Thorsten Sahm

Properties of indium oxide semiconducting sensors deposited by different techniques

Semiconducting In2O3 gas sensors have been fabricated by two different deposition techniques, i.e., spin-coating and screen-printing. In both cases the same starting material – sol-gel-prepared cubic In2O3 – was used for the deposition in order to ensure a better comparability of the different sensing layers. The morphology of the layers has been characterized using scanning electron microscopy (SEM) technique. The layers deposited by different methods show similar grain size and porosity. Furthermore, Dc electrical tests have been performed to analyze the sensing properties of the different gas sensors. Reducing gases (CO and propanal) as well as oxidizing gases (NO2 and ozone) were used as test gases in the background of dry and humidified synthetic air. All measurements were performed at several temperatures. It was found that the spin-coated and screen-printed layers show different sensing properties, i.e., screen-printed sensors showed higher sensor signals than spin-coated sensors for CO, propanal, and NO2. The most striking differences appeared in the detection of ozone. In this case, spin-coated sensors showed a higher performance than screen-printed sensors. Higher ozone concentrations led to saturation effects for the latter.

Flame spray synthesis of tin oxide nanoparticles for gas sensing

Tin oxide nanoparticles for gas sensing application have been synthesized with an aerosol method. The particles were manufactured with the versatile Flame spray Pyrolysis (FSP) method producing highly crystalline powders with closely controlled a primary particle and crystallite size of 10 nm and 17 nm. The single crystalline particles were only slightly aggregated and directly used for thick film sensor deposition by drop coating and screen printing.The flame made SnO 2 nanoparticles showed high and rapidresponse to reducing gases such as propanal and CO.

Formation of Highly Porous Gas-sensing Films by In-situ Thermophoretic Deposition of Nanoparticles from Aerosol Phase

Gas sensors based on tin dioxide nanoparticles show high sensitivity to reducing and oxidizing gases. Dry aerosol synthesis applying the flame spray pyrolysis was used for manufacture and directly (in-situ) deposit nanoparticles on sensor substrates. For the first time this technique has been used to synthesize a combination of two stacked porous layers for gas sensor fabrication. Compared to state-of-the-art techniques, aerosol technology provides a direct and versatile method to produce homogeneous nanoparticle films. Two different sensing layers were deposited directly on interdigital ceramic substrates. These porous bottom layers consisted either of pure tin dioxide or palladium doped tin dioxide. The top layer was a palladium doped alumina nanoparticle film which served as a chemical filter. The fabricated gas sensors were tested with methane, CO and ethanol. In case of CH4 detection, the pure tin dioxide sensor with the Pd/Al2O3 filter layer showed higher sensor signals and significantly improved analyte selectivity with respect to water vapor compared to single tin dioxide films. At temperatures up to 250°C the Pd-doping of the tin dioxide strongly increased the sensitivity to all gases. At higher temperatures the sensor signal significantly decreased for the Pd/SnO2 sensor with a Pd/Al2O3 filter on top indicating high catalytic activity.