Tunable BAW Resonator Stack for Multi-Band Filtering

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Solution Overview

Problem

Existing bulk acoustic wave (BAW) devices face challenges in achieving high quality factor (Q) and suppressing spurious modes while meeting performance and physical size specifications, particularly in radio frequency electronic systems.

Innovation Solution

A tunable BAW device with a floating third electrode that can be connected to the second electrode in a second state, enabled by circuitry such as a switch, transformer, or varactor, allowing operation in two or more frequency bands by switching between resonators sharing a piezoelectric structure.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple separate filters are used to cover different frequency bands, then frequency band coverage is improved, but device complexity and physical size increase

Engineering Contradiction:

Improvefrequency band coverageVSAvoidnumber of filters

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent implements a single BAW filter capable of operating in multiple frequency bands by incorporating two resonators (first and second resonators) that share a common piezoelectric layer structure. The filter can be tuned between different frequency bands by switching the electrical connection state of the third electrode, eliminating the need for multiple separate filters and reducing device complexity while maintaining broad frequency band coverage

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent merges two resonators into a single integrated structure where the first resonator (comprising first electrode, second electrode, and first piezoelectric layer) and second resonator (comprising second electrode, third electrode, and second piezoelectric layer) share common elements including the piezoelectric layer stack. This consolidation reduces the total number of components while enabling multi-frequency operation through electrode switching

Inventive Principle:

Principle #5Merging (Combining)

2Adaptability or versatility

If multiple separate filters are used to cover different frequency bands, then frequency band coverage is improved, but physical size increases

Engineering Contradiction:

Improvefrequency band coverageVSAvoiddevice size

Core Design Contradiction:

Adaptability or versatilityVSVolume of moving object

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

3Ease of manufacture

If traditional BAW device structure is used, then manufacturing simplicity is maintained, but spurious modes are suppressed

Engineering Contradiction:

Improvestructural simplicityVSAvoidspurious modes

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent segments the piezoelectric structure into distinct functional layers (first piezoelectric layer and second piezoelectric layer) with different thicknesses, and divides the electrode structure into multiple independently controllable electrodes (first electrode, second electrode, third electrode). This segmentation allows different portions of the structure to be optimized for different functions: the first resonator for fundamental mode operation and the second resonator for spurious mode suppression, while maintaining a manufacturable layered structure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by making the first piezoelectric layer thinner than the second piezoelectric layer, and by selectively connecting different electrodes for different operating conditions. The third electrode can be floating for fundamental mode operation or connected to the second electrode for spurious mode suppression, allowing local optimization of different regions of the device for different operational requirements

Inventive Principle:

Principle #3Local quality

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 device achieves tunability across multiple frequency bands with maintained high quality factor, reducing the number of filters needed and minimizing insertion loss, thus optimizing performance and reducing system size.

Implementation Method 1

a first piezoelectric layer between the first electrode and the second electrode; a second piezoelectric layer between the second electrode and the third electrode

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS20250350259A1Tunable bulk acoustic wave device

Publication Date: 2025.11.13 SKYWORKS SOLUTIONS INC

AI summary

A bulk acoustic wave device includes a first electrode, a second electrode, a first piezoelectric layer between the first electrode and the second electrode, a third electrode, and a second piezoelectric layer. The second piezoelectric layer is between the second electrode and the third electrode.