Magnetic Sensor Electrode Symmetry for Stress Anisotropy

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Magnetic sensors with electrodes shaped constant in width and elongated in one direction experience stress anisotropy due to temperature changes, leading to degradation in detection accuracy, especially when the ferromagnetic layers have a non-zero magnetostriction constant.

Innovation Solution

The magnetic sensor design features electrodes with first and second portions having three-fold or higher rotationally symmetric shapes, where the diameter of inscribed circles exceeds the width of the coupling portion, alleviating stress anisotropy in magnetoresistive elements by distributing stress more isotropically.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the electrode is shaped to be constant in width and elongated in one direction, then the electrode can be easily manufactured and connected, but stress anisotropy is induced in the magnetoresistive elements due to temperature changes, degrading detection accuracy

Engineering Contradiction:

Improveease of manufactureVSAvoiddetection accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The electrode is designed with a symmetric shape (circular, square, or rectangular with equal dimensions) rather than the conventional asymmetric elongated shape. This symmetry ensures that stress is distributed uniformly in all directions, preventing stress anisotropy from developing in the magnetoresistive elements during temperature changes, thereby maintaining detection accuracy while remaining manufacturable

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The invention changes the geometric parameters of the electrode from an elongated constant-width shape to a symmetric shape where all dimensions are equal or balanced. This parameter change transforms the stress distribution characteristics, eliminating directional stress preferences that would otherwise cause magnetostriction-related accuracy degradation

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If the electrode is shaped to be constant in width and elongated in one direction, then the electrode structure is simple, but stress anisotropy causes stress magnetic anisotropy in ferromagnetic layers with non-zero magnetostriction constant, degrading detection accuracy

Engineering Contradiction:

Improvedevice complexityVSAvoiddetection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The electrode employs a symmetric geometry (circular, square, or equidimensional rectangular) instead of an asymmetric elongated form. This symmetry prevents the development of stress anisotropy in the ferromagnetic layers, eliminating stress magnetic anisotropy effects that would degrade detection accuracy, while the design remains simple and easy to manufacture

Inventive Principle:

Principle #4Asymmetry

3Reliability

If the electrode contacts the end faces of magnetoresistive elements, then electrical connection is achieved, but stress is induced in the magnetoresistive elements during thermal expansion or contraction, potentially causing stress anisotropy

Engineering Contradiction:

Improveelectrical connectionVSAvoiddetection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The electrode uses a symmetric shape that contacts the end faces of magnetoresistive elements, ensuring that mechanical stress during thermal expansion or contraction is distributed uniformly in all directions. This prevents stress anisotropy from developing, maintaining both reliable electrical connection and accurate detection by eliminating stress-induced magnetic anisotropy

Inventive Principle:

Principle #4Asymmetry

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

This design prevents degradation in detection accuracy by reducing stress anisotropy in the ferromagnetic layers, maintaining the sensor's performance across varying temperatures.

Implementation Method 1

magnetic sensor that employs a spin-valve magnetoresistive (MR) element

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Implementation Method 2

first ferromagnetic layer, a nonmagnetic layer, and a second ferromagnetic layer

Methodology Applied

Scientific EffectFerromagnetism: Ferromagnetism

Implementation Method 3

One of the first and second ferromagnetic layers is a magnetization pinned layer whose magnetization direction is pinned

Methodology Applied

Scientific EffectExchange coupling:

Implementation Method 4

the first and second ferromagnetic layers will have a stress magnetic anisotropy

Methodology Applied

Scientific EffectMagnetostriction: Magnetostriction

Data Source

PatentUS8896304B2Magnetic sensor

Publication Date: 2014.11.25 TDK CORP

AI summary

A magnetic sensor includes first and second MR elements, and an electrode electrically connecting the first and second MR elements to each other. The electrode includes a first portion having a first surface, a second portion having a second surface, and a coupling portion coupling the first and second portions to each other. The first surface is in contact with an end face of the first MR element. The second surface is in contact with an end face of the second MR element. Each of the first and second surfaces has a three-hold or higher rotationally symmetric shape. The diameter of a first inscribed circle inscribed in the outer edge of the first surface and the diameter of the second inscribed circle inscribed in the outer edge of the second surface are greater than the width of the coupling portion.