Embedded Capacitor BAW Resonator for Spurious Wave Suppression

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Solution Overview

Problem

Film bulk acoustic wave resonators suffer from spurious acoustic waves that degrade their frequency response due to the non-zero Poisson's ratio of piezoelectric materials, leading to undesirable transverse acoustic waves and increased size when separate capacitors are used in ladder filters.

Innovation Solution

A film bulk acoustic wave resonator design incorporating a buried layer of conductive material within the dielectric layer beneath the cavity and electrodes, which forms a capacitor with the electrodes, allowing for control of the electromechanical coupling coefficient and integration of capacitors within the resonator structure to reduce size and spurious wave generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If separate capacitors are used in ladder filters, then the electromechanical coupling coefficient can be controlled, but the device size increases

Engineering Contradiction:

Improveelectromechanical coupling coefficient controlVSAvoiddevice size

Core Design Contradiction:

Adaptability or versatilityVSVolume of moving object

Solution Approach 1:

The patent merges the capacitor function with the resonator structure by embedding a conductive layer within the dielectric material beneath the cavity. This integration eliminates the need for separate capacitors while maintaining the ability to control the electromechanical coupling coefficient, thereby reducing device size without sacrificing functionality

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The dielectric layer serves multiple functions: it provides mechanical support for the resonator structure and simultaneously acts as the capacitor dielectric medium. The embedded conductive layer within this dielectric serves as one plate of the capacitor while the electrode serves as the other plate, enabling the dielectric layer to fulfill both structural and capacitive roles

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Ease of manufacture

If piezoelectric materials with non-zero Poisson's ratio are used, then the resonator can be manufactured, but spurious transverse acoustic waves are generated that degrade frequency response

Engineering Contradiction:

ImprovemanufacturabilityVSAvoidspurious acoustic waves

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful spurious acoustic waves into a beneficial effect by using the embedded conductive layer as a capacitive element that actively controls the electromechanical coupling coefficient. The same piezoelectric material properties that generate spurious waves are utilized to enable precise tuning of the resonator's electrical characteristics, transforming a manufacturing constraint into a design advantage

Inventive Principle:

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

Solution Approach 2:

The patent changes the electrical parameters of the resonator system by embedding the conductive layer at specific positions and configurations within the dielectric. By adjusting the geometry, position, and electrical properties of this embedded layer, the electromechanical coupling coefficient can be precisely controlled to optimize frequency response while compensating for the effects of Poisson's ratio in the piezoelectric material

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 buried conductive layer reduces the electromechanical coupling coefficient and effectively suppresses spurious acoustic waves, improving frequency response while integrating capacitors to maintain a compact design, thus enhancing the performance and size efficiency of film bulk acoustic wave resonators and ladder filters.

Implementation Method 1

a layer of piezoelectric material

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a layer of conductive material buried within the layer of dielectric material at least partially beneath the cavity and the bottom electrode

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS20240243722A1Embedded capacitors with buried metal layer underneath bulk acoustic wave resonator for electromechanical coupling coefficient control

Publication Date: 2024.07.18 SKYWORKS GLOBAL PTE LTD

AI summary

Aspects and embodiments disclosed herein include a film bulk acoustic wave resonator comprising a substrate including a layer of dielectric material disposed on an upper surface of the substrate, a layer of piezoelectric material, a top electrode disposed on a top surface of the layer of piezoelectric material, a bottom electrode disposed on a bottom surface of the layer of piezoelectric material, a cavity defined between a lower surface of the bottom electrode and an upper surface of the layer of dielectric material, and a layer of conductive material buried within the layer of dielectric material at least partially beneath the cavity and the bottom electrode.