XBAR Ladder Filter Frequency Separation Using Multiple Dielectric Layers

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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 proposed for future wireless communications networks, due to limitations in frequency separation between shunt and series resonators.

Innovation Solution

The use of transversely-excited film bulk acoustic resonators (XBARs) with multiple frequency setting dielectric layers to achieve greater frequency separation between shunt and series resonators, enabling effective filtering across wider communication channel bandwidths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional acoustic wave resonators are used for RF filters, then the filter structure is relatively simple, but the frequency separation between shunt and series resonators is insufficient for higher frequency bands above 3 GHz

Engineering Contradiction:

Improvefrequency separation between resonatorsVSAvoidresonator structure complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The resonator structure is segmented into multiple functional layers: piezoelectric substrate, first dielectric layer, second dielectric layer, and conductive layers. Each layer serves a specific function in frequency tuning and separation, allowing precise control over resonance characteristics while maintaining manageable structural complexity through functional decomposition

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different dielectric layers are applied selectively to specific resonator types (shunt vs. series resonators) with different thicknesses and material properties. This local differentiation enables independent frequency tuning of shunt and series resonators, achieving the required frequency separation for higher frequency bands while keeping the overall device architecture relatively simple

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If dielectric layers are added to adjust resonance frequencies for better frequency separation, then frequency separation improves, but device complexity and manufacturing steps increase

Engineering Contradiction:

Improveresonance frequency tuning precisionVSAvoidmanufacturing process simplicity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The resonance frequencies are tuned by changing dielectric parameters (thickness, permittivity) of the first and second dielectric layers. By adjusting these parameters during the manufacturing process, precise frequency separation is achieved. The method leverages standard semiconductor fabrication techniques for dielectric deposition, making the parameter adjustment process compatible with existing manufacturing capabilities without requiring entirely new process steps

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The dielectric layers are deposited and configured during the initial manufacturing process rather than requiring post-fabrication tuning. This preliminary action integrates frequency tuning into the standard fabrication sequence, reducing the need for additional manufacturing steps and simplifying the overall production process while achieving precise frequency separation

Inventive Principle:

Principle #10Preliminary action

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 approach allows for improved performance of RF filters at higher frequencies, providing enhanced frequency separation and filtering capabilities, which is critical for future wireless communication systems.

Implementation Method 1

comprising a piezoelectric material

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

series resonators and shunt resonators

Methodology Applied

Scientific EffectAcoustic resonance: Resonance

Data Source

PatentUS12267064B2Filter using transversely-excited film bulk acoustic resonators with multiple frequency setting layers

Publication Date: 2025.04.01 MURATA MFG CO LTD

AI summary

Acoustic filters are disclosed. A filter device includes a plurality of resonators connected in a ladder filter circuit, each resonator of the plurality of resonators comprising an interdigital transducer (IDT) with interleaved fingers disposed on a respective piezoelectric diaphragm. A first frequency setting dielectric layer having a first thickness is disposed over the interleaved fingers of one or more IDTs of a first subset of the plurality of resonators. A second frequency setting dielectric layer having a second thickness greater than the first thickness is disposed over the interleaved fingers of one or more IDTs of a second subset of the plurality of resonators, wherein the first subset and the second subset are not identical.