Measurement of ballistic phonon conduction near hotspots in silicon

The Fourier law for lattice heat conduction fails when the source of heat i s small compared to the phonon mean free path. We provide experimental evid ence for this effect using heating and electrical-resistance thermometry al ong a doped region in a suspended silicon membrane. The data are consistent with a closed-form two-fluid phonon conduction model, which accounts for t he severe departure from equilibrium at the hotspot. The temperature rise e xceeds predictions based on the Fourier law by 60% when the phonon mean fre e path is a factor of 30 larger than the resistor thickness. This work is i mproving the constitutive modeling of heat flow in deep-submicron transisto rs. (C) 2001 American Institute of Physics.