MEMS sensors for flow measurement in harsh environments
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Introduction
1
Literature review on flow sensing for harsh environments
1.1
Flow equations and turbulence scales
1.2
Flow measurement techniques
1.2.1
Historical overview
1.2.2
Hot wires
1.2.3
Wall shear stress sensors
1.2.4
Summary table
1.3
Extending MEMS anemometers to harsh environments
1.3.1
Wide bandgap materials
1.3.2
SiC as a mechanical support
1.3.3
SiC as a sensing material
1.3.4
Manufacturing challenges
2
Development of a batch fabrication process for 3C-SiC wall shear stress sensors
2.1
Fabricating electrically insulated suspended 3C-SiC resistors
2.1.1
The challenge to build calorimetric sensors
2.2
3C–SiC calorimeters
2.2.1
Dry etching process
2.2.2
Global flowchart
2.3
Characterizations
2.3.1
Characterization setup
2.3.2
TCR measurement
2.3.3
Resistance-Power characteristic
2.4
Conditioning of hot-wire sensors
2.4.1
Development of a CTA suited for SiC hot wires
2.4.2
Frequency response assessment
3
Sensor testings in real flows
3.1
Wind tunnel testings
3.2
Wind tunnel facility
3.3
Flush-mounting of sensors on the wind tunnel wall
3.4
Wall shear stress calibration
3.4.1
The Coles-Fernholz method
3.4.2
Calorimetric response to wall shear stress
3.5
Square-wave tests
3.5.1
Theory
3.6
Overheat effect
3.7
Dynamic response
Conclusion
References
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2 Development of a batch fabrication process for 3C-SiC wall shear stress sensors
/
2.1 Fabricating electrically insulated suspended 3C-SiC resistors
#
2.1
Fabricating electrically insulated suspended 3C-SiC resistors
figure 2.3
<100> Si
substrate
Si
3C-SiC
BF33
3C-SiC
hetero-
epitaxy
800 nm
backside
grinding
anodic bonding
to a BF33 wafer
Au contacts
deposition
SiC dry
etching
Si isotropic
etching
50 µm
Au
Figure 2.1.
Fabrication flowchart for simple SiC suspended hot wires.
This method works but is not enough to build calorimetric probes because of lateral silicon etching.
#
2.1.1
The challenge to build calorimetric sensors
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3C–SiC calorimeters