MEMS Wafer Sealing With Eutectic Bonding and Integrated Contacts
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Solution Overview
Problem
Existing MEMS devices face challenges in simultaneously sealing the cavity and making electrical connections efficiently, as conventional bonding methods often require separate processes for sealing and connecting electrical contacts, which can lead to inefficiencies and reliability issues.
Innovation Solution
A method involving the use of eutectic metal alloy layers on both the device and cap wafers, aligned and bonded to form both a seal and electrical connections in a single metallic bonding process, utilizing a specific thickness ratio and temperature to ensure a reliable eutectic phase formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate bonding processes are used for sealing and electrical connections, then each process can be optimized independently, but the manufacturing complexity and time increase
Solution Approach 1:
The patent combines sealing and electrical connection functions into a single bonding process by integrating conductive elements directly into the bonding interface. The bonding layer serves dual purposes: creating the seal between substrates and establishing electrical connections simultaneously, eliminating the need for separate bonding steps.
Solution Approach 2:
The bonding layer is designed to perform multiple functions: sealing the cavity, providing electrical connectivity, and serving as a structural interface between substrates. This multi-functional approach reduces the number of required processes while maintaining reliability of both sealing and electrical connections.
2Ease of manufacture
If conventional bonding methods are used, then the process is simpler, but electrical connections cannot be extended through the cap wafer efficiently
Solution Approach 1:
Conductive elements are prepared and positioned on the cap wafer before the bonding process. This preliminary preparation allows electrical connections to be established during the bonding step itself, combining simplicity of process with efficiency of electrical connectivity.
3Strength
If eutectic bonding is used for sealing, then strong sealing is achieved, but additional steps are needed for electrical connections
Solution Approach 1:
The patent integrates conductive traces directly into the eutectic bonding interface, allowing the same bonding step that creates the seal to also establish electrical connections. This merging of functions maintains the strong sealing properties of eutectic bonding while eliminating additional electrical connection steps.
4Ease of operation
If electrical connections are extended through the cap wafer, then accessibility is improved, but the bonding process becomes more complex
Solution Approach 1:
The bonding interface is designed to simultaneously provide mechanical sealing and electrical connectivity functions. Conductive elements are incorporated into the bonding layer itself, allowing electrical contacts to be accessed through the cap wafer while maintaining a relatively simple bonding structure.
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 allows for a robust and efficient sealing of the MEMS device cavity while establishing reliable electrical connections, minimizing tilting and squeeze-out effects, and ensuring uniform composition and thickness of the eutectic metal alloy layers.
Implementation Method 1
Bonding the cap wafer to the device wafer... utilizing a specific thickness ratio and temperature to ensure a reliable eutectic phase formation
Data Source
Figure 1a~1d
Figure 1e~1g
Figure 1h~1j
AI summary
A method for sealing and contacting a microelectromechanical device which comprises a silicon device wafer with MEMS device structures and a cap wafer with an electrical circuit. The device wafer comprises a sealing region and an interconnection region, and the cap wafer comprises a corresponding sealing region and an interconnection region. Layers of eutectic metal alloy material are deposited on the sealing and the interconnection regions of the device wafer and the cap wafer. The cap wafer is bonded to the device wafer so that the interconnection region of the device wafer is aligned with the interconnection region of the cap wafer and the sealing region of the device wafer is aligned with the sealing region of the cap wafer.