Anodic Bonding Microdevice Encapsulation Using Composite Substrates
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Solution Overview
Problem
Existing methods for anodic sealing of micro-devices fail to provide precise control of pressure and gaseous composition in cavities, as borosilicate glass substrates are permeable to noble gases and lead to oxygen degassing, and thin glass layers are fragile and costly to produce.
Innovation Solution
A method involving a thick glass substrate (>300 μm) secured to a non-permeable substrate, with cavities etched through the glass, allowing anodic sealing without PVD deposition, reducing gas permeability and oxygen ingress, and using a getter material to maintain atmosphere quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If borosilicate glass substrate is used for anodic sealing, then hermetic sealing is achieved, but noble gas permeability and oxygen outgassing occur
Solution Approach 1:
The patent uses a composite structure consisting of a glass layer (for anodic bonding capability) combined with a metallic barrier layer (for gas impermeability). This composite material approach allows the sealing structure to simultaneously achieve hermetic sealing through anodic bonding while blocking noble gas permeation and oxygen outgassing that would occur with glass alone.
Solution Approach 2:
The patent applies different material properties to different regions of the sealing structure: the glass layer provides anodic bonding capability at the bonding interface, while the metallic barrier layer provides gas impermeability where needed. This local differentiation of material qualities allows each layer to perform its specific function optimally.
2Object-generated harmful factors
If thin glass layer is used for encapsulation, then gas permeability is reduced, but fragility and manufacturing cost increase
Solution Approach 1:
Instead of using a thin glass layer alone, the patent creates a composite structure with a metallic barrier layer combined with a glass layer. This composite approach reduces gas permeability effectively while the glass layer can be relatively thick, maintaining mechanical strength and reducing fragility during handling and manufacturing.
Solution Approach 2:
The metallic barrier layer acts as an intermediary between the glass layer and the cavity, providing the gas barrier function that the glass alone cannot achieve. This allows the glass layer to focus on providing mechanical strength and anodic bonding capability, while the metallic intermediary handles the gas permeability issue.
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 achieves precise control of cavity atmosphere, reduces fragility and costs, and ensures hermeticity by minimizing noble gas penetration and oxygen degassing, enabling reliable operation of micro-devices across varying pressure ranges.
Implementation Method 1
anodic sealing of the remaining portions of the second substrate against a third substrate comprising the micro-device
Implementation Method 2
such a borosilicate glass substrate has the disadvantage of being permeable to noble gases such as helium or argon
Implementation Method 3
when the electric field is applied during sealing, sodium ions will migrate towards the external surface of the glass and, in return, oxygen ions contained in the glass will migrate towards the internal surface of the substrate and thus enter the cavity
Data Source
Figure 1A~1E
Figure 2A~2D
Figure 3~5
AI summary
The method involves bonding a face of first substrate (102) comprising a material impermeable to noble gases in contact with a second glass substrate. A cavity (108) is etched through the second substrate such that side walls of the cavity are partially formed by remaining portions (110) of the second substrate and that an upper wall of the cavity is formed by portion (112) of a face of the first substrate. Anodic bonding of the remaining portions is performed against a third substrate in which a micro-device (100) is formed, such that the micro-device is encapsulated in the cavity. The material impermeable to noble gases is metal and/or silicon.