Bi-Polar Border Polarization in BAW Resonators for Lateral Mode Control

Solution Overview

Problem

Bulk acoustic wave (BAW) resonators face challenges in achieving ideal phase curves due to spurious modes caused by lateral standing waves, which reduce the quality factor and are difficult to suppress, especially below the series resonance frequency, limiting their performance in high-frequency filter applications.

Innovation Solution

Incorporating a bi-polar border portion in the piezoelectric layer with opposing polarizations in the border region, which confines lateral acoustic energy without additional mass loading, potentially eliminating the need for a border ring and improving spurious mode suppression.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a border ring is used to suppress lateral standing waves, then spurious modes are suppressed, but device complexity and size increase

Engineering Contradiction:

Improvespurious mode suppressionVSAvoidborder ring structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent changes the polarization parameter of the piezoelectric material in the border region from unipolar to bi-polar configuration. By reversing the polarization direction in the border portion relative to the active portion, lateral standing waves are suppressed through electrostatic cancellation effects, achieving spurious mode suppression without adding structural complexity like border rings

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical border ring structure with an electrical field-based solution. Instead of using a physical mass-loaded border ring to suppress lateral waves, the invention uses bi-polar piezoelectric polarization to create opposing electrical fields that cancel out lateral standing waves, substituting a mechanical suppression mechanism with an electrical field mechanism

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If mass loading is applied to suppress lateral modes, then spurious modes are reduced, but device size and weight increase

Engineering Contradiction:

Improvelateral mode suppressionVSAvoidmass loading

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent changes the polarization parameter of the piezoelectric material in the border region from unipolar to bi-polar configuration. By reversing the polarization direction in the border portion relative to the active portion, lateral standing waves are suppressed through electrostatic cancellation effects, achieving spurious mode suppression without adding structural complexity like border rings

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the mechanical border ring structure with an electrical field-based solution. Instead of using a physical mass-loaded border ring to suppress lateral waves, the invention uses bi-polar piezoelectric polarization to create opposing electrical fields that cancel out lateral standing waves, substituting a mechanical suppression mechanism with an electrical field mechanism

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of manufacture

If conventional unipolar piezoelectric structure is used, then manufacturing is simple, but spurious modes reduce quality factor

Engineering Contradiction:

Improvepiezoelectric layer structureVSAvoidquality factor

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the polarization parameter of the piezoelectric material in the border region from unipolar to bi-polar configuration. By reversing the polarization direction in the border portion relative to the active portion, lateral standing waves are suppressed through electrostatic cancellation effects, achieving spurious mode suppression without adding structural complexity like border rings

Inventive Principle:

Principle #35Parameter changes

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 bi-polar border portion effectively suppresses spurious modes near the series resonance frequency, enhances the quality factor, and reduces lateral modes, leading to improved filter performance and reduced size and cost in high-frequency applications.

Implementation Method 1

The piezoelectric material in the active portion has a first polarization. The bi-polar border portion has a first sub-portion and a second sub-portion... The piezoelectric material in the first sub-portion has the first polarization, and the piezoelectric material in the second sub-portion has a second polarization, which is opposite the first polarization.

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11509287B2Bi-polar border region in piezoelectric device

Publication Date: 2022.11.22 QORVO US INC

AI summary

An acoustic device includes a foundation structure and a transducer provided over the foundation structure. The foundation structure includes a piezoelectric layer between a top electrode and a bottom electrode. The piezoelectric layer has an active portion within an active region of the transducer, and a bi-polar border portion within a border region of the transducer. The piezoelectric material in the active portion has a first polarization. The bi-polar border portion has a first sub-portion and a second sub-portion, which resides either above or below the first sub-portion. The piezoelectric material in the first sub-portion has the first polarization, and the piezoelectric material in the second sub-portion has a second polarization, which is opposite the first polarization.