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[email protected] http://www.nanoheat.stanford.edu
Srilakshmi Lingamneni [email protected]
Advisor: Prof. Ken Goodson Department of Mechanical Engineering, Stanford
IEEE SFBA Nanotechnology Council Talk Oct 16, 2012
Novel Thermal Interface Materials for 3D Chip Stacks
IEEE SFBA Nanotechnology Council
Outline
• Stanford Nano Heat Lab
– Overview of Metrology and Materials
• Materials for Thermal Management
– 3D chip attachments and conductive underfills
– High density aligned CNT composites
– Aligned CNT nanotape
– Mechanical Characterization
2 IEEE SFBA Nanotechnology Council
Thermal and Mechanical Characterization
3
Cross-sectional IR Microscopy
Heater
growth substrate
CNT Film
0 200 400 60015
20
25
30
35
40
Distance (um)
Tem
pera
ture
(C
)
CNT
kdx
dT 1
BRT
dx
dTk
1
500 μm
Distance (μm)
Pico/Nanosecond Thermoreflectance
Time
Ref
lect
ed
Sig
nal
TR Signal Heating Pulse
CNT Film
Metal
Metal CNT Catalyst
TransparentSubstrate
Electrothermal Characterization
Thermal and Mechanical Characterization
4
Cross-sectional IR Microscopy
Heater
growth substrate
CNT Film
0 200 400 60015
20
25
30
35
40
Distance (um)
Tem
pera
ture
(C
)
CNT
kdx
dT 1
BRT
dx
dTk
1
500 μm
Distance (μm)
Nanosecond Transient Thermoreflectance
Mechanical Characterization
CNT Film
Photodetector Laser Beam
Microresonators (In-Plane) Nanoindentation (Out-of-Plane)
Laser Doppler Vibrometer
(LDV)
Electrothermal Characterization
Metal
Si
R”top
R”base
R”film Cv, film
Film
Metrology
5
Sample Complexity
Rig
Co
mp
lexit
y
SAMPLE FILM
Kaeding, Skurk, Goodson,
Applied Physics Letters (1993)
Pump-probe optics
Hybrid Optical-Electrical Methods
Multi-property Measurements
IEEE SFBA Nanotechnology Council
Nanodevices and Materials Data Storage
6
Thermoelectrics
C. Xi, C-M Hsu Cui group, Stanford
Numonyx/Intel
Solar Electrodes
R. Noriega and S. Phadke Salleo group, Stanford
Vuckovic et al., Stanford
CMOS Lasers
Thermal Interfaces
Goodson group, Stanford
IEEE SFBA Nanotechnology Council
7
Interface Physics
IEEE SFBA Nanotechnology Council
Novel Composite Substrates for Power Electronics and Photonics
GaN-diamond composite for power HEMTs (courtesy Group4 Labs)
Zijian Li, Elah Bozorg-Grayeli, Jungwan Cho, Si Tan
Physical mechanisms governing electron and phonon transport at interfaces
Phonon & Electron Nonequilibrium at Interfaces Engineered multilayer interface for reducing thermal conductance in phase change memory devices
Extreme UV NanoOptics
Mo/Si Multilayer Structure
Phase Change Memory
8
Electrothermal/Crystallization Modeling
John Reifenberg Zijian Lee
Groups of H.S. Philip Wong (EE) and Kenneth E. Goodson (ME)
Intel (D. Kau, K-W. Chang, Ilya V Karpov, G. Spandini)
NXP (F. Hurckx), Micron (John Smythe), IBM (Raoux, Krebs, et al.)
National Science Foundation (NSF),
Semiconductor Research Corporation (SRC)
Sponsors & Collaborators:
Threshold Switching Phenomena Metal heater
PC
MicroThermal Stage (MTS)
SangBum Kim Rakesh Gnana,
John Reifenberg, Jaeho Lee,
Zijian Li
SiO2
PCMW W
Current (A)V GND
ThermoElectric Effect (Seebeck)
Jaeho Lee, Rakesh Gnana,
Zijian Li
Thermal Characterization
Jaeho Lee Zijian Li Elah Bozorg-Grayeli SangBum Kim John Reifenberg
Sample film (CNT Array)
Heat sink (silicon or metal substrate)
Metal coating
Nanosecond Heating from Nd:YAG
To
Detector
CW Radiation for
Thermometry
GST
Crystalline Amorphous
Novel Geometries, Synthesis, & Multibit
Yuan Zhang Rakesh Gnana Sangbum Kim John Reifenberg
Key Challenges for TEs in Combustion Systems
9
…Low resistance interfaces that are stable under thermal cycling. …High-temperature TE materials that are stable and promise low-cost scaleup. …Characterization methods that include interfaces and correlate better with system performance.
hot side / heat exchanger
insulation / e.g. ceramic plate
conductor/ e.g. copper
insulation / e.g. ceramic plate
cold side / heat exchanger
conductor/ e.g. copper conductor/ e.g. copper
n p
thermal
thermal
electrical
& thermal
electrical
& thermal
thermal
thermal
diffusion barrier
joining technology
contact resistancesHeat
Cooling
hot side / heat exchanger
insulation / e.g. ceramic plate
conductor/ e.g. copper
insulation / e.g. ceramic plate
cold side / heat exchanger
conductor/ e.g. copper conductor/ e.g. copper
n p
thermal
thermal
electrical
& thermal
electrical
& thermal
thermal
thermal
diffusion barrier
joining technology
contact resistancesHeat
Cooling
600 °C
90 °C
Improvements in the intrinsic ZT of TE materials are proving to be very difficult to translate into efficient, reliable power recovery systems.
Major needs include…
IEEE SFBA Nanotechnology Council
Automotive Waste Heat Recovery Thermoelectric Modules and Electro-Thermo Interfaces
10
TE Material
Hot Side Cold Side
IR Camera
250 W
Michael Barako, Lewis Hom, Saniya Leblanc, Yuan Gao, Woosunng Park, Amir Aminfar, Amy Marconnet, Dr. Mehdi Asheghi
Solder Bonding High Temperature IR Imaging
Thermal Cycling of TE Modules
50 μm
Fracture
After 45,000 Cycles
1010
010
110
210
310
410
5
0.5
0.55
0.6
Cycles
ZT
Figure of Merit
~ 400 oC drop across TE module
IEEE SFBA Nanotechnology Council
Thermal Management Challenges for Microprocessors
Importance of Hotspot Thermal Management
• Peak temperatures limit the reliability of interconnects • Thermo-mechanical strains due to temperature non-
uniformities can degrade packaging and interfaces
Challenges Ahead for Thermal Management • Transistor scaling • Increasing number of cores • 3D integration • Constraints of mobile applications
11
Adapted from: http://en.wikipedia.org/wiki/Heat_sink
Images of Electromigration Failure Ralph Group, Cornell University
Solder joint failure due to thermomechanical stress Ridgetop Group Inc.,
IEEE SFBA Nanotechnology Council
Flow = 2 ml/min, Mass Flux = 103 kg/s-m2
0
5
10
15
20
25
0 10 20 30 40 50 60 70
Heat Flux [W/cm2]
P
tot /
P
tot,
lo
Control Vent
Heat Flux [W/cm2]
ΔP
tot/
ΔP
tot,
liq
Hot Spot Detection and Thermal Management
12
(b)
Distributed Temperature
Sensor Network
(c)
Reproduced power map
(a)
Power map
Rapid Hotspot Prediction & Power Distribution
Non uniform heat generating chip
Base
IR transparent window
Imaging lens
To detector
IR radiation
IR transparent fluid
(a)
Through-Wafer Hotspot Imaging
Milnes David, Joe Miler, Lewis Hom, Dr. Mehdi Asheghi To resolve transient chip hotspots with increased accuracy and cool them with high-heat flux cooling solutions
Vapor-Venting Microfluidic Heat Exchangers
David et al.,
IEEE SFBA Nanotechnology Council
[email protected] http://www.nanoheat.stanford.edu
Thermal Interface materials
3D chips: Material Requirements
14
DRAM DRAM
lnterposer
Logic
Chip Carrier
Logic
Memory Memory
Chip Carrier
TIM 1 &2 (metal alloys, particle filled organics, aligned CNT films) - High thermal conductivity - Mechanical compliance
Flowable Underfill - Electrically insulating - Mechanical stiffness - Viscosity and capillary forces - High thermal conductivity
3D Chip Attachment (Adhesives, Thermal compression bonding) - High thermal conductivity - Electrically insulating - Thermal cycling stability
Encapsulation - High thermal conductivity - Electrically insulating (on the side facing the chip) - Mechanical compliance
Goal: Discover and characterize advanced materials containing nanoscale inclusions (particles, platelets, tubes), targeting the unique property needs of packaging applications including TSV, interposer, and 3D
IEEE SFBA Nanotechnology Council
15
Thermal Interface Materials
IEEE SFBA Nanotechnology Council
AlN-(xGNP) Exfoliated Graphene nanoplatelet composites
2 μm
AlN – 10 µm
1 μm
xGNPs – 5-15 nm ┴
2 mm
Aligned CNT Composites
Thermal and Mechanical Characterization Nanotape to Replace Solder Pads
Thermal Conductivity Measurement – IR Imaging
[mm]
[mm
]
1.25 2.50 3.75 5.00 6.25
1.25
2.50
3.75
5.00
6.25
Tem
pera
ture
[C
]
15
20
25
30
35
40
45
50
55
60
65Temperature Controlled
Copper Baseplate
Quartz
QuartzSAMPLE
Heater
Metal Layer
Substrate
16
Calibration & Verification • Emitter tape defines measurement location and uniform emissivity • Emissivity calibrated(@ 65-75 oC) using thermocouples • Verification performed on known materials • Dual heat flux measurement region quantify heat losses
IEEE SFBA Nanotechnology Council
Aligned CNT Nanocomposites
17
Remove 1 vol.% CNT film from growth substrate
Biaxial compression to increase volume fraction
Infiltrate with epoxy (RTM-6)
Ax
ial
Transverse
1 mm
1 vol.% CNT film
2 mm
1 vol.% CNT Composite
Marconnet et al, ACS Nano (2011)
IEEE SFBA Nanotechnology Council
Thermal Conductivity of Aligned CNT Nanocomposites
18
0.01.0
5.0
10.0
15.0
20.0
Th
erm
al C
on
du
cti
vit
y E
nh
an
cem
en
t [k
/kep
oxy]
0% 5% 10% 15% 20%0.0
1.0
2.0
3.0
4.0
5.0T
herm
al C
on
du
ctiv
ity [W
/m/K
]
Volume Fraction
Composites - Axial
Composites - Transverse
Unfilled Arrays - Axial
(Surfaces polished to ~3nm roughness and coated with 200 nm of Pt to ensure nearly identical contact conditions for all samples and improves contact between composite and reference layers)
• Non-linear increase at higher volume fraction suggests that CNT-CNT and CNT-polymer interactions are important to the thermal transport
• CNT’s contribute at a rate of about 10 W/m/K per CNT at low volume fractions, much lower than expected.
Effective medium approach Power law
Axia
l
Transverse
IEEE SFBA Nanotechnology Council
Aligned CNT Nanocomposites
19
Heat Sink
Heat Source
Variation in CNT Heights
CNT-CNT Contacts
Defects
Voids
CNT-Epoxy Boundary Resistance
Composite Interface Resistance
Individual CNT Thermal Conductance
Spatially Varying Alignment
Hea
t Si
nk
Hea
t So
urc
e
CNT-CNT Contacts
CNT-Epoxy Boundary Resistance
Composite Interface Resistance
Spatially Varying Alignment
Heat Sink Individual CNT Thermal Conductance
Transverse Conduction
Axial Conduction
IEEE SFBA Nanotechnology Council
Nanotape to Replace Solder Pads
20
SRC Patent: Hu, Jiang, Goodson, US Patent 7,504,453, issued 2009 SRC Patent: Panzer, Goodson, et al., 2009/0068387 (pending) Panzer, Maruyama, Goodson et al., Nanoletters (2010) Hu, Fisher, Goodson et al., J. Heat Transfer (2006)
Removable
mechanical
backer
Nanofibers
Low melting temperature
binder (e.g. alloys of Ga, In,
Sn) Adhesion layer
Adhesion layer wets nanotubes and
promotes adhesion of binder (Pd, Pt, or Ti).
~100 nm is the
typical variation in
CNT height.
Upon heating, the low melting binder
conforms to CNT and substrate topography.
IEEE SFBA Nanotechnology Council
Bonded CNT Thermal Properties
21
0 0.5 1 1.520
40
60
80
100
Distance [mm]
Tem
pera
ture
[C
]
Glass NF CNT
Temperature Profile
Nanofoil Bond
Indium Bond
CNT Film
Cr/Ni/Au
Bonding Layer 1 μm 1 μm
CNT
Si
Fused Silica
Bonding Layer
Cr/Ni/Au
Cr/Ni/Au
For constant q'', the interfacial temperature drop is reduced by an order of magnitude through solder bonding
Barako et al, ITHERM 2012 IEEE SFBA Nanotechnology Council
Bonded CNT Thermal Properties
22
0 200 400 600 80010
1
102
103
104
Pressure [kPa]
TB
R [
K-m
m2
/W]
Unbonded
Bonded
R ''
CN
T-In
-Gla
ss [
K-m
m2/W
]
Axial Pressure [kPa]
Indium Bonding
R''CNT-In-Glass = 28-71 K-mm2/W
100 200 300 400 500 60010
1
102
103
Pressure [kPa]
TB
R [
K-m
m2/W
]
Unbonded
BondedR
'' C
NT-
NF-
Gla
ss [
K-m
m2/W
]
Axial Pressure [kPa]
Nanofoil Bonding
R''CNT-NF-Glass = 15-50 K-mm2/W
0 200 400 600 8000
0.5
1
1.5
2
Pressure [kPa]
k [
W/m
/K]
No Bonding
Indium Bonding
Nanofoil Bonding
k CN
T [W
/m/K
]
Axial Pressure [kPa]
CNT Bulk Thermal Conductivity • Intrinsic Thermal Conductivity
increases due to improved engagement of CNTs
• Thermal boundary resistance decreases significantly
Barako et al, ITHERM 2012
Thermal Interface Materials
Courtesy of Dr. Boris Kozinsky (Bosch)
Thermo-mechanical Stresses in TEs
1 Gao, Goodson, et al., J. Electronic Materials (2010). Won, Goodson, et al., Carbon, submitted (2011).
GOAL
Thermal Resistivity (m K / W)1.00.1
Elas
tic
Mo
du
lus
(MP
a)
Greases & Gels
Phase Change Materials
Indium/ Solders Adhesives
0.01
Nano-gels
104
103
102
101
Latest Stanford CNT Data1
23
GOAL: Thermal Conductivity + Mechanical Flexibility Implication: Higher package form factor
IEEE SFBA Nanotechnology Council
Mechanical Properties of CNT Films New Technique: Mechanical Resonators
24
Resonator length and shape variation
• LDV (laser Doppler velocimetry) experimental setup : resonant frequency of various thickness films. • Resonant frequency shift : mechanical modulus • Ring-down and fitting measurements : quality factors
Thermal and Mechanical Characterization
CNT on a Cantilever
Experimental Setup
IEEE SFBA Nanotechnology Council
Experimental Method and Data Interpretation
25
Transformed section method
wn
wn,o
ESiISi EcntIcnt
SiASi cntAcnt
SiASiESiISi,o
1
ECNT Esi
ICNT 1
CNTACNTSiASi
1
wn
wn, Si, 0
2
ISi, 0 ISi
i
ii AA i
iiIEEI
Euler-Bernoulli differential equation for multi-layer beam
04
4
2
2
x
wEI
dt
wA
Polysilicon deposition
Resonator outline etching
Catalyst deposition
Carbon Nanotube Growth
Resonator etching
Oxide layer removal
Won et al, Carbon (2011)
Beam thickness, tSi
Carbon nanotube thickness, tcnt
Beam Width, b (25-100 um)
Beam Length, L (200-1000 um)
Si-CNT Cantilever
IEEE SFBA Nanotechnology Council
Mechanical Behavior of CNT Films
26
MWCNTs (Monano)
SWCNTs (U. of Tokyo)
Thickness: 0.5 - 220 µm Modulus : 1 - 370 MPa Density : 25 - 140 kg/m3
MWCNTs (MIT)
IEEE SFBA Nanotechnology Council
Mechanical Behavior of Nonhomogeneous CNT Films
27
Three-layer Analysis
• Interweaving of a thin layer of entangled and randomly oriented nanotubes • Vertical-aligned growth • Density decay
Growth Stages
crust
middle
Dimensionless Effective Modulus
SWCNTs (U. of Tokyo)
MWCNTs (Monano)
MWCNTs (MIT)
Two-layer analysis Three-layer analysis
Stage 1 Stage 2
Self-organization Vertical-growth
crust middle
SWCNT films
Theoretical curve for MWCNT films
wn
wn,Si,0
ESiISi,1 EMiddleIMiddle ETopITop
SiASi MiddleAMiddle TopATop
SiASiESiISi,0
1
: Moduli are scaled by reference sample and volume fraction
IEEE SFBA Nanotechnology Council
Conclusions - Materials for Thermal Management
– Development of novel thermal interface materials is crucial for 3D circuits performance
– Nano tape is a promising replacement to solder pads
– Measurements of aligned CNT films and composites showed thermal conductivity and elastic modulus comparable to or better than commercial TIMs
– Thermal conductivity data of AlN-xGNP nanocomposites showed promising trends and are potential candidates for underfill materials
28 IEEE SFBA Nanotechnology Council
Contact Info: Srilakshmi Lingamneni ([email protected]) Prof. Ken Goodson ([email protected]) http://nanoheat.stanford.edu/