The effect of the addition of carbon black and the increase in film thickness on the sensing layers of ZnO / ZnFe2O4 in polymer thick film gas sensors

The aim of this work is to investigate the effect of increasing the carbon black and the sensing layer thickness on the response of a sensor. Three sensors of 60/40 mol% ZnO/Fe2O3 with different percentages of carbon black (1.5, 2 and 2.5 wt%) were fabricated on alumina substrates and copper thin film electrodes. The base resistance of the 1.5 wt% carbon black sensor was 4MΩ while for the 2 wt% carbon black sensors it was 25.50kΩ. The lowest base resistance was recorded with the 2.5 wt% carbon black sensor to be 8.2kΩ. The sensors were used to detect propanol in the concentration range 2500–5000 ppm, increasing with a step size of 500 ppm, at room temperature. The responses of the sensors were determined as ((Rgas−Rair)/Rair)×100 while the sensitivity was calculated as the slope of the graphs. The sensitivity was increased as the amount of carbon black decreased. The sensitivities of the sensors to propanol at room temperature were 0.0105, 0.005 and 0.002%/ppm for the three sensors. On the other hand, four sensors have different thickness were fabricated used by the same manner. It was found that the response of the sensor increased relatively as the thicknesses of the sensing layer decreased. Results show that the one-layer sensor has the highest response, followed by a decrease in the responses for sensors with higher numbers of layers, 2, 3, 4 and 5 successively.