The influence of sintering additives on the lifetime of the heater for sensor application with Al₂O₃ substrate

A micro-heater was fabricated by co-firing the laminates of Al₂O₃ green sheets with Pt heater pattern and its lifetime characteristics were studied in relation to the substrate conditions by varying the sintering temperatures and the sintering additives such as MgO, CaO, and SiO₂. The MgO-doped heater showed the longer lifetime than undoped, CaO-doped or SiO₂-doped ones, and the heater lifetime increased with the sintering temperature. This arose from the improvement of connectivity and homogeneity of the Pt pattern by the densification of Pt particles or Al₂O₃ substrate. The migration of the Mg²⁺ ion toward the negative electrode was observed as a darkened phase and analyzed by micro-compositional analysis in the heater operated at high temperature. Its tendency was proportional to increasing the MgO doping into high purity Al₂O₃. The desirable amount of MgO doping was 7 mol% both for prevention of Mg²⁺ ion migration and for increasing heater lifetime.