Abstract: The SnO₂ thick film gas sensors were prepared by using a standard screen printing technology and calcined at different temperature and time. By measuring
the sensitivity and long-term stability and using complex impedance analysis, the effects of calcining temperature and time on sensing properties and microstructure
of the thick films were researched. Gas sensors with high sensitivity and long-term stability can be prepared by choicing suitable calcining process parameters. Complex
impedance analysis indicates that the depressed angles of semicircular arc will reduce to zero with the extension of calcining time. The reducing of depressed
angles means the distribution of relaxation time at the grain boundary becomes more uniform. This result shows that the distribution of defects and pores, and the grain
connected shapes at the grain boundary tend to be more uniform and stable with the extension of calcining time.

Key words: SnO₂ gas sensor, thick film, calcining temperature, calcining time, complex impedance