Stepped IDT Bus Bar Layout for Transverse Mode Suppression

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Solution Overview

Problem

Existing elastic wave resonators face issues with transverse modes causing spurious responses and losses in the passband, which need to be suppressed.

Innovation Solution

The design incorporates an interdigital transducer (IDT) electrode with stepped portions on opposing bus bars, aligned parallel to the surface acoustic wave propagation direction, ensuring adjacent stepped portions are equidistant and positioned differently between the bus bars to suppress transverse modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional IDT electrode with straight bus bars is used, then the device structure is simple, but transverse modes are generated causing spurious responses and losses

Engineering Contradiction:

Improvefrequency characteristicsVSAvoidIDT electrode structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The bus bars are segmented into multiple stepped portions along the propagation direction. Each stepped portion is positioned at a different location in the direction from the first bus bar to the second bus bar, creating a segmented structure that suppresses transverse modes while maintaining manufacturing feasibility

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The bus bar structure is extended from a simple linear configuration to a two-dimensional stepped configuration. The stepped portions are arranged at different positions in the direction from the first bus bar to the second bus bar, adding spatial dimensionality to suppress transverse modes

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If curved sections are added to the IDT electrode to suppress transverse modes, then transverse mode suppression is achieved, but the manufacturing complexity increases

Engineering Contradiction:

Improvetransverse mode suppressionVSAvoidIDT electrode fabrication

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Instead of using continuous curved sections, the bus bars are divided into discrete stepped portions. This segmentation simplifies manufacturing by allowing standard photolithography and etching processes to create the stepped structure, avoiding the need for complex curved profile fabrication

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses stepped portions that create an effective curvature in the acoustic wave path without requiring physically curved electrode surfaces. The stepped configuration achieves the desired wave path curvature through discrete level changes, simplifying manufacturing compared to continuous curved sections

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Device complexity

If transverse modes are allowed to propagate, then the device structure remains simple, but energy loss increases due to spurious responses

Engineering Contradiction:

ImproveIDT electrode configurationVSAvoidpassband loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The stepped portions on the first and second bus bars are positioned asymmetrically relative to each other in the direction from the first bus bar to the second bus bar. This asymmetric positioning creates different acoustic paths for transverse modes, causing destructive interference and suppressing transverse mode propagation, thereby reducing energy loss

Inventive Principle:

Principle #4Asymmetry

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 modes, improving the frequency characteristics and reducing energy loss in the elastic wave resonator.

Implementation Method 1

a piezoelectric layer and an interdigital transducer (IDT) electrode formed on the piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

the first bus bar and the second bus bar each have multiple stepped portions on the facing sides, with these stepped portions aligned parallel to the propagation direction of the surface acoustic wave

Methodology Applied

Scientific EffectSurface acoustic wave reflection: Surface Acoustic Wave

Data Source

PatentUS20250337390A1Elastic Wave Device

Publication Date: 2025.10.30 SANAN JAPAN TECH CORP

AI summary

An elastic wave device comprises a piezoelectric layer and an IDT electrode formed on the piezoelectric layer, wherein the IDT electrode includes a first bus bar and a second bus bar opposed to the first bus bar; in a top view, the first bus bar and the second bus bar each have multiple stepped portions on their facing sides, with these stepped portions aligned parallel to a propagation direction of the surface acoustic wave, and a distance between the corresponding stepped portions of the first bus bar and the second bus bar is uniform; wherein adjacent of the stepped portions are arranged at different positions in a direction from the first bus bar to the second bus bar, a step portion is provided between them.