Permeable Membrane Encapsulation for Microelectronic Pressure Control
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Solution Overview
Problem
Current microelectronic device encapsulation techniques face challenges in achieving precise control over pressure in cavities for devices with different residual pressure requirements, such as MEMS and NEMS, where achieving high pressure differences between cavities is difficult due to limitations in getter material capacity and permeation issues.
Innovation Solution
A process involving a substrate with a permeable material for noble gases, allowing precise control of gas injection through controlled dimensions, enabling residual pressures from 10^-1 mbar to 1 bar or higher, and using getter materials to absorb reactive gases, allowing collective encapsulation of devices with different pressure needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If getter material is used to achieve vacuum in cavity, then residual pressure is reduced, but getter material capacity is limited and cannot achieve high pressure differences between cavities
Solution Approach 1:
The invention divides the encapsulation process into two independent stages: first hermetically sealing the cavity at atmospheric pressure, then introducing vacuum through a separate permeable membrane with getter material. This segmentation allows each stage to be optimized independently, enabling pressure differences of several orders of magnitude between cavities without getter material capacity limitations.
Solution Approach 2:
The cavity is hermetically sealed in advance at atmospheric pressure before vacuum introduction. This preliminary sealing action isolates the cavity from the external environment, allowing subsequent vacuum introduction through the permeable membrane without compromising the hermetic seal, thereby enabling precise pressure control within the sealed cavity.
2Productivity
If collective encapsulation of multiple devices is performed, then fabrication cost is reduced, but precise control of different residual pressures in distinct cavities becomes difficult
Solution Approach 1:
The invention applies local quality by making the cap substrate selectively permeable to specific gases (nitrogen and oxygen) through localized permeable membranes at specific cavity regions. This allows different cavities to have different gas permeation characteristics, enabling independent pressure control for each device type (accelerometer vs. gyroscope) while maintaining collective encapsulation processing.
Solution Approach 2:
The invention changes the gas permeation parameter of the cap substrate by incorporating permeable membranes with specific permeability characteristics. This parameter change enables selective gas transport (nitrogen and oxygen permeation) that facilitates different residual pressure conditions in different cavities during collective encapsulation, allowing pressure differentiation without sacrificing collective processing efficiency.
3Reliability
If hermetic seal is made between substrates, then cavity is sealed, but gas permeation through walls and sealing joint affects pressure control
Solution Approach 1:
The invention introduces a permeable membrane as an intermediary element between the hermetically sealed cavity and the external vacuum environment. This membrane allows controlled gas permeation (specifically nitrogen and oxygen) while maintaining the hermetic seal integrity of the main cavity structure, thereby enabling pressure control without compromising seal reliability.
4Manufacturing precision
If different devices are packaged independently, then precise pressure control is achieved, but fabrication cost increases
Solution Approach 1:
The invention makes the cap substrate multi-functional by combining hermetic sealing capability with selective gas permeation properties. This universal cap structure can serve multiple purposes: sealing different types of devices (accelerometers and gyroscopes) collectively while simultaneously enabling different pressure conditions in different cavities through the permeable membrane, thereby eliminating the need for separate packaging processes.
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 process enables precise control of pressure and gas composition in cavities, facilitating the collective encapsulation of microelectronic devices with varying residual pressures, optimizing the functioning of devices like accelerometers and gyroscopes by maintaining desired pressure ranges.
Implementation Method 1
make at least one portion of a first material not permeable to the ambient atmosphere and permeable to at least one noble gas
Implementation Method 2
using getter materials to absorb reactive gases
Data Source
AI summary
A process for encapsulating a microelectronic device, comprising the following steps:make the microelectronic device on a first substrate;make one portion of a first material not permeable to the ambient atmosphere and permeable to a noble gas in a second substrate comprising a second material not permeable to the ambient atmosphere and the noble gas;secure the second substrate to the first substrate, forming at least one cavity inside which the microelectronic device is encapsulated such that said portion of the first material forms part of a wall of the cavity;inject the noble gas into the cavity through the portion of the first material;hermetically seal the cavity towards the ambient atmosphere and the noble gas.