Ammonia gas sensor using thick film of Au-loaded tungsten trioxide

Thick films of Au-loaded WO₃ mixed with glass frit were prepared on an alumina substrate by the printing method, and influences of film thickness, Au-loading and operating temperature on the NH₃ sensing characteristics were investigated. With an increase in film thickness and Au-loading, the maximum sensitivity (K_m) increased, while the temperature for maximum sensitivity (T_m) decreased. An optimum film was revealed to be the 4.0 mass % Au-loaded one of a 250 μm-thickness for the optimum operating temperature of 450°C. The sensor proved excellent NH₃ sensing characteristics in gas sensitivity, response transient, resistance to humidity and long-term stability when subjected to heat cleaning once a day during its operation.