MEMS Packaging Lateral Vent Channels Vacuum Sealing
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Solution Overview
Problem
Current MEMS packaging methods are costly and inefficient, with issues such as additional processing steps for vent channel etching, contamination risks, and difficulty in achieving high-quality vacuum conditions due to limitations in sealing techniques, especially for small cavities.
Innovation Solution
The method involves forming lateral vent channels underneath a cover layer to prevent contamination, using a sacrificial layer and cover layer with chemical treatment to create a porous structure for efficient sacrificial layer removal, and sealing at low pressure to achieve a high-quality vacuum within the MEMS cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If vent channels are etched to allow HF vapor access for cavity formation, then cavity formation is enabled, but additional processing steps are required increasing manufacturing cost
Solution Approach 1:
The patent applies preliminary action by forming the vent channels during the deposition of the sacrificial layer, rather than etching them separately later. The sacrificial layer pattern is designed with vent channel openings built-in, allowing HF vapor access to be established concurrently with cavity formation, eliminating the need for separate vent channel etching steps and reducing manufacturing complexity
Solution Approach 2:
The patent merges the vent channel formation with the sacrificial layer deposition process. The sacrificial layer is deposited with integrated vent channel openings, combining what were previously separate operations (venting and sacrificial layer deposition) into a single integrated step, thereby reducing the total number of processing steps and manufacturing cost
2Ease of manufacture
If vent channels are located directly over the cavity for HF vapor access, then cavity formation is facilitated, but contamination of the cavity with capping material occurs
Solution Approach 1:
The patent segments the sacrificial layer into distinct regions: a main body covering the cavity and separate vent channel openings positioned at the periphery. This segmentation allows HF vapor to access the cavity through the vent channel openings while preventing direct deposition of capping material onto the cavity surface, as the vent channels are located at the edges rather than directly over the cavity
Solution Approach 2:
The patent uses the vent channel openings as intermediaries that facilitate HF vapor access to the sacrificial layer for cavity formation, while simultaneously acting as barriers that prevent capping material from contaminating the cavity. The vent channels serve as controlled pathways that allow the necessary chemical access while blocking unwanted material deposition
3Reliability
If thick capping layers are deposited to seal the cavity, then effective sealing is achieved, but manufacturing cost increases
Solution Approach 1:
The patent employs thin film sealing layers deposited at low temperatures that provide effective cavity sealing without requiring thick capping layers. The thin film sacrificial layer and subsequent sealing layers achieve the necessary seal integrity through precise thickness control and material selection, eliminating the need for thick costly capping layers while maintaining reliable sealing
Solution Approach 2:
The patent changes the deposition temperature parameter from high temperature (950°C) to low temperature processes, enabling the use of thinner sealing layers that are cost-effective to deposit. By altering the thermal parameters of the deposition process, the patent achieves effective sealing with thinner, more economical layers rather than thick high-cost capping layers
4Ease of manufacture
If porous capping material is used for cavity formation, then sacrificial layer removal is enabled, but residual contamination of the cavity is difficult to avoid
Solution Approach 1:
The patent extracts the vent channel function from the porous capping material approach and implements it through discrete, controlled openings in the sacrificial layer. This extraction allows complete removal of the sacrificial layer material while providing dedicated pathways for HF vapor access, eliminating the residual contamination problem associated with porous materials that retain pores after processing
5Reliability
If sealing is performed at high temperature and low pressure, then vacuum quality is improved, but suitable process steps are not available
Solution Approach 1:
The patent applies preliminary action by performing all sealing operations at low temperature before the final high vacuum testing. The sealing layers are deposited and formed at low temperatures using available process steps, and only after sealing is complete is the device subjected to high vacuum conditions. This eliminates the need for high temperature low pressure sealing processes while achieving the desired vacuum quality
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 reduces manufacturing costs, minimizes contamination, and allows for effective sealing and vacuum achievement in MEMS devices, particularly for small cavities, while maintaining structural integrity and preventing damage to other device components.
Implementation Method 1
using a sacrificial layer and cover layer with chemical treatment to create a porous structure for efficient sacrificial layer removal
Implementation Method 2
chemical treatment to create a porous structure for efficient sacrificial layer removal
Implementation Method 3
lateral vent channels underneath a cover layer to prevent contamination, using a sacrificial layer and cover layer with chemical treatment
Implementation Method 4
sealing at low pressure to achieve a high-quality vacuum within the MEMS cavity
Data Source
Figure 1(a)~1(g)
Figure 2a~2c
Figure 2d~2f
AI summary
A method of forming a MEMS device comprises encapsulating a MEMS element (122) with a sacrificial layer portion (130) deposited over a substrate arrangement (100), said portion defining a cavity (150) for the MEMS element, forming at least one strip (132) of a further sacrificial material extending outwardly from said portion, forming a cover layer portion (140) over the sacrificial layer portion, said cover layer portion terminating on the at least one strip, removing the sacrificial layer portion and the at least one strip, the removal of the at least one strip defining at least one vent channel (134) extending laterally underneath the cover layer portion and sealing the at least one vent channel. A device including such a packaged micro electro-mechanical structure (122) is also disclosed.