Piezoelectric Element Electrode Redox Potential Electromigration

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Solution Overview

Problem

The existing piezoelectric elements face performance deterioration due to electromigration, especially when using metals with higher ionization tendencies for the leading electrode, leading to increased electrical resistance and potential breakage, which affects the reliability and accuracy of ultrasonic measurements.

Innovation Solution

A piezoelectric element configuration with a third electrode layer having a smaller difference in standard redox potential with the second electrode layer, where the second electrode layer is exposed through an aperture, and an insulating layer covers the second electrode except for the conductive part, preventing exposure and contact with the liquid phase during etching, thereby suppressing electromigration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If an opening is formed in the protective film to prevent hindrance of piezoelectric element displacement, then the piezoelectric element can move freely, but the second electrode becomes exposed and susceptible to electromigration during leading electrode formation

Engineering Contradiction:

Improvedisplacement of piezoelectric elementVSAvoidperformance of piezoelectric element

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent applies local quality by creating an aperture in the insulating layer that exposes only a specific localized region of the second electrode (the region needed for leading electrode connection), while other regions remain covered. This selective exposure prevents electromigration in protected areas while maintaining functionality in the exposed area, resolving the contradiction between free displacement and preventing electromigration.

Inventive Principle:

Principle #3Local quality

2Reliability

If a continuous protective film covers the first electrode, piezoelectric layer and second electrode, then burning out at boundaries is prevented, but the piezoelectric element displacement is hindered

Engineering Contradiction:

Improveprevention of burning outVSAvoiddisplacement of piezoelectric element

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent segments the protective covering into two functional parts: an insulating layer that provides continuous protection against burning out, and an aperture that creates a localized opening for displacement functionality. This segmentation allows the protective film to maintain its fire-prevention function while enabling the piezoelectric element to move freely in the aperture region.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The insulating layer provides continuous protection across the entire piezoelectric structure, while the aperture introduces a localized modification that enables displacement without compromising the overall protective function. The protective coverage is maintained in all areas except the specific region where displacement is needed.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If metal with higher ionization tendency is used for the leading electrode, then electrical connection is achieved, but electromigration occurs causing separation and breakage of the leading electrode

Engineering Contradiction:

Improveformation of leading electrodeVSAvoidintegrity of leading electrode

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent introduces the insulating layer as an intermediary barrier between the leading electrode and the liquid phase etchant. This intermediary prevents direct contact between the etchant and the metal layers, eliminating the electromigration mechanism that would otherwise cause separation and breakage of the leading electrode during the formation process.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 configuration enhances the reliability and performance of the piezoelectric element by preventing electromigration, ensuring stable drive signal input and maintaining the integrity of the leading electrode, thus improving the accuracy of ultrasonic measurements and device performance.

Implementation Method 1

there is a possibility that electromigration may occur when forming the leading electrode

Methodology Applied

Scientific EffectElectromigration:

Implementation Method 2

a difference in standard redox potential between the second metal and the third metal is smaller than a difference in standard redox potential between the first metal and the third metal

Methodology Applied

Scientific EffectRedox potential difference: Redox Reactions

Data Source

PatentUS10971673B2Piezoelectric element, piezoelectric device, ultrasonic probe and electronic apparatus

Publication Date: 2021.04.06 SEIKO EPSON CORP

AI summary

A piezoelectric element has a first electrode layer, a piezoelectric layer on the first electrode layer, a second electrode layer on the piezoelectric layer, a third electrode layer on part of the second electrode layer and including third metal, and an insulating layer covering at least a part of the piezoelectric layer not provided with the second electrode layer and having an aperture exposing a part of the second electrode layer. The second electrode layer has a first layer including first metal and a second layer including second metal on the first layer. The second layer is exposed in the aperture. A difference in standard redox potential between the second metal and the third metal is smaller than a difference in standard redox potential between the first metal and the third metal.