CONDUCTIVITY BEHAVIOR OF THICK-FILM TIN DIOXIDE GAS SENSORS

SnO2 semiconductor gas sensors undoped and doped with Pt and Pd are prepared by the thick-film technique on Al2O3 substrates with different electrode structures. The SnO2 layer structure is characterized by scanning electron microscopy (SEM) and X-ray diffraction. The temperature dependence of the conductance of these sensors is measured by d.c. and a.c. techniques up to 300 kHz in the temperature range 300 to 800 K under synthetic air and air/250 ppm CO mixtures, as well as the sensor response time due to gas changes from air to air/CO. The results show a temperature-activated conduction mechanism which is discussed using a barrier model. The response time is governed by diffusion processes of the gas into the porous SnO2 layer and surface reaction times.