IDT Electrode Layout for Ripple Suppression and Low-Side Attenuation

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Solution Overview

Problem

Existing boundary acoustic wave filters using longitudinally-coupled resonators struggle to achieve sufficient attenuation at frequencies lower than the passband while suppressing transverse-mode ripples, which limits their use as diversity or duplexer filters.

Innovation Solution

The acoustic wave device incorporates a configuration with narrower-pitch electrode finger portions and normally-shaped electrode finger portions adjacent to them, with apodization applied to the remaining electrode portions, maintaining a ratio of 3% to 20% of normally-shaped electrode finger portions to the total IDT electrodes, enhancing frequency characteristics and suppressing transverse-mode ripples.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If apodized electrode portions are used to suppress transverse-mode ripples, then passband characteristic is improved, but attenuation at frequencies lower than passband is insufficient

Engineering Contradiction:

Improvepassband characteristicVSAvoidattenuation at frequencies lower than passband

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent applies different electrode configurations to different regions: narrower-pitch electrode finger portions are placed at edge regions adjacent to IDT electrodes to provide strong attenuation, while apodized electrode portions are used in other regions to suppress transverse-mode ripples. This local differentiation allows each region to fulfill its specific function.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The electrode structure is divided into distinct segments: narrower-pitch electrode finger portions and normally-shaped electrode finger portions with apodization. These segments are arranged in specific patterns to simultaneously achieve ripple suppression and low-frequency attenuation.

Inventive Principle:

Principle #1Segmentation

2Volume of moving object

If the cross width of IDT electrodes is narrowed to downsize the filter, then filter size is reduced, but transverse-mode ripples appear

Engineering Contradiction:

Improvefilter sizeVSAvoidpassband characteristic

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

Apodization is applied to specific electrode portions rather than uniformly across all electrodes. The apodized portions are strategically placed to suppress transverse-mode ripples that arise from narrowed electrode cross widths, allowing downsizing without compromising passband characteristics.

Inventive Principle:

Principle #3Local quality

3Reliability

If narrower-pitch electrode finger portions are added to suppress transverse-mode ripples, then passband characteristic is improved, but device complexity increases

Engineering Contradiction:

Improvepassband characteristicVSAvoidelectrode configuration complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The narrower-pitch electrode finger portions are localized to specific regions (edge regions adjacent to IDT electrodes) rather than being applied uniformly. This localized approach provides the necessary ripple suppression while minimizing the overall complexity increase.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of applying complex electrode configurations throughout the entire device, the patent uses narrower-pitch portions only where most needed (at edges adjacent to IDT electrodes), achieving sufficient performance with moderate 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 effectively suppresses transverse-mode ripples and achieves significant attenuation (43 dB or more) at frequencies lower than the passband, improving both passband and frequency characteristics.

Implementation Method 1

a piezoelectric material; a first interdigital transducer (IDT) electrode disposed on the piezoelectric material

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The present invention relates to an acoustic wave device using boundary acoustic waves or surface acoustic waves

Methodology Applied

Scientific EffectBoundary acoustic wave: Surface Acoustic Wave

Data Source

PatentUS8289107B2Acoustic wave device having narrower-pitch electrodes, normally-shaped electrodes and apodized electrodes

Publication Date: 2012.10.16 MURATA MFG CO LTD

AI summary

A longitudinally-coupled resonator-type acoustic wave device includes first to third IDT electrodes disposed on a piezoelectric material and first and second reflectors disposed in acoustic wave propagation directions. Each of any two IDT electrodes adjacent to each other in the acoustic wave propagation directions, of the first to third IDT electrodes, has a narrower-pitch electrode finger portion at an edge thereof adjacent to the other IDT electrode. Most portions of the first to third IDT electrodes are apodized, and the narrower-pitch electrode finger portions and the electrode finger portions adjacent thereto are normally shaped.