Acoustic Wave Electrode Layout With Piezoelectric Thickness Tuning

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Solution Overview

Problem

Existing acoustic wave devices using piezoelectric films of LiNbO3 or LiTaO3 often experience unwanted bulk waves that cause ripples in frequency characteristics due to reflections and extractions by support structures or wiring lines, leading to degraded performance.

Innovation Solution

The acoustic wave device incorporates a piezoelectric layer with varying thickness in specific regions to alter the propagation mode of unwanted bulk waves, using a thickness-shear mode bulk wave and adjusting the thickness of the piezoelectric layer in overlapping and non-overlapping areas of electrode films to prevent ripple formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a uniform thickness piezoelectric layer is used, then the device structure is simple and easy to manufacture, but unwanted bulk waves are excited and cause ripples in frequency characteristics

Engineering Contradiction:

Improvepiezoelectric layer fabrication simplicityVSAvoidfrequency characteristic stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The piezoelectric layer is designed with different thicknesses in different regions: a first thickness in regions overlapping the first electrode film and a second thickness in regions not overlapping the first electrode film. This local thickness variation modifies the propagation characteristics of bulk waves in specific areas, preventing unwanted bulk waves from being extracted by the second electrode film while maintaining overall structural feasibility.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the thickness parameter of the piezoelectric layer from a uniform value to a spatially varying value. By controlling the thickness distribution, the invention alters the acoustic impedance and wave propagation characteristics, thereby suppressing bulk wave extraction and eliminating ripples in frequency characteristics.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If wiring lines connected to different potentials face each other, then electrical connection is achieved, but unwanted bulk-wave signals are extracted causing frequency ripple

Engineering Contradiction:

Improveelectrical connection capabilityVSAvoidfrequency characteristic stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The piezoelectric layer thickness is specifically varied in regions associated with the electrode films to create local acoustic impedance differences. This prevents bulk waves generated near the first electrode film from being efficiently extracted by the second electrode film, even when the electrode films are positioned to face each other for electrical connection.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention converts the potential harmful effect of bulk wave propagation into a beneficial outcome by using the thickness variation to redirect or dissipate bulk wave energy. The thickness difference acts as an acoustic barrier that transforms the bulk wave path, preventing it from reaching the second electrode film and causing frequency ripple.

Inventive Principle:

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

3Reliability

If reflectors are arranged on both sides of IDT electrode, then acoustic wave resonance is formed, but bulk waves are reflected by support causing frequency ripple

Engineering Contradiction:

Improveacoustic wave resonance qualityVSAvoidbulk wave reflection

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The piezoelectric layer thickness is modified in specific regions to create acoustic impedance gradients that affect bulk wave propagation. This local thickness variation prevents bulk waves reflected by the support from being extracted by the electrode films, thereby eliminating frequency ripple while preserving the desired acoustic wave resonance.

Inventive Principle:

Principle #3Local quality

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 effectively reduces or prevents ripples in frequency characteristics by setting different propagation modes for unwanted bulk waves, enhancing the device's performance and stability.

Implementation Method 1

a piezoelectric layer 14 on the support substrate 13

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

an unwanted bulk wave may sometimes be excited. The bulk wave propagates in the thickness direction of a piezoelectric substrate

Methodology Applied

Scientific EffectBulk wave propagation: Acoustic Emission

Data Source

PatentUS12355427B2Acoustic wave device

Publication Date: 2025.07.08 MURATA MFG CO LTD

AI summary

An acoustic wave device includes a support substrate, a piezoelectric layer on the support substrate, functional electrodes on the piezoelectric layer, and first and second electrode films positioned on the piezoelectric layer to face each other and having different potentials from each other. A thickness of the piezoelectric layer in at least a portion of a first region overlapping the first electrode film in plan view is different from a thickness of the piezoelectric layer in at least a portion of a second region not overlapping the first electrode film in plan view.