Graphene fillers for ultra-efficient thermal interface materials

Summary form only given. Continuous scaling of Si CMOS devices and circuits, increased speed and integration densities resulted in problems with thermal management of nanoscale device and computer chips. Further progress in information, communication and energy storage technologies requires more efficient heat removal methods and stimulates the search for thermal interface material (TIMs) with enhanced thermal conductivity. The commonly used TIMs are filled with the particles such as silver or silica. The conventional TIMs require high volume fractions of the filler (~70%) to achieve thermal conductivity of ~1-5 W/mK. Recently, some of us discovered that graphene has extremely high intrinsic thermal conductivity, which exceeds that of carbon nanotubes. To use this property for thermal management of nanoscale electronic devices, we utilized the inexpensive liquid-phase exfoliated graphene and multi-layer graphene (MLG) as filler materials in TIMs. The thermal properties of the obtained graphene-epoxy composites were measured using the “laser flash” technique. It was found that the thermal conductivity enhancement factor exceeded a factor of 23 at 10% of the graphene volume loading fraction. This enhancement is larger than anything that has been achieved using other fillers. We have also tested graphene flakes in the electrically-conductive hybrid graphene-metal particle TIMs. The thermal conductivity of resulting composites was increased by a factor of ~5 in a temperature range from 300 K to 400 K at a small graphene loading fraction of 5-vol.-%. The unusually strong enhancement of thermal properties was attributed to the high thermal conductivity of graphene, strong graphene coupling to matrix materials and the large range of the length-scale - from nanometers to micrometers - of the graphene and silver particle fillers. Graphene-based TIMs have a number of other advantages related to their viscosity and adhesion, which meet the industry requirements. Our results suggest that graphene can become excellent filler materials in the next generation of TIMs for the electronic, optoelectronic and photovoltaic solar cell applications.