University of Florida NHA Hydrogen Conference, March 21, 2007 Wireless Hydrogen Sensor Networks Using GaN-based Devices Travis Anderson 1, Hung-Ta Wang 1, Byoung Sam Kang 1, Fan Ren 1, Changzhi Li 2, Zhen Ning Low 2, Jenshan Lin 2, Stephen Pearton 3 1 University of Florida, Chemical Engineering 2 University of Florida, Electrical and Computer Engineering 3 University of Florida, Materials Science and Engineering

University of Florida NHA Hydrogen Conference, March 21, 2007 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:

University of Florida NHA Hydrogen Conference, March 21, 2007 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 H2H2 Gas outlet Single Crystal Nanowires Hydrogen-Selective Sensing at Room Temperature with ZnO Nanorods H 2 Production PEM FC micro grids & Cooling Plate

University of Florida NHA Hydrogen Conference, March 21, 2007 Motivation Application fields: Fuel leak detection for automobile, space shuttle, and aircraft. Fire detection (CO, CO 2 ). Emission, hydrocarbon, and health monitor. Environmental control.

University of Florida NHA Hydrogen Conference, March 21, 2007 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 21, 2007 Device Fabrication 50 µm Optical microscopic image GaN Sapphire Al 0.28 Ga 0.72 N Ti/Au Pt SiN x Ti/Al/Pt/Au Device Cross-section 2DEG

University of Florida NHA Hydrogen Conference, March 21, 2007 Sensing Mechanism H 2  2H(chemisorption on Pt) Diffusion of H atom. H 2 (gas)  2H s  2H b  2H i Creation of a polarized layer at the interface Decrease of barrier height. (Schottky diode); increase of channel cross-section. (FET) H2H2 HsHs HbHb 2DEG HiHi Pt AlGaN GaN

University of Florida NHA Hydrogen Conference, March 21, 2007 Experimental Results ; ΔФ B ~ -50 room T

University of Florida NHA Hydrogen Conference, March 21, 2007 Practical Problem-False Alarm 50 °C 1. Thermal effect to semiconductor and Schottky contact. 2. Voltage drift

University of Florida NHA Hydrogen Conference, March 21, 2007 Differential Diodes Optical microscopic image

University of Florida NHA Hydrogen Conference, March 21, % Hydrogen Test

University of Florida NHA Hydrogen Conference, March 21, 2007 Hardware Design

University of Florida NHA Hydrogen Conference, March 21, 2007 Wireless Sensor Module Client can deactivate alarm

University of Florida NHA Hydrogen Conference, March 21, 2007 Field Test

University of Florida NHA Hydrogen Conference, March 21, 2007 Conclusions GaN-based sensors demonstrate rapid response (<1s) and reversibility Differential sensor devices eliminate sensitivity to temperature and voltage drifts TiB 2 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 We are seeking investors for a startup company

University of Florida NHA Hydrogen Conference, March 21, 2007 Acknowledgements This work at UF is supported by: 1. NSF (CTS , monitored by Dr. M. Burka and Dr. D. Senich) 2. NASA Kennedy Space Center Grant NAG monitored by Mr. Daniel E. Fitch.

University of Florida NHA Hydrogen Conference, March 21, 2007 Hydrogen Sensing Test Schematic illustration of gas sensor system

University of Florida NHA Hydrogen Conference, March 21, 2007 Room Temperature Test

University of Florida NHA Hydrogen Conference, March 21, °C Test

University of Florida NHA Hydrogen Conference, March 21, 2007 Comparison of Pd and Pt Reference: [1] W. Eberhardt, F. Greuter, E. W. Plummer, Phys. Rev. Lett. 46, 1085 (1981). [2] [3] [2][2] [1][1] [3][3]

University of Florida NHA Hydrogen Conference, March 21, 2007 Gas Sensing Devices Resistor[3]Schottky diode [1]HEMT[2] [1] B. S. Kang, F. Ren, B. P. Gila, C. R. Abernathy and S. J. Pearton, Appl. Phys. Lett (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 (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 (2005).