2 August 2007 Jon Brame

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 541Began as an NASA ESMD Student-Faculty Program

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Overview

1. Project Motivation and Goal2. Fabrication Process 3. Outcomes

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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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GoldSi02

Si

Needle

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Prototype

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Process: Catalyst

• Indirect Iron Catalyst Deposition

Vacuum Chamber for Thin Film Deposition

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Process: SWCNT Growth

• Chemical Vapor Deposition (CVD) SWCNT Growth

CVD Growth Furnace

Diagram of CVD Growth Process

SEM Image of SWCNT Mat

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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-Iron-

Chrome– Lift-off

Diagram of SWCNT network, contact pads and iron needle

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Process – Trench• Lithography

(manual)• Etching

– Buffered Oxide Etch

– KOHDiagram of completed device

Au

Au

SWCNTs

Remnantneedle

Trench

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Results

• Completed Magnetometer Prototype

Successfully etched trench with SWCNT spanning gap between gold electrodes

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Results

• Magnetic Field Measurement Testing

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Micrograph of Test Structure

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Gold pad

SWCNT mat

Iron needle

Trench

alignment mark

“Rolled-up” SWCNT mat

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5400

5450

5500

5550

5600

5650

0 200 400 600 800 1000

Time in seconds (Magnet Current Ramping Up)

Dev

ice

Cur

rent

(nA

)

a b

c

Device resistance decreases as magnetic field is increased,

• At some point contact with one of the pads becomes intermittent leading to the noisy signal during time period c

500 seconds into the experiment the field is ramped down (b)Experimental Results

Note: Behavior during a & b are the opposite of what was expected to happen.

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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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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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AcknowledgementsBryan 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

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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