Thermal conductivity and thermal boundary resistance of amorphous Al2O3 thin films on germanium and sapphire

Abstract

Sub-nanometer thickness accuracy and excellent conformity make atomic layer deposited films prevalent in modern electronics, continuously shrinking in size. The thermal resistance of these films plays a major role in the overall energy efficiency of miniaturized devices. We report very sensitive thermal conductivity measurements of amorphous Al2O3 thin films grown using atomic layer deposition in the temperature range of 100–300 K. The 3ω method is used to characterize these films ranging from 17.0 to 119.4 nm in thickness, using a series-resistor model to deconvolve the intrinsic thermal conductivity of the film from thermal boundary resistances inherently present in the multilayer system. The thermal conductivity of amorphous alumina films with a density of 2.77±0.14 g cm−3 is measured to be 1.73±0.08 W m−1 K−1 at 300 K. Measurements were carried out on germanium and sapphire substrates, leading to no substrate dependence of the films’ thermal conductivity, within experimental accuracy. On the other hand, thermal boundary resistances of the systems Pt/Al2O3/substrate are observed to be strongly substrate-dependent, with values ranging from 2.1×10−8 m2 K W−1 to 3.7×10−8 m2 K W−1 at 300 K for films deposited on sapphire and germanium, respectively. These results provide further insights into the significance of interfaces in thermal transport across layered materials, in particular, for potential germanium-based devices.