Indium oxide thin film based ammonia gas and ethanol vapour sensor

A sensor for ammonia gas and ethanol vapour has been fabricated using indium oxide thin film as sensing layer and indium tin oxide thin film encapsulated in poly(methyl methacrylate) (PMMA) as a mini a- ture heater. For the fabrication of miniature heater in dium tin oxide thin film was grown on special high te m- perature corning glass substrate by flash evaporation method. Gold was depo sited on the film using thermal evaporation technique under high vacuum. The film was then annealed at 700 K for an hour. The thermocouple attached on sensing surface measures the appropriate operating temper ature. The thin film gas sensor for ammonia was operated at different concentrations in the te mperature range 323-493 K. At 473 K the sensitivity of the sensor was found to be sat urate. The detrimental effect of humidity on ammonia sensing is removed by intermit tent periodic heating of the sensor at the two te mperatures 323K and 448 K, respectively. The indium oxide ethanol vapour sensor operated at fixed concentration of 400 ppm in the temperature range 293-393 K. Above 373 K, the sensor conductance was found to be saturate. With various thicknesses from 150-300 nm of indium oxide sensor there was no variation in the sensitivity mea - surements of ethanol vapour. The block diagram of circuits for detecting the amm onia gas and ethanol vapour has been included in this paper.