1. ME 381R Fall 2003
Micro-Nano Scale Thermal-Fluid Science and Technology
Lecture 11:
Thermal Property Measurement Techniques For Thin Films and Nanostructures
Dr. Li Shi
Department of Mechanical Engineering
The University of Texas at Austin
Austin, TX 78712

2. Outline Thermal Property Measurements: Thin films
Nanowires and Nanotubes
Reading: Ch2 in Tien et al

3. 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

4. Data Analysis Dotted line - Ts+  Tf Solid line -  Ts
Slope of solid line  ks
Tf  kf

5. 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.

6. Silicon on Insulator (SOI)
Ju and Goodson, APL 74, 3005
IBM SOI Chip
Lines: BTE results
Hot spots!

7. Thin Film Superlattices
SiGe superlattice
(Shakouri, UCSC)
Increased phonon-boundary scattering
decreased k
+ other size effects
 High thermoelectric figure of merit (ZT = S2sT/k)
Si Barrier
Ge Quantum well (QW)

8. Thermal Conductivity of Si/Ge Superlattices
k (W/m-K)
Bulk
Si0.5Ge0.5 Alloy
Circles: Measurement by D. Cahill’s group
Lines: BTE / EPRT results by G. Chen
Period Thickness (Å)

9. 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

10. Nanowires Si Nanowires for Electronic Applications
Bi Nanowires for TE Cooling (Dresselhaus et al., MIT)
Top View
Al2O3 template
Boundary scattering + modified phonon dispersion (group velocity):
 Suppressed thermal conductivity
Volz and Chen, Appl. Phys. Lett. 75, 2065 (1999)

11. 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
I0 sin(wt)
Electrode
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

12. Thermal Measurements of Nanotubes and Nanowires
Themal conductance: G = Q / (Th-Ts)
Suspended SiNx membrane
Long SiNx
beams I Q
Pt resistance
thermometer
Kim et al, PRL 87,
Shi et al, JHT, in press

13. Device Fabrication (c) Lithography Photoresist (a) CVD SiNx SiO2
(d) RIE etch
(b) Pt lift-off Pt
(e) HF etch

14. Nanowires p 22 nm diameter Si nanowire, P. Yang, Berkeley
Increased phonon-boundary scattering
Modified phonon dispersion
 Suppressed thermal conductivity
Ref: Chen and Shakouri, J. Heat Transfer 124, 242
Hot p
Cold

15. (Berkeley Device group)
Si Nanowires
Si Nanotransistor
(Berkeley Device group)
Gate
Source
Drain
Nanowire Channel
D. Li et al., APL
Symbols: Measurements
Lines: Modified Callaway Method
Hot Spots in Si
nanotransistors!

16. Nanotube Nanoelectronics
TubeFET (McEuen et al., Berkeley)
Nanotube Logic (Avouris et al., IBM)

17. Thermal Transport in Carbon Nanotubes
Hot p
Cold
Few scattering: long mean free path l
Strong SP2 bonding: high sound velocity v
 high thermal conductivity: k = Cvl/3 ~ 6000 W/m-K
Heat capacity

18. Thermal Conductivity of Carbon Nanotubes
CVD SWCN
CNT
An individual nanotube has a high k ~ W/m-K at 300 K
k of a CN bundle is reduced by thermal resistance at tube-tube junctions