Multi-Layer FBAR Assembly Using Sacrificial Cavity Alignment

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Solution Overview

Problem

Existing FBAR filter networks are difficult to fabricate at small form factors required for advanced RF systems, particularly in multi-level architectures within integrated circuits.

Innovation Solution

A method for fabricating a multi-layer resonator assembly involves sequentially depositing dielectric layers, forming FBAR cavities, filling them with sacrificial material blocks, and removing these blocks after depositing FBAR material stacks, allowing for vertically-stacked resonator layers with aligned FBAR cavities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If multi-level FBAR architectures are fabricated with FBARs and associated cavities at multiple levels, then the filtering functionality and resonance performance are improved, but the fabrication difficulty increases significantly

Engineering Contradiction:

Improvefiltering functionalityVSAvoidfabrication difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies preliminary action by depositing sacrificial material blocks into cavities at lower levels before fabricating the FBAR structures at upper levels. This allows the cavity structures to be pre-formed and protected during subsequent fabrication steps, eliminating the need for complex sequential cavity formation and reducing overall fabrication difficulty while maintaining multi-level filtering functionality

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses sacrificial material blocks as intermediary structures that facilitate the fabrication process. These blocks temporarily occupy the cavity spaces during manufacturing, serving as placeholders that simplify the deposition and alignment of FBAR material stacks, and are removed only after the complete multi-layer structure is assembled

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If FBAR cavities are formed at multiple levels within the same chip, then the resonator assembly functionality is enhanced, but the manufacturing precision requirements increase

Engineering Contradiction:

Improveresonator assembly functionalityVSAvoidcavity alignment precision

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent improves manufacturing precision by pre-forming sacrificial material blocks in cavity locations at lower levels before depositing FBAR structures at upper levels. This preliminary cavity preparation ensures precise spatial definition of cavity boundaries and positions, which serve as reference features for subsequent alignment operations, thereby reducing the actual precision demands during critical FBAR deposition steps

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent employs disposable sacrificial material blocks that are easily deposited and removed using standard semiconductor fabrication processes. These temporary structures simplify the achievement of precise cavity alignment by providing robust physical templates during manufacturing, and are discarded after serving their alignment and protection function, eliminating the need for high-precision permanent cavity formation structures

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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

Enables the creation of compact, multi-layer FBAR assemblies with aligned cavities, facilitating efficient fabrication and integration into advanced RF systems.

Implementation Method 1

the step of removing the sacrificial material block the at least one FBAR cavity for each resonator layer of the plurality of resonator layers may include exposing the plurality of resonator layers to one of xenon difluoride (XeF2), potassium hydroxide (KOH), hydrogen peroxide (H2O2), or oxygen (O2) plasma

Methodology Applied

Scientific EffectChemical etching: Oxidation

Implementation Method 2

the step of filling the at least one FBAR cavity with a sacrificial material block may include depositing the sacrificial material block using one of chemical vapor deposition, physical vapor deposition, or atomic layer deposition

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Implementation Method 3

Methodology Applied

Scientific EffectChemical vapor deposition: Chemical Vapour Deposition

Data Source

PatentUS20250309862A1Multi-layer resonator assembly and method for fabricating same

Publication Date: 2025.10.02 RAYTHEON CO

AI summary

A method for fabricating a multi-layer resonator assembly includes sequentially fabricating a plurality of vertically-stacked resonator layers including, for each resonator layer of the plurality of resonator layers, depositing a dielectric layer, forming at least one film bulk acoustic resonator (FBAR) cavity in the deposited dielectric layer, filling each FBAR cavity of the at least one FBAR cavity with a sacrificial material block, and depositing a FBAR material stack over the at least one FBAR cavity. The deposited FBAR material stack is in contact with the sacrificial material block and the dielectric layer. The method further includes removing the sacrificial material block from the at least one FBAR cavity for each resonator layer of the plurality of resonator layers subsequent to sequentially fabricating the plurality of resonator layers.