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

Abstract

Here, we demonstrated that polycrystalline (Mn,Ni,Co)3O4 films with a high negative temperature coefficient of resistance (NTCR) behavior can be achieved at low annealing temperatures (≤400 °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 (Ta). 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 °C for the film crystallization with a pure cubic spinel phase. We also studied the dependence of the electrical properties on the Ta in the range of 285–400 °C. It was found that the films were highly conductive and showed a typical NTCR characteristic at annealing temperatures of 300 °C and above. Notably, at Ta ≥ 350 °C, the films exhibited an absolute temperature coefficient of resistance (TCR) exceeding 2.43% K−1 together with a moderate resistivity (ρ) of <3 kΩ cm, indicating their excellent potential for application in infrared detectors. In addition, the films showed good electrical stability with time, as their aging coefficient (ΔR/Ro) varied in a range of 5.9–6.4% after 500 h of aging in air at 150 °C. To the best of our knowledge, there have been no reports on cubic spinel Mn3O4-based thin films at temperatures below 400 °C.