Thermal Conduction in Silicon Micro- And Nanostructures

Silicon micro- and nanostructures are found in integrated circuits, sensors, and actuators, and the performance and reliability of many of these devices are affected by thermal conduction. Conduction processes in micro- and nanostructures are complicated by phonon interactions with grain and material boundaries. Phonon confinement in nanostructures and highly nonequilibrium rates of phonon generation by electrons also influence heat conduction. This article reviews experimental and theoretical studies of the thermal conductivity of single-crystal and polycrystalline silicon films, with a focus on data relevant for modeling heat transport in modern devices. Data for single-crystal films indicate a room-temperature thermal conductivity reduction of up to 50% compared to bulk silicon due to phonon boundary scattering, while grain boundary scattering in polysilicon films results in even lower values. Simple analytical expressions for approximating the room-temperature thermal conductivity of silicon films are provided. Doping modifies heat conduction mainly due to impurity scattering, and thermal conductivity data for boron-, phosphorus-, and arsenic-doped silicon films demonstrate the extent of this effect. Hotspots smaller than the phonon mean free path cause intense localized heating in silicon and severe departure from equilibrium within the phonon system, which can substantially increase the effective thermal resistance for conduction. This review provides an overview of the nanoscale conduction effects that are becoming important for the design of silicon nanostructures.