Adverse effect of substrate surface impurities on O2 sensing properties of TiO2 gas sensor operating at high temperature

It is well known that surface state of substrates greatly influences the sensing characteristics of gas sensors. In this work, alumina (Al2O3) substrates with different distribution of surface impurity concentrations were utilized to prepare TiO2 based lambda sensors. Several methods, including XPS, XRD and SEM were employed to exam the substrate surface impurity contents, as well as the structure of the sensing films and the interface morphology between the substrates and sensing films. The results indicated that the gas sensors prepared on alumina substrates containing higher Ca impurities displayed lower oxygen sensitivities and longer response times at high operating temperatures above 600 °C. Therefore, it was concluded that Ca impurities on alumina substrates had to be limited to lower possible levels when fabricating TiO2 lambda sensors.