MEMS Encapsulation via Angled Flank Cavities
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Solution Overview
Problem
Existing encapsulation methods for MEMS devices fail to produce sealed cavities under low pressure or vacuum conditions efficiently, often requiring complex processes and risking material deposition on the active device components.
Innovation Solution
A method involving the production of a sacrificial layer with angled lateral flanks on a substrate, followed by a cover layer with strategically positioned holes for sacrificial layer elimination and subsequent sealing, allowing for controlled release speed and hermetic sealing under low pressure or vacuum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If release holes are plugged by polymer deposit at atmospheric pressure, then the encapsulation process is simple and effective, but the method is incompatible with low-pressure or vacuum cavity production
Solution Approach 1:
The cavity is sealed hermetically before the plugging operation. The method includes producing a hermetic seal over the release holes prior to depositing the plugging material, thereby preventing material from entering the cavity during the plugging process. This preliminary sealing action enables the use of simple plugging methods while maintaining compatibility with low-pressure and vacuum cavity requirements.
2Object-affected harmful factors
If release holes are made very small with high depth/diameter ratio to prevent material deposition on MEMS device, then material deposition risk is reduced, but release speed of sacrificial layer is greatly reduced
Solution Approach 1:
A hermetic seal is formed over the release holes before the plugging operation. This preliminary sealing prevents plugging material from depositing on the MEMS device during subsequent processing steps, while allowing the release holes to maintain larger dimensions for faster sacrificial layer removal.
Solution Approach 2:
The hermetic seal acts as an intermediary barrier between the release holes and the external environment. It prevents harmful material deposition on the MEMS device while allowing the release holes to function effectively at larger sizes for improved release speed.
3Device complexity
If release holes are moved outside the cavity to reduce plugging height, then plugging complexity is reduced, but the height of holes to be plugged becomes substantial equal to cavity height
Solution Approach 1:
The hermetic seal is formed preliminarily over the release holes before plugging. This allows the holes to remain positioned at their optimal locations with reduced height, as the seal prevents material contamination during plugging, eliminating the need to move holes outside the cavity.
4Adaptability or versatility
If alloy fusion method is used to plug release holes under vacuum, then low-pressure cavity production is enabled, but the process requires multiple technological steps and complex alloy preparation
Solution Approach 1:
A hermetic seal is formed preliminarily over the release holes before the plugging operation. This enables the use of simple deposit-based plugging methods under vacuum conditions, avoiding the need for complex alloy fusion processes while maintaining vacuum compatibility.
Solution Approach 2:
The complex mechanical alloy fusion process is replaced with a simpler deposit-based plugging method. The hermetic seal enables this substitution by preventing material contamination, allowing the use of straightforward deposition techniques instead of complex thermal and mechanical alloy processing.
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 method enables rapid and efficient encapsulation of MEMS devices with reduced material deposition risks, optimized release speed, and compatibility with low-pressure or vacuum conditions, while minimizing complexity and cost.
Implementation Method 1
a cover layer (112) positioned on a face (108) of a substrate (104), the cover layer (112) including lateral flanks (114) forming, with a portion (107) of the face (108) of the substrate (104) positioned in the cavity (120), an angle (α) of less than 90°
Data Source
AI summary
A method for producing a sealed cavity, including: a) producing a sacrificial layer on a substrate; b) producing a cover layer covering at least the sacrificial layer and a portion of the face of the substrate not covered by the sacrificial layer, the cover layer including lateral flanks forming, with the substrate, an angle of less than 90°; c) producing a hole through one of the lateral flanks of the cover layer such that a maximum distance between the substrate and an edge of the hole is less than approximately 3 μm, the hole crossing a portion of the cover layer deposited on a portion of the substrate not covered by the sacrificial layer; d) eliminating the sacrificial layer through the hole, forming the cavity; and e) depositing at least one material plugging the hole in a sealed fashion.