BAW Resonator Phase Shift Structure for Spurious Mode Suppression

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Solution Overview

Problem

Acoustic resonators, particularly bulk acoustic wave (BAW) resonators and stacked crystal filters (SCFs), face limitations in operating bandwidth and are prone to spurious resonances due to excited spurious modes, which current reflector structures struggle to suppress simultaneously across multiple SCF structures.

Innovation Solution

The introduction of modified piezoelectric coupling profiles within SCF layers, including inverted polarity piezoelectric layers, non-piezoelectric layers, and thicker electrodes, to suppress spurious modes and provide built-in phase shift capabilities, enhancing mode suppression and phase balance across operating frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If reflector structures with many layers are used to suppress spurious modes, then spurious mode suppression improves, but device complexity increases

Engineering Contradiction:

Improvespurious mode suppressionVSAvoidreflector structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the polarity parameter of piezoelectric layers to create inverted polarity structures that provide inherent phase shift capabilities. This parameter change allows the same structural element to perform both filtering and phase shifting functions, reducing the need for additional reflector layers while maintaining spurious mode suppression performance.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The inverted polarity piezoelectric layers serve multiple functions simultaneously: they act as filtering elements for spurious mode suppression and as phase shift structures for signal phase adjustment. This multi-functionality reduces the overall device complexity by eliminating the need for separate phase shift components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If multiple SCF structures with different frequencies are used, then operating bandwidth increases, but spurious response suppression becomes more difficult

Engineering Contradiction:

Improveoperating bandwidthVSAvoidspurious response suppression

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies different polarity configurations to different piezoelectric layers within the SCF structure. Each layer can be optimized for its specific frequency range, with inverted polarity layers providing phase shift capabilities tailored to particular frequency bands. This local differentiation allows broad operating bandwidth while maintaining effective spurious response suppression across all frequencies.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If conventional SCF configurations are used, then fabrication is simpler, but phase balance and loss performance are poorer

Engineering Contradiction:

Improvefabrication simplicityVSAvoidphase balance and loss performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent inverts the polarity of certain piezoelectric layers to achieve 180-degree phase shifts. This inversion approach maintains the relatively simple stacked crystal filter fabrication process while dramatically improving phase balance performance. The inverted layers are integrated into the existing SCF structure, requiring minimal additional fabrication complexity.

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

This configuration effectively suppresses spurious modes and improves phase balance, allowing for more symmetrical electrical responses and reduced loss in acoustic resonators, thereby enhancing the performance of acoustic filters in mobile communication systems.

Implementation Method 1

a second piezoelectric layer having a polarity that is opposite a polarity of the first piezoelectric layer to provide a phase shift

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

including piezoelectric materials with different electromechanical coupling values

Methodology Applied

Scientific EffectElectromechanical coupling: Piezoelectric Effect

Implementation Method 3

acoustic resonators, such as bulk acoustic wave (BAW) resonators

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS11146246B2Phase shift structures for acoustic resonators

Publication Date: 2021.10.12 QORVO US INC

AI summary

Acoustic resonators, such as bulk acoustic wave (BAW) resonators, are disclosed that include phase shift structures. Acoustic resonators, including stacked crystal filters (SCFs) and coupled resonator filters (CRFs), may include inverted piezoelectric layers that are configured to provide built-in phase shift capabilities. Circuit topologies that include such SCFs may be provided with simplified structures and reduced loss. Circuit topologies with such CRFs may be provided with more symmetrical electrical connections and improved phase balance over operating frequencies. SCFs with phase shift structures may additionally include spurious mode suppression by modifying piezoelectric coupling profiles within one or more layers. Mode suppression configurations may include structures with one or more inverted polarity piezoelectric layers, one or more non-piezoelectric layers, one or more thicker electrodes of the SCF, and combinations thereof.