MEMS Electrode Cavity Segmentation for Warpage Prevention
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Solution Overview
Problem
Conventional sealing methods for MEMS resonators using resin transfer molding can cause electrode warpage due to external pressure, leading to collisions with movable portions and failure to maintain the required narrow gaps, which are essential for reducing device impedance.
Innovation Solution
A MEMS device structure featuring two cavities separated by an electrode, where the inner surface of the first cavity's side wall is positioned more inside than the second cavity's side wall, preventing stress from being applied to the electrode in a direction that would cause it to move towards the movable portion, thus maintaining the gap and avoiding collisions, and allowing for a thinner sealing membrane to reduce production time and strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resin transfer molding is used for sealing MEMS resonator, then sealing is achieved, but electrode warpage occurs due to external pressure causing collision with movable portion
Solution Approach 1:
The cavity is divided into two separate cavities (first cavity and second cavity) positioned on opposite sides of the electrode. This segmentation allows the electrode to be mechanically supported from both sides, preventing warpage and collision with the movable portion while maintaining the required gap during resin transfer molding sealing.
Solution Approach 2:
The dual cavity structure acts as a counterbalancing mechanism where the cavities on either side of the electrode provide opposing support forces. This counterweight effect prevents the electrode from warping under external pressure during sealing, maintaining the precise gap between the electrode and movable portion.
2Reliability
If sealing membrane thickness is increased to prevent electrode warpage, then electrode protection is improved, but production time increases
Solution Approach 1:
Instead of using a single thick sealing membrane, the structure segments the support function into two separate cavities positioned on opposite sides of the electrode. This segmentation provides effective electrode protection against warpage while allowing the use of a thinner sealing membrane, thereby reducing production time.
3Device complexity
If single cavity structure is used, then structure simplicity is maintained, but electrode warpage prevention is insufficient
Solution Approach 1:
The cavity is segmented into two separate cavities (first and second cavities) positioned on opposite sides of the electrode. This segmentation provides balanced mechanical support to the electrode, preventing warpage and maintaining the precise gap between the electrode and movable portion, while the overall structure remains relatively simple.
Data Source
AI summary
In a MEMS device having a substrate 1, a sealing membrane 7, and a movable portion 3 of beam and an electrode 5 which have a region wherein they overlap with a gap in perpendicular to a substrate 1 surface, a first cavity 9 is on the side of the movable portion 3 in the direction perpendicular to the surface of the substrate, and a second cavity is the other cavity, and an inner surface a of a side wall A in contact with the electrode 5, of the first cavity 9, is positioned more inside than an inner surface b of a side wall B in contact with the electrode 5, of the second cavity 10, in the direction parallel to the substrate surface, such that the movable portion 3 does not collide with the electrode 5 when mechanical stress is applied from outside to the sealing membrane 7.