BAW Sensor Wall Structure for Peel-Resistant Fluidic Passages
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Solution Overview
Problem
Conventional bulk acoustic wave (BAW) devices face challenges in maintaining structural integrity and preventing peeling or delamination of wall structures in fluidic passages, especially when exposed to liquids and humid environments, due to issues with adhesive distribution and bonding between wall structures and substrates.
Innovation Solution
The use of photoresist (e.g., SU-8) or epoxy materials for wall structures with a footer portion having a wider width than the upper wall portion, and incorporating anchoring features like recesses and protrusions on the base structure to enhance adhesion and prevent peeling, along with a hermeticity layer and self-assembled monolayers for improved bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional adhesive bonding is used to attach wall structures to substrates in BAW devices, then assembly is simplified, but peeling and delamination occur in humid and liquid environments
Solution Approach 1:
The wall structure is divided into two distinct portions: a footer portion that interfaces with the substrate and provides bonding, and an upper wall portion that forms the fluidic passage boundaries. This segmentation allows the footer portion to be optimized for adhesion while the upper portion maintains structural integrity, preventing peeling in humid environments.
Solution Approach 2:
The footer portion is designed with a width greater than the upper wall portion, creating a local quality difference. This wider footer provides increased bonding area and mechanical anchoring to the substrate, specifically addressing the adhesion challenge at the wall-substrate interface while maintaining the required fluidic passage dimensions above.
2Volume of moving object
If wall structures with high aspect ratios are used to define fluidic passages, then space efficiency is improved, but peeling resistance deteriorates
Solution Approach 1:
The solution addresses the peel resistance problem by extending the wall structure in the horizontal dimension through the wider footer portion, rather than increasing vertical height. This dimensional change provides enhanced bonding area and mechanical anchoring without compromising the vertical space efficiency of the fluidic passage.
3Strength
If excess adhesive is applied to ensure proper adhesion, then bonding strength is improved, but adhesive flows into fluidic passages causing contamination
Solution Approach 1:
The footer portion is designed with increased width before the bonding process, pre-establishing a larger bonding area. This preliminary structural feature ensures that adequate adhesion is achieved with controlled adhesive application, preventing both insufficient bonding and excessive adhesive overflow into the fluidic passage region.
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 configuration significantly enhances the resistance to peeling and delamination, ensuring robust adhesion and maintaining structural integrity even in humid conditions, thereby improving the reliability of BAW devices for biosensing and biochemical applications.
Implementation Method 1
an acoustic wave that propagates through or on the surface of a piezoelectric material
Implementation Method 2
any changes to the characteristics of the propagation path affect the velocity and/or amplitude of the wave
Data Source
AI summary
Lateral boundaries of a fluidic passage of a fluidic device incorporating at least one BAW resonator structure are fabricated with photosensitive materials (e.g., photo definable epoxy, solder mask resist, or other photoresist), allowing for high aspect ratio, precisely dimensioned walls. Resistance to delamination and peeling between a wall structure and a base structure is enhanced by providing a wall structure that includes a thin footer portion having a width that exceeds a width of an upper wall portion extending upward from the footer portion, and/or by providing a wall structure arranged over at least one anchoring region of a base structure. Anchoring features may include recesses and/or protrusions.