Thermal conduction in nonhomogeneous CVD diamond layers in electronic microstructures

Chemical-vapor-deposited diamond layers of thickness between 0.1 and 5 mu m have the potential to improve conduction cooling in electronic microstructures. However, thermal conduction in these layers is strongly impeded by phonon scattering on defects, whose concentrations can be highly nonhomogeneous, and on layer boundaries. By assuming that defects are concentrated near grain boundaries, this work relates the internal phonon scattering rate to the local characteristic grain dimension and to the dimensionless grain-boundary scattering strength, a parameter defined here that varies little within a given layer. Solutions to the Peierls-Boltzmann phonon transport equation for conduction along and normal to layers account for the nonhomogeneous internal scattering rate. Predictions for conduction along and normal to layers as thin as 0.2 mu m agree well with room-temperature data. This research helps optimize diamond layer thicknesses for specific microstructures, such as silicon-on-diamond (SOD) circuits.