Native Oxide Layer Controls Stress Gradient in Released MEMS Structures
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Solution Overview
Problem
Attaining a desired shape of released metal structures in MEMS devices is problematic due to internal stresses in metal layers, which existing methods fail to address effectively.
Innovation Solution
The formation of MEMS devices involves creating a sacrificial layer over a substrate, followed by depositing a first metal layer and exposing it to an oxidizing ambient to form a native oxide layer, with subsequent layers being added to control stress and shape, allowing for the self-limiting formation of native oxide layers that reduce fabrication complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods are used to form released metal structures, then fabrication can be performed, but internal stresses in metal layers cause unwanted deformation and shape control is problematic
Solution Approach 1:
A stress control layer is introduced between the metal layer and the sacrificial layer. This intermediary layer has specific mechanical properties (lower Young's modulus than the metal layer) that allow it to accommodate stress differential during fabrication and release, preventing unwanted deformation while maintaining manufacturing precision
Solution Approach 2:
The invention changes the mechanical parameters of the structure by introducing a layer with specific elastic modulus and thickness characteristics. The stress control layer's parameters (thickness, material composition) are optimized to balance stress management with final shape requirements
2Manufacturing precision
If multiple metal layers are deposited to achieve desired shape, then shape control improves, but fabrication complexity and cost increase
Solution Approach 1:
The structure is segmented into distinct functional layers: metal layer for structural integrity, stress control layer for stress management, and sacrificial layer for release. This segmentation allows each layer to perform its specific function independently, simplifying the overall fabrication process while achieving complex shape control
Solution Approach 2:
The invention uses composite material structures combining metal layers with stress control layers having different material properties. This composite approach enables tailored mechanical behavior and stress distribution, achieving shape control without requiring excessive numbers of metal layers
3Ease of operation
If sacrificial layer is removed to release metal structure, then device functionality is achieved, but stress gradient and bending moment become uncontrolled
Solution Approach 1:
The stress control layer is deposited and configured before the sacrificial layer is removed. This preliminary action ensures that when the sacrificial layer is etched away, the stress gradient and bending moment are already managed by the pre-positioned stress control layer, maintaining stable stress distribution throughout the release process
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 method provides more process latitude and reproducible stress levels, resulting in a released metal structure with a desired shape, reducing fabrication costs and complexity while minimizing direct contact with solid elements.
Implementation Method 1
the first metal layer is exposed to an oxidizing ambient which oxidizes a surface layer of the first metal layer where exposed to the oxidizing ambient, to form a native oxide layer
Data Source
AI summary
In described examples, a MEMS device is formed by forming a sacrificial layer over a substrate and forming a first metal layer over the sacrificial layer. Subsequently, the first metal layer is exposed to an oxidizing ambient which oxidizes a surface layer of the first metal layer where exposed to the oxidizing ambient, to form a native oxide layer of the first metal layer. A second metal layer is subsequently formed over the native oxide layer of the first metal layer. The sacrificial layer is subsequently removed, forming a released metal structure.