Electrical Characterization of Nanowires Steven Kuo San Jose State University Thesis Advisor Dr. Emily Allen San Jose State University Research Advisor.

Electrical Characterization of Nanowires

Steven Kuo

San Jose State University

Thesis Advisor

Dr. Emily Allen

San Jose State University

Research Advisor

Dr. Geetha R. Dholakia

NASA AMES Center for Nanotechnology

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Task

Synthesis of nanowires by templated sol-gel growth and structural and electronic studies for applications in spin-based devices.

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Outline

Background Research Tasks Methods Results Summary of Work

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Why Nanotechnology?

Limit in today’s electronic device process

Need alternate method to continue shrinking

Nanowires - key group of nanoscale materials in developing devices

Nanoelectronics benefit from knowledge of material characteristics

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Why do we need to characterize nanowires?

Bulk properties differ from nanoscale properties Surface and grain boundary scattering

Need a method of electrical character… nanoscale materials in order to produce useful devices

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Electrical properties need to be studied…but how?

Current method of electrical characterization

Wire diameter is microns wide

What happens when…

Wire diameter is only nanometers wide?

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Research Tasks Task 1: Separation and alignment of nanowires

Removal of nanowires from Quick and easy manipulation of nanowires onto contact pads of

devices Task 2: Setup IV Measurement System

MMR Technologies Cryocooler LabVIEW Instrument interface

Task 3: IV Measurements Determine electrical characteristics of nanowires by a 4 probe

method Resistivity measurements across temperature range of

80K – 400K Determine band gap information for semiconducting nanowires

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Research Steps

Part 1: Liberate nanowires from anodized alumina template (completed)

Part 2: Align nanowires using electric field (completed)

Part 3: Setup temperature dependent measurement system (completed)

Part 4: Band gap measurements on single nanowire

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Band gap information can be determined

From 4 probe measurements Resistivity can be

determined From the relationship

ρ=1/σ Conductivity can be

determined Plot ln σ vs. 1/T Using the equation

where x is 1/T og xk

E ln

2ln

Eg is the band gap of the material

1/T

ln σ

-Eg/2k

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How do we manipulate nanowires when they are so small?

Dielectrophoresis Force which acts on any polarizable object in a

nonuniform electric field

Electrodes

NanowireElectric field

)()( 2rmsmDEP EKF

i

m

mprodK

Re)( where

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E-Field Modeling

Simulation of the expected e-field was calculated using Maxwell software

E-Field expected to be strongest at corners between the electrodes

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E-Field Alignment Device Design and Fabrication

Interdigitated electrodes fabricated at Microelectronics Process Engineering Lab at SJSU

Interdigitated electrodes 3-6 um spacings

200nm Al on 700nm SiO2 insulating layer

4 in. wafer with approx. 33 devices

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Finished Electrode Devices

SEM images of fabricated devices

Optical images of finished wafer and single device

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Nanowire removal from template

AAT removed with NaOH

Nanowires released by sonication

BIG Problem!!

Anodized Alumina Template

TiO2 Nanowires

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E-Field Alignment of Nanowires on Devices TiO2 nanowires are

aligned across 3 – 6 um spaced electrodes by an AC bias 25Hz – 30MHz 10 Vpp

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Temperature Dependent Resistivity Measurements

MMR Technologies Cryocooler 80K – 400K temperature range Verified to 80K

Keithley Electrometer and Current Source LabVIEW interface to control electrometer and current source

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Ongoing Work

Redesign of the test device for accommodation in the MMR cryocooler

Possible new electrode design (not to scale)

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Summary of Work to Date

Nanowire alignment on electrodes has been achieved

Temperature dependent resistivity measurement system completed

Publications Steven Kuo, Geetha R Dholakia and E. L. Allen, “Self

assembly of TiO2 nanowires onto devices by dielectrophoresis,” accepted for poster presentation Spring Materials Research Society Meeting, San Francisco (March 2007).

Geetha R Dholakia , Steven Kuo and E. L. Allen “Self assembly of organic nanostructures and dielectrophoretic assembly of inorganic nanowires,” accepted for presentation at American Physical Society Conference, April 2007.

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Work to be Completed by Aug 07

Task 3: New mask devices

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Acknowledgements

DMEA Grant H94003-06-2-0605 Ms. Rebka Endale, SJSU Dr. Ann Marshall, Stanford

Nanocharacterization Lab Mr. Neil Peters, Microelectronics

Process Engineering Lab Ms. Anastasia Micheals, SEM Lab