Influence of annealing on humidity response of RF sputtered nanocrystalline MgFe2O4 thin films

Humidity response of Radio Frequency sputtered MgFe2O4 thin films onto alumina substrate, annealed at 400 °C, 600 °C and 800 °C has been investigated. Crystalline phase formation of thin films annealed at different temperature was analyzed by X-ray Diffraction. A particle/grain like microstructure in the grown thin films was observed by Scanning Electron Microscope and Atomic Force Microscope images. Film thickness for different samples was measured in the range 820–830 nm by stylus profiler. Log R (Ω) response measurement was taken for all thin films for 10–90% relative humidity (% RH) change at 25 °C. Resistance of the film increased from 5.9 × 1010 to 3 × 1012 at 10% RH with increase in annealing temperature from 400 °C to 800 °C. A three-order magnitude, 1012 Ω to 109 Ω drop in resistance was observed for the change of 10 to 90% RH for 800 °C annealed thin film. A good linear humidity response, negligible humidity hysteresis and minimum response/recovery time of 4 s/6 s have been measured for 800 °C annealed thin film.