  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.
