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 78712www.me.utexas.edu/~lishi

lishi@mail.utexas.edu

Outline

• Thermal Property Measurements:

--Thin films

--Nanowires and Nanotubes

• Thermal Microscopy

• Reading: Ch2 in Tien et al

GMR

Cu Interconnects

Thin Films and Interfaces

Thin Film Thermal Conductivity Measurement

I0 sin(t)

L 2b

Thin Film

Substrate

Metal line

f

s

s LbkPdi

b

D

kLP

T24

2ln21

ln21

)2(2

The 3 methodCahill, Rev. Sci. Instrum. 61, 802 (1990)

• I ~ 1• T ~ I2 ~ 2• R ~ T ~ 2• V~ IR ~3

V

Substrate contribution Film contribution

Data Analysis

•Dotted line - Ts+ Tf

•Solid line - Ts

•Slope of solid line ks

Tf kf

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 T<10k.

Silicon on Insulator (SOI)

IBM SOI Chip

Ju and Goodson, APL 74, 3005

Lines: BTE results

Hot spots!

Thin Film Superlattices

•Increased phonon-boundary scattering

decreased k

+ other size effects

High thermoelectric figure of merit (ZT = S2T/k)

SiGe superlattice(Shakouri, UCSC)

Thermal Conductivity of Si/Ge Superlattices

Period Thickness (Å)

k (W/m-K)

Bulk

Si0.5Ge0.5 Alloy

Circles: Measurement by D. Cahill’s groupLines: BTE / EPRT results by G. Chen

Temperature (K)50 100 150 200 250 300 350 400

Th

erm

al C

on

du

ctiv

ity

(W/m

-K)

0

5

10

15

Si/Si0.4Ge0.6 SL (150 Å)

Si/Si0.7Ge0.3 SL's 300 Å

150 Å

75 Å

45 Å

Si0.9Ge0.1 (3.5 m)

SixGe1-x/SiyGe1-y Superlattice Films

AIM = 1.15SuperlatticePeriod

Huxtable et al., “Thermal conductivity of Si/SiGe and SiGe/SiGe superlattices,” Appl. Phys. Lett. 80, 1737 (2002).

Alloy limit

With a large AIM, can be reduced below the alloy limit.

Anisotropic Polymer Thin Films

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

Ju, Kurabayashi, Goodson, Thin Solid Films 339, 160 (1999)

Nanowire Materials

Sb2Te3 nanowires (potentially high ZT)(X. Li et al., USTC)

Ge nanowires(B. Korgel, UT Austin)

ZnO nanowires(Z.L. Wang, GaTech)

SnO2 nanowires(Z.L. Wang, GaTech)

The 3 method for Nanowires

Conditions: • The sample needs to have a large temperature coefficient of

resistance TCR= (dR/dT)/R• The electrical contact has to be perfect

Substrate

Wire Electrode

-- Lu, Yi, Zhang, Rev. Sci. Instrum. 72, 2996 (2001)

• Low frequency: V(3) ~ 1/k

• High frequency: V(3) ~ 1/C

• Tested for a 20 m dia. Pt wire I0 sin(t)V

Pt resistance thermometer

Suspended SiNx membraneLong SiNx beams

Current (A)

-6 -4 -2 0 2 4 6

T

s (K

)0.00

0.02

0.04

0.06

0.08

0.10

T0 = 54.95 K

QI Current (A)

-6 -4 -2 0 2 4 6

Th

(K

)

0.0

0.5

1.0

1.5T0 = 54.95 K

Thermal Measurements of Nanowires

Kim, Shi, Majumdar, McEuen, Phys. Rev. Lett. 87, 215502Shi, Li, Yu, Jang, Kim, Yao, Kim, Majumdar, J. Heat Tran 125, 881

Device Fabrication

Si

SiO2

SiNx

Pt

Photoresist(a) CVD

(b) Pt lift-off

(c) Lithography

(d) RIE etch

(e) HF etch

Sample Preparation

• Wet deposition

SpinChip

Nanostructure suspension

Pipet

   

• Direct CVD growth

SnO2 nanobelt

Nanotube bundle

Individual Nanotube

• Dielectrophoretic trapping

Thermal Conductance Measurement

sh TT

QG

)]()[( 00 TTTTGQQ shbLh

)( 0TTGQ sb T0

T0

G-1 Gb-1Th Ts

QQh2QL

Gb-1

T h T s

t

Q

I

Beam , G b

Environment T 0

T s R s R h

Q h

Q’

Beam ,G b

V TE

Heating membrane Sensing membrane

Sample

G s Q

V

i

v

QL=IRL

Collaboration: N. Mingo, NASA Ames

Shi et al., Appl. Phys. Lett. 84, 2638 (2004)

SnO2 Nanobelts

Temperature (K)

0 100 200 300

The

rmal

con

duct

ivity

(W

/m-K

)

0

5

10

1564 nm

53 nm 39 nm

53 nm, i

-1 =10-1i, bulk

64 nm

53 nm

Circles: MeasurementsLines: Simulation

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

Temperature (K)

0 50 100 150 200 250 300 350Th

erm

al C

on

du

cti

vity

(W

/m-K

)

0

10

20

30

40

50

60

22 nm

37 nm

56 nm

115 nm DiameterSolid line: Theoretical prediction

Si Nanowires

Li et al., Appl Phys Lett 83, 2934 (2003)

kbulk 135 W m K at 300K

• 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

Source DrainGate

Nanowire Channel

Si Nanotransistor (Berkeley Device

group)

Hot Spots in Si nanotransistors!

Si/SiGe Superlattice Nanowires

SiSiGe

Si/Si0.95Ge0.05

Temperature (K)

0 50 100 150 200 250 300 350

The

rmal

Con

duct

ivity

(W

/m-K

)

0

2

4

6

8

10

12

14

16

58 nm Si/SixGe1-x nanowire

83 nm Si/SixGe1-x nanowire

Si/Si0.7Ge0.3 superlattice film [7]

Si0.9Ge0.1 alloy film [7]

(a)

Li et al., Appl Phys Lett 83, 3186 (2003)

Alloy limit

Boundary scattering of long- wavelength further reduces the thermal conductivity below the alloy limit

• Atomically-smooth surface, absence of defects: Long mean free

path l & Strong SP2 bonding: high sound velocity v

high thermal conductivity: = Cvl/3 ~ 6000 W/m-K

Carbon Nanotubes

Nanotube Electronics (Avouris et al., IBM)

Thermal Conductivity of Carbon Nanotubes

CVD SWCN

Temperature (K)100 101 102 103T

herm

al C

ondu

ctiv

ity

(W/m

-K)

10-2

10-1

100

101

102

103

104

105

148 nm SWCNbundle

10 nm SWCN bundle

1-3 nm CVD SWCN

14 nm MWCN bundle

~ T 1.6

~ T 2

~ T 2.5

• 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

CNT

Silicon Nanoelectronics

• Heat dissipation influences speed and reliability

• Device scaling is limited by power dissipation

IBM Silicon-On-Insulator (SOI) Technology

Carbon Nanoelectronics

TubeFET (McEuen et al., Berkeley)

Nanotube Logic (Avouris et al., IBM)

• Current density: 109 A/cm2

• Ballistic charge transport

- V

Infrared Thermometry 1-10 m*

Laser Surface Reflectance 1 m*

Raman Spectroscopy 1 m*

Liquid Crystals 1 m*

Near-Field Optical Thermometry < 100 nm

Scanning Thermal Microscopy (SThM) < 100 nm

Techniques Spatial Resolution

*Diffraction limit for far-field optics

Thermometry of Nanoelectronics

X-Y-Z Actuator

Scanning Thermal Microscopy

Sample

Temperature sensor

Laser

Atomic Force Microscope (AFM) + Thermal Probe

CantileverDeflectionSensing

Thermal

X

TTopographic

X

Z

Microfabricated Thermal Probes

Pt-Cr Junction

Shi, Kwon, Miner, Majumdar, J. MicroElectroMechanical Sys., 10, p. 370 (2001)

10 m

Pt Line

Cr Line

TipLaser Reflector

SiNx Cantilever

Thermal Imaging of Nanotubes

Multiwall Carbon Nanotube

1 m

Topography

1 m

Topography

3 V88 A

Distance (nm)

Th

erm

al s

ign

al ( V

) 30

20

10

0

4002000-200-400

50 nm

Distance (nm)

Hei

ght

(nm

)

30 nm

10

5

0

4002000-200-400

Distance (nm)

Hei

ght

(nm

)

30 nm

10

5

0

4002000-200-400

Thermal

Shi, Plyosunov, Bachtold, McEuen, Majumdar, Appl. Phys. Lett., 77, p. 4295 (2000)

Spatial Resolution

Metallic Single Wall Nanotube

-20

0

20

200010000-1000-2000

Bias voltage (mV)

Cu

rren

t (

A)

AB C D

Bias voltage (mV)

Cu

rren

t (

A)

AB C D

Topographic Thermal

1 m

A B C D

Low bias:

Ballistic

High bias:

Dissipative (optical phonon emission)

Ttip

2 K

0

SiGe Devices

Future Challenge:Temperature Mapping of NanotransistorsSOI 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 > channel length)• Few thermal measurements are available to verify simulation results