Ceramic thin films by sol-gel processing as novel materials for integrated humidity sensors

Enrico Traversa*, Guglielmina Gnappi, Angelo Montenero, Gualtiero Gusmano

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

158 Scopus citations


Thin films based on 10 at% alkali-doped TiO2 and on iron oxide with very large humidity sensitivity were prepared using a sol-gel technique. Prototype humidity sensors were prepared by depositing metal alkoxide solutions onto Al2O3 substrates with comb-type Au electrodes, by dip-coating and heating in air. Heating to 300°C produces continuous films, free of porosity, which appear as layers covering the substrates, with no detectable grains. The humidity sensing electrical properties of the films were evaluated using electrochemical impedance spectroscopy (EIS) measurements. Resistance changes, although the films are dense, even larger than those reported for porous ceramics are recorded, as high as 9 and 8 orders of magnitude in the relative humidity range tested (4-87%), for the iron oxide and 10 at% K-doped titania films heated to 300°C, respectively. These outstanding results are interpreted in terms of conduction mechanisms different from the mechanism usually accepted for porous ceramics. EIS results confirmed that, for 10 at% alkali-doped TiO2 films, charge carriers are alkali ions and not surface protons.

Original languageEnglish (US)
Pages (from-to)59-70
Number of pages12
JournalSensors and Actuators, B: Chemical
Issue number1-2
StatePublished - Feb 1996
Externally publishedYes


  • Alkali-doped TiO
  • Humidity sensors
  • Iron oxides
  • Sol-gel
  • Thin films

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Condensed Matter Physics
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry


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