TMR Sensor 3-Axis Sensing via Magnetization Merging

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Solution Overview

Problem

Existing magnetic field sensing technologies using tunneling magneto-resistor (TMR) devices face challenges in achieving accurate and cost-effective 3-axis magnetic field sensing due to the need for multiple MTJ devices, which increases fabrication costs and can result in low yield and loss of linearity and accuracy in sensing.

Innovation Solution

The method involves using a pair of TMR sensors with specific angle configurations of their free magnetizations relative to pinned directions in alternating periods to sense magnetic fields, allowing for the summation of conductance differences to determine magnetic field intensity, reducing the number of required MTJ devices and improving sensing accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If multiple MTJ devices are used to achieve accurate 3-axis magnetic field sensing, then sensing accuracy is improved, but fabrication cost increases and yield decreases

Engineering Contradiction:

Improvesensing accuracyVSAvoidnumber of MTJ devices

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent combines multiple sensing functions into a single MTJ device by utilizing different magnetization orientation configurations (first and second magnetization directions) within the same device structure. This allows one device to perform what previously required multiple separate devices, thereby reducing fabrication cost and improving yield while maintaining sensing accuracy.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The MTJ device is designed with multi-functionality by incorporating both first and second magnetization directions that can be selectively activated. This universal design enables the single device to sense magnetic fields in multiple directions (3-axis sensing capability), replacing the need for multiple specialized devices and resolving the contradiction between accuracy and device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If multiple MTJ devices are used for 3-axis magnetic field sensing, then sensing accuracy is improved, but manufacturing cost increases

Engineering Contradiction:

Improvesensing accuracyVSAvoidfabrication cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent merges multiple sensing functions into a single MTJ device structure, eliminating the need to fabricate and integrate multiple separate devices. This reduces manufacturing steps, material costs, and assembly complexity, thereby lowering fabrication cost while maintaining the accuracy required for 3-axis magnetic field sensing.

Inventive Principle:

Principle #5Merging (Combining)

3Adaptability or versatility

If multiple MTJ devices are used for magnetic field sensing, then sensing capability is improved, but yield decreases

Engineering Contradiction:

Improvesensing capabilityVSAvoidyield

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

By combining multiple sensing capabilities into a single device, the patent eliminates the yield losses associated with manufacturing and testing multiple separate MTJ devices. The single device approach ensures consistent performance and reliability while maintaining comprehensive sensing capability across multiple axes.

Inventive Principle:

Principle #5Merging (Combining)

4Device complexity

If asymmetric half range operation is used in bridge circuit for TMR sensors, then device structure is simplified, but linearity and accuracy are lost

Engineering Contradiction:

Improvebridge circuit structureVSAvoidlinearity and accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent employs asymmetric magnetization configurations (first and second magnetization directions at different angles) within the MTJ device to achieve symmetric response characteristics. This allows the device to operate in a full range mode with improved linearity and accuracy, eliminating the need for asymmetric bridge circuit configurations and their associated performance losses.

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 approach enhances the accuracy and reduces the number of MTJ devices needed, thereby lowering fabrication costs and improving yield while maintaining sensing precision across multiple axes.

Implementation Method 1

magnetic field sensing methods and apparatuses using tunneling magneto-resistor devices

Methodology Applied

Scientific EffectTunneling magneto-resistance: Magnetoresistance

Implementation Method 2

the first free magnetization being set to be parallel to the easy-axis and to have a first angle Phi to the first pinned direction

Methodology Applied

Scientific EffectMagnetization orientation: Magnetism

Data Source

PatentUS8816683B2Magnetic field sensing methods and megnetic field sensing apparatuses using tunneling magneto-resistor devices

Publication Date: 2014.08.26 IND TECH RES INST

AI summary

Magnetic field sensing method and apparatus of this disclosure uses two tunneling magneto-resistor (TMR) devices. Angles of the free magnetizations of the two TMR devices with respect to a fixed direction are set in a first to fourth period. In the first to fourth period, the two TMR devices act as a TMR sensing unit and a zero-field reference unit by turns, and each of the conductance difference between the sensing unit and the zero field reference unit is also obtained in each of the first to fourth period. Finally, the four conductance differences are summed up.