Graphene-based Thermal Interface Materials (TIM)

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Graphene-based Thermal Interface Materials (TIM)

• A proposal submitted to
• CTRC (Cooling Technologies Research Center)

Principle investigators Yong P. Chen (Physics,
ECE and Birck Nanotechnology Center) Xiulin Ruan
(ME) Tim S Fisher (ME and Birck Nanotechnology
Center) Purdue University
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Why Graphene

• Graphene building block
• for most carbon materials
• ---incl. graphite and
• carbon nanotubes(CNT)
• Recently, carbon materials
• (incl. both graphite and CNT)
• investigated as attractive
• thermal interface material
• (TIM) motivated by their
• high thermal conductivity

c
b
a
(discovered 2004)

• Other advantages of graphene
• High packing density due to 2D
• rich shapes/geometry
• Easily functionalized
• Possibilities to bond to surface

Graphene extraordinary thermal conductivity
3000-5000 W/mK Nano Lett. 8, 902907, 2008
(highest among materials responsible for the
high thermal conductivity of graphite (ab-plane)
and CNT!
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Research Objectives

• Develop high performance TIM based on graphene
• Approach 1 (focus) Vertically grown (CVD)
  graphene sheets
• between (and bonded to) substrates
• Approach 2 (reference) Graphite micro
  platelets/powder
• between substrates
• Components
• material (TIM) design
• synthesis/fabrication
• thermal measurements
• modeling

Some key issues -Bonding of filler material
(graphene) to surface -Adhesion between filler
materials

• Metrics to Achieve
• Material thermal conductivity gt 1000 W/mK
• Interface thermal resistance lt1 mm2K/W

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Approach 1 Vertically Grown Graphene Sheets by
CVD

• Microwave plasma enhanced (PE)
• chemical vapor deposition (CVD) grows
• vertically aligned graphene sheets
• No catalyst needed
• Works on almost any substrate
• graphene bonded to substrate surface
• can have very high filling/packing density

Malesevic et al., Nanotechnology2008
Key idea CVD grow vertical graphene between two
substrates as TIM
substrate
graphene
interface
substrate
Carbon PECVD apparatus available in Purdue/Birck
(Fisher)
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Approach 2 Graphite Platelets, Powders and
Graphene Composites

• Graphite ab-plane has extraordinary thermal
  conductivity (due to graphene thermal
  conductivity)
• Make graphite (highly ordered pyrolytic
  graphite) platelets with thin (vertical)
  dimension along ab
• Fill such graphite platelets as filler material
  between two substrates as TIM
• Alternative graphite powders (a fraction with
  vertical along ab)
• low cost, low tech, field-applicable
• Will investigate geometric factors (size, aspect
  ratio etc) of filler blocks
• Will investigate various bonding glues/epoxy to
  promote adhesion between fillers and to the
• substrate surface
• This is a reference approach that will be
  compared with the CVD grown graphene based TIM
• to investigate roles of filler materials and
  interface bonding
• Will also investigate graphene composites

(graphene-polysterene composite, courtesy
D.Dikin, NWU)
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Measurement Methods

• Well established methods developed at Purdue
• for thermal conductivity/interface thermal
  resistance measurements, for example
• Electrical
• eg., 3-omega Hu et al., J. Heat Transfer 128,
  1109 (2006)
• Z. Huang et al., presentation at
  CTRC 10/28/08
• Optical
• eg., photoacoustic Cola et al., J. Appl. Phys.
  101, 054303 (2006)
• Photoreflectance

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A General Molecular Dynamics Tool for Thermal
Conductance Prediction

• The tool is based on LAMMPS to perform
  non-equilibrium molecular dynamics simulations
• Parallel simulation
• Various types of interatomic potentials
  incorporated
• 1D, 2D, or 3D arbitrary simulation geometry
• Easy to extend with new features and
  functionality

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Thermal Conductivity Prediction of Graphene

• Non-equilibrium molecular dynamics simulations

• Impose a heat flux and calculate the temperature
  gradient, so the thermal conductivity is derived
  from Fourier law.

Fourier Law

• T. Chonan and S. Katayama, J. Phys. Soc. Japn.

• graphene nanoribbon calculated k1500W/mK
• (take thickness 0.35nm)

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Thermal Conductance Prediction of the Graphene
Based TIM

• Development of the interatomic potentials between
  the carbon atoms and the substrate atoms
• Non-equilibrium molecular dynamics to calculate
  the thermal conductance of the TIM.

• Atomistic Greens function will also be used to
  calculate the phonon transmission, and the
  results will be compared to the MD simulations.

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An interesting MD example thermal rectification
in asymmetric graphene nanoribbon
Rectification factor 3! (largest reported so far)
Jiuning Hu et al., in preparation (2008)
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Deliverables/Benefits

• Optimized recipes and procedures to fabricate
  graphene based thermal interface materials.
• Experimentally validated software simulation tool
  to predict the performance of thermal interface
  materials.

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Budget and Program Plan

• 2 years 01/2009-12/2010
• Each year 45K include
• 1.5 student support, leveraged by fellowship and
  TA to support 2 students on this project
• 5000 materials and supplies
• Student 1 will work on material fabrication and
  thermal measurements
• Student 2 will develop simulation tool and data
  analysis
• 1 ECE and 1 ME grad students have been identified
  and ready to perform this research
• Start TRL3, aim TRL5 at end of program