System-Level Approach for Multi-Phase
Nanotechnology-Enhanced Cooling of HighPower Microelectronic Systems
Objective
Our objective is to develop a robust, lowtemperature thermal management approach for
distributed, large-scale, high-power electronic
systems using improved heat transfer
technologies and system modeling/control
concepts to reduce the total system thermal
resistance so that chip and device temperatures
are
maintained below 65°C.
Overall Challenge
Problem: Operation of a large-scale, distributed electrical/electronic system
including devices with ultra-high heat fluxes that require low surface
temperatures.
65°C
State-of-the-art and Our Goals
Estimates of Conductances in State-of-the-Art
Systems and Future Systems
Thermal Conductance
Device substrate conductance (MW/m2-K) (hchip = 1/ARchip)
State-of-the-art Target
0.1
5.0
0.1-0.5
5.0
Microchannel/micro domain base conductance (MW/m2-K)
(hmc-solid = 1/ARmc-solid)
0.1
5.0
Convective conductance of microchannel to coolant including
area enhancement due to fins (MW/m2-K)
(hmc-coolant = 1/ARmc-coolant)
0.05
0.20
Convective conductance of coolant to condenser (MW/K)
(Hcoolant-condenser = 1/Rcoolant-condenser)
0.06
0.18
Wall conductance in condenser (MW/K)
(Hcondenser wall = 1/Rcondenser wall)
1.65
4.95
Convective conductance of condenser to ocean (MW/K)
(Hcondenser-ocean = 1/Rcondenser-ocean)
0.12
0.36
Interface conductance (MW/m2-K) (hTIM= = 1/ARTIM)
A Multidisciplinary Approach to a Multiscale Problem:
Chip to Ship
Nanoscale Energy Transport and Conversion:
Electrical Engineering, Material Science, SolidState Physics, Statistical Mechanics
Thermal Management of Electronics:
Scale:
10-9
Length:
nm
10-6
μm
10-3
mm
100
m
103
km
Heat Conduction, Material Science,
Microfluidics, Mechanics, Fatigue
Macroscopic Energy Transport and Conversion:
Convective Heat Transfer, Fluid Dynamics,
Thermodynamics
System Scaling and Optimization:
Electrical Engineering, Control Systems
Primary Thrusts
Thrust 1 – Solid/Solid Interfaces
Understanding the origins (interfacial chemistry, structure, and
electron/phonon transport) of solid-solid interfacial thermal resistance,
will lead to the development of a new thermal interface material with a
target conductance of G~5 MW/m2-K.
Thrust 2 – Solid/Liquid Interfaces
Studying flow boiling and condensation at the micro-scale through novel
noninvasive thermometry tools will guide the enhancement of
convective heat transfer using advanced micro-domain configurations,
engineered surface topography, and changes in chemical composition
for control of interfacial physics.
Thrust 3 – System Design and Optimization
Sensor feedback and modern control theory will be used to develop
design and control methodology for the system and devices and the
results of Thrusts 1 and 2 will be integrated in a modular and
scalable testbed.
Integration
Thrust 1: Solid/Solid Interfaces
• Primary Contributors
– UVa: Pam Norris
– ASU: Ravi Prasher
– UC Berkeley: Costas Grigoropoulos
• Thrust Statement/Objectives
– Increase the long-term stable conductance at
solid/solid interfaces
– Understand the origins (interfacial chemistry,
structure, and electron/phonon transport) of solidsolid interfacial thermal resistance
– Use this knowledge to help develop new thermal
interface materials
Thrust 1: Accomplishments for 1st Year
as of June 2008
• Theoretical models developed for thermal transport in mesoscopic
nanowires/nanotubes (thermal conductivity, thermal boundary resistance, specific
heat).
• Measured elastic modulus of vertically aligned CNT arrays under compression, and
studied mechanism.
• Studied the growth mechanism of vertically aligned CNT arrays.
• Fabricated TIM with CNT array with G ~ 1 MW/m2-K through In bonding technique.
• Compared the interface thermal conductance of glass-CNT-Si sandwich structures
with/without In bonding, and with Ti wetting layer as well.
• Investigated the adhesion problem between In film and Ti film.
• Investigated the possibility of enhancing contact between In and Ti by adding Au
bonding layer.
• Examined effects of atomic mixing at Cr/Si interface on G – developed new model
to take into account multiple scattering events from disorder.
• Studied phonon scattering processes at interfaces – developed model to account
for inelastic scattering and separated role of elastic and inelastic scattering in G.
• Experimentally investigated electron-phonon equilibration in thin Au films subject
to short pulsed heat in the presence of the film/substrate interface.
• Determined that interfacial scattering can affect electron-phonon equilibration
time – developed new model based on ballistic electron transport and ballisticdiffusive approximation to the Boltzmann Transport Equation.
Thrust 1: Accomplishments for 2nd Year
as of June 2009
• Characterized the packing density of vertically aligned CNT array using high
resolution SEM.
• Investigated the effect of hydrogen pretreatment on the CNT array density.
• Comprehensively studied the sensitivity of transient opto-thermoreflectance
technique on ultra-small thermal interface resistance measurement.
• Improved the experimental technique to allow high resolution thermal
measurement with improved sensitivity.
• Investigated the effect of variation of packing densities on G.
• Investigated the influence of interstitial metallic layers on G at metal-nonmetal
interfaces.
• Emulated the behavior of metal-CNT contact by making thermal measurements
on metal-graphite samples.
• Identified most probable material systems for ultimate TIM package assembly.
• Preliminary development of the multidimensional diffuse mismatch model.
• Refined UVA TTR setup to allow for measurement on more diffuse surfaces.
• Fabricated CNT-array-based TIM with G ~ 1.5 MW/m2-K.
Thrust 1: Accomplishments for 3rd Year
as of August 2010
• Developed a theoretical model for thermal transport between isotropic films
and anisotropic substrates considering contributions of inelastic scattering.
• Measured boundary conductance between Au films and sp2 carbon
structures, investigating the role of interface structure and chemistry.
• Investigated the role of subconduction band excitations on thermal
conductance at metal-metal interfaces.
• Reviewed the assumptions made in modeling diffusive transport in
nanostructures and their application to specific systems.
• Increased the CNT array packing density to 11% volume fraction.
• Fabricated CNT arrays of various lengths (~250, 200, 150, 100, and
50 μm) by decreasing growth duration of water-assisted synthesis from 3
minutes to 15 seconds, and with nearly fixed CNT array volume fraction of 3%.
• Measured thermal interface (CNT – bonding surface) conductance of high
density (11%) sample to be over 5 MW/m2-K.
Thrust 2: Fluid/Solid Interfaces
• Primary Contributors
– RPI: Michael Jensen, Yoav Peles
– UIUC: David Cahill, Steve Granick
• Thrust Statement/Objectives
– Reduce convective thermal resistances in heat sinks
and heat exchangers
– Understand flow boiling and condensation at the
micro-scale
– Enhance heat transfer through modifications of
surface chemistry, surface topography, and microdomain configurations
Thrust 2: Accomplishments for 1st Year
as of June 2008
• 95%+ complete on construction of three flow loops (boiling, condensation,
microjet).
• 99% complete on test sections for all three loops.
• Calibrations of components in three loops done except for test sections; data
acquisition and reduction programs complete.
• Developed a program to optimize different microdomain geometries
(microchannels, pin fins, etc.) that takes into account heat transfer and
pressure drop characteristics; this will be used for guidance on developing
enhanced boiling and condensing geometries.
• Completed construction and testing of an IR (1.55 micron) femtosecond
pump-probe measurement system capable of probing through the back side
of Si wafers with low doping levels.
• Completed first-generation construction of homebuilt apparatus for surface
plasmon resonance imaging of bubble nucleation events.
Thrust 2: Accomplishments for 2nd Year
as of June 2009
• Obtained data for critical heat flux and boiling heat transfer data for R134a in
microtubes.
• Obtained data for single-phase heat transfer with single micro-jet and with
micro-jet arrays.
• Designed new experiment for multi-jet array impinging on enhanced surface.
• Performed optimization study for single-phase flows with various enhanced
heat transfer techniques in micro-domains.
• Invented two-photon thermometry for ultra-high space and time resolution
of thermal transport.
• Invented surface plasmon thermometry for imaging local nucleation events.
• Invented pump-probe ellipsometry for molecular understanding of heat
transfer from solid to liquid on the picosecond time scale.
Thrust 2: Accomplishments for 3rd Year
as of August 2010
• Completed a detailed experimental study of heat transfer coefficients and
CHF condition for flow boiling of R134a in circular microtubes.
• Completed a parametric study of area-averaged heat transfer coefficient of a
microjet array varying area ratio and using air and water.
• Converted the experimental microjet array apparatus to a closed,
pressurized, refrigerant system charged with R134a, and conducted flow
boiling experiments with R134a.
• Designed and constructed test sections to measure condensation heat flux,
and, using these, completed condensation heat transfer experiments on
square mini-channels.
• Designed micro devices for studying single-phase and flow boiling heat
transfer of jet impingement on micro pin-fin structures; microfabricated the
micro devices using MEMS microfabrication technologies.
• Conducted heat transfer and pressure drop experiments using water as
coolant for jet impingement on micro pin fins.
• Discovered that time-averaged heat transfer during water droplet impacts
can reach 500 W/cm2.
• Observed thermal accommodation between a solid and a condensing vapor
for the first time.
• Directly visualized heat transfer in the nucleation of single bubbles for the
first time.
Thrust 3: System Design and Optimization
• Primary Contributors
– RPI: J. Wen, M. Jensen, Y. Peles
– ASU: P. Phelan, R. Prasher
• Thrust Statement/Objectives
– Integrate results of Thrusts 1 and 2 into a modular
and scalable refrigeration system
• Demonstration of 1 kW/cm2 on single module
• Demonstration of scalability to multi-module systems
– Develop design & control methodology for system
and devices using sensor feedback and modern
control theory
Thrust 3: Accomplishments for 1st Year
as of June 2008
• Development of steady-state vapor compression cycle modeling and
optimization tool (in MATLAB) including CHF consideration. Extensibility to
multiple evaporators, multiple loops, pump cycle.
• Establishment of the two-loop architecture for system design.
• Initial design and setup of a fully instrumented vapor compression cycle
testbed capable of operating at a wide range of conditions.
• Initial design and equipment purchase for the high-heat-flux, single-module
testbed.
• Initial development of dynamic modeling.
Thrust 3: Accomplishments for 2nd Year
as of June 2009
• Developed optimization module for steady-state system design at multiple
operating conditions for a single vapor compression cycle.
• Developed initial steady-state design tool for two-loop system analysis.
• Completed the first phase RPI test facility beds and started model
identification for expansion valve and compressor.
• Nearly (99%) completed construction of ASU test facility.
• Obtained initial transient stability result using singular perturbation.
• Developed Ledinegg instability model based on data from Intel.
• Developed preliminary pressure drop instability model based on data from
Intel.
Thrust 3: Accomplishments for 3rd Year
as of August 2010
Macro-scale Systems
•
•
•
•
•
Validated steady-state vapor compression cycle models (compressor, valve, heat
exchangers) with experimental test facility at RPI.
Developed steady-state design and optimization module for two-loop cooling system
at multiple operating conditions.
Completed dynamic identification for empirical modeling and controller design for
single evaporator case.
Completed evaluation of linear controller design using expansion valve opening to
control evaporator wall temperature.
Investigated the effects of transient heat load on two-phase flow instabilities in
electronics cooling systems.
Micro-scale Systems
•
•
•
Studied micro-thermal-fluid transients, developed new HTC correlation, and
combined extremum-seeking and thermal-fluid stabilizing controller.
Developed pressure drop flow oscillation model and active instability control
strategies for microchannel boiling system.
Proposed non-identical structures for parallel-channel flow instability control.