Encapsulated MEMS Device with SAM Coating for Sticking Prevention
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Solution Overview
Problem
MEMS devices face sticking issues during manufacturing and operation due to contact between movable elements and cavity walls, which can lead to damage under stress or drop tests, and existing solutions like small bump structures are difficult to fabricate and may cause damage.
Innovation Solution
A Self-Assembled Monolayer (SAM) is deposited onto exposed surfaces within the cavity structure of MEMS devices to reduce surface energy and prevent sticking, combined with a hermetic closure using a layer structure to maintain a specific pressure environment, such as vacuum, which minimizes contact forces between MEMS elements and cavity surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If small bump structures are used to reduce sticking, then sticking protection is improved, but fabrication difficulty increases and damage risk occurs
Solution Approach 1:
The patent changes the surface energy parameter of the cavity walls by coating them with a Teflon layer, transforming the surface properties from high energy (prone to sticking) to low energy (resistant to sticking). This allows the MEMS elements to be larger without increasing sticking risk, eliminating the need for small bump structures and their associated fabrication complexities.
2Strength
If MEMS elements are made larger to reduce sensitivity to contact, then robustness is improved, but sticking risk increases
Solution Approach 1:
By modifying the surface energy parameter of the cavity walls through Teflon coating, the patent enables larger MEMS elements to be used. The low surface energy of Teflon reduces adhesion forces, allowing increased element size for robustness without proportionally increasing sticking risk.
Solution Approach 2:
The Teflon coating acts as an intermediary layer between the MEMS elements and the cavity walls. This intermediate layer reduces direct contact and adhesion between the elements and walls, enabling larger element sizes while maintaining reliability.
3Reliability
If hermetic closure is applied to maintain vacuum, then contact forces are reduced, but manufacturing complexity increases
Solution Approach 1:
The cavity structure serves multiple functions: it provides the enclosed vacuum environment for reduced contact forces, and simultaneously its walls are coated with Teflon to provide sticking protection. This multi-functionality reduces the need for additional separate components, offsetting the manufacturing complexity.
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 SAM layer reduces the risk of sticking by lowering surface energies, while the hermetic closure maintains a controlled pressure environment, reducing the likelihood of contact-induced damage and enhancing the stability of MEMS devices under various conditions.
Implementation Method 1
depositing a Self-Assembled Monolayer (SAM) through the opening structure onto exposed surfaces within the inner volume of the cavity structure
Implementation Method 2
The SAM layer reduces the risk of sticking by lowering surface energies
Implementation Method 3
maintain a specific pressure environment, such as vacuum, which minimizes contact forces between MEMS elements and cavity surfaces
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An encapsulated MEMS device and a method for manufacturing the MEMS device are provided. The method comprises providing a cavity structure having an inner volume comprising a plurality of MEMS elements, which are relatively displaceable with respect to each other, and having an opening structure to the inner volume, depositing a Self-Assembled Monolayer (SAM) through the opening structure onto exposed surfaces within the inner volume of the cavity structure, and closing the cavity structure by applying a layer structure on the opening structure for providing a hermetically closed cavity.