The paper describes the design, fabrication and characterisation of a Ti/Pt-electrode system (an interdigital electrode with an aligned heater) on a sapphire substrate. It serves as substrates for subsequent deposition of gas sensitive films. The fabrication has been accomplished on both sides of a sapphire wafer. Wet chemical etching and the lift-off method have, respectively, been used for structuring the electrode and the heater patterns. The mechanical stability and the electrical conductivity of the resultant Ti/Pt-films are greatly affected by the subsequent heat treatment procedures. The diffusion of titanium ions into platinum has been examined using SIMS depth profiles. After annealing at 600 degrees C for 5 h, the temperature coefficient of the Ti/Pt-film stabilised at the value of 0.0033 K-1, which approaches the pure platinum bulk value of 0.0039 K-1. With a good mechanical and thermodynamical stability at high temperatures and under oxidising and reducing conditions, the sapphire based Ti/Pt-electrode system is well suited for gas sensor fabrication. As an example of its application, we report a highly sensitive O-3 gas sensor developed by evaporating a WO3 thin-film onto this electrode. (C) 2000 Elsevier Science Ltd. All rights reserved.
