1. Metal Nanoparticle Hydrogen Sensor
Igor Pavlovsky, Applied Nanotech, Inc.

2. Outline
Review of Pd-based sensor technologies
ANI approach: Pd nanoparticles
Why NANO?
Performance of ANI sensors
Applications and prospects

3. Proposed Technologies
Pd thin film resistor
FET with Pd gate
Pd-coated quartz microbalance
Pd mesowires
Optical methods
Catalytic combustion
Pd nanoparticle network

4. Problems with Pd-based approach
Pd delamination at high H2 concentration due to phase transition in Pd
Limited temperature range (-30 to 50oC)
Low sensitivity in the ppm range
Poisoning (esp. catalytic sensors)
Repeatability and consistency
Cost (manufacturing + testing + QC)

5. Other technologies “Physical” sensors (thermal conductivity etc)
Poor sensitivity at low H2 concentrations
Non-selective to hydrogen
Metal oxide sensors
Require heating, cross-sensitive to reducing gases (e.g. hydrocarbons, CO)
Gas chromatography
Expensive, high power consumption, large size
Electrochemical
Limited temperature range, lower sensitivity to H2 and higher cross-sensitivity to H2O

6. ANI approach: Pd nanoparticles
Smaller Pd nanoparticles make a difference:
Subsurface Pd-H sites form prior to bulk phase change
Lower detection limit
Smooth phase transition
Wide dynamic range
H2 Pressure
Principle of sensor operation: decrease in resistance as Pd nanoparticles change phase
(Pd + H2 → Pd + 2H → PdHx)
bulk
nano
H/Pd ratio

7. Sensor Processing Diagram
Glass
substrate
cleaning
Metal film
deposition
Sensor
Patterning
Contact
pads
deposition
Wafer
dicing
Photograph of a 100-sensor
pattern on a glass wafer
Testing
Conditioning
Electro-
plating
Quality
Control
Packaging
Chip
dicing

8. Pd alloy sensor design
Working
Reference
SEM
Sensor
outline

9. Response of sensor to hydrogen

10. Response of sensor to hydrogen

11. Specifications Operating temperature: -30°C to 120°C
Storage temperature: °C to 80°C
Typical resistance: kΩ
Sensor Power: mW
System Power (w/TEC): ~ 1 W
Operation Range: ppm – 10,000 ppm
Lowest detection limit: ppm
Response Time (t90): sec at 1% H2
Accuracy: ±20% of H2 reading
Repeatability: ±20% of H2 reading

12. Flammability and explosive levels for mixtures of H2 with air
Range of applications
Flammability and explosive levels for mixtures of H2 with air 4%
17%
56%
75%
▲LFL
▲LEL
▲UEL
▲UFL
ppm 1 10
100
1000 1% 4%
Sensitivity range for H2 ANI sensor
Fuel cells
H2 storage tanks
H2 leak detectors
H2 production facilities
Reformers
Power transformers

13. H2 Monitoring in Transformer Oil
Oleophobic
membrane
Sensor response to different H2 concentrations in transformer oil (top left)
Sensor package for use in liquids (top right)

14. Features of ANI H2 sensor
Easy to manufacture
Wide range of sensitivity
Good repeatability
Low cost in volume
Membrane/mesh
TO8/TO5 header
Hermetic package
Easy integration

15. Future development Miniaturization Built-in temperature sensor
Built-in calibration chip
Application-specific design
Functional membranes