SiC MEMS Suspended Beam via Direct Wafer Bonding
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Solution Overview
Problem
Existing silicon carbide (SiC) MEMS structures face challenges with high residual stress, high dislocation density, and thermal expansion mismatch when grown on silicon substrates, limiting their thickness and performance in applications like gyroscope and accelerometer devices.
Innovation Solution
The use of direct wafer bonding of a top hexagonal single-crystal SiC substrate with a semi-insulating SiC substrate to form suspended beam and anchor structures, which reduces residual stress and thermal expansion mismatch, enabling thicker SiC beams with improved mechanical and thermal properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If 3C-SiC material layers are grown on silicon substrate, then SiC MEMS structures can be fabricated, but high residual stress, high dislocation density, and thermal expansion mismatch occur
Solution Approach 1:
The patent uses a silicon oxide interface layer as an intermediary between the silicon substrate and 3C-SiC material layer. This interface layer mediates the thermal expansion mismatch and reduces residual stress transmission, allowing thicker SiC beams to be grown with lower dislocation density and improved structural quality
Solution Approach 2:
The patent changes the growth parameters including using off-axis oriented silicon substrates, controlling oxidation conditions to form specific thicknesses of silicon oxide interface layers, and optimizing CVD growth conditions to reduce dislocation density and residual stress in the SiC layers
2Reliability
If SiC beam thickness is increased to reduce Brownian noise, then noise performance improves, but residual stress and dislocation density increase
Solution Approach 1:
The silicon oxide interface layer acts as a stress buffer that decouples the stress between the thick SiC beam and the silicon substrate, enabling beams thicker than 100 micrometers to be fabricated without excessive residual stress accumulation
Solution Approach 2:
The patent employs off-axis oriented silicon substrates and controlled oxidation processes to create interface layers with specific properties that allow thick SiC beam growth while maintaining low residual stress levels
3Stability of the object's composition
If thermal expansion mismatch between SiC epitaxial layer and silicon substrate is reduced, then structural stability improves, but manufacturing complexity increases
Solution Approach 1:
The silicon oxide interface layer serves as a thermal expansion mediator that accommodates the mismatch between SiC and silicon substrates, providing a gradual transition that reduces stress concentration while maintaining manufacturing feasibility
Solution Approach 2:
The patent optimizes the thickness and oxidation conditions of the silicon oxide interface layer to achieve the right balance between thermal expansion matching and process simplicity, using standard semiconductor fabrication techniques
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 SiC MEMS structures with lower noise, higher stiffness, and improved radiation hardness, enabling thicker suspended beams with reduced Brownian mechanical noise and enhanced performance in high-G applications.
Implementation Method 1
SiC provides higher modulus, higher density, and higher thermal conductivity than silicon
Implementation Method 2
Hexagonal SiC provides superior isoelasticity (rotation symmetry) versus silicon reducing errors in gyroscope functioning
Implementation Method 3
SiC single-crystal hexagonal material bonded to SiC single-crystal hexagonal first substrate provides good thermal expansion match
Implementation Method 4
direct wafer bonding of a top hexagonal single-crystal SiC second substrate used to form a suspended beam and anchor structure to a bottom semi-insulating single-crystal SiC first substrate
Data Source
AI summary
A method of fabricating suspended beam silicon carbide microelectromechanical (MEMS) structure with low capacitance and good thermal expansion match. A suspended material structure is attached to an anchor material structure that is direct wafer bonded to a substrate. The anchor material structure and the suspended material structure are formed from either a hexagonal single-crystal SiC material, and the anchor material structure is bonded to the substrate while the suspended material structure does not have to be attached to the substrate. The substrate may be a semi-insulating or insulating SiC substrate. The substrate may have an etched recess region on the substrate first surface to facilitate the formation of the movable suspended material structures. The substrate may have patterned electrical electrodes on the substrate first surface, within recesses etched into the substrate.