Acoustic Wave Piezoelectric Layer Corners to Prevent Thermal Peeling

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Solution Overview

Problem

The piezoelectric layer in acoustic wave devices with WLP or CSP structures is prone to peeling due to stress concentration at corner portions during thermal cycling, particularly when mounted on a substrate with different thermal expansion coefficients.

Innovation Solution

The corner portions of the piezoelectric layer and electrode pads are designed with a curved or polygonal shape to alleviate stress concentration, reducing the likelihood of peeling by thermal stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the piezoelectric layer has a rectangular shape with sharp corners, then the manufacturing process is simple, but stress concentration occurs at corner portions during thermal cycling causing peeling

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidpeeling resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies curvature by rounding the corner portions of the piezoelectric layer. Instead of sharp rectangular corners, the corner portions are formed with a curved shape having a specific radius of curvature. This curvature distributes the thermal stress that occurs during temperature changes, preventing stress concentration at the corners and thereby preventing peeling of the piezoelectric layer from the support substrate while maintaining manufacturing feasibility.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Adaptability or versatility

If the piezoelectric layer is made larger to accommodate functional elements, then the device functionality is improved, but the area exposed to thermal stress increases causing higher peeling risk

Engineering Contradiction:

Improvedevice functionalityVSAvoidthermal stress exposure

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies curvature to the corner portions of the piezoelectric layer to distribute thermal stress. By rounding the corners with a specific radius of curvature, the stress distribution is improved across the entire piezoelectric layer area, allowing larger device areas to accommodate more functional elements while reducing the peeling risk associated with increased thermal stress exposure.

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

This design effectively prevents or reduces peeling of the piezoelectric layer by distributing thermal stress more evenly, ensuring the structural integrity of the acoustic wave device.

Implementation Method 1

stress is generated due to a difference in a thermal expansion coefficient between the support substrate and a piezoelectric layer in a subsequent temperature decrease process

Methodology Applied

Scientific EffectThermal stress: Thermal Expansion

Data Source

PatentUS12512811B2Acoustic wave device

Publication Date: 2025.12.30 MURATA MFG CO LTD

AI summary

An acoustic wave device includes a support substrate, a piezoelectric layer on the support substrate, and a functional element on the piezoelectric layer. The support substrate and the piezoelectric layer each have a rectangular or substantially rectangular shape in plan view from a direction normal to the support substrate. At least one corner portion of the piezoelectric layer has a curved shape or a polygonal shape.