Bezier-Electrode BAW Resonator for Transverse Mode Suppression

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Solution Overview

Problem

Bulk acoustic wave resonators suffer from transverse parasitic modes due to defects in piezoelectric materials and incomplete C-axis orientation, leading to performance degradation, as existing pentagon electrode designs have a weak restraining effect on transverse acoustic wave propagation.

Innovation Solution

A bulk acoustic wave resonator design featuring a piezoelectric stack structure with a top electrode outline formed by Bezier curves of order greater than or equal to 2, increasing the length of transverse propagation paths and enhancing the restraining effect on transverse acoustic waves, thereby reducing the influence of parasitic modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a pentagon electrode is designed to reduce transverse propagation of acoustic waves, then the parasitic mode is reduced, but the restraining effect on transverse acoustic waves is weak

Engineering Contradiction:

Improvetransverse parasitic modeVSAvoidrestraining effect on transverse acoustic waves

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent applies curvature by designing the top electrode outline using Bezier curves of order greater than or equal to 2, replacing straight lines and sharp corners with smooth curved boundaries. This curved geometry increases the transverse propagation path length of acoustic waves, thereby enhancing the restraining effect on transverse parasitic modes while maintaining electrode functionality.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent changes the geometric parameters of the electrode outline by specifying that it includes at least one Bezier curve of order ≥2, with the curve passing through at least three control points. This parameter change transforms the electrode shape from conventional geometric forms to a mathematically defined curved shape that optimizes acoustic wave restraint.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the resonator longitudinally vibrates only in thickness direction, then ideal filtering function is achieved, but transverse vibration occurs due to piezoelectric material defects and incomplete C-axis orientation

Engineering Contradiction:

Improvefiltering functionVSAvoidtransverse vibration

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The curved Bezier boundary of the top electrode increases the path length that transverse acoustic waves must travel through the piezoelectric material. This extended path length enhances energy dissipation through material damping and acoustic scattering, thereby suppressing transverse vibrations and reducing parasitic modes that degrade filtering performance.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent utilizes the inherent material damping and acoustic scattering properties of the piezoelectric material to convert harmful transverse acoustic wave energy into heat and scattered directions. By designing the electrode geometry to maximize wave path length, the material's natural dissipation mechanisms are enhanced to suppress parasitic modes.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 Bezier curve design increases losses of transverse acoustic waves, improving the performance of bulk acoustic wave filters by effectively reducing the impact of transverse parasitic modes and enhancing the filtering function.

Implementation Method 1

vibration in a longitudinal mode is generated by a piezoelectric effect of piezoelectric materials

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

longitudinally-propagated acoustic signals are generated in a sandwich structure consisting of the top electrode, the bottom electrode and the piezoelectric materials

Methodology Applied

Scientific EffectAcoustic wave propagation: Sound

Implementation Method 3

only radio frequency signals matched with the piezoelectric materials in resonant frequency can be transmitted through the bulk acoustic wave resonator

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS20230102044A1Bulk acoustic wave resonator and bulk acoustic wave filter

Publication Date: 2023.03.30 WUHAN MEMSONICS TECH CO LTD

AI summary

This present disclosure provides a bulk acoustic wave resonator and a bulk acoustic wave filter, and relates to the technical field of filters. A substrate and a piezoelectric stack structure arranged on the substrate are included. The piezoelectric stack structure includes a bottom electrode, a piezoelectric material layer and a top electrode which are sequentially stacked, and an outline of an orthographic projection of the top electrode on the substrate includes at least one Bezier curve of order greater than or equal to 2. Accordingly, a length of a transverse propagation path of transverse acoustic waves can be increased, thereby increasing losses of the transverse acoustic waves during propagation, and reducing influences of the transverse acoustic waves on a transverse parasitic mode caused by the bulk acoustic wave resonator, and namely, an effect of restraining the transverse parasitic mode is improved by the bulk acoustic wave resonator, thereby improving performance of the bulk acoustic wave filter.