Functionalization mediates heat transport in graphene nanoflakes

TL;DR

This study demonstrates that functionalization of graphene with graphene oxide and silane molecules can unexpectedly enhance its in-plane thermal conductivity, improving heat management in microelectronic devices.

Contribution

It reveals that functionalization can increase graphene's thermal conductivity and contact quality, contrary to previous degradation effects, through combined experimental and theoretical analysis.

Findings

Thermal conductivity of supported graphene can be enhanced by functionalization.

Functionalized graphene reduces hotspot temperatures in high-power transistors.

Simulations show constrained phonon scattering improves heat conduction.

Abstract

Self-heating is a severe problem for high-power microelectronic devices. Graphene and few-layer graphene have attracted tremendous attention for heat removal thanks to their extraordinarily high in-plane thermal conductivity. However, this high thermal conductivity undergoes severe degradations caused by the contact with the substrate and the functionalization-induced point defects. Here we show that thermal management of a micro heater can be substantially improved via introduction of alternative heat-escaping channels implemented with graphene-based film covalently bonded to functionalized graphene oxide through silane molecules. Theoretical and experimental results demonstrate a counter-intuitive enhancement of the thermal conductivity of such a graphene-based film. This increase in the in-plane thermal conductivity of supported graphene is accompanied by an improvement on the graphene-substrates thermal contact. Using infrared thermal imaging, we demonstrate that the temperature of the hotspots can be lowered by 12 $^o$C in transistors operating at 130 W mm$^{-2}$ , which corresponds to half of an order-of-magnitude increase in the device lifetime. Ab initio and molecular dynamics simulations reveal that the functionalization constrains the cross-plane scattering of low frequency phonons, which in turn enhances in-plane heat conduction of the bonded graphene film by recovering the long flexural phonon lifetime.