Thermal and Thermoelectric Characterization of Nanostructures

1
Thermal and Thermoelectric Characterization of
Nanostructures

• Li Shi, PhD
• Assistant Professor
• Department of Mechanical Engineering
• Center for Nano and Molecular Science and
  Technology,
• Texas Materials Institute
• The University of Texas at Austin
• Tutorial on Micro and Nano Scale Heat Transfer,
  2003 IMECE

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Outline

• Scanning Thermal Microscopy of Nanoelectronics
• Thermoelectric Measurements of Nanostructures

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Silicon Nanoelectronics

• Heat dissipation influences speed and
  reliability
• Device scaling is limited by power dissipation

IBM Silicon-On-Insulator (SOI) Technology
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Carbon Nanoelectronics
TubeFET (McEuen et al., Berkeley)
Nanotube Logic (Avouris et al., IBM)

• Current density 109 A/cm2
• Ballistic charge transport

V
-
5
Thermometry of Nanoelectronics
Techniques
Spatial Resolution
Infrared Thermometry
1-10 mm Laser Surface Reflectance
1 mm Raman Spectroscopy
1 mm Liquid Crystals
1 mm Near-Field
Optical Thermometry lt 100 nm
Scanning Thermal Microscopy (SThM) lt 100 nm
Diffraction limit for far-field optics
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Scanning Thermal Microscopy
Atomic Force Microscope (AFM) Thermal
Probe
Laser
Deflection Sensing
Cantilever
Temperature sensor
Sample
X-Y-Z Actuator
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Microfabricated Thermal Probes
Pt Line
Tip
Pt-Cr Junction
Laser Reflector
SiNx Cantilever
Cr Line
Shi, Kwon, Miner, Majumdar, J. MicroElectroMechani
cal Sys., 10, p. 370 (2001)
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Thermal Imaging of Nanotubes
Multiwall Carbon Nanotube
Topography
Topography
3 V
m
88
A
m
m
1
m
1
m
Spatial Resolution
V)
m
50 nm
Thermal signal (
Distance (nm)
Shi, Plyosunov, Bachtold, McEuen, Majumdar, Appl.
Phys. Lett., 77, p. 4295 (2000)
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Metallic Single Wall Nanotube
Topographic
Thermal
DTtip
A
B
C
D
2 K
0
1 mm
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Polymer-coated Nanotubes
Topography
Thermal
After coating
Before coating
-2 V, 4.4 mA
2 V, 7.8 mA
1 mm
GND
GND

• Asymmetric heating at the two contacts

The polymer melted at a 3V bias
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Future Challenge Temperature Mapping of
Nanotransistors
SOI Devices
SiGe Devices

• Low thermal conductivities of SiO2 and SiGe
• Interface thermal resistance
• Short (10-100 nm) channel effects (ballistic
  transport, quantum transport)
• Phonon bottle neck (optical-acoustic phonon
  decay length gt channel length)

• Few thermal measurements are available to verify
  simulation results

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Thermal Transport in Nanostructures
Carbon Nanotubes
Hot
Cold
p

• Long mean free path l
• Strong SP2 bonding high sound velocity v
• ? high thermal conductivity k Cvl/3 6000
  W/m-K
• Below 30 K, thermal conductance ? 4G0 ( 4 x
  10-12T) W/m-K, linear T dependence (G0 Quantum
  of thermal conductance)

Heat capacity
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Semiconductor Nanowires
Nano-patterned Si Nanotransistor (Berkeley
Device group)
VLS-grown Si Nanowires (P. Yang, Berkeley)
Gate
Drain
Source
Nanowire Channel
Hot Spots

• Increased phonon-boundary scattering
• Modified phonon dispersion
• ? Suppressed thermal conductivity
• Ref Chen and Shakouri, J. Heat Transfer 124, 242

Hot
p
Cold
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Efficient Peltier Cooling using Nanowires
Bi Nanowires
Thermoelectric figure of merit
Low k ? high COP
Dresselhaus et al., Phys. Rev. B. 62, 4610
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Thermal Measurements of Nanostructures
Suspended SiNx membrane
Long SiNx beams
Pt resistance thermometer
Kim, Shi, Majumdar, McEuen, Phys. Rev. Lett. 87,
215502 Shi, Li, Yu, Jang, Kim, Yao, Kim,
Majumdar, J. Heat Tran 125, 881
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Sample Preparation

• Dielectrophoretic trapping

• Wet deposition

     
Chip
SnO2 nanobelt
Nanotube bundle
Individual Nanotube
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Thermal Conductance Measurement
-
1
-
1
T
G
G
T
-
1
G
h
b
s
b
T
T
0
0
Q
2QL
Q
h
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Measurement Errors and Uncertainties

• Contact Resistance

d
d 2
-- G-1Sample /G-1Contact decreases with d, and is
estimated to larger than 10 for measurements
reported here

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Carbon Nanotubes
CVD SWCN

• An individual nanotube has a high k 2000-11000
  W/m-K at 300 K
• The diameter and chirality of a CN may be probed
  using Raman spectroscopy
• k of a CN bundle is reduced by thermal
  resistance at tube-tube junctions

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SnO2 Nanobelts
Phonon scattering rate
64 nm
64 nm
53 nm
39 nm
Umklapp Boundary Impurity
Collaboration N. Mingo, NASA Ames
tU-1 tU,bulk-1 ti-1 ti,bulk-1 tb-1 v/FL
v phonon group velocity FL effective
thickness
53 nm
53 nm, ti-1 10t-1i, bulk
Circles Measurements Lines Simulation using a
Full Dispersion Transmission Function approach

• Phonon-boundary scattering is the primary effect
  determining the suppressed thermal conductivities

Shi, Hao, Yu, Mingo, Kong, Wang, submitted
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Si Nanowires
Symbols Measurements Lines Simulation using a
modified Callaway method

• Phonon-boundary scattering is the primary effect
  determining the suppressed thermal conductivities
  except for the 22 nm sample, where boundary
  scattering alone can not account for the
  measurement results.

Li, Wu, Kim, Shi, Yang, Majumdar, Appl. Phys.
Lett. 83, 2934 (2003)
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Seebeck Coefficient
Th
S VTE / (Th Ts)
I

• Oxygen doped
• Quasilinear (metallic) behavior
• Phonon drag effect at low T

Ts
VTE
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Future ChallengeNanomanufacturing of Nanowire
Arrays as Efficient Peltier Devices

• Nano- imprint Pattering of Thermoelectric
  Nanowire Arrays

10 nm Cr nanowire array
40 nm Cr nanowire array

• Test-bed Peltier devices for cooling IR sensors

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Summary

• Scanning Thermal Microscopy of Nanoelectronics
• -- Thermal imaging with 50 nm spatial resolution
• Thermoelectric (k, s, S) Measurements of
  Nanostructures Using a Microfabricated Device
• -- Super-high k of nanotubes
• -- Suppressed k of nanowires

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Acknowledgment

• Students
• Choongho Yu Jianhua Zhou Qing Hao Rehan
  Farooqi Sanjoy Saha
• Anastassios Marvrokefalos Anthony Hayes Carlos
  Vallalobos
• Collaborations
• UC Berkeley Arun Majumdar Deyu Li (now at
  Vanderbilt) Philip Kim (now at Columbia) Paul
  McEuen (now at Cornell) Adrian Bachtold (now at
  Paris) Sergei Plyosunov
• UT Austin C. K. Ken Shih Ho-Ki Lyeo Zhen
  Yao Brian Korgel
• GaTech Z. L. Wang
• NASA Natalio Mingo
• UCSC Ali Shakouri
• MIT Rajeev Ram Kevin Pipe
• Support
• NSF CTS (CAREER Instrumentation)