MEMS Interdigitated Comb Fingers Mitigate ARDE Striation
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Solution Overview
Problem
Aspect Ratio Dependent Etching (ARDE) during Deep Reactive Ion Etching (DRIE) of Microelectromechanical Systems (MEMS) structures with abrupt aspect ratio changes leads to striation, side wall defects, and reduced signal quality.
Innovation Solution
A MEMS structure design featuring a stator and a rotor with interdigitated comb fingers, where the gap between them gradually increases in regions with abrupt aspect ratio changes, minimizing the ARDE effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If DRIE is used to etch MEMS structures with abrupt aspect ratio changes, then high aspect ratio structures can be fabricated, but ARDE effect causes striation and side wall defects
Solution Approach 1:
The comb structure is divided into multiple individual comb fingers with gaps between them. This segmentation allows the etching process to work on smaller, uniform sections rather than large abrupt transitions, reducing ARDE effects while maintaining the overall high aspect ratio geometry
Solution Approach 2:
The gap width is specifically optimized in critical regions where aspect ratio changes occur. By localizing the gap feature at the base of comb fingers, the design addresses ARDE problems only where they occur most severely, rather than uniformly across the entire structure
2Manufacturing precision
If shielding structure is added to control aspect ratio gradient, then ARDE effect is reduced, but extra design space is required
Solution Approach 1:
The gap feature serves dual purposes: it acts as a shielding structure to control aspect ratio gradient during etching, and simultaneously functions as the active electrostatic gap between stator and rotor comb fingers. This merging eliminates the need for separate shielding structures, preserving design space
Solution Approach 2:
The gap between comb fingers is designed to perform multiple functions: providing electrostatic actuation clearance, reducing ARDE during fabrication, and defining the mechanical range of motion. This multi-functionality eliminates the need for additional dedicated shielding elements
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 design effectively eliminates the ARDE effect, resulting in high-quality MEMS structures with improved geometry and reduced defects.
Implementation Method 1
One problem which arises when etching the design locations with the abrupt change in the aspect ratio and where the dimensions are close to critical values is Aspect Ratio Dependent Etching (ARDE)
Data Source
AI summary
A device is provided that includes a stator including a stator element and a row of stator comb fingers, wherein the stator comb fingers extend away from the stator element in a y-direction. A device may include a rotor including a rotor element and a row of rotor comb fingers, wherein the rotor comb fingers extend away from the rotor element in a direction which is opposite to the y-direction, and wherein the stator comb fingers are interdigitated with the rotor comb fingers, and form an interdigitated row, and each pair of adjacent stator comb finger and rotor comb finger are separated from each other by a x-gap in a x-direction, which is perpendicular to the y-direction.