Elastic Wave Device IDT Electrode Bandwidth

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Solution Overview

Problem

Existing elastic wave devices have a narrow fractional bandwidth and are prone to frequency variations due to the configuration of the interdigital transducer (IDT) electrode covered by a dielectric layer.

Innovation Solution

The elastic wave device incorporates a piezoelectric material layer with an IDT electrode having a first and second electrode layer, where the second electrode layer is inclined with respect to the thickness direction and has a lower density than the first electrode layer, with wavelength normalized film thicknesses of each layer equal to or greater than 1.25%, to increase the fractional bandwidth and reduce frequency variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the IDT electrode is covered by a dielectric layer, then the IDT electrode is protected from damage, but the fractional bandwidth becomes narrow

Engineering Contradiction:

Improveprotection of IDT electrodeVSAvoidfractional bandwidth

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The IDT electrode is segmented into multiple electrode layers (first electrode layer and second electrode layer) with different densities and thicknesses. This segmentation allows each layer to contribute differently to the acoustic wave generation, enabling broader bandwidth operation while maintaining structural integrity and protection through the layered configuration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the IDT electrode structure are assigned different properties: the first electrode layer has greater wavelength-normalized thickness for strong coupling, while the second electrode layer has lesser thickness for bandwidth extension. This local differentiation of electrode layer properties enables simultaneous achievement of electrode protection and broad fractional bandwidth.

Inventive Principle:

Principle #3Local quality

2Reliability

If the IDT electrode is covered by a dielectric layer, then the IDT electrode is protected from damage, but frequency variations increase

Engineering Contradiction:

Improveprotection of IDT electrodeVSAvoidfrequency stability

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The IDT electrode is constructed as a composite structure with multiple electrode layers made of different materials or with different physical properties (different densities and thicknesses). This composite configuration stabilizes the resonant frequency by distributing the acoustic energy across multiple interfaces, reducing sensitivity to dielectric layer variations and minimizing frequency drift.

Inventive Principle:

Principle #40Composite materials

3Power

If the wavelength normalized film thickness of electrode layers is increased, then the coupling strength is improved, but the device complexity increases

Engineering Contradiction:

Improvecoupling strengthVSAvoidelectrode layer structure

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

Instead of uniformly increasing the thickness of all electrode layers, the invention applies partial action by selectively designing the first electrode layer with greater wavelength-normalized thickness for strong coupling, while keeping the second electrode layer thinner to control complexity. This selective thickness distribution achieves the desired coupling strength without excessive device complexity.

Inventive Principle:

Principle #16Partial or excessive action

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 achieves a wider fractional bandwidth and minimizes frequency variations, ensuring more stable performance in elastic wave devices.

Implementation Method 1

an elastic wave device includes a piezoelectric material layer, an interdigital transducer (IDT) electrode disposed on the piezoelectric material layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The IDT electrode includes a first electrode layer and a second electrode layer laminated on the first electrode layer

Methodology Applied

Scientific EffectSurface acoustic wave generation: Surface Acoustic Wave

Data Source

PatentUS11070193B2Elastic wave device, radio-frequency front-end circuit, and communication device

Publication Date: 2021.07.20 MURATA MFG CO LTD

AI summary

An elastic wave device includes a piezoelectric material layer, an IDT electrode on the piezoelectric material layer, and a dielectric film covering the IDT electrode. The IDT electrode includes a first electrode layer and a second electrode layer laminated on the first electrode layer. Each of wavelength normalized film thicknesses of the first and second electrode layers is equal to or greater than about 1.25%, and is normalized using a wave length defined by the electrode finger pitch of the IDT electrode. The second electrode layer has a density lower than that of the first electrode layer. The side of the second electrode layer is inclined with respect to the thickness direction of the IDT electrode.