MEMS Anchors with Insulating Cavities
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Solution Overview
Problem
Current MEMS/NEMS technologies in monocrystalline silicon lack electrically insulating anchors, leading to mechanical stress and poor quality factors, especially in resonant structures, due to the use of polycrystalline materials in anchoring zones.
Innovation Solution
The method involves forming cavities with a monocrystalline protective layer, filling them with insulating material, and epitaxially growing a semiconductor layer to create electrically insulating anchors, ensuring the mechanical element is attached to a monocrystalline substrate with reduced stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polycrystalline silicon is used in anchoring zones to provide electrical insulation, then electrical insulation is achieved, but mechanical stress increases and quality factor deteriorates
Solution Approach 1:
The patent applies local quality by using monocrystalline silicon specifically in the anchoring zones where mechanical strength and low stress are critical, while allowing other zones to use different materials for electrical insulation. This localized material selection optimizes both mechanical performance and electrical properties in their respective critical areas.
Solution Approach 2:
The patent employs composite material structures combining monocrystalline silicon anchors with insulating layers (such as silicon oxide or silicon nitride). This composite approach maintains monocrystalline material in stress-critical anchoring zones while adding insulation through separate layers, resolving the contradiction between mechanical quality and electrical insulation.
2Reliability
If monocrystalline silicon is used throughout the structure, then mechanical properties and quality factor are improved, but electrical insulation in anchoring zones is lost
Solution Approach 1:
The patent segments the anchoring zone into distinct functional layers: a monocrystalline silicon base providing mechanical strength and low stress, and separate insulating layers (such as silicon oxide or silicon nitride) providing electrical insulation. This segmentation allows each layer to perform its specialized function without compromising the other.
Solution Approach 2:
The patent introduces insulating layers as intermediary elements between the monocrystalline silicon anchoring zones and adjacent conductive elements. These intermediary layers prevent electrical short circuits while allowing the monocrystalline silicon to maintain its mechanical advantages in the anchoring regions.
3Reliability
If epitaxial silicon thickness is increased to avoid dislocations, then material quality improves, but thickness is limited to a few hundred nanometers
Solution Approach 1:
The patent uses preliminary actions during the epitaxial growth process, such as optimized temperature profiles, pressure control, and doping sequences, to produce high-quality monocrystalline silicon layers of sufficient thickness without dislocations. These preliminary process optimizations enable achieving both adequate thickness and high material quality.
Solution Approach 2:
The patent applies parameter changes in the epitaxial growth process, including temperature, pressure, gas flow rates, and doping concentrations, to control crystal growth and prevent dislocation formation. By optimizing these parameters, the patent achieves monocrystalline layers with thickness sufficient for mechanical strength while maintaining high material 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 results in better mechanical properties, improved quality factors, and enhanced shock resistance by maintaining monocrystalline silicon in anchoring zones, allowing for precise control over the release process and access to varied patterns.
Implementation Method 1
The etching leaving at least part of said overhang
Implementation Method 2
an epitaxy step comprising the epitaxy of a semiconductor material from the first protection layer
Data Source
Figure 1A~1C
Figure 1D~1F
Figure 2~3B
AI summary
Method for making a MEMS/NEMS structure from a substrate made of single-crystal semiconductor material, the structure comprising a flexible mechanical element attached to the substrate by at least one anchoring zone made of partially single-crystal material (9,10).