Novel sputtering method for Pd-Al2O3 UV transparent conductive coatings

Transparent conductive layers like indium tin oxide (ITO) or zinc oxide, that are commonly used as signal electrodes of vidicon television tubes, have an absorption edge in the visible range (350-400 nm) and therefore are not transparent in the ultra-violet (UV). We have developed the Pd-Al₂O₃ thin film structure which is appropriate as a signal electrode for the vidicon operating in the near UV region. The films were deposited using a novel sputtering method. The 20 Å thick Pd layer served as the conducting plate while the 30-50 Å thick Al₂O₃ coating functioned as the transparent protective film. The obtained signal plates had a sheet resistance of 2.5 kΩ and a transparency coefficient of 71% at a wavelength of 250 nm, which is suitable for near ultra-violet applications. The main advantage of vidicons equipped with such signal plates is that their dark current was less than 0.05 nA