Piezoelectric Actuator Electrode Tapering for Stress Reduction

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Solution Overview

Problem

Piezoelectric actuators in liquid ejection heads face stress concentration and cracking issues at the boundaries between driving and non-driving regions, leading to reliability concerns.

Innovation Solution

A piezoelectric actuator design with a second electrode having a narrower third portion connecting the first and second portions, preventing the formation of corner portions with right or acute angles, thereby reducing stress concentration and enhancing reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the second electrode has a constant width (first portion and second portion with equal width), then the manufacturing is simpler, but corner portions with right or acute angles are formed at the boundary between driving and non-driving regions, causing stress concentration and cracking

Engineering Contradiction:

Improveelectrode fabrication simplicityVSAvoidpiezoelectric layer cracking resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The second electrode is designed with different widths in different regions: a first width in the first portion, a second width (smaller) in the second portion, and a third width in the third portion that transitions between them. This local variation in electrode width eliminates corner portions with right or acute angles at the boundary between driving and non-driving regions, thereby reducing stress concentration and preventing cracking in the piezoelectric layer while maintaining manufacturability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The third portion of the second electrode is designed with a curved or tapered transition between the first and second portions, avoiding sharp corners. This curvature or gradual transition in the electrode geometry smooths the stress distribution at the boundary between driving and non-driving regions, preventing stress concentration that would lead to cracking.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Device complexity

If the third portion of the second electrode has a constant width, then the electrode structure is simpler, but stress concentration occurs at the boundaries between driving and non-driving regions

Engineering Contradiction:

Improveelectrode structure complexityVSAvoidstress concentration at boundaries

Core Design Contradiction:

Device complexityVSStress or pressure

Solution Approach 1:

The third portion of the second electrode is designed with a width that gradually transitions from the first width to the second width, creating a tapered or curved structure. This local variation in width distribution smooths the stress distribution at the boundary between driving and non-driving regions, reducing stress concentration while adding minimal complexity to the overall electrode structure.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If corner portions with right or acute angles are formed on the boundary surface of the driving region, then the electrode layout is more straightforward, but excess stress concentration occurs around the boundary between driving and non-driving regions

Engineering Contradiction:

Improveelectrode layout simplicityVSAvoidstress resistance at boundaries

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

The third portion of the second electrode is designed with a curved or tapered transition instead of sharp corners, eliminating corner portions with right or acute angles. This curved geometry distributes stress more evenly across the boundary between driving and non-driving regions, enhancing the strength and stress resistance of the piezoelectric actuator while maintaining ease of manufacturing.

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 design effectively suppresses cracking and improves the reliability of the piezoelectric actuator by moderating stress concentration at the boundaries between driving and non-driving regions, allowing for larger piezoelectric layer crystallization and enhanced performance.

Implementation Method 1

The piezoelectric actuator has a piezoelectric layer which is sandwiched between an upper electrode and a lower electrode. If the piezoelectric layer is deformed by a driving signal or the like, a vibration plate can be bent.

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS8702197B2Piezoelectric actuator, liquid ejection head, and liquid ejection apparatus

Publication Date: 2014.04.22 SEIKO EPSON CORP

AI summary

A piezoelectric actuator includes a vibrating plate having a base surface, a first electrode, a piezoelectric layer, and a second electrode which extends in a first direction. In the piezoelectric actuator, the second electrode has a first portion having a first width, a second portion having a second width which is smaller than the first width, and a third portion which connects the first portion and the second portion, the first electrode has a first side which forms an outer circumference of the first electrode on a plan view, and the third portion of the second electrode is arranged at an upper side of the first side of the first electrode and a third width of the third portion is made narrower from the first portion toward the second portion.