Microfabrication and reliability study of sapphire based Ti/Pt-electrodes for thin-film gas sensor applications
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 600C for 5h, the temperature coefficient of the Ti/Pt-film stabilised at the value of 0.0033K?1, which approaches the pure platinum bulk value of 0.0039K?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 O3 gas sensor developed by evaporating a WO3 thin-film onto this electrode.
sapphire ti/pt-electrode thin-film diffusion thermodynamic stability harsh environment ozone sensor