Multilayer BAW Resonators for High-Coupling Harmonic Modes

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Solution Overview

Problem

Conventional SAW and BAW resonator technologies struggle to achieve high quality factors (Q) and large electromechanical coupling coefficients (Keff2) above 6 GHz, limiting their ability to support mm-Wave frequency bands and design low loss, wide bandwidth filters.

Innovation Solution

A bulk acoustic wave resonator is designed with a transduction structure comprising multiple layers alternating between piezoelectric material and a material with negative piezoelectric effect, maintaining a constant electromechanical coupling coefficient across harmonic resonance modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional SAW and BAW resonator technologies are used, then the resonators can operate at lower frequencies, but they cannot achieve high quality factors and large electromechanical coupling coefficients above 6 GHz

Engineering Contradiction:

Improvequality factorVSAvoidfrequency

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent employs a composite transduction structure consisting of alternating layers of piezoelectric material and material with negative piezoelectric effect. This composite structure enables the resonator to achieve high quality factors and large electromechanical coupling coefficients at mm-Wave frequencies above 6 GHz, resolving the limitation of conventional single-material resonators.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent changes the physical parameters of the transduction structure by introducing materials with negative piezoelectric coefficients and configuring alternating layers. This parameter change enables the resonator to maintain high performance at higher frequencies, overcoming the frequency-dependent degradation of conventional resonators.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If conventional resonator structures are used, then the design is simpler, but they cannot support mm-Wave frequency bands with wide bandwidth filters

Engineering Contradiction:

Improvefrequency band supportVSAvoidtransduction structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent uses composite transduction structures with alternating piezoelectric and negative piezoelectric material layers to enable support for mm-Wave frequency bands and wide bandwidth filters, accepting increased structural complexity as necessary for achieving the desired frequency adaptability.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The transduction structure is segmented into multiple alternating layers of different materials, each contributing specific piezoelectric properties. This segmentation allows the resonator to achieve the required frequency band support and bandwidth performance.

Inventive Principle:

Principle #1Segmentation

3Device complexity

If single layer piezoelectric transduction structures are used, then the device complexity is reduced, but the electromechanical coupling coefficient decreases at higher harmonic modes

Engineering Contradiction:

Improvetransduction structureVSAvoidelectromechanical coupling coefficient

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent employs composite transduction structures with alternating piezoelectric and negative piezoelectric material layers to maintain high electromechanical coupling coefficients at higher harmonic modes, resolving the degradation issue of single-layer structures while managing device complexity.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent applies local quality by using materials with negative piezoelectric coefficients in specific layers of the transduction structure. This localized application of special material properties enhances the electromechanical coupling coefficient at higher harmonic modes without requiring the entire structure to be complex.

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 resonator achieves high electromechanical coupling coefficients comparable to fundamental modes, enabling the design of filters with low insertion losses and wide bandwidths at high microwave and millimeter-wave frequencies.

Implementation Method 1

The transduction structure includes at least a first layer of piezoelectric material and a second layer of a material that exhibits a negative piezoelectric effect

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a second layer of a material that exhibits a negative piezoelectric effect

Methodology Applied

Scientific EffectNegative piezoelectric effect: Converse Piezoelectric Effect

Data Source

PatentUS12206388B2Bulk acoustic wave resonators employing materials with piezoelectric and negative piezoelectric coefficients

Publication Date: 2025.01.21 THE RGT UNIV OF MICHIGAN

AI summary

Bulk acoustic wave resonators are presented. Such resonators typically operate based on a dynamic nonuniform effective piezoelectricity in composite multilayer ferroelectrics with large electrostriction coefficients, like barium strontium titanate (BST). Harmonic resonance modes of a multilayer bulk acoustic wave resonator can be selectively excited with an electromechanical coupling coefficient equal to the fundament mode, which is contrary to the trend K2∝1/n2 exhibited by conventional piezoelectric bulk acoustic resonators. Such a resonator allows for the design of a new class of band-switching filters.