BAW Resonator Stack With Alternating AlN Axes for Low Acoustic Loss

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Solution Overview

Problem

Existing Bulk Acoustic Wave (BAW) resonators and filters face performance issues at higher 5G frequencies due to scaling problems and significant increases in acoustic losses.

Innovation Solution

The development of bulk acoustic wave resonator structures with a stack of alternating axis piezoelectric layers, specifically using Aluminum Nitride (AlN) layers with varying polarization axes, coupled with multilayer metal acoustic reflectors, to enhance frequency response and reduce acoustic losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional BAW resonator structures are used, then manufacturing is relatively easier compared to SAW, but performance deteriorates at higher 5G frequencies due to scaling issues and acoustic losses

Engineering Contradiction:

Improveperformance at high frequencyVSAvoidacoustic losses

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The piezoelectric layer is segmented into multiple sub-layers with alternating polarization axes (e.g., c-axis AlN layers alternating with a-axis or m-axis AlN layers). This segmentation allows each sub-layer to contribute differently to the acoustic wave propagation, reducing overall acoustic losses and improving quality factor at high frequencies while maintaining the BAW structure's inherent advantages

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite piezoelectric structures combining different crystal orientations (c-axis, a-axis, m-axis AlN layers) within a single resonator device. This composite approach leverages the complementary properties of different crystal orientations to reduce acoustic losses and improve high-frequency performance while retaining manufacturing advantages of BAW structures

Inventive Principle:

Principle #40Composite materials

2Speed

If BAW resonators are used for higher 5G frequencies, then frequency response improves, but acoustic losses increase significantly

Engineering Contradiction:

Improvefrequency responseVSAvoidacoustic losses

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

Different regions of the piezoelectric layer are assigned different crystal orientations and properties. Specifically, c-axis AlN layers provide strong piezoelectric coupling for high frequency response, while alternating a-axis or m-axis layers are positioned to reduce acoustic losses at specific interfaces, creating local quality variations that collectively improve overall high-frequency performance

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

Instead of using a single uniform piezoelectric orientation, the patent inverts the conventional approach by alternating between different crystal orientations (c-axis, a-axis, m-axis) in sequence. This alternating pattern creates constructive and destructive interference effects that cancel out acoustic losses while maintaining the desired frequency response characteristics

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 improves the frequency response and reduces acoustic losses at higher frequencies, enabling better performance in 5G applications by maintaining high quality factors and reducing insertion loss.

Implementation Method 1

a stack of piezoelectric layers, each having a polarization axis in a direction substantially perpendicular to a surface of the substrate, wherein an axis of the polarization alternates between adjacent layers in the stack

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

coupled with multilayer metal acoustic reflectors

Methodology Applied

Scientific EffectAcoustic reflection: Reflection

Implementation Method 3

Bulk Acoustic Wave (BAW) resonator structures

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS12301206B2Bulk acoustic wave (BAW) resonator structures, devices and systems

Publication Date: 2025.05.13 QXONIX INC

AI summary

Techniques for improving Bulk Acoustic Wave (BAW) resonator structures are disclosed, including filters, oscillators and systems that may include such devices. First and second layers of piezoelectric material may be acoustically coupled with one another to have a piezoelectrically excitable resonance mode. The first layer of piezoelectric material may have a first piezoelectric axis orientation, and the second layer of piezoelectric material may have a second piezoelectric axis orientation that opposes the first piezoelectric axis orientation of the first layer of piezoelectric material. A top acoustic reflector including a first pair of top metal electrode layers may be electrically and acoustically coupled with the first layer of piezoelectric material to excite the piezoelectrically excitable main resonance mode at a resonant frequency.