Acoustic Wave Substrate Layout for Thermal Stress Isolation

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Solution Overview

Problem

Acoustic wave devices with piezoelectric thin films on support substrates experience characteristic deterioration due to stress strain caused by differences in linear expansion coefficients between the support substrate and the mounting substrate, leading to thermal stress and potential deformation of the piezoelectric film.

Innovation Solution

Incorporating a hollow portion in the support substrate, which redirects thermal stress away from the central portion where the piezoelectric film is stacked, and ensuring the external connection electrode does not overlap the piezoelectric body layer to prevent direct stress application.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the support substrate is made as a solid continuous structure, then the mechanical strength is improved, but thermal stress concentrates in the central portion causing piezoelectric film deformation

Engineering Contradiction:

Improvemechanical strength of support substrateVSAvoidthermal stress concentration

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The support substrate is divided by introducing hollow portions that segment the continuous structure. This segmentation allows thermal stress to be distributed and concentrated in the hollow portions rather than accumulating in the central portion, preventing piezoelectric film deformation while maintaining overall structural integrity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The hollow portions are strategically positioned to act as stress absorption zones that convert harmful thermal stress concentration into a beneficial stress distribution pattern. The hollow portions absorb and redirect thermal stress away from the piezoelectric film region, transforming the potential harm into a protective mechanism

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Device complexity

If the external connection electrode overlaps the piezoelectric body layer, then the electrical connection is simplified, but stress is directly applied to the piezoelectric film causing characteristic deterioration

Engineering Contradiction:

Improveelectrical connection structureVSAvoidacoustic wave device characteristics

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The external connection electrode is extracted from the region overlapping the piezoelectric body layer. By positioning the external connection electrode in a region where no piezoelectric body layer is present, direct stress application to the piezoelectric film is eliminated while electrical connection functionality is maintained through alternative routing

Inventive Principle:

Principle #2Taking out (Extraction)

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 reduces thermal stress and strain on the support substrate, thereby stabilizing the piezoelectric film and maintaining the acoustic wave device's characteristics, such as bandpass characteristics, by concentrating stress in the hollow portion and preventing deformation.

Implementation Method 1

stress at the time of bonding the metal bumps as the external connection terminals is not directly applied to a layered portion of the layered film. When the acoustic wave device described in International Publication No. 2016/208427 is mounted on a mounting substrate, when a coefficient of linear expansion of the support substrate and a coefficient of linear expansion of the mounting substrate are different from each other, stress strain may occur in a central portion of the support substrate due to a difference in coefficient of linear expansion

Methodology Applied

Scientific EffectThermal stress: Thermal Expansion

Implementation Method 2

a piezoelectric body layer provided on a support substrate, an interdigital transducer electrode provided on the piezoelectric body layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11616486B2Acoustic wave device and electronic component module

Publication Date: 2023.03.28 MURATA MFG CO LTD

AI summary

An acoustic wave device includes a support substrate, a piezoelectric body layer, an interdigital transducer electrode, and an external connection electrode. The piezoelectric body layer is on the support substrate. The interdigital transducer electrode is on the piezoelectric body layer. The external connection electrode is electrically connected to the interdigital transducer electrode. The external connection electrode does not overlap the piezoelectric body layer in a plan view from a thickness direction of the support substrate. The support substrate includes a hollow portion. The hollow portion is at least on an end portion of the support substrate in a plan view from the thickness direction.