Transcript Optomechanical Uncooled Infrared Imaging System

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
Outline

Scanning Thermal Microscopy of Nanoelectronics

Thermoelectric Measurements of Nanostructures
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
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
< 100 nm
Scanning Thermal Microscopy (SThM)
< 100 nm
*Diffraction limit for far-field optics
Scanning Thermal Microscopy
Atomic Force Microscope (AFM) + Thermal Probe
Laser
Deflection
Sensing
Cantilever
Temperature sensor
Thermal
Sample
Z Topographic
X
X-Y-Z
Actuator
T
X
Microfabricated Thermal Probes
Pt Line
Pt-Cr
Junction
Tip
Laser Reflector
SiNx Cantilever
10 mm
Cr Line
Shi, Kwon, Miner, Majumdar, J. MicroElectroMechanical Sys., 10, p. 370 (2001)
Thermal Imaging of Nanotubes
Multiwall Carbon Nanotube
Topography
Thermal
3V
88 mA
1 mm
Height (nm)
10
5
30 nm
0
-400
-200
0
200
Distance (nm)
400
Thermal signal ( m V)
Spatial Resolution
30
20
50 nm
10
0
-400
-200
0
200
400
Distance (nm)
Shi, Plyosunov, Bachtold, McEuen, Majumdar, Appl. Phys. Lett., 77, p. 4295 (2000)
Current (mA)
Metallic Single Wall Nanotube
20
0
A
B C
D
-20
-2000
-1000
0
1000
2000
Bias voltage (mV)
Topographic
1 mm
Thermal
A
B
C
Low bias:
Ballistic
High bias:
Dissipative (optical
phonon emission)
D
DTtip
2K
0
Polymer-coated Nanotubes
Topography
Before coating After coating
Thermal
2 V, 7.8 mA
-2 V, 4.4 mA
1 mm
GND
GND
• Asymmetric heating at the two contacts
The polymer melted at a ~3V bias
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 > channel length)
• Few thermal measurements are available to verify simulation results
Thermal Transport in Nanostructures
Carbon Nanotubes
Hot
p
Cold
• Long mean free path l
Strong SP2 bonding: high sound velocity v
 high thermal conductivity: k = Cvl/3 ~ 6000 W/m-K
Heat capacity
• Below 30 K, thermal conductance  4G0 = ( 4 x 10-12T) W/m-K,
linear T dependence (G0 :Quantum of thermal conductance)
Semiconductor Nanowires
VLS-grown Si Nanowires
(P. Yang, Berkeley)
Nano-patterned Si Nanotransistor
(Berkeley Device group)
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
Efficient Peltier Cooling using Nanowires
Nanowires
of
Bi, BiSb,Bi2Te3,SiGe
Al2O3 template
Top View
Nanowire
Bi
Nanowires
Seebeck coefficient
Electrical conductivity
ZT 
S 2

T
Temperature
COPmax
Thermoelectric figure of merit:
2
1
TH = 300 K
TC = 250 K
Bi2Te3
0
0
Thermal conductivity
Freon
1
2
3
4
5
ZT
Low   high COP
Dresselhaus et al., Phys. Rev. B. 62, 4610
Thermal Measurements of Nanostructures
1.5
DTh (K)
Suspended SiNx membrane
Long SiNx beams
T0 = 54.95 K
1.0
0.5
0.0
I
-6
Q
-4
-2
0
2
4
6
4
6
Current (mA)
0.10
Pt resistance thermometer
D Ts (K)
0.08
T0 = 54.95 K
0.06
0.04
0.02
0.00
-6
Kim, Shi, Majumdar, McEuen, Phys. Rev. Lett. 87, 215502
Shi, Li, Yu, Jang, Kim, Yao, Kim, Majumdar, J. Heat Tran 125, 881
-4
-2
0
2
Current (mA)
Sample Preparation
• Dielectrophoretic trapping
• Wet deposition
Pipet
Nanostructure
suspension
Chip
Spin
• Direct CVD growth
SnO2 nanobelt
Nanotube bundle
Individual Nanotube
Thermal Conductance Measurement
Heating membrane
Sensing membrane
Th
Ts
Rs
Ts
Rh
Sample
Gs
Qh
t
Q
QL=IRL
Beam, Gb
Beam,Gb
Q’
Environment
T0
Q
Q
G
Th  Ts
VTE
V
v
I
i
Gb-1 Th
G-1
Ts
Gb-1
T0
T0
2QL
Q
Qh
Q  Gb (Ts  T0 )
Qh  QL  Gb[(Th  T0 )  (Ts  T0 )]
Measurement Errors and Uncertainties
•Contact Resistance
1
1
1
GMeasured
 GContact
 GSample
GContact
tContact

kC AContact
G Sample 
~d
G-1
/G-1
LSample
1
k S ASample
~d2
-Sample
Contact decreases with d, and is
estimated to larger than 10 for measurements
reported here
• Size
G-1Measured at 290 K (106 K/W)
1
50
40
30
20
10
0
0
50
100
150
200
-- Thickness: 1 nm uncertainty in tapping mode AFM Sample Thickness (nm)
d/d = 10 % for d = 10 nm
d/d = 50 % for d = 2 nm (individual SWCN) Raman Spectroscopy
250
Thermal Conductivity (W/m-K)
Carbon Nanotubes
105
104
1-3 nm CVD SWCN
103
14 nm MWCN bundle
~T2
102
101
100
10-1
~ T 2.5
~ T 1.6
10-2
100
10 nm SWCN CVD SWCN
bundle
148 nm SWCN
bundle
101
102
Temperature (K)
103
• An individual nanotube has a high  ~ 2000-11000 W/m-K at 300 K
• The diameter and chirality of a CN may be probed using Raman spectroscopy
•  of a CN bundle is reduced by thermal resistance at tube-tube junctions
Thermal conductivity (W/m-K)
SnO2 Nanobelts
15
64 nm
64 nm
10
53 nm
39 nm
Umklapp Boundary Impurity
Collaboration:
N. Mingo, NASA Ames
5
53 nm
53 nm,
ti-1 =10t-1i, bulk
0
0
100
200
Phonon scattering rate:
t 1  tU1  t b1  t i1
300
tU-1 = tU,bulk-1
ti-1 = ti,bulk-1
tb-1 = v/FL
v: phonon group velocity
FL: effective thickness
Temperature (K)
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
Thermal Conductivity (W/m-K)
Si Nanowires
60
Symbols: Measurements
Lines: Simulation using a modified Callaway method
115 nm
50
40
56 nm
30
37 nm
20
10
22 nm
0
0
50
100
150
200
250
300
350
Temperature (K)
• 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)
Seebeck Coefficient
Th
S = VTE / (Th –Ts)
Seebeck Coefficient (mV/K)
• Oxygen doped
• Quasilinear (metallic) behavior
• Phonon drag effect at low T
I
Ts
102
10 nm SWCN bundle
101
~T
VTE
148 nm SWCN bundle
~T
100
3x101
~ T 2.6
102
Temperature (K)
4x102
Future Challenge:
Nanomanufacturing 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
Current
300
Suspended
optical
diode
sensor
Current
250
Tc (K)
Etching
pit
200
150
p-doped
nanowire
n-doped
nanowire
Long
beam
Cold
junction
100
0
5
10
Z x 103 (K-1)
15
20
Summary
•
Scanning Thermal Microscopy of Nanoelectronics:
-- Thermal imaging with 50 nm spatial resolution
•
Thermoelectric (k, , S) Measurements of Nanostructures
Using a Microfabricated Device:
-- Super-high  of nanotubes
-- Suppressed  of nanowires
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)