Variable-Width XBAR Electrodes for High-Frequency RF Filters

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Solution Overview

Problem

Existing RF filters using acoustic wave resonators are not well-suited for higher frequency communications bands, such as those defined in the 5G NR standard, due to limitations in handling higher transmit power and achieving wide bandwidth.

Innovation Solution

The use of transversely-excited film bulk acoustic resonators (XBARs) with specific design features, including a two-layer interdigital transducer (IDT) finger structure and varying upper layer shapes, to minimize spurious acoustic modes and enhance thermal and electrical conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If conventional acoustic wave resonators are used, then existing RF filter designs can be maintained, but they cannot effectively handle higher transmit power and achieve wide bandwidth in higher frequency communications bands

Engineering Contradiction:

Improvetransmit power handlingVSAvoidperformance at higher frequencies

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent changes the excitation direction parameter from longitudinal to transverse, and modifies the electrode geometry parameters (varying width in the direction of propagation) to enable effective operation at higher frequencies with improved power handling and bandwidth characteristics

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a width variation dimension to the electrode structure, where the electrode width changes in the direction of wave propagation. This additional geometric dimension enables control over acoustic mode generation and improves power handling capability

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If conventional electrode structures are used, then manufacturing processes remain simple, but spurious acoustic modes are generated that degrade filter performance

Engineering Contradiction:

Improvereduction of spurious modesVSAvoidelectrode structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies local quality by varying the electrode width specifically in the direction of wave propagation while maintaining other structural aspects. This localized geometric modification targets the generation of spurious acoustic modes without requiring complete redesign of the entire resonator structure

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent introduces asymmetry in the electrode structure by making the width different at various positions along the propagation direction. This asymmetric geometry disrupts the conditions for spurious mode generation while maintaining the primary acoustic mode

Inventive Principle:

Principle #4Asymmetry

3Productivity

If higher frequency communications bands are used, then wider communication channel bandwidths are achieved, but thermal management becomes more challenging

Engineering Contradiction:

Improvecommunication bandwidthVSAvoidthermal management

Core Design Contradiction:

ProductivityVSTemperature

Solution Approach 1:

The transverse excitation configuration and varying electrode width change the distribution of acoustic energy and heat generation, improving thermal management by reducing concentrated heating effects that occur in conventional longitudinal excitation at high frequencies

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

XBARs effectively address the challenges of higher frequency communications by providing improved frequency handling, reduced spurious modes, and enhanced thermal management, leading to more efficient and reliable RF filters.

Implementation Method 1

transversely-excited film bulk acoustic resonators (XBARs)

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

varying upper layer shapes, to minimize spurious acoustic modes

Methodology Applied

Scientific EffectAcoustic wave propagation: Acoustics

Implementation Method 3

enhanced thermal and electrical conductivity

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 4

enhanced thermal and electrical conductivity

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS20250125783A1Transversely-excited film bulk acoustic resonators with electrodes having a second layer of variable width

Publication Date: 2025.04.17 MURATA MFG CO LTD

AI summary

An acoustic resonator device is provided that includes a piezoelectric layer; and an interdigital transducer (IDT) at a surface of the piezoelectric layer, the IDT comprising interleaved fingers. At least one interleaved finger of the interleaved fingers comprises a first layer and a second layer over the first layer, wherein the first layer is between the piezoelectric layer and the second layer. Moreover, a shape of the second layer varies with respect to at least one other interleaved finger of the interleaved fingers. A thickness of the first layer is less than a thickness of the second layer.