2010 Volume 18 Pages 62-66
There is an increasing interest in applications of wide-gap materials to high-temperature and high-power electronics. It is necessary to radiate extra heat efficiently through an aluminum heat sink coated with a heat-resistant material with high thermal conductivity. Diamond has the highest thermal conductivity in all materials, which at room-temperature is above 1000 W/mK. However, at high temperatures, diamond films show low adhesion to aluminum substrates due to a large difference in thermal expansion coefficient between diamond and aluminum.
Nanocrystalline diamond films are composed mainly of two carbon phases: the diamond phase in form of nanograins and amorphous carbon at the grain boundaries. The thermal expansion coefficient can also be controlled if the diamond/amorphous carbon ratio in the films can be varied. The author has showed a way of increasing the diamond/amorphous carbon ratio in plasma-enhanced CVD. In this study, we examine the thermal and electrical transport properties of nanocrystalline diamond films.
The films were deposited on aluminum and silica substrates. The room-temperature thermal conductivity increased when the diamond fraction was increased. Nitrogen addition increased the electrical conductivity, however, the thermal conductivity decreased. This was attributed to an increase in thermal resistance at the grain boundaries due to a decrease in the diamond/amorphous ratio.