MEMS Bump Stop Structure for Stiction Control
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Solution Overview
Problem
Micromechanical devices, such as MEMS, are vulnerable to capillary pull-in and stiction during manufacturing, particularly due to meniscus formation and surface tension forces during drying processes, which can lead to structural damage and reduced cavity pressure in vacuum-packaged devices like accelerometers.
Innovation Solution
The design incorporates recesses connected to the outside ambient by channels that guide the meniscus along a specific path during drying, reducing capillary pull-in forces, and includes a bump stop structure with a smaller footprint to minimize cavity volume and enhance cavity pressure by allowing gas outgassing after sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a meniscus forms during drying, then liquid is retained in the cavity, but capillary pull-in force damages the MEMS structure
Solution Approach 1:
The patent extracts the harmful meniscus from the cavity by providing escape paths (channels or openings) that allow the liquid meniscus to exit through designated routes during drying, preventing it from exerting damaging capillary forces on the MEMS structure while maintaining structural integrity
Solution Approach 2:
The patent introduces intermediary structures (channels or openings) that mediate between the liquid meniscus and the external environment, providing a controlled path for meniscus evacuation that prevents direct contact between the meniscus and the MEMS structure, thereby eliminating capillary pull-in forces
2Stress or pressure
If the cavity volume is reduced, then cavity pressure is improved for vacuum-packaged devices, but the space for gas outgassing is limited
Solution Approach 1:
The patent segments the cavity into functional zones by introducing bump stop structures that create designated outgassing regions, allowing different portions of the cavity to serve distinct purposes: maintaining vacuum pressure in the main cavity while providing localized spaces for gas outgassing without compromising overall cavity volume
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 approach effectively reduces capillary stiction and pull-in forces, maintaining structural integrity and achieving critically damped conditions for MEMS devices, thereby improving their performance and reducing vibration sensitivity.
Implementation Method 1
one or more recesses connected to the outside ambient by one or more channels. At the outset of the drying phase of the manufacturing process, a meniscus forms on the outermost surface of the structure. As the volume of liquid trapped under the structure decreases (e.g., through evaporation), the meniscus can be drawn through the channels
Implementation Method 2
it is desirable for an accelerometer to operate in a critically damped condition. This damping can be achieved in a vacuum-packaged process by including a material in the cavity that outgasses after sealing
Data Source
AI summary
The present invention relates to semiconductor devices, such as microelectromechanical (MEMS) devices, with improved resilience during manufacturing. In one embodiment, a MEMS device includes a MEMS structure; a substrate situated parallel to the MEMS structure and positioned a first distance from the MEMS structure; and a bump stop structure formed on the substrate between the substrate and the MEMS structure, wherein the bump stop structure substantially traces a perimeter of the substrate, wherein the bump stop structure extends from the substrate to a second distance from the MEMS structure, and wherein the second distance is greater than zero and less than the first distance.