Heat conduction in novel electronic films

Heat conduction in novel electronic films influences the performance and re liability of micromachined transistors, lasers, sensors, and actuators. Thi s article reviews experimental and theoretical research on heat conduction in single-crystal semiconducting and superconducting films and superlattice s, polycrystalline diamond films, and highly disordered organic and oxide f ilms. The thermal properties of these films can differ dramatically from th ose of bulk samples owing to the dependence of the material structure and p urity on film processing conditions and to the scattering of heat carriers at material boundaries. Predictions and data show that phonon scattering an d transmission at boundaries strongly influence the thermal conductivities of single-crystal films and superlattices, although more work is needed to resolve the importance of strain-induced lattice defects. For polycrystalli ne films, phonon scattering on grain boundaries and associated defects caus es the thermal conductivity to be strongly anisotropic and nonhomogeneous. For highly disordered films, preliminary studies have illustrated the influ ences of impurities on the volumetric heat capacity and, for the case of or ganic films, molecular orientation on the conductivity anisotropy. More wor k on disordered films needs to resolve the interplay among atomic-scale dis order, porosity, partial crystallinity, and molecular orientation.