MEMS Microphone Backside Cavity Ribs Prevent Bubble Formation
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Solution Overview
Problem
Conventional MEMS microphones face challenges in removing oxide from through-holes due to bubble formation in the backside cavity when immersed in liquid etchants, and the rounded shape of the cavity fails to adequately support the backplate, leading to drooping or bowing.
Innovation Solution
The backside cavity is designed with inward-protruding ribs or vertices on its sidewalls, which prevent bubble formation and allow liquid to penetrate, while also providing structural support to the backplate, ensuring effective oxide removal and reducing bowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a generally rounded backside cavity is used, then the cavity can be easily manufactured, but the liquid cannot penetrate into the cavity due to bubble formation around the opening
Solution Approach 1:
The backside cavity is segmented by adding internal ribs that divide the cavity space. These ribs create multiple access paths for liquid to enter the cavity, preventing bubble formation by disrupting the liquid surface tension that causes bubble formation in rounded cavities.
Solution Approach 2:
The internal ribs are strategically positioned at specific locations within the backside cavity to create local geometric features that promote liquid entry. The ribs create localized regions with different surface properties that facilitate liquid penetration while maintaining the overall rounded cavity shape for ease of manufacture.
2Ease of manufacture
If a generally rounded backside cavity is used, then the manufacturing process is simplified, but the backplate is not adequately supported and droops or bows
Solution Approach 1:
The backside cavity is divided into multiple sections by internal ribs, which act as support structures. These ribs are positioned to provide mechanical support to the backplate, preventing drooping and bowing while maintaining the simplified rounded outer cavity shape for easy manufacture.
Solution Approach 2:
The internal ribs serve multiple functions simultaneously: they provide structural support to prevent backplate deformation, create liquid access paths to prevent bubble formation, and maintain the overall cavity geometry. This multi-functionality resolves the contradiction between ease of manufacture and backplate support capability.
3Ease of operation
If mechanical force is applied to break bubbles (e.g., blowing air), then liquid can enter the through-holes, but the process complexity increases
Solution Approach 1:
The backside cavity geometry with internal ribs is designed to automatically prevent bubble formation and facilitate liquid entry without requiring external mechanical intervention. The geometric features themselves perform the function of bubble prevention, eliminating the need for additional complexity such as air blowing mechanisms.
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
The shaped backside cavity enables efficient removal of oxide from through-holes without mechanical assistance and minimizes backplate bowing, enhancing the operational efficiency and reliability of MEMS microphones.
Implementation Method 1
the liquid often forms a bubble around the opening of the backside cavity
Implementation Method 2
the liquid may remove the material from the walls. The material may include an oxide and the liquid may include a hydrofluoric acid
Data Source
AI summary
A MEMS microphone has a backplate, a diaphragm movable relative to the backplate, and a backside cavity adjacent to the backplate or the diaphragm. The backside cavity has sidewalls with at least one rib protruding inward toward a center of the backside cavity.