XBAR Filter Dielectric Decoupling for Narrower Resonance Separation

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Solution Overview

Problem

Current RF filters using acoustic wave resonators, such as SAW and BAW resonators, are not well-suited for higher frequencies and wider bandwidths required by future communication networks, particularly for 5G NR standards like bands n77 and n79, which demand improved performance in terms of frequency handling and bandwidth.

Innovation Solution

The introduction of a decoupling dielectric layer between the IDT fingers and the piezoelectric diaphragm in Transversely-Excited Film Bulk Acoustic Resonators (XBARs) reduces electromechanical coupling, allowing for a narrower difference between resonance and anti-resonance frequencies, making them more suitable for high-frequency applications by incorporating a decoupling dielectric layer to tailor the coupling for specific filter requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a decoupling dielectric layer is added between IDT fingers and piezoelectric diaphragm, then electromechanical coupling is reduced and bandwidth is improved, but device complexity increases

Engineering Contradiction:
ImprovebandwidthVSAvoiddevice complexity
Core Design Contradiction:
Adaptability or versatilityVSDevice complexity

Solution Approach 1:

A decoupling dielectric layer is introduced as an intermediary element between the IDT fingers and the piezoelectric diaphragm. This dielectric layer reduces the electromechanical coupling coefficient by decoupling the electrical and mechanical fields, thereby enabling wider bandwidth operation while maintaining the fundamental XBAR structure

Inventive Principle:
Principle #24Intermediary (Mediator)

Solution Approach 2:

The resonator employs a composite structure combining multiple materials: the piezoelectric diaphragm material, the decoupling dielectric layer material, and the IDT finger material. This composite approach allows optimization of electromechanical coupling characteristics while achieving the desired bandwidth performance

Inventive Principle:
Principle #40Composite materials

2Speed

If electromechanical coupling is reduced for high-frequency applications, then frequency handling capability is improved, but resonance and anti-resonance frequency separation decreases

Engineering Contradiction:
Improvefrequency handling capabilityVSAvoidresonance and anti-resonance frequency separation
Core Design Contradiction:
SpeedVSManufacturing precision

Solution Approach 1:

The electromechanical coupling coefficient is adjusted as a key parameter through modification of the decoupling dielectric layer properties (thickness, material, position). By changing this parameter, the resonator can be optimized for high-frequency operation while maintaining adequate frequency separation for manufacturing tolerances

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

This approach enables the design of filters with tailored electromechanical coupling, enhancing their performance for high-frequency applications, such as 5G NR band N79, by reducing the difference between resonance and anti-resonance frequencies, thus improving filter bandwidth and frequency handling capabilities.

Implementation Method 1

The introduction of a decoupling dielectric layer between the IDT fingers and the piezoelectric diaphragm in Transversely-Excited Film Bulk Acoustic Resonators (XBARs) reduces electromechanical coupling

Methodology Applied
Scientific EffectElectromechanical coupling: Piezoelectric Effect

Implementation Method 2

Transversely-Excited Film Bulk Acoustic Resonators (XBARs)

Methodology Applied
Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS12126318B2Filters using decoupled transversely-excited film bulk acoustic resonators
Publication Date: 2024.10.22 MURATA MFG CO LTD
  • US12126318B2 patent drawing
  • US12126318B2 patent drawing
  • US12126318B2 patent drawing

AI summary

Filter devices and methods of fabrication are disclosed. An acoustic filter device includes a substrate and a piezoelectric plate, a first portion of the piezoelectric plate spanning a first cavity in the substrate and a second portion of the piezoelectric plate spanning a second cavity in the substrate. A decoupling dielectric layer on a front surface of the first and second portions of the piezoelectric plate has a first thickness td1 on the first portion and a second thickness td2, greater than the first thickness, on the second portion. Interleaved fingers of a first interdigital transducer (IDT) are on the decoupling dielectric layer over the first portion of the piezoelectric plate, and interleaved fingers of a second IDT are on the decoupling dielectric layer over the second portion of the piezoelectric plate.