Influence of Thickness on Ethanol Sensing Characteristics of Doctor-bladed Thick Film from Flame-made ZnO Nanoparticles

ZnO nanoparticles were produced by flame spray pyrolysis (FSP) using zincnaphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%). The particleproperties were analyzed by XRD, BET, and HR-TEM. The sensing films were produced bymixing the particles into an organic paste composed of terpineol and ethyl cellulose as avehicle binder and were fabricated by doctor-blade technique with various thicknesses (5,10, 15 μm). The morphology of the sensing films was analyzed by SEM and EDS analyses.The gas sensing characteristics to ethanol (25-250 ppm) were evaluated as a function of filmthickness at 400°C in dry air. The relationship between thickness and ethanol sensingcharacteristics of ZnO thick film on Al2O3 substrate interdigitated with Au electrodes wereinvestigated. The effects of film thickness, as well as the cracking phenomenon, though,many cracks were observed for thicker sensing films. Crack widths increased withincreasing film thickness. The film thickness, cracking and ethanol concentration havesignificant effect on the sensing characteristics. The sensing characteristics with variousthicknesses were compared, showing the tendency of the sensitivity to ethanol decreasedwith increasing film thickness and response time. The relationship between gas sensingproperties and film thickness was discussed on the basis of diffusively and reactivity of thegases inside the oxide films. The thinnest sensing film (5 μm) showed the highest sensitivityand the fastest response time (within seconds).