  We use infrared thermometry of carbon nanotube network (CNN) transistors and
find the formation of distinct hot spots during operation. However, the average
CNN temperature at breakdown is significantly lower than expected from the
breakdown of individual nanotubes, suggesting extremely high regions of power
dissipation at the nanotube junctions. Statistical analysis and comparison with
a thermal model allow the extraction of the average tube-tube junction thermal
resistance, ~4.4x10^11 K/W (thermal conductance ~2.27 pW/K). This indicates
that nanotube junctions have a much greater impact on CNN transport,
dissipation, and reliability than extrinsic factors such as low substrate
thermal conductivity.
