ME 381R Lecture 10:

1
ME 381R Lecture 10 Thermal Measurement
Techniques for Thin Films and Nanostructured
Materials
Dr. Li Shi Department of Mechanical Engineering
The University of Texas at Austin Austin, TX
78712 www.me.utexas.edu/lishi lishi_at_mail.utexas.
edu
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Outline

• Thermal Property Measurements
• --Thin films
• --Nanowires and Nanotubes
• Thermal Microscopy
• Reading Ch2 in Tien et al

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Thin Films and Interfaces
GMR
Cu Interconnects
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Thin Film Thermal Conductivity Measurement
The 3w method Cahill, Rev. Sci. Instrum. 61, 802
(1990)
Metal line
Thin Film
L
2b
V

• I 1w
• T I2 2w
• R T 2w
• V IR 3w

I0 sin(wt)
Substrate
Substrate contribution
Film contribution
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Data Analysis

• Dotted line - ?Ts ? Tf
• Solid line - ? Ts
• Slope of solid line ? ks
• ?Tf ? kf

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Thermal Conductivity of Thin Si Films
(M.Asheghi,etc.,1997)
Size effect on the conductivity can exceed two
orders of magnitude for layers of thickness near
1 ?m at Tlt10k.
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Silicon on Insulator (SOI)
Ju and Goodson, APL 74, 3005
IBM SOI Chip
Lines BTE results
Hot spots!
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Thin Film Superlattices
SiGe superlattice (Shakouri, UCSC)

• Increased phonon-boundary scattering
• ?decreased k
• other size effects

? High thermoelectric figure of merit (ZT
S2sT/k)
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Thermal Conductivity of Si/Ge Superlattices
k (W/m-K)
Bulk
Si0.5Ge0.5 Alloy
Circles Measurement by D. Cahills group Lines
BTE / EPRT results by G. Chen
Period Thickness (Å)
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SixGe1-x/SiyGe1-y Superlattice Films
Superlattice Period
AIM 1.15
Alloy limit
With a large AIM, k can be reduced below the
alloy limit.
Huxtable et al., Thermal conductivity of Si/SiGe
and SiGe/SiGe superlattices, Appl. Phys. Lett.
80, 1737 (2002).
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Anisotropic Polymer Thin Films
Ju, Kurabayashi, Goodson, Thin Solid Films 339,
160 (1999)

• By comparing temperature rise of the metal line
  for different line
• width, the anisotropic thermal conductivity can
  be deduced

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Nanowire Materials
ZnO nanowires (Z.L. Wang, GaTech)
Sb2Te3 nanowires (potentially high ZT) (X. Li et
al., USTC)
Ge nanowires (B. Korgel, UT Austin)
SnO2 nanowires (Z.L. Wang, GaTech)
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The 3w method for Nanowires
-- Lu, Yi, Zhang, Rev. Sci. Instrum. 72, 2996
(2001)

• Low frequency V(3w) 1/k
• High frequency V(3w) 1/C
• Tested for a 20 mm dia. Pt wire

V
Electrode
I0 sin(wt)
Wire
Substrate

• Conditions
• The sample needs to have a large temperature
  coefficient of resistance TCR (dR/dT)/R
• The electrical contact has to be perfect

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Thermal Measurements of Nanowires
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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Device Fabrication
(c) Lithography
Photoresist
(a) CVD
SiNx
SiO2
(d) RIE etch
Si
(b) Pt lift-off
Pt
(e) HF etch
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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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SnO2 Nanobelts
64 nm
64 nm
53 nm
39 nm
Collaboration N. Mingo, NASA Ames
53 nm
53 nm, ti-1 10t-1i, bulk
Circles Measurements Lines Simulation

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

Shi et al., Appl. Phys. Lett. 84, 2638 (2004)
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Si Nanowires
Si Nanotransistor (Berkeley Device group)
Gate
Drain
Source
Solid line Theoretical prediction
Nanowire Channel
Hot Spots in Si nanotransistors!
Li et al., Appl Phys Lett 83, 2934 (2003)

• Phonon-boundary scattering is the primary effect
  determining the suppressed thermal conductivity
  except for the 22 nm sample, where boundary
  scattering alone can not account for the
  measurement results and confinement effects on
  density of states might have played an role

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Si/SiGe Superlattice Nanowires
Boundary scattering of long- wavelength further
reduces the thermal conductivity below the alloy
limit
Alloy limit
Li et al., Appl Phys Lett 83, 3186 (2003)
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Carbon Nanotubes
Nanotube Electronics (Avouris et al., IBM)

• Atomically-smooth surface, absence of defects
  Long mean free path l Strong SP2 bonding high
  sound velocity v
• ? high thermal conductivity k Cvl/3 6000
  W/m-K

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Thermal Conductivity of Carbon Nanotubes
CVD SWCN
CNT

• An individual nanotube has a high k 2000-11000
  W/m-K at 300 K
• k of a CN bundle is reduced by thermal resistance
  at tube-tube junctions
• Potential applications as heat spreading
  materials for electronic packaging applications

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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
-
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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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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 bottleneck (optical-acoustic phonon
  decay length gt channel length)

• Few thermal measurements are available to verify
  simulation results