BAW Resonator Wafer Packaging With Epoxy Wall Cavities

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Solution Overview

Problem

Current wafer-level packaging technologies face challenges in efficiently integrating and packaging bulk acoustic wave resonator devices within the frequency range of 1 GHz to 20 GHz, particularly in maintaining device thickness and compatibility with temperature profiles for mobile device applications.

Innovation Solution

The use of an epoxy-based photoresist material to form wall cavity structures around bulk acoustic wave resonator devices on a wafer, followed by a cap layer to seal them, allowing for singulation and integration into mobile devices while maintaining structural integrity and frequency response.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If conventional wafer-level packaging technologies are used for bulk acoustic wave resonator devices, then device integration is achieved, but device thickness increases and compatibility with mobile device temperature profiles is compromised

Engineering Contradiction:

Improvedevice thicknessVSAvoidtemperature profile compatibility

Core Design Contradiction:

Length of moving objectVSReliability

Solution Approach 1:

The patent modifies the curing parameters of the epoxy-based photoresist material to enable curing at lower temperatures (e.g., 80°C to 150°C) that are compatible with mobile device temperature profiles. This parameter change allows the packaging material to be cured without exposing the acoustic wave resonator devices to temperatures that would degrade their performance, thereby resolving the contradiction between achieving proper curing (reliability) and maintaining temperature compatibility.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite packaging structure consisting of an epoxy-based photoresist material combined with a cap layer. This composite material system provides both the structural integrity needed for wafer-level packaging and the thermal properties required to maintain compatibility with mobile device operating temperatures, while keeping the overall device thickness minimal.

Inventive Principle:

Principle #40Composite materials

2Productivity

If wafer-level packaging is performed before singulation, then manufacturing efficiency is improved, but device thickness increases

Engineering Contradiction:

Improvemanufacturing efficiencyVSAvoiddevice thickness

Core Design Contradiction:

ProductivityVSLength of moving object

Solution Approach 1:

The patent extracts and removes excess epoxy-based photoresist material after curing, leaving only the minimal necessary packaging structure around each device. This extraction process eliminates unnecessary material thickness while maintaining the benefits of wafer-level packaging, thereby resolving the contradiction between manufacturing efficiency and device thickness.

Inventive Principle:

Principle #2Taking out (Extraction)

3Strength

If epoxy-based photoresist material is used to form wall cavity structures, then structural integrity is maintained, but manufacturing complexity increases

Engineering Contradiction:

Improvestructural integrityVSAvoidmanufacturing complexity

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent replaces complex mechanical packaging structures with a chemically-cured epoxy-based photoresist material that forms wall cavity structures through photopolymerization. This substitution of chemical processing for mechanical assembly simplifies the manufacturing process while maintaining structural integrity, as the cured epoxy provides robust packaging without requiring complex mechanical components.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enables the packaging of bulk acoustic wave resonator devices within the specified frequency range, providing thinner product thickness and compatibility with existing temperature profiles, enhancing the integration of these devices into mobile devices.

Implementation Method 1

The use of an epoxy-based photoresist material to form wall cavity structures around bulk acoustic wave resonator devices on a wafer

Methodology Applied

Scientific EffectPhotopolymerisation: Photopolymerisation

Data Source

PatentUS20240258991A1Methods of packaging acoustic wave resonator devices on wafers and related wafers and structures

Publication Date: 2024.08.01 AKOUSTIS TECHNOLOGIES CORP

AI summary

A wafer including an array of bulk acoustic wave resonator devices can include a first bulk acoustic wave resonator device on the wafer, the first bulk acoustic wave resonator device including a passivation layer on a piezoelectric layer, a second bulk acoustic wave resonator device on the wafer directly adjacent to the first bulk acoustic wave resonator device, the second bulk acoustic wave resonator device including the passivation layer and the piezoelectric layer, a wall layer on the wafer forming first and second wall cavity structures that extend around the first and second bulk acoustic wave resonator devices, respectively, a capping layer extending over the wall layer to cover the first and second wall cavity structures that include the first and second bulk acoustic wave resonator devices, respectively, a metallization layer coupling together bulk acoustic wave resonators included in the first or second bulk acoustic wave resonator device and a pillar that protrudes vertically from the metallization layer to contact the cap layer.