mems based optical hydrogen sensor

7/29/2019 mems based optical hydrogen sensor

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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

mems based optical hydrogen sensor

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