BAW Resonator Edge Texture for Energy Loss Reduction

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Solution Overview

Problem

Bulk acoustic wave (BAW) resonators experience significant energy loss due to unwanted excitation of high-energy loss modes, such as lateral modes, which lowers their quality factor (Q), despite conventional profile shaping approaches that can introduce additional unwanted modes.

Innovation Solution

A BAW resonator design featuring a disrupted texture region with controlled thickness and a material segment at the edge, reducing electromechanical coupling into unwanted modes while maintaining coupling into the desired longitudinal mode, achieved through a combination of surface disruption and precise thickness shaping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a shaped region is provided close to the edge of the BAW resonator to contain energy, then energy loss in lossy modes is reduced, but additional unwanted lateral modes are introduced within the shaped region

Engineering Contradiction:

Improveenergy lossVSAvoidunwanted lateral modes

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The patent applies local quality by creating a shaped region with non-uniform thickness only at specific edge portions of the resonator where energy loss occurs, while maintaining uniform thickness in the central region. This localized thickness variation reduces energy loss at edges without introducing unwanted modes across the entire resonator structure.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The resonator is segmented into distinct regions: a central uniform-thickness region and peripheral shaped regions with varying thickness. This segmentation allows different functional zones to address different problems - the central region maintains resonator integrity while edge regions provide energy containment.

Inventive Principle:

Principle #1Segmentation

2Stability of the object's composition

If conventional profile shaping is applied to control energy, then energy containment in longitudinal mode is improved, but the quality factor Q is reduced due to introduced lateral modes

Engineering Contradiction:

Improveenergy containmentVSAvoidquality factor Q

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent changes the thickness parameter locally at the resonator edges by creating a shaped region with gradual thickness variation. This parameter change allows energy to be contained more effectively in the longitudinal mode while the controlled, gradual transition prevents the excitation of lateral modes that would degrade the quality factor.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If the resonator profile is shaped to reduce energy loss, then energy control in desired mode is improved, but additional modes are excited that cause significant energy loss

Engineering Contradiction:

Improveenergy lossVSAvoidmode structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The shaped region is applied partially only to specific edge portions of the resonator rather than the entire structure. This partial application is sufficient to contain energy at the loss-prone edges without excessively complicating the overall resonator structure or introducing unwanted modes across the full device.

Inventive Principle:

Principle #16Partial or excessive action

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 design significantly reduces energy loss by minimizing coupling into unwanted modes, thereby increasing the resonator's quality factor (Q) compared to conventional approaches.

Implementation Method 1

When an electric field is applied across the upper and lower electrodes of the BAW resonator, the electric field can cause the layer of piezoelectric material to vibrate

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

a disrupted texture region, which reduces electromechanical coupling into unwanted modes

Methodology Applied

Scientific EffectAcoustic absorption: Acoustic Absorption

Data Source

PatentUS7795781B2Bulk acoustic wave resonator with reduced energy loss

Publication Date: 2010.09.14 CHEMTRON RESEARCH LLC

AI summary

According to an exemplary embodiment, a bulk acoustic wave (BAW) resonator includes a piezoelectric layer having a disrupted texture region, where the disrupted texture region is situated in a controlled thickness region of the BAW resonator. The BAW resonator further includes lower and upper electrodes situated on opposite surfaces of the piezoelectric layer. The controlled thickness region has controlled electromechanical coupling and includes a segment of material situated over the upper electrode. The segment of material can be a metal or a dielectric material. The disrupted texture region can be situated at an edge of the BAW resonator and can extend along a perimeter of the BAW resonator.