Dewetting Behavior of PS-ZnO Thin Film Coated on Ultrathin Au Layer Grown on Si Substrate

Abstract

Electronic packaging by coating device component surfaces with polymer thin film is an important step to protect the components from harsh environments. However, along with the device miniaturization to improve its performance, scaling down the coating film can cause a decrease in film durability. Therefore, the thermal stability of pure polystyrene (PS) and zinc oxide-incorporated polystyrene (PS-ZnO) nano-thin films coated on gold (Au) layer with different nano thicknesses on Si substrate were examined to determine the smallest Au thickness at which the polymer films would exhibit optimal stability, and to investigate the effects of the Au component on film resistance to thermal dewetting. With the requirement of having a transparent and conductive Au electrode, the thickness of 20 nm was identified as the optimal value for the Au layer on which both the PS and PS-ZnO films could withstand environment temperatures at 150oC for up to a few hours while the PS-ZnO film exhibited outstanding thermal stability for over 10 days. Such excellent durability was ascribed to the physio-chemical framework in which the coating film can experience forces from the coated layers which potentially affect the mobility of polymer chains. Considering the increase of Au content and Au film roughness with increasing Au film thickness and realizing the similar surface adhesion forces of these Au layers, several possible influences of the Au material on the stability of PS matrix were discussed. The findings provide an insight into heat-resistant coatings for nano-thin Au layers grown on Si, which may also be of benefit in the design and understanding of relevant electronic protection and functional polymeric coatings.