Comparative study on micromorphology and humidity sensitive properties of thin-film and thick-film humidity sensors based on semiconducting MnWO4

Based on our experience of developing thick-film MnWO4 humidity sensors, a thin-film humidity sensor with nano-sized MnWO4 grains has been fabricated using the sol-gel technique. The thin-film sensor shows smaller humidity se nsitivity than that compared to a thick-film sensor. However, it exhibits a fast response to humidity change and also has a very low temperature coeff icient within the temperature range of 20-60 degrees C. The absence of capi llary pores in the well defined thin-films makes water condensation, and he nce electrolytic conduction, impossible. The physically adsorbed multi-laye red water molecules on the surface of the thin sensing film play a dominati ng role for the humidity sensing mechanism. Studies on thin-film sensors ba sed on MnO and WO3 indicate that the W+6 sites in the hubnerite material co ntribute strongly to the humidity sensing mechanism. (C) 2000 Elsevier Scie nce S.A. All rights reserved.