intermediate layer with atomic radius between 1.45 Å and 1.60 Å is introduced between the magnetic free layer and the capping layer. This intermediate layer acts as a stress buffer that decouples the mechanical stress from the magnetic free layer, preventing stress-induced magnetic anisotropy while maintaining the sensor's magnetic field detection capability

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the material parameter (atomic radius) of the intermediate layer to fall within a specific range (1.45-1.60 Å) that optimizes the lattice matching with the magnetic free layer. This parameter optimization minimizes lattice mismatch and reduces stress transfer to the magnetic layer, thereby stabilizing the magnetic properties against temperature and lifetime-induced stress

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If the sensor stack is subjected to mechanical stress during packaging and operation, then the sensor chip is assembled and operated, but additional magnetic anisotropy axes are introduced leading to angle errors

Engineering Contradiction:

Improvesensor chip assemblyVSAvoidangle measurement accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The non-magnetic intermediate layer serves as a protective intermediary that shields the magnetic free layer from mechanical stress during packaging and operation. This layer absorbs and distributes the stress, preventing it from reaching the magnetic layer and causing unwanted magnetic anisotropy

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The intermediate layer is designed beforehand to provide stress cushioning to the magnetic free layer. By pre-configuring this protective layer with appropriate material properties (atomic radius 1.45-1.60 Å), the sensor is prepared in advance to withstand mechanical stress during packaging and operation without developing stress-induced magnetic anisotropy

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 design minimizes lattice mismatch and reduces stress/strain sensitivity, leading to improved accuracy and reliability of magnetoresistive sensors by stabilizing their magnetic properties.

Implementation Method 1

The second non-magnetic layer comprises a non-magnetic material having an atomic radius within 10% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer

Methodology Applied

Scientific EffectLattice mismatch:

Implementation Method 2

Ferromagnetic materials may exhibit a magnetostrictive effect, i.e. upon an external magnetic field a geometric dimension changes

Methodology Applied

Scientific EffectMagnetostriction: Magnetostriction

Implementation Method 3

The inverse effect is the so-called magnetoelastic effect, i.e. a change of a geometric dimension leads to the generation of a magnetic anisotropy axis

Methodology Applied

Scientific EffectMagnetoelastic effect: Magnetoelastic Effects

Data Source

PatentUS11346899B2Magnetoresistive sensor with reduced stress sensitivity

Publication Date: 2022.05.31 INFINEON TECHNOLOGIES AG

AI summary

A magnetoresistive sensor includes a first non-magnetic layer, a second non-magnetic layer, and a magnetic free bi-layer. The magnetic free bi-layer is disposed between first non-magnetic layer and the second non-magnetic layer, the magnetic free bi-layer including a first magnetic free layer coupled to a second magnetic free layer. The first magnetic free layer is coupled to the first non-magnetic layer, and the second magnetic free layer is coupled to the second non-magnetic layer. The second non-magnetic layer comprises a non-magnetic material having an atomic radius within 10% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer.