Laminated Piezoelectric Elements With Stress-Relieving Adhesive Gaps

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing laminated piezoelectric elements experience a decrease in sound pressure over time due to repeated warping and peeling at the interface between the piezoelectric film and adhesive layer, leading to defects during long-term use.

Innovation Solution

A laminated piezoelectric element design with adhesive layers having a specific ratio of gap portions to adhesive layers and thickness ratios, allowing for stress relaxation and improved adhesion, preventing peeling and maintaining high sound pressure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the laminated piezoelectric element is used to generate sound from a vibration plate by being attached and vibrating, then a high initial sound pressure can be obtained, but the sound pressure decreases with time due to repeated warping and peeling at the interface

Engineering Contradiction:

Improvesound pressureVSAvoiddurability of sound pressure

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The adhesive layer is segmented into multiple sub-layers with different material properties. The first adhesive sub-layer has higher adhesion strength to prevent peeling, while the second adhesive sub-layer has lower adhesion strength to allow stress relaxation. This segmentation resolves the contradiction by providing both strong bonding and stress accommodation capabilities within the adhesive structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the adhesive layer are assigned different local properties through the multi-sublayer structure. The first adhesive sub-layer is optimized for adhesion strength at the piezoelectric film interface, while the second adhesive sub-layer is optimized for stress relaxation. This local differentiation allows the adhesive layer to simultaneously prevent peeling and accommodate warping stresses.

Inventive Principle:

Principle #3Local quality

2Strength

If the adhesive layer is made thick to improve adhesion, then peeling resistance increases, but stress accumulation and warping defects increase

Engineering Contradiction:

Improveadhesion strengthVSAvoidstress-induced peeling

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The adhesive layer is divided into multiple sub-layers with different thicknesses and material properties. The first adhesive sub-layer provides strong adhesion, while the second adhesive sub-layer provides stress relaxation. This segmentation allows the adhesive layer to achieve both strong bonding and stress accommodation without requiring excessive overall thickness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The adhesive layer uses a composite structure combining different adhesive materials with complementary properties. The first adhesive sub-layer material is selected for high adhesion strength, while the second adhesive sub-layer material is selected for stress relaxation capabilities. This composite approach resolves the contradiction between adhesion strength and stress accommodation.

Inventive Principle:

Principle #40Composite 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 design maintains high sound pressure over long-term use by reducing stress-induced peeling and ensuring efficient energy transfer to the vibration plate.

Implementation Method 1

a piezoelectric film in which a piezoelectric layer is sandwiched between an electrode layer and a protective layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

the adhesive layer has an adhesive region and a gap portion in an in-plane direction of a main surface of the piezoelectric films

Methodology Applied

Scientific EffectStress relaxation: Stress Relaxation

Data Source

PatentUS20250331425A1Laminated piezoelectric element and electroacoustic transducer

Publication Date: 2025.10.23 FUJIFILM CORP

AI summary

Provided are a laminated piezoelectric element and an electroacoustic transducer, in which a high sound pressure can be obtained even after long-term use of a laminated piezoelectric element obtained by laminating a piezoelectric film in a plurality of layers. In the laminated piezoelectric element, in which a plurality of piezoelectric films are laminated with adhesive layers interposed between the plurality of piezoelectric films, the adhesive layer has an adhesive region and a gap portion, in a case where a cross section of the piezoelectric films of the laminated piezoelectric element in a lamination direction is observed with a scanning electron microscope in each of one in-plane direction of a main surface of the piezoelectric films, a direction orthogonal to the one direction, a direction inclined by 45° with respect to the one direction, and a direction inclined by 135° with respect to the one direction to acquire ten continuous visual fields, and an average value of thicknesses of the piezoelectric films observed in each visual field is denoted by d1 and an average value of thicknesses of the adhesive layers observed in each visual field is denoted by d2, a ratio d2/d1 is 0.15 or more and 1.0 or less, and a ratio of a total area of the gap portions to a total area of the adhesive layers observed in each visual field is 1% or more and less than 40%.