Buried-Air-Cavity BAW Filter for Heat and Strength Constraints

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing bulk acoustic wave filters, particularly FBAR filters, face challenges such as complexity and cost in manufacturing, overheating, mechanical weakness, and difficulty in miniaturization due to requirements for precise flatness and the formation of air cavities.

Innovation Solution

A bulk acoustic wave filter is designed with an air cavity buried in a semiconductor substrate, featuring resonators with active layers sandwiched between electrodes, and optionally including multiple resonators with asymmetric top electrodes, improving thermal dissipation and mechanical strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If FBAR filters use air cavity structure for better acoustic insulation, then filtering efficiency is improved, but manufacturing complexity and cost increase

Engineering Contradiction:

Improvefiltering efficiencyVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the air cavity formation process with the semiconductor manufacturing process by creating the cavity through sacrificial layer removal during standard fabrication steps, rather than as a separate complex process. This combines multiple functions into unified manufacturing steps.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent introduces a sacrificial layer as an intermediary element that enables air cavity formation. This temporary structure facilitates the creation of the desired air cavity geometry during manufacturing, then is removed to leave the final structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If FBAR filters require precise flatness control during manufacturing, then resonator performance is improved, but manufacturing difficulty increases

Engineering Contradiction:

Improveflatness controlVSAvoidmanufacturing difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent employs self-aligned fabrication techniques where subsequent layers automatically align to previous structures without requiring additional alignment steps. The resonator structures self-organize during deposition, eliminating the need for separate flatness control operations.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent divides the manufacturing process into discrete deposition and patterning steps, where each layer is formed independently with controlled thickness. This segmentation allows precise control of each interface without requiring global flatness control across the entire structure.

Inventive Principle:

Principle #1Segmentation

3Reliability

If FBAR filters implement air cavity formation by removing sacrificial layer, then acoustic insulation is improved, but manufacturing steps become more difficult

Engineering Contradiction:

Improveacoustic insulationVSAvoidmanufacturing steps

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent forms the air cavity structure as a preliminary feature during the early stages of fabrication, before depositing the resonator layers. The sacrificial layer is patterned and positioned in advance, enabling subsequent layers to be deposited directly over the intended cavity region without requiring later cavity creation steps.

Inventive Principle:

Principle #10Preliminary action

4Volume of moving object

If existing FBAR filters are miniaturized, then device size is reduced, but mechanical strength and thermal performance deteriorate

Engineering Contradiction:

Improvedevice sizeVSAvoidmechanical strength

Core Design Contradiction:

Volume of moving objectVSStrength

Solution Approach 1:

The patent employs composite structures combining semiconductor substrate material with suspended resonator membranes. This composite approach maintains mechanical strength through the rigid substrate while enabling miniaturization through the lightweight suspended structure. The asymmetric electrode design further optimizes stress distribution in the miniaturized geometry.

Inventive Principle:

Principle #40Composite materials

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 solution enhances thermal performance and mechanical strength, facilitating easier miniaturization and simplifying the manufacturing process while maintaining effective signal filtering capabilities.

Implementation Method 1

the air cavity provides an acoustic insulation higher than that obtained with a Bragg mirror having several bilayers

Methodology Applied

Scientific EffectAcoustic insulation: Acoustic Absorption

Implementation Method 2

a piezoelectric layer located on the membrane, and sandwiched between bottom and top electrodes

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 3

Bulk Acoustic Wave (BAW) filters

Methodology Applied

Scientific EffectAcoustic wave generation: Acoustics

Data Source

PatentUS20260025124A1Bulk acoustic wave filter

Publication Date: 2026.01.22 STMICROELECTRONICS INT NV

AI summary

The present disclosure provides a bulk acoustic wave filter. An example bulk acoustic waver filter is formed in and on a semiconductor substrate. The filter comprises: an air cavity buried in the semiconductor substrate; and at least one resonator formed in line with the air cavity, the resonator comprising an active layer sandwiched between bottom and top electrodes.