Stacked Crystal Filter Coupling Profiles for Spurious Mode Suppression

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Solution Overview

Problem

Acoustic resonators, particularly stacked crystal filters (SCFs), face challenges in suppressing spurious modes that lead to degraded filter rejections due to limited reflector selectivity and overlapping spurious responses, which complicates the design of high-performance filters for advanced mobile communication systems.

Innovation Solution

The introduction of modified piezoelectric coupling profiles within SCFs, incorporating inverted polarity piezoelectric layers, non-piezoelectric layers, and thicker electrodes, allows for effective suppression of spurious modes by configuring different electromechanical coupling values and stress profiles across input and output sides, thereby enhancing mode suppression capabilities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If reflector structures with many reflector layers are used to suppress spurious modes, then filter rejection improves, but device complexity and fabrication difficulty increase

Engineering Contradiction:

Improvefilter rejectionVSAvoidreflector structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the spurious mode suppression function from the reflector structure and relocates it to the piezoelectric coupling profile of the SCF. By modifying the piezoelectric layers directly, the invention eliminates the need for complex reflector structures with multiple layers, achieving mode suppression at the source rather than through additional suppression components.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent applies local quality by creating non-uniform piezoelectric coupling profiles within specific regions of the SCF. By varying the coupling strength at different locations (strong coupling at input, weak coupling at output, or inverted polarity regions), the invention achieves targeted mode suppression without affecting the entire structure uniformly, thereby simplifying the overall design.

Inventive Principle:

Principle #3Local quality

2Speed

If multiple SCFs with different frequencies are used to achieve broader bandwidth, then operating bandwidth improves, but spurious responses from multiple SCFs do not overlap and require separate suppression

Engineering Contradiction:

Improveoperating bandwidthVSAvoidspurious response suppression

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent applies universality by designing a piezoelectric coupling profile modification approach that can suppress spurious modes across multiple frequency bands simultaneously. The modified coupling profile in the SCF structure provides broadband suppression capability, meaning a single SCF design can handle spurious modes from multiple frequency ranges without requiring separate suppression mechanisms for each frequency.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If inverted polarity piezoelectric layers are introduced to suppress spurious modes, then mode suppression improves, but fabrication complexity increases

Engineering Contradiction:

Improvemode suppressionVSAvoidfabrication simplicity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent directly applies inversion by using inverted polarity piezoelectric layers to create destructive interference for spurious modes. The inverted polarity regions generate acoustic waves that are 180 degrees out of phase with the spurious modes, causing them to cancel each other out. This approach achieves effective mode suppression by inverting the polarity rather than adding complex suppression structures.

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 approach effectively suppresses spurious modes, improving filter rejection and bandwidth, and simplifies the fabrication of acoustic resonators, enabling better integration with evolving mobile communication systems by providing symmetric electrical responses and reduced coupling to undesired modes.

Implementation Method 1

a first piezoelectric layer; a second piezoelectric layer; a third piezoelectric layer between the second electrode and the shared electrode, the third piezoelectric layer having a polarity that is opposite a polarity of the second piezoelectric layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

Acoustic resonators, including stacked crystal filters (SCFs), are disclosed that include spurious mode suppression by modifying a piezoelectric coupling profile within one or more layers of an SCF

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS11146245B2Mode suppression in 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 mode suppression structures. Acoustic resonators, including stacked crystal filters (SCFs), are disclosed that include spurious mode suppression by modifying a piezoelectric coupling profile within one or more layers of an SCF. 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. Symmetric input and output electrical response for SCFs with mode suppression configurations may be exhibited by including piezoelectric materials with different electromechanical coupling values and/or by dividing stress profiles differently by configuring different thicknesses for input and output sides of SCFs.