Atomic Layer Deposition of Zirconium
Oxide for Fuel Cell Applications
UIC REU – Summer 2011
AMReL Lab, UIC
Department of Bioengineering and
Department of Chemical Engineering
Christine James
University of Michigan, Department of Chemical Engineering
Overview
•
•
•
•
Background
Atomic Layer Deposition
Data Collected
Future Work
Fossil fuel
Fuel Cell Advantages
• Provides clean energy
– Hydrogen fuel cells
– only emit water
2007
Natural
Gas 23 %
Coal 23 %
Nuclear
Power 8 %
• Very efficient
Renewable
Energy 6 %
– Fuel Values
• Hydrogen: 141.8 kJ/g
• Gasoline: 48 kJ/g
• Coal: 15-27 kJ/g
Santhanam et al., Introduction to Hydrogen
Technology, 2009, Hoboken, NJ: J. Wiley.
Petroleum 40 %
Source: US Energy
Information Agency
Environmentally friendly
Sections of the Fuel Cell
• Cathode
– Oxygen is reduced
SOFC FUEL CELL
Electrical Current
Fuel In
Air In
• Electrolyte
– Transports the oxygen ions
• Anode
– Hydrogen is oxidized
Excess
Fuel and
Water
Unused
Gases
Out
www1.eere.energy.gov
Solid Oxide Fuel Cells (SOFCs)
• Current SOFCs are high temperature
– Temperature: about 1000 °C
• Intermediate Temperature Fuel Cells
– Temperature: 600-800°C
– Smaller scale applications
– Allows use of alternate materials
– Starts and stops faster
– Reduces corrosion
– Offers a wide range of possibilities
Problem with Reducing Temperature
• High temperatures needed to transport O2- ions
– Requirement can be as high as 1200° C
– Low temperatures cause ionic resistance
Approach
• Deposit electrolytes and analyze
– Samples from atomic to bulk-like thickness
– Method to be used:
• Atomic Layer Deposition
• Deposit oxide layers on silicon then platinum (Pt)
Atomic Layer Deposition (ALD)
Tri-methyl
aluminum
Al(CH3)3(g)
Methyl group
(CH3)3(g)
Hydroxyl (OH)
from surface
absorbed H2O
Methane reaction
product CH4
Reaction of
TMA with OH
H2 O
www.cambridgenanotech.com/ald
Chosen Precursor
www.aloha.airliquide.com
Precursors
Metal Precursor O source
ZyALD
Ozone
Growth Temperature
Range (°C) Preferred (°C) Saturation verified
at 300 °C
250-400
300
Yes
Niinistö, et al., Advanced Engineering Materials, 2009, 11, No.4, 223.
Impurities
C [-at%] H [-at%]
<1
N.R.
ALD System
ZyALD
ZyALD
Pulse and Purge times required
Reactor Temperature: 300°C
Bubbler Temperature: 50°C
Bubbler Pressure: 10 torr
Precursor: ZyALD
6s
Precursor Pulse Time: Varied
Precursor Purge Time: 10
20
s
Varied
1ss
1.5
Oxidizer Pulse Time: Varied
Oxidizer Purge Time: 17
Varied
s
Run for 40 cycles
Zr
(Å/cycle)
Growth
Rate
(Å/cycle)
Growth
Rate
(Å/cycle)
Growth
(Å/cycle)
Growth
RateRate
1111
0.95
0.95
0.9
0.95
0.9
0.9
0.8
0.9
0.85
0.85
0.8
0.8
0.85
0.7
0.75
0.75
0.60.8
0.7
0.7
0.75
0.5
0.65
0.65
0.7
0.4
0.6
0.6
2
20.2
12
www.cambridgenanotech.com/ald
4
0.4 13
3 0.6
6
140.84
8
115
10
5 1.2 16
12
14
1.4 6 171.6
1.8
18
7
Precursor
PurgeTime
Time(s)
(s)
Precursor
Oxidizer
Oxidizer Pulse
Purge
Time
(s)
Temperature Window
Reactor Temperature: Varied
Bubbler Temperature: 50°C
Bubbler Pressure: 10 torr
Precursor: ZyALD
2
Growth Rate (Å/cycle)
1.8
1.6
1.4
1.2
Temperature
Window
1
0.8
0.6
Precursor Condensation
Precursor Decomposition
0.4
0.2
0
50
100
150
200
250
Temperature (°C)
300
350
400
Comparison to Work from another
group
Growth Rate (Å/cycle)
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
225
Niinistö, et al., J. Mater. Chem. 18, 5243 (2008).
250
275
300
Temperature (°C)
325
350
Thickness vs. Cycles Run
Reactor Temperature: 300°C
Bubbler Temperature: 50°C
Bubbler Pressure: 10 torr
Precursor: ZyALD
160
Thickness (Å)
140
120
Slope: .87
R² = 0.9973
100
80
60
40
20
0
0
50
100
Number of Cycles Run
150
Future Work
1. Deposit the zirconium oxide on Platinum
2. Run electrochemical analysis
Electrolyte: Zirconium Oxide
Silicon
Platinum
Substrate
Summary
• Goal is to lower operating temperature of the fuel cell
– By decreasing electrolyte layer thickness
• Atomic Layer Deposition (ALD) is being used
• Have determined some necessary parameters:
– Pulse and Purge times
– Temperature Window for ALD
• Have compared cycles and thickness
– Proved linear relationship
• Next Steps:
– Deposit on Platinum
– Run Electrochemical analysis
Acknowledgements
• National Science Foundation
– EEC-NSF Grant # 1062943
• Graduate Mentor: Runshen Xu
• Professor Takoudis and Professor Jursich