Nanocomposite Zn2SnO4/SnO2 Thick films as a Humidity Sensing Material

Nanocomposite Zn
₂
SnO
₄
/SnO
₂
powder was obtained by solid state synthesis from homogenized starting nanopowders of ZnO and SnO
₂
mixed in the 1:1 molar ratio, structurally and morphologically characterized using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Thick film paste was made by adding organic vehicles to the obtained powder. Three to five layers (layer thickness approx. 12 μm) were screen printed on alumina substrate with small test PdAg electrodes and fired at 600°C 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 50°in a humidity chamber where the relative humidity (RH) was 30-90% and measured frequency 42 Hz - 1 MHz. With increase in film thickness the overall sensor 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 from 6.8 to 0.02 MΩ (36 μm) at 25°C, while at 50°C the overall measured impedance was lower, and reduced from 14 MΩ to 0.72 MΩ (48 μm) for RH 30 and 90%, respectively. The response (8 s) and recovery (10 s) was fast, showing that this nanocomposite has potential for application in humidity sensing.