Wireless Hydrogen Sensor Networks Using GaN-Based Devices

Fan Ren1, Jenshan Lin2, Stephen Pearton3 , Hung-Ta Wang1, Changzhi Li2, Zhen Ning Low2, Xiaogang Yu2,

Travis Anderson1, and Byoung Sam Kang1, and John Painter4

1 University of Florida, Chemical Engineering2 University of Florida, Electrical and Computer Engineering3 University of Florida, Materials Science and Engineering 4 J Painter Consulting LLC, Deltona, FL 32738

NASA Funded Hydrogen Research at UF

• $10M funding over 4 years• 27 Projects• 60 Faculty members, post-docs, and graduate

students combinedUF NASA Funded Hydrogen Research Web Site:

http://www.mae.ufl.edu/NasaHydrogenResearch

NASA Funded Hydrogen Research at UFResearch Thrust Areas• Fuel Cells (PEM and SOFC)• Hydrogen Production, Storage, and Transport• Nano Sensors - Hydrogen Leak Detection

Gas inlet

H2

Gas outlet Single Crystal NanowiresHydrogen-Selective Sensing at Room Temperature with

ZnO NanorodsH2 Production

PEM FC micro grids & Cooling Plate

Motivation

Application fields:• Fuel leak detection for

automobile, space shuttle, and aircraft.

• Fire detection (CO, CO2).• Emission, hydrocarbon,

and health monitor.• Environmental control.

Why AlGaN/GaN HEMT ?• GaN device technology is commercially available (blue LED)• Wide range band gap(6.2-3.4eV) for high temperature operation• Outstanding mechanical and electronic properties• Chemical inertness (only NaOH at 450oC), harsh environment• High electron mobility without impurity scattering- fast response -

excellent sensitivity-signal amplification• Different sensors can be integrated in a single chip

GaNAlGaN

GaN Diode Fabrication

50 µm

Optical microscopic image

GaN

Sapphire

Al0.28Ga0.72N

Ti/AuPt

SiNx

Ti/Al/Pt/Au

Device Cross-section

2DEG

• H2→2H• Diffusion of H• Creation of a polarized

layer at the interface• Barrier-lowering• H2(gas) ↔ 2HS ↔ 2Hb ↔ 2Hi

Pd, Pt

Hi Hi

Semiconductor

H2

Hs Hs

Hb Hb

Sensing Mechanism

Experimental Results

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0

4

8

12

16

20

Cu

rren

t(m

A)

Biased Voltage (V)

Nitorgen

1% Hydrogen

−

−

= 1expexp2**F

nkTeV

kTq

TAJ Bφ ; ? ? B~ -50 meV @ room T

GaN/AlGaN HEMT Sensor for Hydrogen

Source

Source

Gate Drain

GaN

Sapphire

AlGaN

Ti/Al/Pt/AuTi/Au

Pt

Hardware Design

AC Wall Transformer

Regulator Regulator

Battery Backup Control

+−

+−

Sensor

Reference

ZigBeeTransceiver

Internet

Wireless Network ServerInternet Server

Cell Phone

Microcontroller

Battery/Energy Harvest

R0

R0

Ω1M

Ω1M

Ω2M

Ω2M

Vout

YES

NO

YESNO

Initialization

SLEEP

Timer set?

Collect Data

Analyze DataThresholdDetected? Transmit Pulse

Warm up: 30 seconds 1s5s

MonitorTx data

MonitorTx data

MonitorTx data

MonitorTx data

Power Up

Power Down

1s5s 1s5s 1s5s

State flow diagram of level monitoring

Robust Detection of Hydrogen Using AlGaN/GaN HEMT Sensing Diodes

Sensor 1 Above Car Bay

Sensors 4 And 6 Above Bus Bay

Field Test

Practical Problem-False Alarm

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0

4

8

12

16

20

Cu

rren

t(m

A)

Biased Voltage (V)

Nitrogen

1% Hydrogen

Room temperature 50 °C

1. Thermal effect on semiconductor and Schottky contact.2. Voltage drift

Differential Diodes

Optical microscopic image

Robust Detection of Hydrogen Using Differential AlGaN/GaN Sensing Diodes

http://ren.che.ufl.edu/app/default.aspx

Wireless Monitoring of Hydrogen Detection

Wireless Sensor Module

Client can deactivate alarm

Wireless pH Remote version 1.1

Features• Reconfigurable over-the-air• Ultra-low-power• 2.4Ghz wireless• Rechargeable battery• Different sensors can be implemented with

minimal design changes

Sensor

Nordic2.4Ghz TransceiverMSP430F2013Power

ManagementBattery

Conclusions

n GaN-based sensors demonstrate rapid response (<1s) and reversibility

n Differential sensor devices eliminate sensitivity to temperature and voltage drifts

n TiB2 can be used in ohmic contacts to improve reliabilityn These sensors have been implemented in a wireless

detection circuitn Field testing is underway at Greenway Ford, Orlando, FLn We are seeking investors for a startup company