Production of NTCR thermistor devices based on NiMn2O4+δ

NiMn2O4+δ ceramics exhibit a logarithmic increase of resistance with decreasing temperature (NTCR), which makes the compound well suited for use as a thermistor material in temperature sensing applications. In bulk material there are often problems with poor stability and reproducibility due to incomplete intergranular contact. These difficulties can be minimised in even and dense polycrystalline films. Screen-printing, electron-beam evaporation and rf magnetron sputtering processes have been developed for the production of thin and thick film NTCR thermistor devices. The source powder production, the experimental set-up, the process parameters and the resulting film properties for each of the processes are presented and compared. The surface topology was examined by scanning-electron microscopy (SEM) and atomic force microscopy (AFM). The phase purity of the source powder and the films was assessed by X-ray diffractometry (XRD). The electrical properties were analysed by measuring the resistance - temperature characteristics. This study suggests that rf magnetron sputtering processes are most advantageous.