In this work, the properties of Indium-Zinc-Tin-Oxide (IZTO) thin films, deposited on polyethylene naphthalate (PEN) with a SiO2 buffer layer, were analyzed with different working pressures. After depositing the SiO2 buffer layer on PEN substrates by plasma-enhanced chemical vapor deposition (PECVD), the IZTO thin films were deposited by RF magnetron sputtering with 1 to 7-mTorr working pressure. All the IZTO thin films show an amorphous structure, regardless of the working pressure. The best morphological, electrical, and optical properties are obtained at 3-mTorr working pressure, with a surface roughness of 2.112-nm, a sheet resistance of 8.87-Ω/sq, and a transmittance at 550-nm of 88.44%. These results indicate that IZTO thin films deposited on PEN have outstanding electrical and optical properties, and the PEN plastic substrate is a suitable material for display devices.