HEAT CONDUCTION IN NOVEL ELECTRONIC FILMS

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Abstract
Heat conduction in novel electronic films influences the performance and relia- bility of micromachined transistors, lasers, sensors, and actuators. This article reviews experimental and theoretical research on heat conduction in single-crystal semiconducting and superconducting films and superlattices, polycrystalline dia- mond films, and highly disordered organic and oxide films. The thermal properties of these films can differ dramatically from those of bulk samples owing to the dependence of the material structure and purity on film processing conditions and to the scattering of heat carriers at material boundaries. Predictions and data show that phonon scattering and transmission at boundaries strongly influence the ther- mal conductivities of single-crystal films and superlattices, although more work is needed to resolve the importance of strain-induced lattice defects. For poly- crystalline films, phonon scattering on grain boundaries and associated defects causes the thermal conductivity to be strongly anisotropic and nonhomogeneous. For highly disordered films, preliminary studies have illustrated the influences of impurities on the volumetric heat capacity and, for the case of organic films, molecular orientation on the conductivity anisotropy. More work on disordered films needs to resolve the interplay among atomic-scale disorder, porosity, partial crystallinity, and molecular orientation.