Micromechanical Component With Segmented Cap Wafer
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Solution Overview
Problem
Conventional micromechanical sensors with thin-film caps are prone to deformation under atmospheric pressure and require additional supporting structures, which limits their compactness and sensitivity to external pressure fluctuations, while wafer caps have limited internal pressure and moisture-tightness issues.
Innovation Solution
A micromechanical component with a thin-layer cap is sealed by a cap wafer, which shields the thin-layer cap from external pressure and mechanical stress, eliminating the need for supporting structures and ensuring hermetic sealing, allowing for compact and pressure-insensitive inertial sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a thin-layer cap is used to hermetically seal the cavern, then the internal pressure can be reduced to very low levels and the sensor can be made compact, but the thin-layer cap bends under atmospheric pressure requiring additional supporting structures
Solution Approach 1:
The encapsulation structure is segmented into three distinct layers: the carrier wafer with the micromechanical structure, the thin-layer cap for hermetic sealing, and the cap wafer for mechanical support. This segmentation allows each layer to perform its specific function optimally without compromise.
Solution Approach 2:
The thin-layer cap acts as an intermediary element between the carrier wafer and the cap wafer. It provides hermetic sealing while being protected from atmospheric pressure by the cap wafer, thus maintaining its integrity without requiring internal support structures.
2Strength
If supporting structures are integrated to support the thin-layer cap, then the cap can withstand atmospheric pressure, but the sensor size increases and external pressure fluctuations cause erroneous signals
Solution Approach 1:
The support function is separated from the sealing function. The cap wafer provides mechanical support and pressure resistance, while the thin-layer cap provides hermetic sealing. This segmentation eliminates the need for supporting structures within the sensor cavity.
Solution Approach 2:
Instead of adding supporting structures that would increase sensor size and cause signal errors, the solution uses a cap wafer that replicates the carrier wafer's dimensions and bonding interface, providing external support without interfering with the micromechanical structure.
3Reliability
If a wafer cap with metallic bond connections is used, then hermetic sealing is achieved, but the process temperature is limited and moisture-tightness is insufficient over the equipment lifespan
Solution Approach 1:
The encapsulation uses a composite structure combining the carrier wafer (with micromechanical structure), the thin-layer cap (providing hermetic seal), and the cap wafer (providing mechanical support). This composite approach allows each material to be optimized for its specific function.
Solution Approach 2:
The bonding process parameters are changed by using thin-film technology that allows bonding at very high temperatures, enabling the encapsulation to withstand subsequent high-temperature processes while maintaining hermetic sealing and moisture tightness over the equipment lifespan.
Data Source
AI summary
A micromechanical component, having a carrier wafer having at least one micromechanical structure that is situated in a cavern; a thin-layer cap situated on the carrier wafer, by which the cavern is hermetically sealed; and a cap wafer situated on the thin-layer cap in the region of the cavern having the micromechanical structure, the cap wafer hermetically sealing a region of the thin-layer cap above the cavern.