Strain Gauge Laminate with Noble Protective Layer for Etching Precision

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Solution Overview

Problem

Existing strain gauges face challenges in accurately measuring strain on small measurement targets due to resistance variations caused by photolithography and etching processes, making it difficult to reduce the size of the strain gauge for precise measurements.

Innovation Solution

A strain gauge with a laminate structure comprising a strain resistance layer and a protective layer, where the protective layer is electrochemically more noble and has higher resistivity than the strain resistance layer, reducing undercut variations and enhancing sensitivity through controlled wet etching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If photolithography and etching techniques are used to form the strain resistor pattern, then the strain gauge can be manufactured with desired patterns, but resistance value variations occur due to process variations

Engineering Contradiction:

Improvepattern formation capabilityVSAvoidresistance value consistency

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent changes the material parameter of the protective layer by selecting a material that is electrochemically more noble than the strain resistance layer. This parameter change causes the protective layer to be etched at a slower rate during wet etching, which stabilizes the etching process and reduces resistance value variations, thereby improving manufacturing precision without compromising ease of manufacture.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite structure consisting of a strain resistance layer and a protective layer made of different materials. The protective layer material is specifically selected to be electrochemically more noble, creating a bimetallic or composite structure that exploits differential etching rates to improve pattern formation precision and resistance consistency.

Inventive Principle:

Principle #40Composite materials

2Adaptability or versatility

If a resistive wiring pattern is provided to adjust resistance, then resistance value can be tuned, but the size of the strain gauge increases

Engineering Contradiction:

Improveresistance adjustment capabilityVSAvoidstrain gauge size

Core Design Contradiction:

Adaptability or versatilityVSArea of moving object

Solution Approach 1:

Instead of adding extra resistive wiring patterns to adjust resistance, the patent changes the material parameters of the protective layer to control the etching rate. This allows precise control of the strain resistor geometry and resistance value during the etching process itself, eliminating the need for additional resistance adjustment structures and keeping the strain gauge compact.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If the protective layer is etched during wet etching, then the pattern can be formed, but undercut variations increase causing resistance variations

Engineering Contradiction:

Improvepattern formationVSAvoidundercut consistency

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent changes the electrochemical parameter of the protective layer by selecting a material that is more noble than the strain resistance layer. This parameter change reverses the etching behavior: the protective layer is now etched at a slower rate, which reduces undercut variations and improves the consistency of the strain resistor pattern during wet etching.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent inverts the traditional etching approach where the protective layer is etched faster. Instead, it selects a protective layer material that is etched slower than the strain resistance layer, reversing the etching rate relationship to improve pattern precision and reduce undercut variations.

Inventive Principle:

Principle #13The other way round (Inversion)

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 enables high-accuracy strain measurement on small targets by minimizing resistance variations and increasing detection sensitivity, while maintaining the protective layer's etchability and stability.

Implementation Method 1

the protective layer being electrochemically more noble than the strain resistance layer

Methodology Applied

Scientific EffectElectrochemical nobility:

Implementation Method 2

when wet etching is performed to form the pattern of the laminate

Methodology Applied

Scientific EffectWet etching:

Implementation Method 3

the protective layer preferably has a higher resistivity than the strain resistance layer

Methodology Applied

Scientific EffectElectrical resistivity: Electrical Resistance

Data Source

PatentUS20250102379A1Strain gauge, method for producing strain gauge, and strain sensor

Publication Date: 2025.03.27 ALPS ALPINE CO LTD

AI summary

A strain gauge according to an embodiment of the present invention includes a strain gauge having a pattern of a laminate including a strain resistance layer and a protective layer having a portion in contact with the strain resistance layer, the protective layer being electrochemically more noble than the strain resistance layer. Thus, when wet etching is performed to form the pattern of the laminate, the protective layer is not easily etched in the vicinity of the strain resistant layer. This inhibits resist pattern peeling or the like, reducing variations in the amount of undercut.