Film Bulk Acoustic Resonator Cavity Bonding for Piezoelectric Uniformity

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Solution Overview

Problem

Current methods for fabricating film bulk acoustic resonators are hindered by issues such as uneven polishing during chemical mechanical polishing, which affects the uniformity of the piezoelectric layer, and incomplete removal of sacrificial layers, leading to reduced Q values and potential breakage of the resonator.

Innovation Solution

A method involving the formation of a support layer with a cavity on a second substrate, bonding it with a first substrate, removing the first substrate, and patterning the electrode and piezoelectric layers to create a film bulk acoustic resonator with improved structural integrity and performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If chemical mechanical polishing (CMP) is used to planarize the substrate and sacrificial layer, then the surfaces are flattened to enable subsequent deposition, but uneven polishing occurs due to different polishing rates, affecting the uniformity of the piezoelectric layer

Engineering Contradiction:

Improveuniformity of piezoelectric layerVSAvoidpolishing process complexity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent uses a sacrificial layer that is replicated or copied onto the substrate, which is then planarized together with the substrate. This copying approach allows the sacrificial layer to be removed later without affecting the uniformity of the piezoelectric layer, as the planarization is performed on the combined substrate-sacrificial layer structure rather than on the sacrificial layer alone.

Inventive Principle:

Principle #26Copying

2Reliability

If a sacrificial layer is used to form the cavity, then the cavity structure is achieved, but incomplete removal of the sacrificial layer occurs, leading to reduced Q values and potential breakage of the resonator

Engineering Contradiction:

Improvequality factor (Q value)VSAvoidsacrificial layer removal difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent performs preliminary actions by forming the sacrificial layer, planarizing it with the substrate, depositing the piezoelectric layer and electrodes, and patterning the structure before finally removing the sacrificial layer. This sequence of preliminary actions ensures that all other components are in place and properly aligned before the sacrificial layer removal, which prevents breakage and ensures complete removal to maintain high Q values.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The sacrificial layer acts as an intermediary element that facilitates the formation of the cavity structure. It is temporarily present during the fabrication process to enable proper alignment and deposition, then completely removed to create the final cavity. The intermediary approach allows the cavity to be formed without directly etching through the substrate, which would be more difficult to control.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If the resonator structure is formed with through-holes in the electrode for sacrificial layer removal, then the cavity is created, but the resonator becomes more susceptible to breakage during the removal process

Engineering Contradiction:

Improvestructural integrityVSAvoidfabrication process difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent performs preliminary patterning of the electrode and piezoelectric layer to create a robust structure before sacrificial layer removal. The electrodes are patterned to extend over the sacrificial layer, providing mechanical support during the removal process. This preliminary structuring prevents breakage that would occur if through-holes were created earlier in the process.

Inventive Principle:

Principle #10Preliminary 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 approach enhances the uniformity of the piezoelectric layer and ensures complete removal of sacrificial layers, thereby improving the quality factor and reducing the risk of breakage, leading to more reliable film bulk acoustic resonators.

Implementation Method 1

The inverse piezoelectric effect of the piezoelectric film layer is used to convert electrical energy into mechanical energy

Methodology Applied

Scientific EffectInverse piezoelectric effect: Piezoelectric Effect

Implementation Method 2

finally, the acoustic signal is converted into an electrical signal output through the piezoelectric effect

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11942917B2Film bulk acoustic resonator and fabrication method thereof

Publication Date: 2024.03.26 NINGBO SEMICON INT CORP

AI summary

The present disclosure provides a film bulk acoustic resonator and its fabrication method. The fabrication method includes providing a first substrate, and sequentially forming a first electrode layer, a piezoelectric material layer, and a second electrode layer, on the first substrate; forming a support layer on the second electrode layer and forming a cavity with a top opening in the support layer, where the cavity passes through the support layer; providing a second substrate and bonding the second substrate with the support layer; removing the first substrate; and patterning the first electrode layer, the piezoelectric material layer, and the second electrode layer to form a first electrode, a piezoelectric layer, and a second electrode.