MEMS Reference Chambers for Post-Bonding Ammonia Filling
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Solution Overview
Problem
Existing methods for manufacturing hermetically sealed chambers for photoacoustic gas sensors fail to reliably and safely introduce corrosive and explosive gases like ammonia without damaging MEMS components or electronic circuits, and are limited by high temperatures during bonding processes.
Innovation Solution
A method involving bonding wafers to form a reference chamber with an opening, filling it with the gas in a coating system outside the bonding process, and sealing it to prevent damage, allowing gases like ammonia to be introduced and sealed hermetically without exposure to high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If gases are introduced into the reference chamber during the bonding process, then the chamber can be filled with the required gas, but the high temperatures during bonding can damage MEMS components and electronic circuits
Solution Approach 1:
The process is divided into two separate stages: first, the bonding of wafers to form the reference chamber structure; second, the introduction and sealing of gas into the chamber. This segmentation allows the bonding to occur without gas present, avoiding thermal damage to components, while still achieving the required gas filling of the chamber.
Solution Approach 2:
The bonding of wafers is performed as a preliminary action before introducing the gas into the reference chamber. By completing the structural formation and sealing operations first, the system prepares the chamber in a state ready for gas introduction, thereby avoiding exposure of sensitive components to both high temperatures and corrosive gases simultaneously.
2Quantity of substance
If corrosive gases like ammonia are introduced during bonding, then the reference chamber can be filled, but the corrosive gas can damage MEMS components and electronic circuits
Solution Approach 1:
The manufacturing process is segmented into distinct phases: chamber formation through wafer bonding, followed by gas introduction and sealing. This separation ensures that corrosive gases are never present during the bonding process, eliminating corrosion risks to MEMS components and electronic circuits while still achieving complete gas filling of the reference chamber.
Solution Approach 2:
A temporary opening or access structure serves as an intermediary mechanism that allows gas to be introduced into the sealed chamber after bonding, without requiring the chamber to be open during the bonding process itself. This intermediary approach enables gas filling while maintaining component protection throughout the critical bonding phase.
3Reliability
If the reference chamber is sealed hermetically, then gas containment is reliable, but introducing gas after bonding requires additional process steps
Solution Approach 1:
The wafer bonding and chamber sealing are performed as preliminary actions before gas introduction. By establishing the hermetic seal first through bonding, the system creates a reliable containment structure that can subsequently be selectively opened or accessed for gas filling, thereby maintaining reliability while enabling post-bonding gas introduction.
Solution Approach 2:
The gas introduction function is extracted from the bonding process itself and performed as a separate, subsequent operation. This extraction allows the bonding process to maintain its simple, reliable hermetic sealing function, while the gas filling is handled through a dedicated access mechanism or process step that does not compromise the seal integrity.
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
Enables the safe and efficient introduction and containment of corrosive and explosive gases like ammonia within MEMS cells, protecting components and ensuring a compact, reliable design suitable for mass production and various applications.
Implementation Method 1
Photoacoustic spectroscopy (PAS) is a physical investigation method based on the photoacoustic effect... If this molecule is present in the beam path, modulated absorption occurs, leading to heating and cooling processes whose timescales reflect the modulation frequency of the radiation. These heating and cooling processes lead to expansion and contraction of the gas, causing sound waves with the modulation frequency.
Data Source
Figure 1A~1B
Figure 2A~2E
Figure 2F~2H
AI summary
In a first aspect, the invention relates to a method for producing a gas-filled reference chamber that is hermetically sealed. According to the method, the gas with which the reference chamber is filled is introduced via an opening in a separate coating chamber only once the wafers forming the reference chamber are bonded. MEMS components have preferably been incorporated in the reference chamber. In a further aspect, the invention relates to a photoacoustic gas sensor comprising such a reference chamber within which a MEMS sensor is situated.