Elastic Wave Filter Layout for Ripple Suppression and High Q

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Solution Overview

Problem

Existing filter devices with LiTaO3 films suffer from deterioration in insertion loss and generation of transverse mode ripples due to inclined busbars and high acoustic velocity films, leading to reduced Q values and increased insertion loss.

Innovation Solution

A filter device incorporating a longitudinally coupled resonator elastic wave filter with specific electrode configurations and film thicknesses, including a piezoelectric film with LiTaO3, high acoustic velocity members, and low acoustic velocity regions, which reduces transverse mode ripples and improves Q values by implementing a piston mode and inclination angles in IDT electrodes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-generated harmful factors

If upper and lower busbars are inclined with respect to the propagation direction of elastic waves, then transverse mode ripples are reduced, but Q value is deteriorated

Engineering Contradiction:

Improvetransverse mode ripplesVSAvoidQ value

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The patent applies local quality by creating distinct acoustic velocity regions within the IDT electrode structure. Low acoustic velocity regions are positioned in outer side portions of center regions, while high acoustic velocity regions are positioned in outer side portions of the low acoustic velocity regions. This localized differentiation of acoustic properties allows the device to reduce transverse mode ripples while maintaining high Q value, resolving the technical contradiction between ripple reduction and Q value preservation.

Inventive Principle:

Principle #3Local quality

2Speed

If a high acoustic velocity film is laminated on the support substrate, then surface acoustic waves are enhanced, but transverse mode ripples are generated

Engineering Contradiction:

Improveacoustic velocityVSAvoidtransverse mode ripples

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The patent resolves this contradiction by implementing local quality through spatially differentiated acoustic velocity regions. Instead of using a uniform high acoustic velocity film throughout, the invention creates specific low and high acoustic velocity regions within the IDT electrode structure. This localized approach allows certain areas to enhance surface acoustic wave propagation while other areas suppress transverse mode ripples, thereby resolving the contradiction between wave enhancement and ripple generation.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent converts the potentially harmful effect of acoustic velocity differences into a beneficial structure. By intentionally designing regions with different acoustic velocities (low and high velocity regions) within the IDT electrode, the invention transforms what could be a source of distortion into a mechanism for ripple suppression. The high acoustic velocity member, when properly configured with these regional variations, becomes a tool for eliminating transverse mode ripples rather than generating them.

Inventive Principle:

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

3Device complexity

If the piezoelectric film thickness is reduced, then device integration is improved, but Q value is deteriorated

Engineering Contradiction:

Improvefilm thicknessVSAvoidQ value

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent applies parameter changes by optimizing the piezoelectric film thickness to be equal to or smaller than about 10λ (where λ is the wavelength determined by the pitch of electrode fingers). This parameter optimization, combined with the specific acoustic velocity region configuration, allows the device to maintain high Q value despite reduced film thickness, resolving the contradiction between device integration and Q value preservation.

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

Significantly reduces insertion loss, increases Q values, and minimizes transverse mode ripples, enhancing the performance of filter devices by optimizing the acoustic velocity regions and electrode configurations.

Implementation Method 1

a piezoelectric film including LiTaO3

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

surface acoustic waves propagating in the LiTaO3 film

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Implementation Method 3

an acoustic velocity of elastic waves propagating in the piezoelectric film

Methodology Applied

Scientific EffectAcoustic wave propagation: Sound

Data Source

PatentUS10469055B2Filter device including longitudinally coupled resonator elastic wave filter and elastic wave resonator

Publication Date: 2019.11.05 MURATA MFG CO LTD

AI summary

A filter device includes a longitudinally coupled resonator elastic wave filter that includes IDT electrodes including low acoustic velocity regions in outer side portions of center regions of the IDT electrodes and high acoustic velocity regions in outer side portions of the low acoustic velocity regions in a direction orthogonal or substantially orthogonal to an elastic wave propagation direction, and defines and functions as a first bandpass filter, and elastic wave resonators that are electrically connected to the longitudinally coupled resonator elastic wave filter.