Paper NS+NC-FrM7
Nanoscale Ballistic Heat Conduction in Silicon

Friday, October 24, 2008, 10:20 am, Room 311

Today’s electronic devices operations are affected by thermal issues determined by physical dimensions that are smaller or comparable to the mean free path of phonons in silicon. Controlling and understanding heat dissipation on nanometer scale can improve the thermal efficiency and power management of electronic circuits. Here we investigate heat conduction on nanometer scale employing metallic nanoheater with dimensions ranging from 100 nm up to 5 um. The nanoheaters are used both for heat generation and also for local temperature measurement. We investigate how the thermal resistance of individual nanoheaters and heat conduction across gaps ranging from 100 nm to 400 nm is changing as the sample temperature is varied from room temperature down to 30 K. As the temperature is lowered the phonon mean free path increases by more than 2 orders of magnitude compared with room temperature value and ballistic heat conduction (localized heating effects) start to play an important role. The thermal resistance of nanoheaters is a complex interplay between the thermal conductance of silicon substrate, localized heating effect and interface thermal resistance and their relative contribution changes as the phonon mean free path increases. A simple model considering the spreading thermal resistance, the interface thermal resistance, and the localized heating effect is proposed and used to model the experimental results. While for large heaters, the phonon mean free path is comparable to the size of the hot spots even at low temperature, for the small heaters, the mean free path is much larger than the heater size, and the localized heating effect plays a significant role in the total thermal resistance. The ballistic heat transport impact on nanoscale heat conduction has been evaluated in terms of heater size and phonon mean free path.