Ultra-low resistivity aluminum doped ZnO thin films on flexible substrates using sol-gel solution deposition

The effect of a combination of low temperature heat treatments, microwave annealing, and low temperature vacuum annealing on the resistivity of 1% Al-doped ZnO thin films (AZO) deposited on both flexible polyimide films and rigid silicon substrates was investigated. The sol-gel deposition technique was used to deposit successive layers with a 0.5-hour heat treatment application prior to the deposition of additional layers. Following the final layer deposition and 0.5-hour treatment, the samples either underwent a final thermal annealing or microwave plus thermal annealing. Finally, a post-treatment annealing in a high vacuum chamber at 300 °C was administered. The films exhibited ultra-low resistivity of 14 Ω-cm on the polyimide with good adhesion qualities and a 0.08 Ω-cm resistivity on silicon wafers. A hexagonal wurtzite structure with the (002) c-axis orientation in the film growth direction was evident along with a dense microstructure of homogeneously distributed grains.