Annealing temperature dependent structural and electrical properties of (Mn,Ni,Co)3O4 thin films

Here, we demonstrated that polycrystalline (Mn,Ni,Co)(3)O-4 films with a high negative temperature coefficient of resistance (NTCR) behavior can be achieved at low annealing temperatures (<= 400 degrees C) via a liquid flow deposition method. The processing conditions applied to obtain the high-quality films were investigated with focus on the flow rate of the oxidizing agent (H2O2) and annealing temperature (T-a). The introduction of an appropriate amount of H2O2 solution into the deposition system led to the partial oxidation of Me2+ ions (Me = Mn, Ni and Co) to Me3+ which subsequently adsorbed to the films, with only little effect on the film surface quality. The pre-existing Mn3+ ions enabled the possibility of reducing the final annealing temperature to 300 degrees C for the film crystallization with a pure cubic spinel phase. We also studied the dependence of the electrical properties on the T-a in the range of 285-400 degrees C. It was found that the films were highly conductive and showed a typical NTCR characteristic at annealing temperatures of 300 degrees C and above. Notably, at T-a >= 350 degrees C, the films exhibited an absolute temperature coefficient of resistance (TCR) exceeding 2.43% K-1 together with a moderate resistivity (rho) of< 3 k Omega cm, indicating their excellent potential for application in infrared detectors. In addition, the films showed good electrical stability with time, as their aging coefficient (Delta R/R-o) varied in a range of 5.9-6.4% after 500 h of aging in air at 150 degrees C. To the best of our knowledge, there have been no reports on cubic spinel Mn3O4-based thin films at temperatures below 400 degrees C.