Nanocomposite Zn2SnO4/SnO2 Thick Films as a Humidity Sensing Material

Abstract

Nanocomposite Zn2SnO4/SnO2 powder wasobtained by solid state synthesis from homogenizedstarting nanopowders of ZnO and SnO2, mixed in the 1:1molar ratio, structurally and morphologically characterizedusing X-ray diffraction (XRD) and Scanning ElectronMicroscopy (SEM). Thick film paste was made by addingorganic vehicles to the obtained powder. Three to fivelayers (layer thickness approx. 12 µm) were screen printedon alumina substrate with small test PdAg electrodes andfired at 600oC for 30 minutes. SEM analysis confirmed formation of a porous structure suitable for humidity sensing.Impedance response was studied at the working temperatures of 25 and 50oC in a humidity chamber where therelative humidity (RH) was 30-90% and measured frequency 42 Hz – 1 MHz. With increase in film thickness the overallsensor impedance increased. It reduced at 100 Hz from 36 to 0.25 MΩ (60 µm), from 23.4 to 0.25 MΩ (48 µm) and from6.8 to 0.02 MΩ (36 µm) at 25 oC, while at 50 oC and also 100 Hz it reduced from 14 MΩ to 0.72 MΩ (48 µm) for RH 30 and90%, respectively. The response (8 s) and recovery (10 s) was fast, showing that this nanocomposite has potential forapplication in humidity sensing.