Sealed MEMS Sensor Cavity Using Epitaxial Silicon Lid Bonding
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Solution Overview
Problem
Existing semiconductor components, such as acceleration sensors, face challenges in maintaining constant low damping of the oscillating seismic mass over their lifetime, primarily due to friction with gas molecules, which affects the sensor's accuracy and reliability.
Innovation Solution
A method involving a silicon-based substrate with an oxide layer, a polycrystalline silicon layer, a crystalline silicon layer grown epitaxially, and a glass- or silicon-based lid is used to minimize outgassing and ensure optimal imperviousness, thereby reducing friction and maintaining consistent damping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sealed cavity is used to accommodate the seismic mass, then mechanical damping is reduced, but friction with gas molecules increases damping over time due to outgassing
Solution Approach 1:
The patent applies this principle by creating a vacuum environment within the sealed cavity. The cavity is evacuated to remove gas molecules that would cause friction with the oscillating seismic mass, thereby eliminating the harmful damping effect while maintaining the sealed structure for long-term reliability.
Solution Approach 2:
The patent applies this principle by extracting the gas molecules from the cavity through vacuum evacuation. By removing the gas phase medium that causes friction, the seismic mass can oscillate with minimal damping, and the sealed structure prevents recontamination over the component's lifetime.
2Reliability
If a lid is mounted on the crystalline silicon layer to seal the cavity, then outgassing is prevented, but the bonding strength and imperviousness must be optimized
Solution Approach 1:
The patent applies this principle by using a lid made of glass or silicon that bonds to the crystalline silicon layer. This composite structure combines the advantages of different materials: the lid provides sealing functionality while the crystalline silicon layer provides structural integrity and bonding compatibility, achieving both seal integrity and manageable process complexity.
Solution Approach 2:
The patent applies this principle by using the crystalline silicon layer as an intermediary bonding interface between the substrate and the lid. This intermediate layer facilitates reliable bonding and ensures imperviousness while simplifying the overall bonding process through its compatible material properties and structural role.
3Ease of manufacture
If polycrystalline silicon is used for the electronic component, then manufacturing flexibility is improved, but a separate crystalline silicon layer is needed for the lid connection
Solution Approach 1:
The patent applies this principle by segmenting the silicon layers into distinct functional regions: a polycrystalline silicon layer for the electronic component (providing manufacturing flexibility) and a separate crystalline silicon layer for the lid connection (providing bonding integrity). This segmentation allows each layer to be optimized for its specific function without compromising the other.
Solution Approach 2:
The patent applies this principle by assigning different crystal structures to different regions: polycrystalline silicon where electronic component fabrication flexibility is needed, and crystalline silicon where lid bonding and seal integrity are critical. This local differentiation of material quality optimizes both ease of manufacture and device complexity management.
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 frictional damping, ensuring consistent sensor performance and accuracy by preventing outgassing and maintaining a sealed environment around the seismic mass, thus enhancing the reliability of semiconductor components like acceleration sensors.
Implementation Method 1
depositing a polycrystalline silicon layer on the oxide layer and simultaneously a crystalline silicon layer on the substrate
Data Source
AI summary
A method of producing a semiconductor component includes: providing a silicon-based substrate; depositing an oxide layer on the silicon-based substrate; depositing a polycrystalline silicon layer on the oxide layer and simultaneously a crystalline silicon layer on the silicon-based substrate; producing an electronic component based on the polycrystalline silicon layer; and mounting a glass- or silicon-based lid on the crystalline silicon layer.