Elastic Wave Layer Structure for SAW Confinement and Higher Q

Solution Overview

Problem

Existing elastic wave devices face issues with significant propagation loss and inability to effectively confine surface acoustic waves, leading to low Q factors and energy leakage into dielectric substrates, which hinders frequency enhancement.

Innovation Solution

The device incorporates a high-acoustic-velocity supporting substrate with a low-acoustic-velocity film and a piezoelectric film, where energy is distributed between these layers to enhance confinement and reduce leakage, using materials like silicon oxide and aluminum nitride to adjust acoustic velocities and electromechanical coupling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a hard dielectric layer is disposed between the dielectric substrate and the piezoelectric film to increase acoustic velocity, then the frequency of the surface acoustic wave device can be increased, but there is considerable propagation loss and surface acoustic waves cannot be effectively confined within the piezoelectric thin film, causing energy leakage into the dielectric substrate and low Q factor

Engineering Contradiction:

Improveacoustic velocityVSAvoidpropagation loss

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The device structure is segmented into distinct functional layers: a high-acoustic-velocity supporting substrate for frequency enhancement, a low-acoustic-velocity film for wave confinement, and a piezoelectric film for electromechanical conversion. This segmentation allows each layer to perform its specific function optimally without interfering with others.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The low-acoustic-velocity film acts as an intermediary layer between the high-acoustic-velocity supporting substrate and the piezoelectric film. It mediates the acoustic wave propagation by confining the surface acoustic waves within the piezoelectric film region, preventing energy leakage into the substrate while allowing the high-velocity substrate to enhance the overall frequency.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Speed

If a hard dielectric layer is used to increase acoustic velocity, then frequency enhancement is achieved, but surface acoustic waves leak into the dielectric substrate resulting in low Q factor

Engineering Contradiction:

Improveacoustic velocityVSAvoidQ factor

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The device structure is segmented into distinct functional layers: a high-acoustic-velocity supporting substrate for frequency enhancement, a low-acoustic-velocity film for wave confinement, and a piezoelectric film for electromechanical conversion. This segmentation allows each layer to perform its specific function optimally without interfering with others.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The low-acoustic-velocity film acts as an intermediary layer between the high-acoustic-velocity supporting substrate and the piezoelectric film. It mediates the acoustic wave propagation by confining the surface acoustic waves within the piezoelectric film region, preventing energy leakage into the substrate while allowing the high-velocity substrate to enhance the overall frequency.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Power

If the piezoelectric film thickness is increased to enhance electromechanical coupling, then the band width ratio can be enhanced, but the acoustic velocity and frequency characteristics may be affected

Engineering Contradiction:

Improveelectromechanical coupling coefficientVSAvoidacoustic velocity

Core Design Contradiction:

PowerVSSpeed

Solution Approach 1:

The patent optimizes the thickness of the piezoelectric film as a critical parameter to achieve the desired balance between electromechanical coupling and acoustic velocity. By carefully controlling the film thickness within specific ranges, the device achieves enhanced electromechanical coupling while maintaining appropriate acoustic velocity characteristics for the intended frequency range.

Inventive Principle:

Principle #35Parameter changes

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 structure increases the Q factor, enhances electromechanical coupling, and improves frequency stability and temperature characteristics, allowing for higher frequency operation and reduced energy loss.

Implementation Method 1

a piezoelectric film stacked on the low-acoustic-velocity film

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

some portion of energy of an elastic wave propagating in the piezoelectric film is distributed into the low-acoustic-velocity film and the high-acoustic-velocity supporting substrate

Methodology Applied

Scientific EffectAcoustic wave confinement: Surface Acoustic Wave

Data Source

PatentUS12445105B2Elastic wave device and method for manufacturing the same

Publication Date: 2025.10.14 MURATA MFG CO LTD

AI summary

An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.