Nanoscale thermal and thermoelectric transport in silicon

Hotspots on microchips are a major challenge for the semiconductor industry. To understand heat conduction from hotspots on silicon, measurements of the thermal resistance and transfer function have been performed using patterned nanoheater/sensor pairs with width from 100 nm up to 5000 nm at temperature range of 30 ∼ 300 K. Calculations of the thermal resistance based on a simple thermal model, considering resistances by spreading, interface, and localized heating match with the measurements. The results reveal several important trends indicating the prevalence of localized heating or sub-continuum transport phenomena in the vicinity of a nanoscale hotspot.;Thermoelectric cooling is a possible solution to cope with the hotspot issue. Silicon, in a nanostructured form, is an interesting thermoelectric material, because of significantly reduced thermal conductivity. However, further improvement in thermoelectric efficiency is highly desirable. Thermopower measurements of silicon nanoribbons with an integrated gate have been performed. The gate in the device is used to provide strong carrier confinement and enable tunability of the carrier density over a wide range, which is fully compatible with conventional silicon processing and microelectronics. It therefore offers a promising alternative to doping when considering the thermoelectric engineering of nanostructures. An enhancement of thermoelectric power factor has been observed in silicon nanoribbons. This enhancement can be understood by considering its behavior as a function of carrier density. We identify the underlying mechanisms for the power factor in the nanoribbon, which include quantum confinement, low scattering due to the absence of dopants, and, at low temperatures, a significant phonon drag contribution.