Nanocrystalline SnO2-Zn2SnO4 composite thick films applied as humidity sensors

Abstract

Starting ZnO and SnO2 nanopowders (<100 nm) were mixed in a suitable ratio and calcined at 1050 °C for 2 hours to obtain nanocrystalline SnO2-Zn2SnO4 composite powder. Structural characterization performed by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) showed that a nanocrystalline composite SnO2-Zn2SnO4 powder was obtained. Thick film paste was made by adding organic vehicles to the powder. Screen printing of four and five layers of thick film paste was performed on two interdigitated test electrode configurations. They were calcined at 500 and 600 °C for 30 minutes. Impedance response was analyzed at several working temperatures (20-60 °C) in the relative humidity range 30-90% and frequency 42 Hz to 1 MHz. Increase in relative humidity lead to a decrease in impedance, especially at lower frequencies. The sensor time delay between absorption and desorption processes was low and the response and recovery times fast showing that the nanocystalline SnO2-Zn2SnO4 composite has potential for application in humidity sensing.