A novel three-stage process to produce NTCR sensors is presented. In this process, an uncalcined powder mixture of NiO and Mn₂O₃ was deposited onto an alumina substrate via aerosol co-deposition (AcD). Then, an electrode structure was screen-printed onto the surface and the composite film was sintered in a multifunctional temperature treatment. Thereby, the sintering of the electrode, the formation of the NiMn₂O₄ spinel and the removal of film strains took place simultaneously. This enabled a significant reduction in energy demand and workload. The manufactured sensors, both as first prototypes, as well as miniaturized chip components, were characterized by a single-phase cubic NiMn₂O₄ spinel structure, mechanical stability and electrical properties that were similar to those of classical NiMn₂O₄ bulk ceramics or tempered aerosol deposited (AD) NiMn₂O₄ films. Particularly noteworthy was the high reproducibility and low variation of the NTCR parameters, such as the specific resistivity at 25 °C ρ25, the electrical resistance at 25 °C R25 and the thermistor constant B. The NTCR parameters were as aging-stable as for NiMn₂O₄ bulk ceramics or tempered NiMn₂O₄ AD-films and could even be further improved by thermal post-treatment.
Keywords: NTCR device; NiMn2O4 ceramic; aerosol deposition method (ADM), RTIC; temperature sensor; thick film thermistor.