TLP Metal Bonding Stack for Stable Hermetic MEMS Packaging
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Solution Overview
Problem
Hermetic packaging of MEMS devices, such as digital micro-mirror devices, faces challenges due to high surface energy substances causing adhesion issues and the instability of transient liquid phase (TLP) metal bonding materials, which leads to metal diffusion and restrictions on fabrication processes.
Innovation Solution
A TLP metal bonding material is developed with a base metal layer, a metal fuse layer, and a terminal metal layer, where the metal fuse layer is between 200 to 400 Å thick and positioned between the base metal and terminal metal layers, providing stability at room temperature and allowing for low-temperature bonding without significant metal diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TLP metal bonding materials are used for hermetic bonding, then bonding capability is improved, but metal diffusion occurs over hours reducing material stability
Solution Approach 1:
A thin oxide layer is intentionally formed on the metal bonding surface to act as an intermediary barrier that prevents metal diffusion while allowing TLP bonding to proceed. This oxide layer mediates between the need for bonding capability and material stability, blocking harmful metal diffusion during storage and handling without preventing the bonding process when needed.
Solution Approach 2:
The surface oxidation state is changed from a defect to a controlled parameter. By controlling the oxide layer thickness and composition through surface treatment, the material's stability is improved for storage while maintaining bonding capability when required. This parameter change transforms the unstable metallic surface into a stable oxidized surface that prevents diffusion.
2Strength
If processing temperatures are increased to −150° C. for hermetic bonding, then bonding strength is improved, but getter system degradation occurs at temperatures above 175° C.
Solution Approach 1:
The bonding temperature parameter is changed from high temperature (−150° C.) to room temperature processing. This parameter change allows the bonding process to proceed without degrading the temperature-sensitive getter system, while the oxide-mediated TLP bonding mechanism ensures adequate bonding strength is achieved at the lower temperature.
3Ease of manufacture
If metal layers are plated into the stack for TLP bonding, then bonding material is provided, but significant metal diffusion occurs reducing stack stability
Solution Approach 1:
The oxide layer serves as a mediator that is compatible with plated metal layers while preventing their diffusion. This allows the ease of manufacture benefit from plating to be retained while the harmful metal diffusion is blocked by the intermediary oxide barrier.
Solution Approach 2:
A composite structure is created combining the plated metal layer with the oxide layer. This composite material combines the manufacturing advantages of plated metals with the diffusion-blocking properties of the oxide, achieving both ease of manufacture and stack stability.
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
The solution enables stable hermetic bonding at room temperature, reducing processing costs and avoiding material waste, while maintaining the mechanical robustness and corrosion resistance necessary for MEMS devices.
Implementation Method 1
Transient liquid phase (TLP) metal bonding materials are useful to form such hermetic bonds and packaging
Implementation Method 2
the materials plated into the stack are often prone to significant metal diffusion
Data Source
AI summary
In described examples, a transient liquid phase (TLP) metal bonding material includes a first substrate and a base metal layer. The base metal layer is disposed over at least a portion of the first substrate. The base metal has a surface roughness (Ra) of between about 0.001 to 500 nm. Also, the TLP metal bonding material includes a first terminal metal layer that forms an external surface of the TLP metal bonding material. A metal fuse layer is positioned between the base metal layer and the first terminal metal layer. The TLP metal bonding material is stable at room temperature for at least a predetermined period of time.