EVALUATION OF GAS-MIXTURES WITH DIFFERENT SENSITIVE LAYERS INCORPORATED IN HYBRID FET STRUCTURES

We have developed a new hybrid technique for gas sensors based on fiel d effect structures (GASFET). A wide range of materials can be used as sensitive layer (e.g., inorganic or organic, metal or oxide) for a se lective detection of different gases. GASFET with an air gap using as sensitive layer different materials (Pt, SnO2, Ga2O3, V2O5) were built . The interactions of these different sensitive layers with various ga ses were investigated. Gas measurements were carried out at room tempe rature (25-degrees-C) and at 70-degrees-C. Work function changes of th ese sensitive layers upon exposure to hydrogen, ammonia, nitrogen diox ide and carbon monoxide as well as all mixtures of two gases were reco rded. The carrier gas was synthetic air. Matrices representing the sig nals as a function of two gas concentrations were obtained. By means o f pattern recognition and analytical techniques we are able to identif y the gaseous species and to evaluate their concentration if only one gas is present in the gas mixture. When two gases are mixed, they can be identified and their concentrations can be approximated.