MONOLITHIC THIN-FILM METAL-OXIDE GAS-SENSOR ARRAYS WITH APPLICATION TO MONITORING OF ORGANIC VAPORS

This paper presents the study of eight-element gas-microsensor arrays that have been developed by silicon-based microfabrication and micromachining techniques combined with the reactive sputtering and etching of tin(IV) oxide or tin dioxide, zinc oxide, and tungsten trioxide. The mixed metal-oxide array has been fabricated on a 3 mm x 3 mm silicon chip. The process-compatibility problem encountered when delineating multiple sensing materials into a single device is resolved by combining ion-beam milling, 'lift-off', and wet chemical etching methods. The microsensor arrays are used to monitor benzene, toluene, and methanol and to analyze benzene-toluene mixtures with various multivariate calibration methods. The range of sensitivity of the arrays is tested with concentrations between 50 and 500 ppm of the organic vapors. Prediction errors for benzene-toluene mixtures are 29.8 ppm and 17.0 ppm, respectively, using projection pursuit regression.