Fluxgate Core Rounded Contour Crack Prevention

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Solution Overview

Problem

Fluxgate magnetometer sensors in microelectronic devices face mechanical failure due to stress in thin film magnetic material from deposition processes and thermal cycling, leading to cracking of dielectric material surrounding the fluxgate core.

Innovation Solution

An integrated fluxgate device with a fluxgate magnetometer sensor featuring a crack-resistant structure at the end of the fluxgate core, including a laterally rounded contour with corner radii of at least 2 microns, a lower metal end structure extending under the core, or an upper metal end structure extending over the core.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the fluxgate core is made thicker to provide desired sensitivity, then the sensitivity is improved, but the stress from thermal cycling increases causing dielectric material cracking

Engineering Contradiction:

ImprovesensitivityVSAvoidmechanical failure resistance

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The fluxgate core is designed with a rounded contour at its end, specifically with corner radii of at least 2 microns. This curvature eliminates sharp corners that would concentrate stress during thermal cycling, thereby preventing cracks in the surrounding dielectric material while maintaining the required core thickness for sensitivity

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent applies different structural characteristics to different parts of the fluxgate core. The main body of the core maintains sufficient thickness for sensitivity, while the end regions are specifically modified with rounded contours and extended metal structures to handle stress concentration, creating localized stress management zones

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If standard sharp-cornered fluxgate core structures are used, then manufacturing is simpler, but stress concentration causes dielectric material cracking

Engineering Contradiction:

Improvefabrication simplicityVSAvoidcrack resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The rounded contour design with corner radii of at least 2 microns is integrated into the standard fabrication process through photolithography and etching. This curvature can be achieved using standard semiconductor manufacturing techniques with appropriately designed masks, adding minimal complexity while dramatically improving crack resistance

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Manufacturing precision

If the fluxgate core has sharp corners, then the manufacturing precision requirements are lower, but stress concentration leads to mechanical failure

Engineering Contradiction:

Improvecorner sharpness toleranceVSAvoidstress resistance

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The design specifies corner radii of at least 2 microns, which is a precise geometric parameter that can be controlled through standard photolithography processes. This curvature requirement is more demanding than sharp corners but remains within achievable precision for semiconductor manufacturing, trading modest precision increases for significant stress resistance improvements

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 crack-resistant structure effectively reduces instances of dielectric material cracking, enhancing the mechanical reliability and sensitivity of the fluxgate sensor while maintaining a balance between sensitivity and cost.

Implementation Method 1

The crack-resistant structure includes at least one of a laterally rounded contour of the fluxgate core at the end having corner radii of at least 2 microns

Methodology Applied

Scientific EffectStress concentration reduction through geometric curvature:

Implementation Method 2

there is further stress from thermal cycling of the integrated fluxgate device due to thermal expansion mismatch between the fluxgate core and the surrounding dielectric material

Methodology Applied

Scientific EffectThermal expansion mismatch stress: Thermal Expansion

Implementation Method 3

there is further stress from thermal cycling of the integrated fluxgate device due to thermal expansion mismatch between the fluxgate core and the surrounding dielectric material

Methodology Applied

Scientific EffectThermal expansion mismatch stress: Thermal Expansion

Data Source

PatentUS20250020740A1Layouts for interlevel crack prevention in fluxgate technology manufacturing

Publication Date: 2025.01.16 TEXAS INSTRUMENTS INC

AI summary

An integrated fluxgate device includes a substrate that includes a dielectric layer. A fluxgate core is located over the dielectric layer. Lower windings are disposed in a lower metal level between the fluxgate core and the dielectric layer, and upper windings are disposed in an upper metal level above the fluxgate core. A metal structure in the upper metal level or the lower metal level overlaps an end of the fluxgate core and is conductively isolated from the upper and lower windings.