Capacitive Resonator Comb Electrodes with Air-Gap Support Frames

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Solution Overview

Problem

Acoustic resonators, particularly laterally coupled resonator filters (LCRFs), face challenges in designing specific pass-bands and suffer from spurious modes due to complex simulations and physical space requirements, making them difficult to implement effectively in high-frequency applications.

Innovation Solution

The introduction of air-gaps between electrodes and a piezoelectric layer in acoustic resonator devices, combined with doping the piezoelectric layer with rare earth elements, enhances the electromechanical coupling coefficient and allows for the creation of smaller, more efficient resonator designs, such as LCRF and contour mode resonator (CMR) devices with support frames or pillars, decoupling electrical excitation from acoustic propagation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If LCRF structure is used to reduce physical space and simplify fabrication, then device footprint is reduced, but spurious modes appear and pass-band design becomes difficult

Engineering Contradiction:

Improvedevice footprintVSAvoidspurious modes

Core Design Contradiction:

Area of stationary objectVSObject-generated harmful factors

Solution Approach 1:

A support frame structure is introduced as an intermediary element between the piezoelectric layer and the top comb electrodes. This support frame decouples the electrical excitation from the acoustic propagation path, preventing direct mechanical coupling that causes spurious modes while maintaining the compact LCRF footprint

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The top electrode structure is segmented into comb-like fingers with gaps between them. This segmentation allows the electrical signal to be applied through the comb electrodes while the support frame prevents direct mechanical coupling, enabling independent control of electrical and acoustic fields to eliminate spurious modes

Inventive Principle:

Principle #1Segmentation

2Reliability

If air-gaps are introduced between electrodes and piezoelectric layer, then electromechanical coupling coefficient is enhanced, but device structure becomes more complex

Engineering Contradiction:

Improveelectromechanical coupling coefficientVSAvoiddevice structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The support frame that creates air-gaps is merged with the existing LCRF structure, serving dual functions: providing mechanical support and creating the necessary air-gaps for enhanced electromechanical coupling. This integration minimizes additional structural complexity while achieving the desired performance improvement

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If piezoelectric layer is doped with rare earth elements, then electromechanical coupling coefficient is enhanced, but manufacturing process becomes more complex

Engineering Contradiction:

Improveelectromechanical coupling coefficientVSAvoidmanufacturing process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The piezoelectric layer undergoes parameter change through doping with rare earth elements, which modifies its material properties to enhance electromechanical coupling. This material-level modification achieves performance improvement without requiring additional device structural elements, simplifying the overall manufacturing process

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

This approach results in reduced footprint, power consumption, and cost, enabling efficient implementation of wide-band applications with improved signal conversion and impedance transformation capabilities.

Implementation Method 1

reciprocal or inverse piezoelectric effect causes the acoustic stack to mechanically expand or contract depending on the polarization of the piezoelectric material. As the input electrical signal varies over time, expansion and contraction of the acoustic stack produces acoustic waves

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

Methodology Applied

Scientific EffectElectromechanical coupling: Piezoelectric Effect

Data Source

PatentUS9698754B2Capacitive coupled resonator and filter device with comb electrodes and support frame separation from piezoelectric layer

Publication Date: 2017.07.04 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

A capacitive coupled resonator device includes a substrate, a bottom electrode, a piezoelectric layer, a top electrode, and at least one support frame positioned between the piezoelectric layer and the top electrode and/or positioned between the piezoelectric layer and the bottom electrode. The top electrode includes a first top comb electrode having a first top bus bar and first top fingers extending in a first direction from the first top bus bar, and a second top comb electrode having a second top bus bar and second top fingers extending in a second direction from the second top bus bar, the second direction being substantially opposite to the first direction such that the first and second top fingers form a top interleaving pattern. The at least one support frame includes air-gaps separating at least one of the top electrode and the bottom electrode from the piezoelectric layer, respectively.