Effect of substrate on NO2-sensing properties of WO3 thin film gas sensors

A WO3 thin film with a 1.2 mum thickness was deposited onto several substra tes, including unpolished alumina, polished alumina, and silicon, using a t hermal evaporating method with Pt meander electrodes and a heater. The WO3 thin films were annealed at 600 degreesC in air for 2 h, thereafter, the mi crostructure and NO2-sensing properties of the thin films grown on the diff erent substrates were investigated. The WO3 thin film on the unpolished alu mina exhibited the highest sensitivity of 10-70 ppm NO2 at an operating tem perature of 300 degreesC, whereas the film on the silicon substrate showed the lowest sensitivity of 3 ppm. The crystal structures of the thin films g own on the various substrates were nearly the same, however, their surface roughnesses were very different according to the kind of substrate. The sen sitivity of WO3 to NO2 is highly dependent on the roughness of the substrat e since this is also the main cause of modifications to the surface morphol ogy of the sensing film. (C) 2000 Elsevier Science S.A. All rights reserved .