Miniaturized SnO2-based suitable for temperature-tailored lambda-ratio sensors

A sol-gel method for the fabrication of miniaturized SnO₂ sensors, compatible with Si technology, is described. The fabrication procedure consists of deposition and patterning of Pt heating elements and sensor contact pads. The SnO₂ sensing element is formed through a new sol-gel method exploiting a lift-off step for patterning. Sintering of the sensor at a temperature of 600°C finalizes the fabrication. Preliminary results of sensor characteristics are reported. In addition, the behaviour of SnO₂ sensors fabricated using a pressed-pallet method with anomalous characteristics is addressed. The temperature-dependent response of SnO₂-based sensors as a λ-ratio sensing device is reported. A low-high transition in the sensor conductivity, occurring at a ratio of combustible to oxygen gases away from the stoichiometric value, is reported for the first time. The ratio at which this transition arises, happens at values higher than the stoichiometric point for CO and by raising the temperature, it moves towards the stoichiometric point. This phenomenon is reversed for C₂H₆.