Abstract
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.
Highlights
Due to their high-temperature sensitivity, reliability, and low-cost, ceramic NTC thermistors are widely used as temperature sensors in industrial, domestic and medical applications [1,2,3,4]
A way to simplify the process is the novel method described in this paper. It combines the already known method of aerosol co-deposition (AcD), which is the deposition of a ceramic powder mixture, as described in References [25,26,27], with a multifunctional sintering step, in which the composite film is in situ calcined, tempered, and the screen-printed electrodes are sintered simultaneously
An improvement in the aging stability of aerosol co-deposited films was possible through the formation of multi-phase ceramics
Summary
Due to their high-temperature sensitivity, reliability, and low-cost, ceramic NTC thermistors are widely used as temperature sensors in industrial, domestic and medical applications [1,2,3,4]. A way to simplify the process is the novel method described in this paper It combines the already known method of aerosol co-deposition (AcD), which is the deposition of a ceramic powder mixture, as described in References [25,26,27], with a multifunctional sintering step, in which the composite film is in situ calcined, tempered, and the screen-printed electrodes are sintered simultaneously. This process eliminates the second milling and drying step, and combines the previous three temperature treatments (powder calcination, electrode firing, film tempering) into one thermal process step.
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