Effect of Post Deposition Annealing on the Sensing Properties of Thin Film Ruthenium Oxide (RuO₂) pH Sensor

The use of ruthenium oxide (RuO2) as a pH sensor is a relatively novel idea and understanding how preparation of the sensor effects and its sensing properties is crucial. In this article, the effect of annealing temperature on the sensing properties of the sputtered RuO2 thin-film pH sensor was examined. It was found that annealing RuO2 at temperatures above 200 °C resulted in increased crystallinity and did not significantly alter the elemental composition. The sensor performance however was found to decrease with increased annealing temperature. Electrodes annealed above 400 °C had significantly higher hysteresis widths and drift rates, almost ten times the values of electrodes annealed at below 400 °C. Electrodes annealed at temperatures below 400 °C exhibited acceptable hysteresis widths of less than 2.5 mV. Consequently, in the manufacture of functional RuO2 pH sensors with a screen-printed Pt contact layer, it is recommended that the manufacturing temperature should not exceed 400 °C, post sputter deposition of RuO2.