LOW-TEMPERATURE DEPOSITION OF GLASS MEMBRANES FOR GAS SENSORS

To enhance the stability and selectivity of metal oxide conductivity s ensors for organic gases in air a new sensor concept has been realized . A special chemical vapour deposition technique, using hydrolysis of tetraethylorthosilicate, was developed to produce selectively permeabl e SiO2 coatings of a few nanometres thickness on top of SnO2 detector films at 300-degrees-C. The SiO2 membranes were characterized with X-r ay-excited photoelectron spectroscopy and secondary-neutral mass spect rometry. Electrical conductivity measurements at the uncovered as well as at the coated SnO2 were performed while an air flow with pulsed ad ditions of various concentrations of methane and propane passed the sa mple. The SiO2 membrane enhances the sensitivity to methane by a facto r of eight, whereas the sensitivity to propane is not affected. The re sponse time was measured to be about 50 s with and without coating at concentrations larger than 500 ppm.