BAW Resonator Cavity Isolation Using Trench-Sealed Die Attach

Solution Overview

Problem

The outgassing of die attach material in bulk acoustic wave (BAW) devices adversely affects the accuracy and reliability of the resonator operating frequency due to its polymeric nature, which is not effectively addressed in existing technologies.

Innovation Solution

A sidewall structure with a trench is used to enclose the die attach material, separating it from the cavity, thereby preventing outgassing and enhancing long-term performance and reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If die attach material is used to form cavity sidewalls, then ease of manufacture is improved, but outgassing adversely impacts resonator frequency accuracy and reliability

Engineering Contradiction:

Improveease of manufactureVSAvoidreliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The cavity structure is segmented into two distinct parts: the resonator cavity formed by metal sidewalls extending from the first die, and the die attach material contained within a separate trench structure. This segmentation prevents the polymeric die attach material from directly contacting and outgassing into the resonator cavity, thereby maintaining frequency accuracy and reliability while still using polymeric materials for die attachment.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The die attach material is extracted from its traditional role as cavity sidewall material and relocated into a dedicated trench structure. This extraction separates the die attach material from the resonator cavity environment, eliminating the outgassing problem while preserving the ease of manufacture benefit from using polymeric die attach materials.

Inventive Principle:

Principle #2Taking out (Extraction)

2Ease of manufacture

If die attach material is used to form cavity sidewalls, then ease of manufacture is improved, but frequency accuracy deteriorates due to outgassing

Engineering Contradiction:

Improveease of manufactureVSAvoidfrequency accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The cavity structure is segmented into two distinct parts: the resonator cavity formed by metal sidewalls extending from the first die, and the die attach material contained within a separate trench structure. This segmentation prevents the polymeric die attach material from directly contacting and outgassing into the resonator cavity, thereby maintaining frequency accuracy and reliability while still using polymeric materials for die attachment.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The die attach material is extracted from its traditional role as cavity sidewall material and relocated into a dedicated trench structure. This extraction separates the die attach material from the resonator cavity environment, eliminating the outgassing problem while preserving the ease of manufacture benefit from using polymeric die attach materials.

Inventive Principle:

Principle #2Taking out (Extraction)

3Ease of manufacture

If die attach material is used to form cavity sidewalls, then ease of manufacture is improved, but performance stability deteriorates due to outgassing

Engineering Contradiction:

Improveease of manufactureVSAvoidperformance stability

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The cavity structure is segmented into two distinct parts: the resonator cavity formed by metal sidewalls extending from the first die, and the die attach material contained within a separate trench structure. This segmentation prevents the polymeric die attach material from directly contacting and outgassing into the resonator cavity, thereby maintaining frequency accuracy and reliability while still using polymeric materials for die attachment.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The die attach material is extracted from its traditional role as cavity sidewall material and relocated into a dedicated trench structure. This extraction separates the die attach material from the resonator cavity environment, eliminating the outgassing problem while preserving the ease of manufacture benefit from using polymeric die attach materials.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS20250373226A1Bulk acoustic wave cavity isolation from die attach material outgassing

Publication Date: 2025.12.04 TEXAS INSTRUMENTS INC

AI summary

An electronic device includes a first die having a first side, a resonator along the first side, and a sidewall extending outward from the first side, the sidewall laterally spaced apart from and encircling the resonator and including a distal end spaced apart from the first side, a second die spaced apart from the first die and having a second side facing the first die, the second side engaging the distal end of the sidewall to seal a cavity defined by portions of the first and second sides and the sidewall, a trench in one of the second side and the distal end of the sidewall, and a die attach material in the trench and adhering the second side to the distal end of the sidewall to prevent outgassing of the die attach material in the cavity.