Piezoelectric Device Low Density Region Stress Reduction

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Solution Overview

Problem

Piezoelectric devices face stress concentration issues near the side surfaces of piezoelectric elements, leading to potential cracks and reduced reliability, particularly in applications like liquid ejecting heads where high precision is required.

Innovation Solution

A piezoelectric device design incorporating a low density region with voids at the side of the first piezoelectric element, where the side surface of the element and electrode are angled to reduce stress concentration, and a manufacturing method involving heat-treating to form this low density region, which reduces stress and enhances reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional piezoelectric device structure is used with uniform density, then the device is simple to manufacture, but stress concentrates at the side surface of the first piezoelectric element causing cracks and reducing reliability

Engineering Contradiction:

ImprovereliabilityVSAvoidstructure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies local quality by creating a low density region with voids at the side surface of the first piezoelectric element. This localized structural modification reduces stress concentration at the critical side surface area without changing the entire device structure, thereby improving reliability while maintaining overall structural simplicity

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent introduces a porous structure by forming a low density region containing voids at the side surface of the first piezoelectric element. This porous modification allows the material to better accommodate stress, preventing crack formation and improving device reliability

Inventive Principle:

Principle #31Porous materials

2Reliability

If the side surface of the first piezoelectric element is made slanted at a larger angle, then stress concentration is reduced, but the manufacturing precision requirements increase

Engineering Contradiction:

Improvestress distributionVSAvoidslant angle precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent changes the geometric parameter of the side surface by creating a slanted configuration at a specific angle. This parameter modification redistributes stress more evenly across the piezoelectric element, reducing stress concentration while the angle can be optimized to balance stress reduction with manufacturing feasibility

Inventive Principle:

Principle #35Parameter changes

3Reliability

If ions are injected into the piezoelectric element to form a low active region, then stress concentration is reduced, but the manufacturing process becomes more complex

Engineering Contradiction:

Improvestress reductionVSAvoidmanufacturing process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent uses a porous low density region with voids as an alternative to ion injection. This approach achieves stress reduction through structural modification rather than chemical treatment, simplifying the manufacturing process while maintaining the benefit of reduced stress concentration

Inventive Principle:

Principle #31Porous materials

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 proposed design effectively reduces stress concentration and enhances the reliability of piezoelectric devices by forming a low density region with voids, thereby minimizing the risk of cracks and improving the performance of piezoelectric actuators and liquid ejecting heads.

Implementation Method 1

a low density region which is formed at a side of the first piezoelectric element and has density lower than that of the first piezoelectric element

Methodology Applied

Scientific EffectStress concentration reduction through density variation:

Implementation Method 2

the side surface of the first piezoelectric element slants at a first angle relative to an upper surface of the substrate, and a side surface of the first electrode slants at a second angle relative to the upper surface of the substrate

Methodology Applied

Scientific EffectElectric field concentration reduction through geometric angling:

Implementation Method 3

depositing a second precursor layer that covers the first piezoelectric element and the first electrode; forming a second piezoelectric element layer by heat-treating and crystallizing the second precursor layer

Methodology Applied

Scientific EffectCrystallization through heat treatment: Crystallisation

Data Source

PatentUS8870352B2Piezoelectric device and method for manufacturing the same, piezoelectric actuator, liquid ejecting head, and liquid ejecting apparatus

Publication Date: 2014.10.28 SEIKO EPSON CORP

AI summary

A piezoelectric device includes: a substrate; a first electrode formed over the substrate; a first piezoelectric element formed over the first electrode; a low density region which is formed at a side of the first piezoelectric element and has density lower than that of the first piezoelectric element; a second piezoelectric element which is formed to cover the first piezoelectric element and the low density region; and a second electrode formed over the second piezoelectric element.