STRUCTURAL AND MICROSTRUCTURAL EFFECTS ON THE THERMAL CONDUCTIVITY OF ZIRCONIA THIN FILMS

Abstract

Thermal properties of thin films are involved in a large number of applications such as electronic and electrooptical devices, or thermal barrier coating. It is known that the structure and the microstructure of thin solid films have a strong influence on the thermal conductivity, which may be considerably lower than for bulk materials. The aim of this study is to highlight the role of structure and microstructure on the thermal conductivity of ZrO 2 thin films (stabilized with Y 2 O 3 or not). Investigations have focused on the influence of film thickness, substrate roughness, and crystallites size on the thermal properties of dielectric thin film samples. For this purpose, a new photothermal method has been developed to measure the thermal conductivity of such films on various kind of substrates with an accuracy better than 10%. It has been observed that a decrease in the dielectric thickness leads to a drastic drop of the apparent thermal conductivity, k a , whatever the ZrO 2 phase is. k a is affected by an additional thermal resistance, R fs , especially between ZrO 2 and alumina substrate. This resistance R fs varies linearly with the substrate roughness. Finally, the influence of crystallite size and grain boundaries on k a have been shown.