Characterization of Al-doped Mn–Co–Ni–O NTC thermistor films prepared by the magnetron co-sputtering approach

A serial of Al-doped Mn–Co–Ni–O thermistor thin films were prepared by a magnetron co-sputtering system using an Mn1.4Co1.3Ni0.3 alloy target and an Al target. The composition and electrical properties of the thin films could be well controlled by adjusting the sputtering power of the Al target. It was found that the Mn3+, Mn4+, and Co2+ cations at the octahedral sites of the compact and flat films were gradually replaced by the Al3+ cation during doping. The amount of Al dopant in the compound film was easily adjusted by controlling the sputtering power applied to the doping Al target. The experimental results demonstrate that the NTC characters were found in all films. The optimum point (15 W) of Al sputtering power was determined, at which both the maximum material constant B value (4112 K) and the lowest carrier concentration (2.46 × 1014 cm−3) was characterized in the film. The significant enhancement of the B value for NTC thin films can potentially widen the temperature measurement range for sensing applications. © 2020 Elsevier B.V.