Atomic Layer Deposition of
Cerium Oxide for Solid Oxide
Fuel Cells
Rachel Essex,
Rose-Hulman Institute of Technology
Jorge Ivan Rossero Agudelo, Christos G. Takoudis,
Gregory Jursich
University of Illinois at Chicago
1
Benefits of Solid Oxide Fuel Cells as
Alternate Power Source
No NOx, SOx, or hydrocarbon emissions
 Reduced CO2 emissions
 Fuel flexibility
 Higher power density than batteries
 High efficiency

R.M., Ormerod: Chemical Society Reviews, 2003, 32, 17-28.
2
How a Solid Oxide Fuel Cell Works
O2 (air)

Solid oxide fuel cells
components:
◦ Cathode
◦ Solid inorganic oxide
electrolyte
◦ Anode
O-2
Cathode
e-
Electrolyte
Anode
CO2
H2 and CO
and
Fuel
H2 O
(hydrocarbon and
steam or oxygen)
R.M., Ormerod: Chemical Society Reviews, 2003, 32, 17-28.
3
The biggest setback for solid oxide
fuel cell use is the high operating
temperature
Operating temperature: 800-1000 ºC
 Long heat up and cool down periods
 Limited materials

M. Cassir and E. Gourba: Annales de Chimie Science des Matériaux, 2001, 26,
49-58.
4
Decreasing Operating Temperatures
New materials with lower ion resistivity
 Decreasing thickness can increase ion
permeability
 Thickness can be decreased using thin
films

M. Cassir and E. Gourba: Annales de Chimie Science des Matériaux, 2001, 26,
49-58.
5
Deposition of thin films

Physical vapor deposition -thin film
deposition method by the condensation
of a vaporized form a desired material
onto surface
o Purely physical process
o High temperature vacuum
evaporation or plasma sputter
bombardment
6
Deposition of thin film (con’t)

Chemical vapor deposition -chemical
process used to produce high-purity, highperformance solid materials
◦ Metal organic chemical vapor deposition
(MOCVD)
◦ Atomic Layer Deposition (ALD)
7
Atomic Layer Deposition
Each exposure to precursor saturates the
surface with a monolayer
 Purge of inert gas in-between precursor
exposures
 Each cycle creates one monolayer

S.M. George: Chem. Rev., 2010, 110, 111-131
8
Atomic Layer Deposition is a cyclic
process consisting of four steps
Step One: Substrate
is exposed to
precursor
substrate
Step Two: Reactor is
purged of first
precursor
substrate
9
Step Three: Substrate
is exposed to
coreactant
substrate
Step Four: Reactor is
purged of coreactant
and byproducts
substrate
Process is repeated until the
film is at the desired thickness
10
Cerium oxide was created using
atomic layer deposition





Precursor:
tris(i-propylcyclopentadienyl)cerium
Coreactant/Oxidizer: water
Purge and Carrier Gas: Nitrogen
Uses in solid oxide fuel cells: anode and
electrolyte
Cerium oxide has lower ion resistivity at lower
temperatures than yttrium stabilized zirconium
11
Goals of This Project

Find optimum ALD conditions including:
◦
◦
◦
◦
◦
Precursor Temperature
Oxidizer Pulse Length
ALD window
Saturation Curve
Linear Growth
12
ALD Operating Conditions
TReactor
170 mTorr
Plug: short time
pulse of precursor
160 ºC
150 ºC
140 ºC
130 ºC
Q. Tao, Ph.D. Thesis, University of Illinois at Chicago, 2011
13
Growth Rate, Å/cycle
Precursor Temperature of 140 ºC
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
225
230
235
240
245
250
255
Reactor Temperature, °C
14
50 ms Water Pulse
Growth Rate, Å/cycle
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
2
4
6
8
10
Number of Plugs
15
Growth Rate, Å/Cycle
ALD Window
2.3
2.0
1.8
1.5
1.3
1.0
0.8
0.5
0.3
0.0
180
200
220
240
260
280
300
Temperature, °C
Conditions: 170 mTorr, 130 °C Precursor Temperature, 140 °C
Valve Temperature, 150 °C Leg Temperature, 160 °C Manifold
Temperature, 50 Cycles, 55 ms Water Pulse, 6 plugs, Silicon Wafer
are cleaned with standard RCA-1 treating, Silicon Oxide Layer is
reduced using HF 2% giving a oxide layer of 8-10 Å
16
Saturation Curve
Growth Rate, Å/Cycle
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
2
4
6
8
10
12
Number of Plugs
Conditions: 170 mTorr, 130 °C Precursor Temperature, 140 °C Valve
Temperature, 150 °C Leg Temperature, 160 °C Manifold Temperature,
250 ºC Reactor Temperature, 50 Cycles, 55 ms Water Pulse, Silicon Wafer
standard RCA-1 treating, Silicon Oxide Layer is reduced using HF 2%
giving a oxide layer of 8-10 Å
17
Linear Growth
600
Thickness, Å
500
400
300
200
y=1.2x-5.4
R2=0.9954
100
0
0
100
200
300
Number of Cycles
400
500
Conditions: 170 mTorr, 130 °C Precursor Temperature, 140 °C Valve
Temperature, 150 °C Leg Temperature, 160 °C Manifold Temperature,
250 ºC reactor temperature, 5 plugs, 55 ms Water Pulse, Silicon Wafer
are cleaned with standard RCA-1 treating, Silicon Oxide Layer is reduced
using HF 2% giving a oxide layer of 8-10 Å
18
Conclusions

Optimum ALD conditions of cerium oxide
were found.
◦ Precursor Temperature: 130 ºC
◦ Oxidizer Pulse Length: 55 ms
◦ ALD window: 210-280 ºC- previous work
indicated the no ALD window existed when
tris(i-propylcyclopentadienyl)cerium was used
◦ Saturation: 4 plugs of precursor pulse and higher
◦ Linear growth: deposition follows a linear trend
with 1.2 Å/cycle
M. Kouda, K. Ozawa, K. Kakushima, P. Ahmet, H. Iwai, Y. Urabe, and T. Yasuda:
Japanese Journal of Applied Physics, 2011, 50, 6-1-6-4.
19
Future Work
Dope CeO2 films with yttrium and test as
electrolyte in solid oxide fuel cells
 Dope CeO2 films with nickel and test as
anode in solid oxide fuel cells

20
Acknowledgements
National Science Foundation, EEC Grant
# 1062943
 National Science Foundation, CBET Grant
# 1067424
 Air Liquide (provided the precursor)

21