XBAR Ladder Filter Tuning for 6 GHz Wi-Fi Bandwidth

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Solution Overview

Problem

Existing RF filters using acoustic wave resonators are not well-suited for higher frequencies and wider bandwidths required in future communications networks, such as the 5G NR standard and Wi-Fi bands at 5 GHz and 6 GHz.

Innovation Solution

The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) in RF filters, which provide high electromechanical coupling and frequency capability, enabling effective filtering in higher frequency bands.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If conventional acoustic wave resonators (SAW, BAW, FBAR) are used in RF filters, then the filters can operate at standard frequencies, but they cannot effectively handle higher frequencies and wider bandwidths required for future communication systems

Engineering Contradiction:

Improvefrequency capabilityVSAvoidperformance at higher frequencies

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent changes the fundamental operating parameters of the resonator by transitioning from surface acoustic wave modes to bulk acoustic wave modes with transverse excitation. This parameter change enables the resonator to operate effectively at higher frequencies (above 3 GHz) while maintaining high electromechanical coupling, thereby resolving the limitation of conventional resonators at higher frequency bands

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional longitudinal excitation mechanism with a transverse excitation mechanism using interdigital transducers. This mechanical substitution creates a new mode of acoustic wave propagation (shear horizontal mode) that enables higher frequency operation and wider bandwidth performance, overcoming the limitations of traditional acoustic wave resonator designs

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If higher frequency bands are used to achieve wider bandwidths, then communication capacity increases, but existing resonator technologies cannot maintain adequate power handling and filtering performance

Engineering Contradiction:

Improvecommunication bandwidthVSAvoidfiltering performance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

By changing the excitation mode from longitudinal to transverse, the resonator achieves high electromechanical coupling coefficients that enable wide bandwidth operation while maintaining excellent filtering performance. The parameter change in excitation direction allows the resonator to handle higher transmit powers and wider bandwidths simultaneously, supporting advanced communication standards

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite structures combining piezoelectric materials with specific crystal orientations optimized for transverse excitation. This composite approach creates resonators with enhanced electromechanical coupling and improved performance at higher frequencies, enabling both wide bandwidth and reliable filtering in demanding communication applications

Inventive Principle:

Principle #40Composite materials

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 enable the design of RF filters that can handle the higher transmit power and wider bandwidths needed for future communication systems, improving system performance with better frequency selectivity and reduced spurious modes.

Implementation Method 1

The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

Methodology Applied

Scientific EffectPiezoelectric effect: Converse Piezoelectric Effect

Implementation Method 3

The Transversely-Excited Film Bulk Acoustic Resonator (XBAR) is an acoustic resonator structure for use in microwave filters. The XBAR provides very high electromechanical coupling and high frequency capability.

Methodology Applied

Scientific EffectAcoustic resonance: Resonance

Data Source

PatentUS12289098B2Filter using transversely-excited film bulk acoustic resonators

Publication Date: 2025.04.29 MURATA MFG CO LTD

AI summary

A 6 GHz Wi-Fi bandpass filter includes a ladder filter circuit with two or more shunt transversely-excited film bulk acoustic resonators (XBARs) and two or more series XBARs. Each of the two or more shunt XBARS includes a diaphragm having an LN-equivalent thickness greater than or equal to 310 nm, and each of the two or more series XBARS includes a diaphragm having an LN-equivalent thickness less than or equal to 305 nm.