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Advances In Wireless Hydrogen Sensor
Networks
Travis Anderson1, Hung-Ta Wang1, Byoung Sam Kang1,
Fan Ren1, Changzhi Li2, Zhen Ning Low2,
Jenshan Lin2, Stephen Pearton3, A. Osinsky4, Amir
Dabiran4, P. Chow4, C. Balaban5, John Painter6
1 University of Florida, Chemical Engineering
2 University of Florida, Electrical and Computer Engineering
3 University of Florida, Materials Science and Engineering
4 SVT Associates
5 University of Florida, NASA Hydrogen Research Program
6 J. Painter Associates, LLC
University of Florida
NHA Hydrogen Conference, March 31, 2008
NASA Funded Hydrogen Research at UF
• $10M funding over 4 years
• 27 Projects
• 60 Faculty members, post-docs, and graduate
students combined
UF NASA Funded Hydrogen Research Web Site:
http://www.mae.ufl.edu/NasaHydrogenResearch
University of Florida
NHA Hydrogen Conference, March 31, 2008
NASA Funded Hydrogen Research at UF
Research Thrust Areas
• Fuel Cells (PEM and SOFC)
• Hydrogen Production, Storage, and Transport
• Nano Sensors - Hydrogen Leak Detection
Gas inlet
H2
Gas outlet
H2 Production PEM FC micro grids
& Cooling Plate
University of Florida
Single Crystal Nanowires
Hydrogen-Selective Sensing
at Room Temperature with
ZnO Nanorods
NHA Hydrogen Conference, March 31, 2008
Motivation
Application fields:
• Fuel leak detection for
automobile, space shuttle,
and aircraft
• Fire detection (CO, CO2)
• Emission, hydrocarbon,
and health monitor
• Environmental control
University of Florida
NHA Hydrogen Conference, March 31, 2008
Advantages of Group III Nitride
• Outstanding mechanical and
electronic properties
• Controllable wide range band
gap(3.4eV-6.2eV AlGaN)
• High thermal stability
• Chemical inertness
• AlGaN/GaN 2DEG for high
power and high frequency.
University of Florida
NHA Hydrogen Conference, March 31, 2008
Sensing Mechanism
• Chemisorption on Pt
– H22H
• Diffusion of H atom
– 2Hs 2Hb 2Hi
• Creation of a polarized layer at
the interface
• Decrease of barrier height
University of Florida
NHA Hydrogen Conference, March 31, 2008
Experimental Results
qB eV
JF A**T 2 exp
exp
1
kT nkT
ΔФB~ -50 meV @ room T
• Sensitivity is demonstrated to 100 ppm under forward bias and 10 ppm
under reverse bias
• Barrier height decrease is ~5-50 meV depending on concentration
• Time-dependent measurements show good repeatability and recyclability
University of Florida
NHA Hydrogen Conference, March 31, 2008
Bias Polarity and Temperature Effects
• Increased sensitivity under reverse bias is demonstrated
– This is due to amplification of the dipole effect
• Increased sensitivity under elevated temperature is demonstrated
– This is due to improved efficiency of hydrogen cracking on the
surface
University of Florida
NHA Hydrogen Conference, March 31, 2008
Hydrogen Concentration Effect
• Logarithmic response on both
ppm and percentage hydrogen
scales
• This is relevant for marketable
sensor applications
University of Florida
NHA Hydrogen Conference, March 31, 2008
Wireless Integration
• Sensors are packaged in a low-cost plastic
housing
• Microcontroller circuit monitors current
level and transmits data to base station,
which can be monitored remotely via the
internet
• Software can be programmed to call
emergency personnel if alarm is triggered
University of Florida
NHA Hydrogen Conference, March 31, 2008
Practical Problem – False Alarms
•
Current increases with temperature at fixed
bias - A differential detection device was
introduced to eliminate this temperature
effect
•
Standard Ti/Al/Pt/Au ohmic contacts
demonstrated poor long-term stability,
causing drift in the current level
University of Florida
NHA Hydrogen Conference, March 31, 2008
Field Test at Greenway Ford, Orlando
• Differential detection and TiB2-based
contacts provide improved stability
• Field testing has been underway for over
a year at a hydrogen bus service station
in Orlando, FL
• Data can be monitored in real time
remotely through Dr. Ren’s website
http://ren.che.ufl.edu/app/realtimesensing.htm
University of Florida
NHA Hydrogen Conference, March 31, 2008
Conclusions
GaN-based sensors demonstrate rapid response (<1s) and
reversibility
Sensitivity is improved under reverse bias and elevated
temperature
Response can be related to hydrogen concentration
Differential sensor devices eliminate sensitivity to
temperature and voltage drifts
TiB2 can be used in ohmic contacts to improve reliability
These sensors have been implemented in a wireless
detection circuit
Field testing is underway at Greenway Ford, Orlando, FL
University of Florida
NHA Hydrogen Conference, March 31, 2008
Acknowledgements
This work at UF is supported by:
1. ONR (N00014-98-1-02-04, H. B. Dietrich)
2. NSF(CTS-0301178, monitored by Dr. M. Burka
and Dr. D. Senich)
3. NASA Kennedy Space Center Grant NAG 10-316
monitored by Mr. Daniel E. Fitch
4. Florida Department of Environmental Protection,
U.S. Dept. of Energy(DE-FG26-05R410962 by
Jill Stoyshich)
University of Florida
NHA Hydrogen Conference, March 31, 2008
Hydrogen Sensing Test
Schematic illustration of gas sensor system
University of Florida
NHA Hydrogen Conference, March 31, 2008
Room Temperature Test
University of Florida
NHA Hydrogen Conference, March 31, 2008
50 °C Test
University of Florida
NHA Hydrogen Conference, March 31, 2008
Comparison of Pd and Pt
[1]
[3]
[2]
Reference:
[1] W. Eberhardt, F. Greuter, E. W. Plummer, Phys. Rev. Lett. 46, 1085 (1981).
[2] http://www.rebresearch.com/H2sol2.htm
[3] http://www.rebresearch.com/H2perm2.htm
University of Florida
NHA Hydrogen Conference, March 31, 2008
Gas Sensing Devices
Schottky diode [1]
HEMT[2]
Resistor[3]
[1] B. S. Kang, F. Ren, B. P. Gila, C. R. Abernathy and S. J. Pearton, Appl. Phys. Lett. 84 1123 (2004).
[2] B. S. Kang, R. Mehandru, S. Kim, F. Ren, R. C. Fitch, J. K. Gillespie, N. Moser, G. Jessen, T. Jenkins, R. Dettmer, D. Via, A. Crespo, B.
P. Gila, C. R. Abernathy and S. J. Pearton, Appl. Phys. Lett. 84 4635 (2004).
[3] H. T. Wang, B. S. Kang, F. Ren, L. C. Tien, P. W. Sadik, D. P. Norton, S. J. Pearton, Jenshan Lin, Appl. Phys. Lett. 86 243503 (2005).
University of Florida
NHA Hydrogen Conference, March 31, 2008