Low-temperature sintered NTC ceramics for thick film temperature sensors and multilayer thermistors

Printed thick film NTC thermistors and multilayer devices are frequently used for temperature control in hybrid circuits. NiMn2O4 and substituted spinels are the most established materials for this application. For low-temperature sintering at 900°C the shrinkage behavior of the thermistor material has to be adjusted by the addition of proper sinter additives. We investigated the chemical stability of NiMn2O4 and substituted spinels in air between 25°C and 1200°C. The compound NiMn2O4 is stable from 700°C to 970°C only and interacts with the sinter additives. Stable cubic spinels were found in the system ZnxNi0,5Mn2-zO4. Addition of liquid phase sintering additives to the spinel powders results in complete densification at 900°C. No chemical interaction between spinel and additive was obs erved. The effect of Cu.substitution into the spinel was also investigated. Functional NTC pastes were printed on alumina substrates and post-fired at 900°C. The NTC thermistor films have a sheet resistivity of about 300kOhm/sq and B = 3300K. The firing behavior, microstructure formation and electric properties of NTC thick films will be reported.