Fabrication and Testing of a
Strain-Based Carbon
Nanotube Magnetometer
Structure
Jon A. Brame, Johnathan Goodsell,
Stephanie A. Getty¹, Y. Zheng¹
And David A. Allred
Brigham Young University
¹NASA GSFC Code 541
Began as an NASA ESMD Student-Faculty Program
2 August 2007
Jon Brame
Overview
1. Project Motivation and Goal
2. Fabrication Process
3. Outcomes
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Jon Brame
CNT Properties
• Change in Conductivity with Strain
– Tombler, et al
(Nature, 2000)
– Single tube
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CNT Properties
• Change in Conductivity with Strain
– Tombler, et al
(Nature, 2000)
– Single tube
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Motivation
• Space Magnetometry
– Spacecraft Orientation
– Magnetic Field Studies
• Planetary Exploration
– Astronaut/Rover
Orientation
– Planetary Geology
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Device Operation
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Gold
Si02
Needle
Si
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Prototype
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Process: Catalyst
• Indirect Iron Catalyst Deposition
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Vacuum Chamber for
Thin Film Deposition
Process: SWCNT Growth
• Chemical Vapor Deposition (CVD)
SWCNT Growth
CVD Growth Furnace
2 August 2007
Diagram
of CVD
Growth Process
Jon Brame
SEM Image of SWCNT Mat
Process – Electrical Contact
• Gold Contact Pads
– Detector Development Lab (DDL)
– E-Beam Lithography
– Deposition: Chrome(100Å)Gold(1000Å)
– Lift-off
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Process – Iron Needle
• Iron Needle
– Device Alignment
– E-Beam Lithography pattern
– Deposition: Chrome-IronChrome
– Lift-off
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Diagram of SWCNT network, contact pads and iron needle
Process – Trench
• Lithography
(manual)
• Etching
– Buffered
Oxide Etch
– KOH
Diagram of completed device
Au
SWCNTs
Trench
Au
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Remnant
needle
Results
• Completed Magnetometer Prototype
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Successfully etched
trench with SWCNT
spanning gap between gold electrodes
Results
• Magnetic Field Measurement Testing
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Micrograph of Test Structure
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alignment
mark
SWCNT mat
Gold pad
Iron needle
“Rolled-up”
SWCNT mat
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Trench
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Device
resistance
as
500
seconds
into thedecreases
experiment
Experimental
Results
magnetic
field isdown
increased,
the field is ramped
(b)
Device Current (nA)
5650
a
5600
b
5550
5500
5450
5400
• Note:
At someBehavior
point contact with
one of the
pads
becomes
during
a
&
b
are
the
intermittent leading to the
opposite
what
was
noisy signalof
during
time
period c
expected
to happen.
0
200
400
600
c
800
1000
Time in seconds (Magnet Current Ramping Up)
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CONCLUSIONS
1. A fabrication process for magnetometer test
structures has been demonstrated.
2. An array of prototype magnetometer test structures
has been successfully fabricated.
3. The test structures consist of a high aspect-ratio
iron needle suspended above a trench by a mat of
SWCNT. Gold pads electrically contact the SWCNT
mat. This fabrication process is now available and
being used in various field sensing applications.
4. Initial magnetic testing indicates that there is some
correlation between magnetic field and measured
resistance in the device.
5. Further device fabrication and testing is necessary
to establish the extent of this relationship.
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Jon Brame
The design for the next
iteration of gold-pad
geometry features three
separate sets of pads
(labeled a, b & c) to
contact specific sections
of nanotubes.
In this figure the black Xs
represents the nanotube
mat and the horizontal
line is the needle.
Dividing the pads into three
sets makes it possible to
uses the outer set of pads
(labeled a & c) to measure
the strain across the outer
portions of the nanotubes.
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Jon Brame
Acknowledgements
Bryan Hicks, Rachel Bis, Melissa Harrison
• Branch 541: Dewey Dove, D. Stewart
Bruno Munoz, Carl Taylor, Len Wang, D.
Rowland
• BYU: Prof. Richard Vanfleet, Dr. Jeffrey
Farrer, Prof. Robert Davis, David
Hutchinson
• Other: Lynda Goodsell, Bill Heaps
• Division 540; Dick Fahey; Joshua
Halpern; ESMD; Rocky Mountain Space
Grant
Consortium
Jon Brame
2 August
2007
We gratefully acknowledge financial
support from NASA GSFC Director’s
Discretionary Fund, the NASA Internal
Research and Development Fund , the
Rocky Mountain Space Grant
Consortium , and the Student/Faculty
Internship Program for the summers of
2006 and 2007 which provided support
for J. A. Brame, J. E. Goodsell, & D. D.
Allred
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Outcome: BYU Collaboration
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