3D Chip Stacks Novel Thermal Interface Materials -...

[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


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


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


7

Interface Physics


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


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


conductor/ e.g. copper


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…


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


http://www.nsf.gov/index.jsp

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.,


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.,


[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


15

Thermal Interface Materials


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


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)


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


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


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.


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

]


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

]


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


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


CNT on a Cantilever

Experimental Setup


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


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)


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


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/

mailto:[email protected]

mailto:[email protected]

http://nanoheat.stanford.edu/

http://nanoheat.stanford.edu/

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