BAW Resonator Overtone Stack for High Frequency and Low Spurious Waves

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Solution Overview

Problem

Existing bulk acoustic wave (BAW) resonators face challenges in achieving higher operating frequencies without compromising manufacturing repeatability, operational reliability, and electrode resistance due to the thinness of piezoelectric material layers, which also generate spurious acoustic waves.

Innovation Solution

Designing BAW resonators to utilize the overtone or higher harmonics of the piezoelectric material film stack as the main acoustic wave, increasing the thickness of piezoelectric and electrode layers while incorporating interposer and temperature compensation layers to generate a second overtone vibrational mode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the thickness of piezoelectric material layers is increased to improve manufacturing repeatability and reduce electrode resistance, then the operating frequency of the resonator decreases

Engineering Contradiction:

Improvemanufacturing repeatabilityVSAvoidoperating frequency

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent utilizes higher order vibrational modes (overtones) of the piezoelectric material layer stack. By exciting the second overtone mode instead of the fundamental mode, the resonator achieves higher operating frequencies despite having thicker piezoelectric layers. This resolves the contradiction by changing the vibrational mode rather than reducing layer thickness.

Inventive Principle:

Principle #18Mechanical vibration

Solution Approach 2:

The patent changes the vibrational mode parameter from fundamental mode to second overtone mode, which fundamentally alters the frequency-thickness relationship. This parameter change allows the system to operate at higher frequencies with thicker layers, simultaneously improving manufacturing repeatability and electrical performance.

Inventive Principle:

Principle #35Parameter changes

2Strength

If the thickness of piezoelectric material layers is increased to improve ruggedness, then spurious acoustic wave generation increases

Engineering Contradiction:

ImproveruggednessVSAvoidspurious acoustic waves

Core Design Contradiction:

StrengthVSObject-generated harmful factors

Solution Approach 1:

The patent introduces interposer layers between the piezoelectric material layers. These interposer layers act as intermediaries that suppress the generation of spurious acoustic waves while allowing the thicker piezoelectric layers to provide improved ruggedness. The interposer layers mediate between the conflicting requirements of thickness and spurious wave generation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent extracts or removes the harmful spurious acoustic waves by using interposer layers that specifically target and suppress these unwanted vibrations, while preserving the beneficial effects of thicker piezoelectric layers for ruggedness.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If the thickness of electrode layers is increased to reduce electrode resistance, then the device complexity increases

Engineering Contradiction:

Improveelectrode resistanceVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the electrode structure into multiple layers (bottom electrode, top electrode, and interposer layers). This segmentation allows each layer to be optimized independently, achieving low overall resistance through the stacked configuration without requiring excessively thick single electrodes, thus managing device complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses composite material structures with multiple layers of different materials (piezoelectric materials, interposer layers, electrodes). This composite approach allows optimization of electrical resistance through material selection and stacking, while managing overall device complexity through systematic layer integration.

Inventive Principle:

Principle #40Composite materials

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 BAW resonators to operate at higher frequencies with improved ruggedness and reduced electrode resistance, minimizing spurious acoustic wave generation and enhancing manufacturing reliability.

Implementation Method 1

a first piezoelectric material layer disposed on an upper surface of the bottom electrode, and a second piezoelectric material layer disposed on the first piezoelectric material layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

the interposer layer has a thickness sufficient to cause the bulk acoustic wave resonator to generate a second overtone vibrational mode

Methodology Applied

Scientific EffectOvertone vibration: Vibration

Data Source

PatentUS20260012155A1Bulk acoustic wave resonator utilizing overtone modes

Publication Date: 2026.01.08 SKYWORKS GLOBAL PTE LTD

AI summary

Aspects and embodiments disclosed herein include a bulk acoustic wave resonator including a material layer stack located in a central active region of the bulk acoustic wave resonator, the material layer stack comprising a bottom electrode, a first piezoelectric material layer disposed on an upper surface of the bottom electrode, a second piezoelectric material layer disposed on the first piezoelectric material layer, a polarity of the second piezoelectric material layer being opposite a polarity of the first piezoelectric material layer, an interposer layer disposed between the first piezoelectric material layer and the second piezoelectric material layer, and a top electrode having a lower surface disposed on an upper surface of the upper piezoelectric material layer.