MEMS Protrusion Coating to Prevent Movable Element Stiction
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Solution Overview
Problem
Microelectromechanical systems (MEMS) devices often suffer from stiction, a phenomenon where movable elements become stuck to surrounding features due to friction, occurring during both operation and manufacturing, particularly during wet and dry processes like photoresist strips, water rinses, and plasma etch steps, which impede device functionality.
Innovation Solution
The MEMS structure incorporates protrusions with a low surface energy coating, such as TiN, that extend into a cavity where movable elements can contact, reducing attractive forces and electrostatic attraction by being electrically coupled to ground or the same potential as the movable elements, thereby minimizing the likelihood of stiction during manufacturing and operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet processes (photoresist strips, water rinses, solvent cleans) are used during MEMS manufacturing, then cleaning and fabrication are achieved, but stiction occurs causing movable elements to become stuck
Solution Approach 1:
The patent applies preliminary anti-action by forming protrusions with low surface energy coatings (such as TiN) on the substrate before the movable element is fully assembled. These protrusions are positioned to contact the movable element during operation, and their low surface energy properties preemptively prevent stiction by reducing attractive forces before they can cause the element to stick during manufacturing processes like photoresist stripping, water rinsing, or solvent cleaning.
2Ease of manufacture
If dry processes (plasma etch, plasma clean) are used during MEMS manufacturing, then patterning and cleaning are achieved, but stiction occurs causing movable elements to become stuck
Solution Approach 1:
The patent applies preliminary anti-action by forming protrusions with low surface energy coatings (such as TiN) on the substrate before the movable element is fully assembled. These protrusions are positioned to contact the movable element during operation, and their low surface energy properties preemptively prevent stiction by reducing attractive forces before they can cause the element to stick during manufacturing processes like plasma etching or plasma cleaning.
3Reliability
If protrusions with low surface energy coating are added to prevent stiction, then stiction is reduced, but device complexity increases
Solution Approach 1:
The patent applies local quality by adding low surface energy coatings (such as TiN) only to specific protrusions that are strategically positioned in areas where stiction is most likely to occur, rather than coating the entire substrate or movable element. This localized approach prevents stiction at critical contact points while minimizing the overall added complexity and material usage.
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 use of low surface energy coatings on protrusions significantly reduces the likelihood of stiction, ensuring proper operation and manufacturing of MEMS devices by minimizing attractive forces and electrostatic attraction, thus preventing movable elements from becoming stuck.
Implementation Method 1
The protrusion comprises a surface having a low surface energy relative a silicon oxide surface
Implementation Method 2
reducing attractive forces and electrostatic attraction by being electrically coupled to ground or the same potential as the movable elements
Data Source
AI summary
A microelectromechanical system (MEMS) device includes a substrate and a movable element at least partially suspended above the substrate and having at least one degree of freedom. The MEMS device further includes a protrusion extending from the substrate and configured to contact the movable element when the movable element moves in the at least one degree of freedom, wherein the protrusion comprises a surface having a water contact angle of higher than about 15° measured in air.