Characterization of very low thermal conductivity thin films

Characterization of thermal transport in nanoscale thin films with very low thermal conductivity (< 1 W m(-1) K-1) is challenging due to the difficulties in accurately measuring spatial variations in temperature field as well as the heat losses. In this paper, we present a new experimental technique involving freestanding nanofabricated specimens that are anchored at the ends, while the entire chip is heated by a macroscopic heater. The unique aspect of this technique is to remove uncertainty in measurement of convective heat transfer, which can be of the same magnitude as through the specimen in a low conductivity material. Spatial mapping of temperature field as well as the natural convective heat transfer coefficient allows us to calculate the thermal conductivity of the specimen using an energy balance modeling approach. The technique is demonstrated on thermally grown silicon oxide and low dielectric constant carbon-doped oxide films. The thermal conductivity of 400 nm silicon dioxide films was found to be 1.2 W m(-1) K-1, and is in good agreement with the literature. Experimental results for 200 nm thin low dielectric constant oxide films demonstrate that the model is also capable of accurately determining the thermal conductivity for materials with values < 1 W m(-1) K-1.