Overtone BAW Resonator Structure for High-Frequency Temperature Stability

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Solution Overview

Problem

Achieving high resonant frequencies in bulk acoustic wave (BAW) resonators for filtering higher frequency radio frequency signals is challenging due to technical issues such as smaller size leading to spurious modes, edge energy leakage, reduced power handling, and manufacturing difficulties with thinner piezoelectric layers.

Innovation Solution

The use of an overtone mode as the main mode in BAW devices, with a combination of a piezoelectric layer and a temperature compensation layer positioned between electrodes, where the total thickness excites the overtone mode, providing better power handling and temperature compensation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the piezoelectric layer is made thinner to achieve higher resonant frequencies, then the resonant frequency increases, but spurious modes appear and manufacturing precision deteriorates

Engineering Contradiction:

Improveresonant frequencyVSAvoidmanufacturing precision

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The patent uses a composite structure consisting of a piezoelectric layer combined with a temperature compensation layer (such as silicon oxide or silicon nitride). This composite configuration allows the piezoelectric layer to be sufficiently thin for high frequency operation while the compensation layer provides mechanical support and reduces spurious modes, thereby enabling high resonant frequencies without compromising manufacturing precision

Inventive Principle:

Principle #40Composite materials

2Speed

If the piezoelectric layer is made thinner to achieve higher resonant frequencies, then the resonant frequency increases, but edge energy leakage increases

Engineering Contradiction:

Improveresonant frequencyVSAvoidedge energy leakage

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The temperature compensation layer forms a composite structure with the piezoelectric layer, providing mechanical reinforcement at the edges. This composite configuration reduces edge energy leakage by distributing stress more evenly and preventing energy escape at the boundaries, allowing the piezoelectric layer to be thin enough for high frequency operation

Inventive Principle:

Principle #40Composite materials

3Speed

If the piezoelectric layer is made thinner to achieve higher resonant frequencies, then the resonant frequency increases, but power handling capability reduces

Engineering Contradiction:

Improveresonant frequencyVSAvoidpower handling

Core Design Contradiction:

SpeedVSPower

Solution Approach 1:

The temperature compensation layer provides additional mechanical strength and thermal management capabilities to the composite structure. This allows the piezoelectric layer to operate at high frequencies with reduced thickness while the compensation layer absorbs thermal stress and prevents failure, thereby maintaining power handling capability despite the thinner active piezoelectric layer

Inventive Principle:

Principle #40Composite materials

4Speed

If the piezoelectric layer is made thinner to achieve higher resonant frequencies, then the resonant frequency increases, but device reliability deteriorates

Engineering Contradiction:

Improveresonant frequencyVSAvoiddevice reliability

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The composite structure of piezoelectric layer and temperature compensation layer enhances device reliability by distributing mechanical and thermal stresses. The compensation layer acts as a protective element that prevents failure modes such as delamination, cracking, and electrode displacement, thereby improving reliability for high frequency applications

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent changes the physical and thermal parameters of the composite structure by introducing a material with different thermal expansion characteristics. This parameter change allows the structure to accommodate thermal stresses at high frequencies without failure, improving reliability

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 allows for higher resonant frequencies with fewer spurious modes, improved power handling, and reduced temperature coefficient of frequency variation, making it suitable for advanced applications like 5G New Radio filtering.

Implementation Method 1

In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

at least one temperature compensation layer positioned between the first and second electrodes

Methodology Applied

Scientific EffectTemperature compensation: Thermal Expansion

Data Source

PatentUS20240364297A1Overtone mode acoustic wave device with temperature compensation layer

Publication Date: 2024.10.31 SKYWORKS SOLUTIONS INC

AI summary

A bulk acoustic wave device that is configured to excite an overtone mode as a main mode is disclosed. The bulk acoustic wave device can include a first electrode, a second electrode, a piezoelectric layer disposed between the first and second electrodes, and a temperature compensation layer between the first and second electrodes. A total thickness of the piezoelectric layer and the temperature compensation layer is sufficiently thick to excite the overtone mode as the main mode. Related filters, multiplexers, radio frequency modules, wireless communications devices, and methods are also disclosed.