MEMS Cap V-Shaped Spreading Prevention Hermetic Seal
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Solution Overview
Problem
The existing metal bonding techniques in MEMS devices often result in hermetic seal breakage and defects due to the spreading of bonding materials, which can diffuse into silicon substrates and compromise the seal.
Innovation Solution
A MEMS device design featuring a cap with a cavity and a diffusion prevention layer, along with a spreading prevention portion having a V-shape in cross-section, is implemented to prevent the bonding material from spreading and diffusing, using a bonding layer of materials like gold, tin, chromium, or aluminum, and an oxide film diffusion prevention layer to maintain a hermetic seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal bonding technique is used for hermetic seal, then bonding strength is improved, but bonding material spreads into cavity and breaks seal
Solution Approach 1:
The bonding layer is segmented into multiple functional layers including a diffusion barrier layer and a spreading prevention structure. The spreading prevention structure divides the bonding interface into a bonding region and a non-bonding region, preventing material spread while maintaining bonding strength.
Solution Approach 2:
A diffusion barrier layer is introduced as an intermediary between the bonding material and the silicon substrate. This barrier layer prevents diffusion of bonding material into the substrate while allowing the bonding process to proceed effectively.
2Reliability
If spreading prevention structure is added, then hermetic seal integrity is improved, but device complexity increases
Solution Approach 1:
The spreading prevention structure is merged with the bonding layer itself, forming an integrated multi-layer bonding structure. This combines the bonding function and spreading prevention function into a single integrated component, reducing overall device complexity.
Solution Approach 2:
The bonding layer structure serves multiple functions simultaneously: providing bonding strength, preventing material spread, and preventing diffusion into the substrate. This multi-functionality reduces the need for separate components.
3Strength
If bonding material is applied, then bonding strength is improved, but material diffuses into substrate and causes defects
Solution Approach 1:
A diffusion barrier layer is positioned between the bonding material and the silicon substrate to prevent diffusion. This intermediary layer allows the bonding material to maintain its strength while blocking its harmful diffusion into the substrate.
Solution Approach 2:
The harmful diffusion property of the bonding material is extracted and prevented by the barrier layer, while the useful bonding strength property is retained. The barrier layer selectively removes the harmful effect while preserving the beneficial effect.
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 design effectively prevents the occurrence of defects by preventing the bonding material from flowing into the cavity and diffusing into the silicon substrate, thus maintaining a reliable hermetic seal.
Implementation Method 1
a diffusion prevention layer formed on at least a portion of the cap
Implementation Method 2
a spreading prevention portion disposed between the bonding layer and the cavity and having a V-shape in cross-section
Data Source
AI summary
A MEMS device includes a substrate, a MEMS element portion disposed on a surface of the substrate, a cap having a cavity formed to oppose the MEMS element portion, and a diffusion prevention layer formed on at least a portion of the cap, wherein at least one of the cap and the substrate includes a bonding layer disposed outside of the cavity, and wherein the cap includes a spreading prevention portion disposed between the bonding layer and the cavity and having a V-shape in cross-section.