Optica spectra of indium-tin-oxide films deposited an flexible colorless polyimide substrates

We report optical spectra measurements on indium tin oxide (ITO) films deposited on colorless fluorine-containing aromatic polyimide substrates. As the deposition temperature (T-D) of the substrates increases from room temperature to 200 degrees C, the transmittance and the reflectance spectra exhibit more metallic features. However, the detailed dependence of the optical parameters on TD is not consistent with the dc-conductivity (sigma(dc)), We attribute this to a reduced mean free time (tau) of charge carriers for the high T-D samples. For T-D > 100 degrees C, tin atoms migrate from grain boundaries to regular lattice sites, acting as impurities and thereby decreasing tau. As a consequence, in spite of the increasing charge carrier density with T-D as revealed by the optical measurements, the reduced tau limits sigma(dc) for the high T-D samples.