IMPROVED LONG-TERM STABILITY FOR AN LAF(3) BASED OXYGEN SENSOR

The oxygen-sensitive field-effect structure Si/LaF3/Pt combines the ad vantages of a solid-state sensor with a fast response at room temperat ure of about t90=90 s. However, drawbacks are a large drift and a poor long-term stability because of an increase in response time. To solve these problems we developed a method for periodical reactivation of t he sensor directly at the measuring place consisting in a short anneal ing of the LaF3/Pt interface at 350-degrees-C in air. When the heating impulse is reduced to 100 mus using the platinum electrode as electri c heater, the energy consumption is so low that the temperature rise o f the whole chip is smaller than 1 K. The reactivation of the sensor c an be repeated without restriction. Even 8 months after preparation th e same response time as for the new sensor was obtained. Furthermore t he activation process causes a significant reduction of the sensor dri ft. The mechanisms of both the reactivation and the potential forming processes will be discussed using XPS results and sensor characteristi cs such as the temperature function and the influence of oxygen partia l pressure and humidity on the response kinetics.