BAW Resonator Coupler Structure for Improved TCF at High Order Modes

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Solution Overview

Problem

BAW resonators face challenges in high-frequency applications due to increased electrical loss, poor temperature coefficient of frequency (TCF), and fabrication difficulties with high order mode operation, particularly when using piezoelectric layers with opposite polarities.

Innovation Solution

Incorporating a coupler layer with a dielectric material and conductive vias between piezoelectric layers of the same polarity to excite high order modes, ensuring the stress field aligns in the same direction and reducing potential difference across electrodes, thereby improving TCF and simplifying fabrication.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If BAW resonators use thinner electrodes and smaller resonator areas to operate at higher frequencies, then frequency of operation is improved, but electrical loss increases

Engineering Contradiction:

Improvefrequency of operationVSAvoidelectrical loss

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The patent transitions from fundamental mode operation to high order mode operation, effectively changing the dimensional characteristics of the acoustic wave propagation. This allows the resonator to achieve higher frequencies while maintaining larger electrode areas and resonator dimensions, thereby reducing electrical loss while operating at frequencies greater than 5 GHz

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Power

If BAW resonators use cascaded structure with multiple piezoelectric layers to reduce power density, then power density is reduced, but temperature coefficient of frequency deteriorates

Engineering Contradiction:

Improvepower densityVSAvoidtemperature coefficient of frequency

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent modifies the stress profile parameters within the piezoelectric layers by operating in high order modes. This changes the mechanical stress distribution such that the net stress on the piezoelectric material is reduced, thereby improving the temperature coefficient of frequency while maintaining the power density benefits of the cascaded structure

Inventive Principle:

Principle #35Parameter changes

3Speed

If BAW resonators use high order mode operation with polarity inversion in piezoelectric layers, then frequency of operation is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvefrequency of operationVSAvoidfabrication difficulty

Core Design Contradiction:

SpeedVSEase of manufacture

Solution Approach 1:

The patent inverts the conventional approach to high order mode operation. Instead of using piezoelectric layers with opposite polarities, it uses layers with the same polarity and achieves high order mode operation through boundary conditions and layer thickness design. This eliminates the complex polarity inversion fabrication process while maintaining high frequency operation capabilities

Inventive Principle:

Principle #13The other way round (Inversion)

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

The proposed resonator structure achieves improved TCF, reduced power density, and simplified manufacturing by eliminating the need for polarity inversion, while maintaining a larger resonator area and electromechanical coupling.

Implementation Method 1

a first piezoelectric layer, a second piezoelectric layer... The BAW resonator is configured to excite a high order mode through the first piezoelectric layer, the coupler layer, and the second piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

the dielectric layer includes a dielectric material having a positive temperature coefficient of velocity (TCV)

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 3

at least one conductive via electrically connecting the first metal layer and the second metal layer

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS12562713B2Acoustic resonator structure with improved temperature coefficient of frequency (TCF)

Publication Date: 2026.02.24 QORVO US INC

AI summary

An acoustic resonator includes a first piezoelectric layer, a second piezoelectric layer, and a coupler layer between the first piezoelectric layer and the second piezoelectric layer. The first piezoelectric layer and the second piezoelectric layer have a same polarity. The coupler layer includes a first metal layer, a second metal layer, a dielectric layer between the first metal layer and the second metal layer, and conductive vias through the dielectric layer and electrically connecting the first metal layer and the second metal layer. A first electrode is positioned on the first piezoelectric layer opposite the coupler layer. A second electrode is positioned on the second piezoelectric layer opposite the coupler layer.