Nucleation and growth of crystalline Indium Tin Oxide (ITO) coatings on polyethylene terephthalate (PET)

We present the nucleation and growth mode of crystalline ITO ( c-ITO) on polymeric substrates. Crystallinity is known to be one of the most important factors that determine the functional and structural properties of ITO coated as electrodes. We sputter–deposit ITO on polymeric substrates at low temperatures varying deposition conditions. The thermal energy supplied from a heated substrate during deposition or from thermal annealing is known to be as important as deposition parameters to make the growth of high quality c-ITO possible. However, raising temperatures of the polymeric substrates is quite limited due to low glass transition temperatures ( T g). The nucleation and growth patterns of c-ITO from amorphous ITO ( a-ITO) are observed using high resolution transmission electron microscopy (HR TEM) and are compared with those on Si or glass substrates that were reported by others. The sheet resistance ( R s) of ITO is also measured and the relationship to the microstructures is investigated. Our results reveal that crystallites are nucleated on growing surfaces of a-ITO and grow with little interruption to be columnar grains in ITO on the polymeric substrates. This is different from the random nucleation and competitive growth mode of columnar grains from the interface with Si or glass substrates at similar deposition conditions. The lattice distortion in ITO due to mismatches in physical and chemical properties with the substrate is more severe on polymers than on Si or glasses, which seems to be one of the potential reasons that the ITO between the interface and columnar grains remains mostly amorphous.