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MEMS Based Optical HydrogenSensors
FABRICATION AND CHARACTERIZATION OF MEMS BASED OPTICAL
HYDROGEN SENSORS(2012)
HWANGIL HWANG
SAKTHIVISHNU.R
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Need for sensor
Energy crisis - limited resources of fossil fuels.
Hydrogen - most attractive energy resources for its high
efficiency, renewability.
Fact is environmentally friendly.
Hydrogen - fuel for internal-combustion engines and fuel cells.
Ubiquitous in automobiles and homes - cleaner emissions -
industrial combustion engines.
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Need for sensor - safety General hydrogen sensors like catalytic, electrochemical and
semiconductor sensors use electrical leads.
Which may induce sparks and provide a cause for ignition in
hazardous atmospheres.
Optical type hydrogen sensors based on fiber optics allow
working in an explosive environment too.
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Schematic diagram of MEMSbased sensors
Transparent 3c-sic
membrane
Sensing layer
Photovoltaic effect
Detecting layer
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Sensing layer
oxide wafer
2 m 3C-SiC thin film,
sensing part
Gasochromic materials of Pd
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Gasochromic devices
Gasochromic devices, which consists of an electrochromic layer
and a thin catalyst coating.
Can reversibly react with hydrogen & exhibiting significant
changes in their optical properties.
Transition metal oxide WO3 are well known electrochromic
materials.
Pure palladium has high selectively and very highly permeable
to hydrogen.
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An alpha-beta phase transition which occurs at temperatures
below 310C makes the metal dimensionally unstable and liable
to severe distortion and failure.
Current interest in gasochromic devices arises a interest on the
application over the optical based sensor.
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Detection layerPhotovoltaic effect
N-type 3C-SiC
P-typeSi
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Sensing part 3C SiC
3C-SiC Schottky barrier diode - atmospheric pressure chemical
vapor deposition technique.
The barrier height, ideality factor and series resistance
IV
characteristic - 0.44 eV, 1.55 and 1.02 104, respectively.
The transient photocapacitance measurements indicate that the
capacitance of the 3C-SiC Schottky diode is very sensitive to
illumination.
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Silicon carbide is a semiconductor, which can be doped to n-
type by nitrogen or phosphorus and p-type by aluminium,boron, gallium or beryllium
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Responses graph
Responses of the sensors towarddifferent
H2 concentrations at room
temperature for Pd.
Pd/WO3 shows low photovoltaic
compared with Pd only
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Photovoltaic variations for Pd &Pd/WO3
Non - linear response
linear response
R d i f Pd d
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Response and recovery time of Pd and
Pd/WO3 with hydrogen
concentration
Pd was 300, 900 sec
Pd/WO3 was 180, 500
sec
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Variation of response factor (%) withhydrogen concentration.
H2 (%) Pd Pd/WO3
2 7.69 1.334 12.30 4
6 34.61 5.33
8 38.46 7.33
10 42.3 10
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Response factor (%)
Response factor (%)
= ( ) /()100
Vinitial is the voltage measured in air
Vresponse is the voltage at each hydrogen concentrations.
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Conclusion
Pd, output signal decreased at high concentration of hydrogen
by phase transition.
Pd/WO3 shows linear response signal with hydrogen
concentrations.
However, Pd/WO3 structure shows low response factors
compared with pd.
This means the Pd/WO3 has more low penetration ratio
compared with Pd
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REFERENCE
Raman spectroscopic studies of gasochromic a-WO3 thin
films, DCH Technology inc., Valencia CA 91355, USA
Palladium alloy diffusion cells COMMERCIAL UNITS FOR
THE PRODUCTION OF ULTRA-PURE HYDROGEN by
H. Connor, B.Sc. Platinum development department, Johnson
Matthey & co limited.
Electrochromism - Wikipedia, the free encyclopedia
Silicon carbide - Wikipedia, the free encyclopedia.
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Thank you
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