Influence of the nature of the screen-printed electrode metal on the transport and detection properties of thick-film semiconductor gas sensors

In the design of semiconductor gas sensors, commercially available metallic inks or pastes have been used more or less indifferently for making the electrical contacts with the oxide. It has usually been assumed that the metallic electrodes do not take any part in the electrical and gas-detection processes. Careful measurements with layers of tin oxide and iron oxide, screen printed above interdigitated electrodes made with metallic inks of gold, platinum, platinum/gold, nickel and silver/palladium and with sputtered gold, show that the nature of the metal as well as the type of deposition (screen printing or sputtering) may have a considerable influence on both resistances and gas sensitivities. An interpretation based on the formation of an additional interface resistance while firing the oxide layer is proposed.