Lithium Tantalate Acoustic Wave Stack to Prevent Multiplexer Ripple

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Solution Overview

Problem

In acoustic wave devices where a piezoelectric body made of lithium tantalate is stacked on a silicon substrate, higher order modes appear on the high-frequency side of the main mode, risking ripple generation in adjacent acoustic wave filters and degrading filter characteristics in multiplexers.

Innovation Solution

The acoustic wave device includes a silicon substrate, a silicon nitride film, a silicon oxide film, a lithium tantalate piezoelectric body, and an IDT electrode, with specific wavelength normalized film thicknesses and Euler angles set to ensure that the response intensity of first, second, and third higher order modes is greater than -2.4, preventing ripple generation in adjacent filters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a piezoelectric body made of lithium tantalate is stacked on a silicon support substrate, then heat resistance is improved, but higher order modes appear causing ripple in adjacent filter pass bands

Engineering Contradiction:

Improveheat resistanceVSAvoidhigher order mode ripple

Core Design Contradiction:

TemperatureVSObject-generated harmful factors

Solution Approach 1:

An acoustic low-pass filter is introduced as an intermediary component between the acoustic wave resonator and the series resonance circuit. This filter selectively transmits the main mode frequency while attenuating higher order modes, thereby preventing ripple generation in adjacent filter pass bands while maintaining the heat resistance benefits of the lithium tantalate on silicon substrate structure

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent optimizes specific parameters of the acoustic wave resonator including the thickness of the piezoelectric body (0.3λ to 1.5λ), the electrode finger pitch, and the propagation direction angle (30° to 60° from the normal direction) to control the characteristics of higher order modes and minimize their impact on adjacent filters

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If acoustic wave filters with different frequencies are connected via common connection, then multiplexer functionality is achieved, but ripple from lower frequency filter's higher order mode degrades higher frequency filter characteristics

Engineering Contradiction:

Improvemultiplexer functionalityVSAvoidfilter characteristic degradation

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The harmful higher order mode signals are extracted and removed from the signal path by the acoustic low-pass filter, which allows only the desired main mode frequency to pass through to the series resonance circuit, thus protecting adjacent filters from ripple interference

Inventive Principle:

Principle #2Taking out (Extraction)

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 the response of higher order modes, minimizing ripple effects and maintaining filter characteristics in multiplexers and communication devices.

Implementation Method 1

a piezoelectric body stacked on the silicon oxide film and made of lithium tantalate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

an InterDigital Transducer (IDT) electrode provided on one main surface of the piezoelectric body

Methodology Applied

Scientific EffectSurface acoustic wave generation: Surface Acoustic Wave

Data Source

PatentUS11552616B2Acoustic wave device, multiplexer, radio-frequency front end circuit, and communication device

Publication Date: 2023.01.10 MURATA MFG CO LTD

AI summary

An acoustic wave device includes a support substrate, a silicon nitride film stacked on the support substrate, a silicon oxide film stacked on the silicon nitride film, a piezoelectric body stacked on the silicon oxide film and made of lithium tantalite, and an IDT electrode provided on one main surface of the piezoelectric body. For a wavelength normalized film thickness of the piezoelectric body, an Euler angle of the piezoelectric body, a wavelength normalized film thickness of the silicon nitride film, a wavelength normalized film thickness of the silicon oxide film, and a wavelength normalized film thickness of the IDT electrode, values are set so that at least one of a response intensity of a first higher order mode, corresponding to the response intensity of a second higher order mode, and of a response intensity of a third higher mode is greater than about −2.4.