NO₂ sensitive LaFe₃ thin films prepared by r.f. sputtering

LeFeO₃ thin films with different thicknesses have been fabricated by the r.f. magnetron sputtering method on Al₂O₃ substrates with comb-type Au electrodes. The influence of annealing temperatures and times on the NO₂ sensitivity of the thin films has been investigated. The thin films are annealed at temperatures from 600 to 1000 °C in flowing air for 30 or 60 min. The conductivity of thin films increases noticeably when NO₂ gas is introduced into the measuring chamber, and returns to its original level after NO₂ is removed. The NO₂ response curve of LaFeO₃ thin films shows two distinct phases: an initial fast and large conductivity change, followed by a much slower change. These phases are attributed to the surface chemisorption process of NO₂ and the oxidation process of the bulk, respectively. The material's structure plays a fundamental role in its NO₂ response, while the influence of film thickness is less important. The annealing temperature and time of LaFeO₃ sputtered thin films determine their NO₂ sensitivity. The thinner films show higher resistivities, slightly greater NO₂ sensitivities and less stable results.