Preparation of Hematite Based Humidity Sensors by Means of Electrophoretic Deposition Technique

International audienceHematite based humidity sensors were prepared by means of electrophoretic deposition technique (EPD). Water was used as a suspension medium for electrophoretic forming and a food gelatine was employed to stabilise the suspensions. Prior to powders additions, the gels were mechanically broken down and the suspensions were finally stirred for some minutes. Commercial alumina substrates for electronics were employed as substrates and their surfaces were graphitized, by means of a scanning electron microscope glue, to become conductive. First, a commercial iron powder was used, then an hematite one was preferred. During the EPD process, the DC tension was kept constant while the intensity died down with the increasing thickness of the formed layer. After deposition, the sensors were dried overnight at 20°C and fired at 1250°C. Gold electrodes were screen printed onto the thick films which were dried and finally heat treated at 520°C. The investigated parameters were the following: the gelatine amount, the powder concentration (2-16 g/100 mL of water), the deposition time (2 s to 5 min) and the applied tension (5-60 V). The best results were obtained with hematite powder: the sensors resistance continuously decreased starting from about 30 % relative humidity