A large reduction of heat conduction through silicon-silicon sintered interface by local oxide nanostructures is quantitatively demonstrated by a newly developed method to directly measure thermal boundary conductance across bonded interfaces. Together with the theoretical analysis that relates the thermal boundary conductance to thermal conductivity of densely-packed bulk nanocrystalline silicon, we identify a route to significantly reduce the thermal conductivity from the state-of-art value, even to approach the amorphous silicon value. The finding is useful for designing nanostructured bulk silicon thermoelectrics

Using the recently developed method to directly measure thermal boundary conductance (TBC) across bonded interfaces, we report the measurements of TBC at interfaces bonded by surface activated bonding at room temperature. The TBC of as-bonded silicon-silicon interface is limited to 1.3 × 102 MW m−2 K−1, which is equivalent to thermal conductance of micrometer-thick bulk silicon. We further show that the TBC can be greatly improved by recrystallizing the amorphous interlayer, which here is realized by thermal annealing. The dependence of the TBC on the annealing temperature is highly nonlinear, which can be explained in terms of thermal activation of crystal growth.

A measurement technique of quasi-ballistic thermal transport in tens of nanometers has been developed by using time-domain thermoreflectance of gold nano-islands. The suppressed apparent thermal conductivity of transparent substrates (fused quartz, crystal quartz, and sapphire) due to quasi-ballistic thermal transport is obtained through the transient temperature change of the gold nano-islands formed on the substrate surface, and the size effect of thermal conductivity in the range of tens of nanometers is quantified by varying the gold nano-island sizes. Furthermore, characteristic phonon mean free paths of the substrates were obtained by fitting the measured size effect with a solution of a Boltzmann transport equation. The results identify that the size-effect of amorphous fused quartz at room temperature becomes significant when the size is reduced below 60 nm.

When installing thermal interface material (TIM) between heat source and sink to reduce contact thermal resistance, the interfacial thermal resistance (ITR) between the TIM and heat source/sink may become important, especially when the TIM thickness becomes smaller in the next-generation device integration. To this end, we have investigated ITR between TIM and aluminum surface by using the time-domain thermoreflectance method. The measurements reveal large ITR attributed to the depletion of filler particles in TIM adjacent to the aluminum surface. The thickness of the depletion layer is estimated to be about 100 nm. As a consequence, the fraction of ITR to the total contact thermal resistance becomes about 20% when the TIM thickness is about 50 μm (current thickness), and it exceeds 50% when the thickness is smaller than 10 μm (next-generation thickness).

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